The term therapeutic relates to the treatment of disease or physical disorder, and exercise refers to bodily exertion for the sake of training or improvement of health. This chapter on therapeutic exercise therefore addresses the use of activities requiring physical exertion in the prevention, treatment, and rehabilitation of illness and disabling conditions. The pertinent exercises considered in this chapter include those to develop endurance, strength, flexibility, and proprioception.
The use of therapeutic exercise in the treatment of injuries is not a new concept. Hippocrates (460–370 b.c.) reportedly advocated exercise as an important factor in the healing of injured ligaments, and the Hindus and Chinese used therapeutic exercise in the treatment of athletic injuries as early as 1000 b.c. Today the various types of exercise probably account for the most commonly used treatments in the field of physical medicine and rehabilitation. Therefore, it is important for clinicians in the field to have a thorough understanding of this area.
The concepts forming the basis for therapeutic exercise come from studies in basic physiologic science and applied exercise physiology. In recent years, epidemiologic investigations have provided additional insight into the importance of exercise in prevention of disease. Consequently, much of this chapter is devoted to this basic information that provides the foundation for the clinical use of exercise.
THE NEEDS ANALYSIS
A needs analysis is a process that consists of answering a series of questions that will assist in the design of a resistance training program (256). The major questions in a needs analysis are
What muscle groups need to be trained?
What are the basic energy sources (e.g., anaerobic, aerobic) that need to be trained?
What type of muscle action(s) (e.g., isometric, eccentric actions) need to be trained?
What is the prior injury history and what are the primary sites of injury for the particular activities in which the individual participates?
What are the specific needs for muscle strength, hypertrophy, endurance, power, speed, agility, flexibility, body composition, balance, and coordination?
Biomechanical Analysis to Determine What Muscles Need to Be Trained
The first question requires an examination of the muscles and the specific joint angles that need to be trained. This involves a basic analysis of the movements performed and muscles involved with an activity. The decisions made at this stage will help define the choice of exercises, which is one of the program variables.
Because the principle of specificity is a major tenet in resistance training, understanding exactly what movement one is trying to mimic during resistance training is an important aspect of program design. Such analyses will allow one to use specific exercises that require the proper muscles and actions to be used in a manner specific to the activity for which one is being trained.
Resistance training for any sport or activity should include full range-of-motion exercises around all the major body joints. However, training designed for improving specific movements should also be included in the exercise protocol to maximize the contribution of strength training to function. The best way to select such exercises is to analyze the biomechanics of the activity and match it to exercises. The importance of movement-specific resistance training programs (e.g., functional training) has surfaced over the past decade and has led to the development of specific equipment (i.e., stability balls, wobble boards) and programs targeting core stability, rotational strength and power, balance, reaction, speed, acceleration, and agility (257).
The principle of specificity is an overriding rule in any of the choices made for the design of a resistance training program. Each exercise and resistance used in a program will have various amounts of transfer to another activity or sport. The amount of transfer will be related to the degree of specificity that can be achieved with the available equipment. When training for improved health and well-being, the specificity of the training will be related to picking the right exercises that can impact a given physiologic variable (e.g., bone mineral density). Other program variables (e.g., rest periods) will also interact to optimize the metabolic system for positive effects as well. Thus, each decision that is made for the choice of exercise will interact with other program variables to create an integrated stimulus of a specific workout protocol.
Assessment of the Primary Sites of Injury
It is also important to determine the primary sites for potential injury in a work or sport activity. Furthermore, it is important to understand the injury profile of the individual. The prescription of resistance training exercises will be directed at enhancing the strength and function of tissue so that it better resists injury or reinjury, recovers faster when injured, and reduces the extent of damage related to an injury. The concept of “prehabilitation†refers to preventing initial injury by training the joints and muscles that are most susceptible to injury in an activity. The prevention of reinjury can also be an important goal of a resistance training program. Thus, understanding the typical sites of injury for the activity (e.g., knee joints in alpine skiing or low back in construction workers) and the individual's prior history of injury can help in properly designing a resistance training program. Resistance exercise stress causes muscle tissue damage or disruption, which stimulates hypertrophy and is mediated in part by many of the same inflammatory, immune, and endocrine processes that are involved in the repair of injury. Resistance training most likely helps to condition and prepare these systems for more extensive repair activities needed for faster injury repair as well as less tissue damage due to stronger tissue components.
Determination of the Need for Various Components of Muscular Fitness
Determination of the magnitude of improvement needed for variables such as muscle strength, power, hypertrophy, endurance, speed, balance, coordination, flexibility, and body composition is a very important step in the overall resistance training program design. It may seem reasonable to assume that a resistance training program should be designed to optimize all these variables, but that may not necessarily be the case. For example, many sports require a high strength-to-mass or a high power-to-mass ratio. In such a case, resistance training programs should be designed to maximize strength and power while minimizing increases in body mass. This is evident in sports that use weight classes such as weightlifting, power lifting, and wrestling and for those sports that require maximal sprinting speed or jumping ability (e.g., high jump, long jump) where increasing body mass may be detrimental to the maximal height or distance attained, as well as speed. In addition, some sports, such as American football, benefit from increasing lean body mass, where the force of impact is greater for a given body mass, assuming power is increased accordingly. Thus, the need for these components of muscular fitness
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must be evaluated so that proper resistance training partitioning may be used.
Program Design
After the needs analysis has been completed, a specific workout is designed that leads to the development of a training program. These workout sequences should address the specific goals and needs of the individual. Program variables serve as the framework of one specific resistance training session. Changes in the program variables will make up the progression plan for an entire training period. Periods of training are now planned over a training cycle, and “periodization†of training becomes a vital concept in the manipulation of the program variables in chronic program design. In the rehabilitation setting, such periodization may mean that focused strengthening exercises are shifted to more functional exercises emphasizing the development of muscular endurance. In addition, neuromuscular recovery is often a vital factor in the rehabilitation setting, and using the concept of periodized training will allow for both variation in the exercise stimuli and planned recovery.
PROGRAM VARIABLES
A number of variables can be manipulated in any resistance training prescription (220). These program variables are capable of providing a general description of any single workout protocol.
Choice of Exercise
As described in the needs analysis, the choices of exercises will be related to the biomechanical characteristics of the targeted goals for improvement. The number of possible angles and exercises are almost as limitless as the body's functional movements. A change in angle affects which muscle tissue is activated. Using magnetic resonance imaging (MRI) technology, investigators have shown that the type of resistance exercise (relative to joint angle and loading method) alters the activation pattern of the muscle (259). Therefore, it is important to understand that if the muscle tissue is not activated by using the most appropriate resistance load (periodized loadings) or joint angles, the desired tissue may not be affected and therefore the optimal rehabilitation progression will not occur.
Exercises can be arbitrarily designated as primary exercises and assistance exercises. Primary exercises are the exercises that train the prime movers in a particular movement. They are typically major muscle group exercises (e.g., squat, bench press, hang pulls). Assistance exercises are exercises that train smaller muscle groups and aid in the movement produced by the prime movers (e.g., triceps press, bicep curls).
Exercises can also be classified as structural (i.e., multiple-joint) or body-part (i.e., isolated joint). Structural exercises include those whole body lifts that require the coordinated action of several muscle groups. Power cleans, power snatches, deadlifts, and squats are good examples of structural whole-body exercises. Multiple-joint exercises are those that use more than one joint to perform the movement. An example is the bench press, which involves movement of both the elbow and shoulder joints. Other examples of multiple-joint exercises include the lat pull-down, military press, and leg press.
Exercises that attempt to isolate a particular muscle group are known as body-part or single-joint exercises. Bicep curls, sit-ups, knee extensions, and knee curls are examples of isolated single-joint or body-part exercises. Many assistance exercises may be classified as body-part or single-joint exercises.
Structural or multiple-joint exercises require neural communication between muscles and promote coordinated use of multiple-joint movements. This has recently been shown scientifically in a study that demonstrates that multiple-joint exercises require a longer initial learning or neural phase than single-joint exercises (260). It is especially important to include structural and multiple-joint exercises in a program when-whole-body-strength movements are required for a particular activity. In fact, most sports and functional activities in everyday life depend on structural multiple-joint movements.
For individuals interested in basic fitness, structural exercises may only be advantageous when there is a limited amount of training time and it is necessary to train more than one muscle group at a time. The time economy achieved with structural and multiple-joint exercises is an important consideration for an individual or team with a limited amount of time per training session.
Muscle Action
Whether the muscle action is performed concentrically, eccentrically, or isometrically has an influence on the adaptation to the resistance exercise. Greater force is produced during eccentric muscle actions with the advantage of requiring less energy per unit of muscle force (261,262,263). It has been known for some time that there is a need for an eccentric component to optimize muscle hypertrophy (230,231). This is why techniques such as “heavy negatives,†“forced negatives,†and “slow negatives†have been used by individuals (e.g., bodybuilders) to maximize muscle hypertrophy. With pure eccentric resistance exercise, especially in untrained individuals, delayed-onset muscle soreness can be more prominent than with concentric actions (264). In addition, performing a high-intensity training session or performing new exercises at novel angles can result in greater muscle soreness when an eccentric action is involved. Nevertheless, dynamic strength improvements and hypertrophy are greatest when eccentric actions are combined with concentric actions in a repetition (230).
Isometric muscle actions are less metabolically demanding and less conducive to hypertrophy than dynamic muscle actions (265,266). Isometric strength increases are specific to the joint angles trained (i.e., angular specificity) but have shown carryover of up to ± 30 degrees of the trained angle (267). However, the magnitude of carryover appears greatest at joint angles corresponding to greater muscle lengths (268). Dynamic and isokinetic muscle actions can improve isometric strength, but not to the extent of isometric training itself, further supporting the concept of specificity (269,270). Interestingly, a major criticism of several strength training studies is that subjects were trained dynamically yet tested isometrically (271).
Order of Exercise
Traditionally, it has been recommended that resistance training workouts sequence large muscle group exercises before the exercises involving smaller muscle groups. Exercising the larger muscle groups first, may result in a superior training stimulus being presented to all the muscles involved. This is thought to be mediated by stimulating a greater neural, metabolic, endocrine, and circulatory response, which may augment the training effects of subsequent muscles trained in the workout. This concept was also used in the sequencing of structural or multiple- and single-joint exercises. In this system the more complex multiple-joint exercises (e.g., power cleans) were performed initially followed by the less complex single-joint exercises (e.g., bicep curls). This sequencing rationale is that the exercises performed in the beginning of the workout require the greatest amount of muscle mass and energy for optimal performance. Thus, these sequencing strategies focus on attaining a greater training effect for the large muscle groups. If structural
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exercises are performed early in the workout, more resistance can be used due to a limited amount of fatigue.
Contrary to the preceding discussions pertaining to exercise order, different types of “preexhaustion†methods have been used by bodybuilders in the United States and by weight lifters in the former Soviet bloc countries in their training. These approaches reverse the order of the exercises so that the small muscle groups are exercised before the larger muscle groups, or a single-joint exercise (e.g., dumbbell flye) is performed before a multiple-joint exercise (e.g., bench press). It is theorized that the fatigued smaller muscles will contribute less to the movement, thereby placing greater stress or intensity on the large muscle groups. Nevertheless, the preexhaustion techniques do not appear to be as effective for maximizing strength as the traditional sequencing method (220).
Another consideration in the exercise order is placing exercises that are being taught or practiced (especially complex movements) in the beginning of the exercise order. For example, if an athlete was learning how to perform power cleans, this exercise would be placed in the beginning of the workout, so learning motor skills of an exercise would not be inhibited by prior fatigue.
The order of exercises used in various types of circuit weight training protocols is another issue. The issue relates to whether one follows a leg exercise with another leg exercise or whether it is appropriate to proceed to another muscle group. The concept of preexhaustion can come into play here. Arm-to-leg ordering allows for some recovery of the arm muscles while the leg muscles are exercised. This is the most common order used in designing circuit weight training programs. Beginning lifters are less tolerant of preexhaustion and arm-to-arm and leg-to-leg exercise orders or stacking exercises for a particular muscle group due to high blood lactate concentrations (10 to 14 mmol/L), especially when rest periods between exercises are short (10 to 60 seconds) (272,273). In contrast, stacking exercises is a common practice among elite bodybuilders in an attempt to bring about muscle hypertrophy.
For strength training it is recommended that basic strength exercises such as the squat and bench press be performed initially during the workout. Training for enhanced speed and power entails performance of total-body explosive lifts such as the power clean and jump squats in the beginning of a workout. Bodybuilding entails performance of many exercises under various conditions where training through fatigue is paramount. Improper sequencing of exercises can compromise the lifter's ability to perform the desired number of repetitions with the desired load. Therefore, exercise order needs to correspond with specific training goals. A few general methods for sequencing exercises for both multiple or single muscle group training sessions are
Rotation of push/pull exercises for total-body sessions.
Rotation of upper-/lower-body exercises for total-body sessions.
Large muscles before smaller ones.
Multiple-joint exercises performed before single-joint exercises.
Weak-point exercises performed before stronger ones.
Olympic lifts before basic strength and single-joint exercises.
Most intense exercises performed before least intense (particularly when performing several exercises consecutively for the same muscle group).
One final consideration for exercise order is the fitness level of the individual. As discussed earlier, training sessions should never be designed that are too stressful for an individual, especially a beginning trainee.
Number of Sets
First, it should be noted that not all exercises in a training session need to be performed for the same number of sets. The number of sets is one of the factors in any volume-of-exercise equation (e.g., sets ×3). Typically, three to six sets are used to achieve the optimal gains in strength, and the physiologic responses appear to be different with three versus one set of exercises in a total body workout (274,275). It has been suggested that multiple-set systems work best for development of strength and local muscular endurance (276,277), and the gains made will be at a faster rate than gains achieved through single-set systems (278). In most training studies, one set per exercise performed at the 8 to 12 repetition maximum (RM) at a slow velocity has been compared with both periodized and nonperiodized multiple-set programs. In untrained subjects, several studies have reported similar-strength increases between single- and multiple-set programs, and some have reported superiority of multiple sets. Studies examining resistance-trained individuals have shown multiple-set programs superior for strength, power, hypertrophy, and high-intensity endurance improvements (277,279,280,281,282). Most studies of 14 weeks or longer (especially in trained individuals) demonstrate the superiority of varied, multiple-set programs for long-term improvement. These findings have prompted the recommendation from the American College of Sports Medicine for periodized multiple-set programs when long-term progression (not maintenance) is the goal (283). No study has shown single-set training superior to multiple-set training in either trained or untrained individuals. Therefore, it appears that both programs are effective for increasing strength in untrained subjects during short-term training periods (i.e., 6 to 12 weeks). However, some short-term and all long-term studies support the contention that higher volume of training is needed for further improvement and progression in physical development and performance. Still, the need for variation is also critical for continued improvement, and this includes the use of lower-volume training programs for certain phases of the overall training cycle. The key factor is the use of “periodization†of training volume rather than number of sets, which represents only one factor in a volume and intensity periodization model.
Considering the number of variables involved in resistance training, comparing single- and multiple-set protocols may be an oversimplification. For example, several of the previously mentioned studies compared programs of different set number regardless of differences in intensity, exercise selection, and repetition speed. In addition, the use of untrained subjects during short-term training periods has raised criticism (284), as untrained subjects have been reported to respond favorably to most programs (285). Part of this has evolved because of the popularity of a specific single-set program in which researchers desired to compare it with other protocols. Based on the available data, it appears that previously untrained individuals may not be sensitive to training volume during the initial 6 to 12 weeks of training. The use of a single-set program may be effective for individuals during this time (286). However, it appears that greater volume (within reasonable limits) is needed beyond this point in training to produce optimal improvements. In advanced lifters, further increases in volume may be counterproductive, but it appears that the correct manipulation of both volume and intensity produces optimal performance gains and avoids overtraining (287,288).
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Multiple sets of an exercise present a training stimulus to the muscle during each set. Once initial fitness has been achieved, a multiple presentation of the stimulus (three to six sets) with specific rest periods between sets that allow the use of the desired resistance is superior to a single presentation of the stimulus. The concept that a muscle or muscle group can only perform maximal exercise for a single set has not been demonstrated. In fact, multiple sets at a 10 RM using the same resistance can be repeated with as little as 1 minute rest in highly trained bodybuilders (289) or athletes trained to tolerate short-rest-period protocols (280).
The importance of the exercise volume (sets ×3 repetitions) is a vital concept of training progression. This is especially true in individuals who have already achieved a basic level of training or strength fitness. The time course of volume changes is important to the change in the exercise stimulus in periodized training. Use of a constant volume program may lead to staleness and lack of adherence to training. Ultimately, the variation of training volume (i.e., using both high- and low-volume protocols) to provide different exercise stimuli over long-term training periods will be important to provide rest and recovery periods.
The number of sets performed per workout for multiple-set programs is highly variable and has not received much attention in the literature. In general, the total number of sets per workout will be affected by (a) the muscle groups trained and their consequent size (e.g., large- versus small-muscle-mass exercises); (b) intensity (fewer sets for high intensity and vice versa); (c) training phase (whether the goal is strength, power, hypertrophy, endurance); (d) training frequency and workout structure (e.g., total-body versus upper/lower body splits versus muscle group split workouts); (e) level of conditioning; and (f) use of anabolic drugs (which enable lifters to tolerate higher than normal training volumes). It is common to see resistance training programs incorporating anywhere from 10 to 40 sets per workout. The correct number is based on the individual and depends on the preceding factors.
Rest Periods Between Sets, Exercises, and Repetitions
An understanding of the influence that rest periods have in dictating the stress of the workout and influencing the amount of resistance has been a topic of study over the past 10 years. Rest periods between sets and exercises determine the magnitude of ATP-CP energy source resynthesis and the concentrations of lactate in the blood. The length of the rest period significantly alters the metabolic, hormonal, and cardiovascular responses to an acute bout of resistance exercise, as well as performance of subsequent sets (272,273,280,289,290). Kraemer (280) reported differences in performance with 3- versus 1-minute rest periods. All subjects were able to perform 10 repetitions with 10-RM loads for three sets with 3-minute rest periods for the leg press and bench press. However, when rest periods were reduced to 1 minute, 10, eight, and seven repetitions were performed, respectively.
For advanced training for absolute strength or power, rest periods of at least 3 to 5 minutes are recommended for structural exercises (e.g., squat, power clean, deadlift) using maximal or near-maximal loads, whereas less rest may be needed for smaller-muscle-mass exercises or single-joint movements. For novices to intermediate-level lifters, 2 to 3 minutes of rest may suffice for structural lifts, as loading used during this stage of resistance training appears less stressful to the neuromuscular system (i.e., advanced lifters require resistances closer to his/her genetic potential where maximizing energy stores is crucial to attainment of that level of strength). Robinson et al. (291) reported a 7% increase in squat performance after 5 weeks of training when 3-minute rest periods were used, compared with only a 2% increase when 30-second rest periods were used. Pincivero et al. (292) reported significantly greater strength gains (5% to 8%) when 160-second rest intervals were used compared with 40-second ones. Strength and power performance are highly dependent on anaerobic energy metabolism, primarily through the phosphagen system. It appears that the majority of phosphagen repletion occurs within 3 minutes (293,294). In addition, removal of lactate and other metabolites may require at least 4 minutes (291). Therefore, performance of maximal lifts requires maximal energy substrate availability before the set with minimal or no fatigue. Stressing the glycolytic and ATP-CP energy systems may enhance training for muscle hypertrophy (e.g., bodybuilding). Thus, less rest between sets appears to be effective for hypertrophy, whereas the use of both types of protocols may be important for optimizing strength and size.
In studies by Kraemer et al. (272,273,290), a combination of workouts was used to compare the impact of rest changes on lactate responses. The 5/3 workout consisted of using a 5-RM resistance for all exercises with 3 minutes of rest between sets and exercises. The 5/1 workout consisted of using a 5 RM for all exercises with 1 minute of rest between sets and exercises. The 10/3 and 10/1 workouts consisted of using 10 RM with either a 3- or 1-minute rest between sets and exercises, respectively. Comparisons of the 5/1 to 5/3 and 10/1 to 10/3 demonstrated the dramatic effect rest periods have on blood lactate concentrations. Short rest periods significantly elevated blood lactate concentrations compared with longer rest periods. Comparisons of 5/1 to 10/1 and 5/3 to 10/3 demonstrated the effects on blood lactate concentrations of repetitions at an RM resistance and total work (repetitions × resistance × distance resistance moved) performed. These comparisons indicated that higher volumes of work (10 RM) resulted in higher blood lactate concentrations. The effect that rest periods between sets and exercises, and the total work performed have on blood lactate concentrations is similar for both genders.
These studies indicate that the heavier resistance does not necessarily result in higher blood lactate concentrations. It is the amount of work performed and the duration of the force demands placed on the muscle(s) that influence the blood lactate concentrations. In other words, to produce high concentrations of blood lactate the high-intensity-exercise stimuli must be maintained for a relatively longer time (>20 seconds) than for pure ATP-PC phosphagen metabolism. In addition, repeating the stimuli with limited rest continues to drive the accumulating amounts of lactate in the blood to higher levels. The classic 10 RM performed in a multiple-set fashion (e.g., three sets) provides for such stimuli (272). In addition, a significant amount of muscle mass (e.g., leg exercises versus arm curls) must be stimulated. High force that produces a greater time under tension may also stimulate greater lactate responses than work-matched, higher-velocity, lighter-resistance, and higher-power protocols (295).
From a practical standpoint, it has been demonstrated that short-rest programs can cause greater psychological anxiety and fatigue (296). This might be due to the greater efforts, discomfort, muscle fatigue, and metabolic demands. The psychological ramifications of using short-rest workouts must also be carefully considered when designing a training session. The increased anxiety appears to be due to the dramatic metabolic demands characterized by short rest workouts (i.e., 1 minute or less). Although the psychological demands are higher, the
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changes in mood states do not constitute abnormal psychological changes and may be a part of the arousal process before a demanding workout.
The frequent use of such high-intensity workouts with short rest periods and heavy loading should be slowly introduced into a training program to enable a gradual improvement in tolerance to increased muscle and blood acid levels (decreased pH), and improvements in acid-base buffer mechanisms (297). When such adaptations are vital to an activity (e.g., wrestling or 400- to 800-m track events), the progression of training protocols from long to short rest period lengths is important to improve function. Usually such a program is performed within the context of a more classical strength/power training program for a sport (e.g., two high-lactate workouts and two strength-power workouts in a week cycle) or as a preseason program for 8 to 12 weeks before the start of the sport season. Short rest period length is also characteristic of circuit weight training, but the resistances used are typically lighter (i.e., 40% to 60% of 1 RM are used) (254). This type of training session does not result in blood lactate concentrations as high as those of short-rest-period 10-RM sessions.
Lactic acid may not be the “bad guy†we have often thought it to be (298). Although it may contribute to fatigue, it can be used as a source of energy. Furthermore, it provides a relative comparison of the stress and accumulative utilization of the anaerobic glycolysis system. The type of training session, including rest periods, will determine to a great extent the amount of lactic acid that is produced and removed from the body. Recent studies have shown that elevations in blood lactate concentrations may be important for increases in muscle strength and hypertrophy (299,300). Thus, the role of lactic acid during resistance training appears to be important, depending on the rehabilitation or training goals.
If a particular needs analysis identifies lactic acid as the primary energy source, the rest periods may be gradually shortened to allow the buildup of blood lactate, thus encouraging an increased tolerance and buffering of more acidic conditions. This type of training design (particularly for preseason training) may allow better tolerance for such anaerobic athletes as wrestlers, sprinters (400 to 800 m), and basketball players. Other anaerobic athletes, such as baseball players, rely primarily on the ATP-CP energy system to perform their skills. Consequently, resistance training programs that elevate lactic acid concentrations may not be necessary to improve performance of such sports. Careful manipulation of rest periods is essential to avoid placing inappropriate and needless stresses on the individual during training. Furthermore, because of fatigue created by a high-volume, short-rest workout, it may be inappropriate to place such a workout immediately before a training session designed to develop skill in the sport or activity. Exceptions to this rule of thumb may be in sports such as wrestling, where all skills are performed under conditions of high lactate concentrations.
Training for improved local muscular endurance implies the individual (a) performs several repetitions (or long-duration sets), (b) trains to and beyond the point of fatigue, and/or (c) minimizes recovery between sets (i.e., training in a semifatigued state). Therefore, many repetitions and shorter rest periods (30 to 90 seconds or less) for local muscular endurance training appear to be most effective (301).
The amount of rest taken between repetitions has only been partially addressed. Rooney et al. (302) had subjects train using six to 10 consecutive high-intensity repetitions or six to 10 repetitions separated by 30-second rest periods. They reported significantly greater strength improvement with consecutive repetitions (56%) than with extended rest between repetitions (41%). These findings demonstrate that fatigue may contribute to the strength training stimulus. However, if a high percentage of the peak velocity or power is desired for each repetition in the workout, longer rest periods with fewer repetitions for several sets may need to be performed. Future research will need to address this aspect of rest between repetitions, as the “quality†of each repetition begins to take on greater importance in producing gains in strength and power. Rethinking of the old “rest-pause†training system may be one of the new directions for research in optimizing quality of the training session. With new feedback systems on resistance exercise equipment allowing signaling of other performance factors beyond just lifting a weight, the quality of each repetition can be evaluated based on the percent of peak velocity or maximal power. The concept of a quality repetition in a workout will start to see more scrutiny and evaluation. Interestingly, it remains to be determined where the above “fatigue†stimuli and the later, more “full recruitment†stimuli requiring a longer rest period interface for optimal training effects. Most likely both styles of training may be needed to gain different aspects of strength, size, and power fitness.
Resistance Used (Intensity)
The amount of resistance used for a specific exercise is probably one of the key factors in any resistance training program (278). It is the major stimulus related to changes observed in measures of strength and local muscular endurance. When designing a resistance training program, a resistance for each exercise must be chosen. Either repetition maximums (RM) or the specific resistance that only allows a specific number of repetitions to be performed probably provides the easiest way to determine a resistance. Typically, one uses a training RM target (a single RM target such as 10 RM) or RM target zone (a range such as 3 to 5 RM). As the strength level of the lifter changes over time, the resistance is adjusted so a true RM target or RM target zone resistance is used.
Research has supported the basis for an RM continuum (276,278,301,303). This continuum simply relates RM resistances to the broad training effects derived from their use. An inverse relationship exists between the amount of weight lifted and the number of repetitions performed. Several studies have indicated that training with loads corresponding to 1 to 6 RM was most conducive to increasing maximal dynamic strength (304,305). Although significant strength increases have been reported using loads corresponding to 8 to 12 RM (233,280,306) and this load range appears most effective for increasing muscular hypertrophy (307), loads lighter than this (i.e., 12 to 15 RM and lighter) have only had small effects on maximal strength in previously untrained individuals (301). However, they have been shown to be very effective for increasing local muscular endurance (308). Contrary to early studies in resistance training, it appears that using a variety of training loads is most conducive to increasing muscular fitness as opposed to performing all exercises with a 6-RM load, for example (309). Therefore, periodized training in which great load variation is included appears most effective for long-term improvements in muscular fitness.
Moving away from the 6-RM or less strength stimulus zone, the gains in strength diminish until they are negligible. The strength gains achieved above 25-RM resistances are typically small to nonexistent in untrained individuals (276,301) and may be related to enhanced motor performance or learning effects when they occur. Various individual responses due to genetic predisposition and pretraining status affect the training
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improvements observed. But after initial gains have been made as a result of learning effects, heavier resistances will be needed to optimize muscle strength and size gains.
Another method of determining resistances for an exercise involves using a percentage of the 1 RM (e.g., 70% or 85% of the 1 RM). If the trainee's 1 RM for an exercise is 100 lb, 80% of the 1 RM would be 80 lb. This method requires that the maximal strength in various lifts used in the training program be evaluated regularly. If 1-RM testing is not done regularly (e.g., each week), the percentage of 1-RM used in training decreases and therefore the training intensity is reduced. From a practical perspective, use of percentage of 1-RM determination for many lifts may not be feasible because of the amount of testing time required. Use of an RM target or RM target zone allows the individual to adjust resistances in response to an ability to perform greater repetitions in order to stay at the RM target or within the RM target zone.
The use of a percentage of the 1-RM resistance is warranted for lifts related to the competitive Olympic lifts of the clean and jerk, snatch, and variations. Since these lifts require coordinated movements and optimal power development from many muscles to result in correct lifting technique, the movements cannot be performed at a true RM or to momentary failure. The reduction in velocity and power output experienced in the last repetition of an RM set is not conducive to such structural lifts. Therefore, a percentage of the 1-RM should be to correctly calculate resistances for such lifts.
In two studies by Hoeger et al. (310,311), the relationship between the percent of 1-RM and the number of repetitions that can be performed was studied in both trained and untrained men and women. It was demonstrated that this relationship varies with amount of muscle mass needed to perform the exercise (i.e., leg press uses more muscle mass than knee extensions). When using machine resistances with 80% of the 1-RM, previously thought to be primarily a strength-related prescription, the number of repetitions that could be performed was typically greater than 10, especially for large-muscle-group exercises such as the leg press. The larger-muscle-group exercises appear to need much higher percentages of the 1-RM to keep them in the strength RM zone of the repetition continuum.
In a study by Kraemer et al. (312), it was shown that power lifters could lift 80% of their 1-RM in the leg press for 22 repetitions (e.g., 80% of the 1-RM equated to the 22-RM resistance) and the untrained controls could only perform 12 repetitions at 80% of their 1-RM (e.g., 80% of the 1-RM equated to the 12 RM). Such data, along with the data presented in the two important studies by Hoeger et al. (310,311), clearly indicate that the method used to determine the resistance to be used for specific exercises in a training program must be carefully considered for each muscle group and for each specific type of lift and the exercise mode used (e.g., free weight squat versus leg press machine). In general, a certain percentage of the 1-RM with free weight exercises will allow fewer repetitions than the same percentage of 1-RM on a similar exercise performed on a machine. This is probably due to the need for greater balance and control in space when using free weights.
Charts have been developed to predict the 1-RM from the number of repetitions performed with a submaximal load or to help determine an RM (e.g., from 1 to 10) from the 1-RM resistance that can be lifted. Unfortunately, most of these charts assume a linear relationship between these variables, which is not the case. Thus, such charts and the resulting values should only be used as rough estimates of a particular resistance to use for an RM resistance or to predict an individual's 1-RM. A variety of prediction equations are available to predict 1-RM, but these equations have the same inherent weaknesses as the prediction charts.
The amount of weight lifted per repetition or set is highly dependent on other variables, such as exercise order, volume, frequency, muscle action, repetition speed, and rest period length (313). Altering the training load can significantly affect the acute metabolic (314,315), hormonal (272,273,316), neural (221,317), and cardiovascular (318) responses to training.
The load required to increase maximal strength may depend on training status. A load of at least 45% to 50% of 1-RM is needed to increase dynamic muscular strength in beginners (319). However, greater loads are needed in more experienced subjects. Häkkinen et al. (317) reported that at least 80% of 1-RM was needed to produce any further neural adaptations during resistance exercise. Neural adaptations are crucial to resistance training, as they precede hypertrophy during intense training periods. Thus, it appears that a variety of loads conducive to increasing both neural function (i.e., increased motor unit recruitment, firing rate, and synchronization) and hypertrophy is most effective for strength training.
Repetition Speed
The speed used to perform dynamic muscle actions affects the adaptations to resistance training. Repetition speed is dependent on training loads, fatigue, and training goals, and has been shown to significantly affect neural (262,317), hypertrophy (320,321), and metabolic (322) adaptations to resistance training. Force production and repetition speed directly interact during exercise performance. Generally, force production is greatest at slower speeds and lowest during high-speed movements. This relationship is graphically represented as by the force-velocity curve discussed earlier in this chapter. The implications of the force-velocity relationship is that training at slow velocities with maximal tension will be effective for strength training and training with high velocities will be effective for power/speed enhancement. This generally is the case; however, an interaction between both extremes of the velocity spectrum may be most effective for both strength and power enhancement.
Generally, moderate to rapid speeds (i.e., 1 to 2 seconds concentric, 1 to 2 seconds eccentric) are most effective for enhancing gains in strength and power performances compared with slow speeds, which appear most effective for increasing local muscular endurance and isometric strength for a specific number of repetitions. LaChance and Hortobagyi (323) reported significantly greater average power, work, and total number of repetitions performed using a self-selected (rapid) speed, compared with 2-second concentric and 2- or 4-second eccentric repetition speeds. Thus, improving set performance (i.e., number of repetitions or load) may be best accomplished with use of moderate to fast speeds.
A distinction needs to be made when examining intentional and unintentional slow-speed repetitions. Unintentional slow lifting speeds are used during high-intensity repetitions (i.e., strength training) in which either the loading and/or fatigue are responsible for the longer repetition duration. For example, the positive phase of a 1-RM bench press and the last repetition of a 5-RM set may last 3 to 5 seconds (324). This may be considered slow by comparison; however, lifting the weight faster is not possible during maximal efforts. These types of unintentionally slow lifting speeds are crucial to maximal strength development.
Intentional slow-speed repetitions are used with submaximal loads, where the lifter has greater control of the speed.
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Keogh et al. (325) showed that the force produced during the concentric phase was significantly lower for intentionally slow (5-second concentric, 5-second eccentric) lifting compared with traditional (i.e., moderate) speed with a corresponding lower integrated electromyographic (IEMG) activity for the slow speed. This study shows that motor unit activity may be limited when attempting to intentionally lift slowly. In addition, the lighter loads required to lift slowly may not provide an optimal stimulus for strength enhancement. Therefore, intentionally slow lifting appears to be most suitable for increasing local muscular endurance, where the time under tension is greater than moderate and fast speeds.
In comparison, both fast and moderate lifting speeds can increase local muscular endurance, depending on the number of repetitions performed and rest between sets. Training with fast speeds is the most effective way to enhance muscular power and speed, and is effective for strength enhancement (326) but not as effective for hypertrophy at slow or moderate speeds (317). High-speed repetitions impose fewer metabolic demands in exercises such as the leg extension, squat, row, and curl than slow and moderate speeds (322). In addition, training for power is best accomplished through lighter loads (30% of the 1-RM) performed at maximal speeds (<1:1.5 ratio) (327).
A popular technique used for both strength and power training is compensatory acceleration (328,329). Compensatory acceleration requires the lifter to accelerate the load maximally throughout the motion (regardless of momentum) during the positive phase, thus striving to increase bar velocity to maximal levels. A major advantage is that this technique can be used with heavy loads and is quite effective, especially for multiple-joint exercises (330). Hunter and Culpepper (331) and Jones et al. (330) reported significant strength and power increases throughout the range of the movement when compensatory acceleration was used, and the increases were greater than those for training with a slower speed (330).
Rest Periods between Workouts (Training Frequency)
The number of training sessions performed during a specific period time (e.g., 1 week) may affect subsequent training adaptations. Frequency also includes the number of times certain exercises or muscle groups are trained per week and depends on several factors, such as volume and intensity, exercise selection, level of conditioning and/or training status, recovery ability, nutrition, and training goals. Training with heavy loads increases the recovery time needed before subsequent sessions, especially for multiple-joint exercises (319). The use of extremely heavy loads (90% to 100% of 1-RM) may require 72 hours of recovery, whereas low and moderate loads (60% to 85% of 1-RM) may require less recovery time (48 and 24 hours, respectively) (332). In addition, reduced frequency is adequate during maintenance training. Training 1 or 2 days per week is adequate for muscle mass, power, and strength retention (319). However, this appears effective for short time periods, as such long-term maintenance training (i.e., reduced frequency and volume) may lead to detraining.
Heavy eccentric training requires greater recovery time between workouts. Loading during eccentric training may be substantially more than concentric (i.e., 120% to 130% of 1-RM). Studies show that eccentric exercise is more conducive to delayed-onset muscle soreness (DOMS) (264,333,334). Eccentric training causes greater muscle fiber and connective-tissue disruption, enzyme release, DOMS, and impaired neuromuscular function that limits force production and range of motion (335). Recovery times of at least 72 hours are required before initiating another session requiring several heavy sets or supramaximal eccentric lifts (332). Thus, frequency modulation is needed for heavy eccentric training. A recent study in untrained subjects compared frequencies of 1 day/week to 2 or 3 days/week (336). Each session consisted of seven sets of 10 1- or 2-second eccentric-only contractions for the quadriceps muscles. Both training groups showed improvement following training. However, the results showed that eccentric training once per week was effective for maintenance, whereas two times per week was more effective for strength increases. Thus, the inclusion of heavy eccentric repetitions may necessitate a change in frequency (or the muscle groups trained per session) to accommodate the greater muscle damage.
Numerous resistance training studies have used frequencies of 2 or 3 alternating days per week in untrained subjects (230,337). This has been shown to be a very effective initial frequency. If the resistance training is not excessive, only moderate amounts of delayed muscular soreness should be experienced 1 day after the session. Some studies have shown 3 days/week to be superior to 2 days/week (338), whereas 3 to 5 days were superior in other studies (339,340). The progression from beginning to more aggressive training does not necessitate a change in frequency but may be more dependent on alterations in other acute variables, such as exercise selection, volume, and intensity. However, it is common to see three or four training sessions per week among those individuals training more aggressively. Increasing training frequency allows for greater specialization (i.e., greater exercise selection per muscle group and/or volume in accordance with more specific goals). To achieve a higher frequency of training, more detailed workouts should be developed, as simply performing the same exercises four times rather than three times per week is not the optimal approach to increasing frequency. Programs should use exercises that involve similar muscle groups but use different angles for particular movements (referred to as split programming) (220). For example, a 4-day-per-week routine that involves performing the bench press all 4 days would be better designed by having the individual perform a regular bench press on 2 days and an alternate type of bench press (e.g., incline bench press) on the other 2 days. Thus, split programming allows for more variety in the exercise choices, because of the increase in the number of training days available. In addition, total-body or split-body-part workouts have been used to allow more training variety. Both styles of training (total-body or split-body-part workouts) have been shown to produce improvements in muscle strength and size (341). However, it is recommended that similar muscle groups or selected exercises not be performed on consecutive days during split-routine workouts to allow adequate recovery and to minimize the risk of overtraining.
Training frequency for advanced or elite athletes may vary considerably (depending on intensity, volume, and training goals) and is typically greater than in intermediate lifting. One study demonstrated that football players training 4 or 5 days/week achieved better results than those self-selected frequencies of 3 and 6 days/week (342). Weight lifters and bodybuilders typically use high-frequency training (i.e., four to six sessions per week). The frequency for elite weight lifters and bodybuilders may be greater. Double-split routines (i.e., two training sessions per day) are common (332,343,344) during preparatory training phases, which may result in eight to 12 training sessions per week. Frequencies as high as 18 sessions per week have been reported in Bulgarian weight lifters (332). The rationale for this high-frequency training is that frequent short sessions followed by periods of recovery, supplementation, and food intake allow for high-intensity training via maximal energy utilization and reduced fatigue during exercise performance (319). Häkkinen and Kallinen (343) reported greater
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increases in muscle size and strength when training volume was divided into two sessions per day as opposed to one among female athletes. In addition, exercises performed by Olympic lifters (i.e., total body lifts) require technique mastery that may increase total training volume and frequency.
Elite power lifters typically train with frequencies of four to six sessions per week (345). The superior conditioning of these athletes allows them to tolerate such high-frequency programs. However, training at these high frequencies would result in overtraining in most individuals. It is important that the individual be able to tolerate the physical stress so that an overtraining phenomenon does not develop (346). The development of periodized training cycles uses variations in training frequency to alter the exercise stimulus and provide for recovery and enhance the exercise stimulus.
Using a training program of 3 days a week for all situations and sports is not ideal. It is the individual needs and goals that determine the amount of exercise required to increase a particular physiologic or performance variable. Progression in frequency is also a key component to resistance training. Frequency of training will vary, depending on phase of the training cycle, fitness level of the individual, goals of the program, and training history. Careful choices need to be made regarding the rest between training days. These choices are based on the planned progress toward specific training goals and the tolerance of the individual to the program changes made. If excessive soreness is present the morning after a training session, this may indicate that the exercise stress is too demanding. If this is the case, the workout loads, sets, and/or rest periods between sets and training frequency need to be evaluated and adjusted.
The configuration of these variables results in the exercise stimulus for a particular workout. Workouts must be altered to meet changing training goals and to provide training variation. Within this paradigm for the description of resistance exercise workouts, careful control of various components can be gained in manipulating variables to create new and optimal training programs (347). Because so many different combinations of these variables are possible, an almost unlimited number of workouts can be developed. Understanding the influence and importance of each of the program variables in achieving a specific training goal is vital to creating the optimal exercise stimulus.
Each program must be designed to meet the individual's needs and training goals with recognition of the individual's initial fitness level. It is important to remember that evaluation of a fitness level (e.g., 1-RM strength test) is typically not done until it is known that the individual can tolerate the test demands so that the data generated are meaningful (348). One of the most serious mistakes made in designing a resistance workout is placing too much stress on the individual before it can be tolerated.
FLEXIBILITY
Importance
It is important to maintain a range of motion adequate to perform one's desired activities. Lost range of motion can interfere with such functional activities as ambulation, self-care, or attendant care. Severe restrictions in range of motion may even produce complications such as skin breakdown. Even relatively small reductions in range may result in biomechanical accommodations that place abnormal stress on tissues elsewhere in the body that can induce secondary problems.
Although it is clear that restoration and maintenance of a functional range of motion is desirable, the benefits from greater flexibility are not clear. Proponents of stretching have claimed numerous positive effects, including the prevention of musculoskeletal injuries and improved performance in sports, reduced postexercise muscle soreness, and improved general well-being. Nevertheless, the objective support for these claims is limited. Preexercise stretching has been demonstrated to have no effect on the development of delayed-onset muscle soreness (349). It has also recently been demonstrated that running economy is even better among those who have some lower-extremity tightness (350,351). This has been suggested to be related to the ability to better use elastic storage and recovery and minimize the need for muscle-stabilizing activity. In contrast, the performance of a rebound bench press (no pause between the eccentric and concentric work) among power lifters has been demonstrated to be improved through enhanced flexibility (352). This finding was attributed to a reduction in stiffness of the musculotendinous unit that allowed better utilization of elastic storage and recovery.
Factors Affecting Range of Motion
A number of factors can limit joint range of motion, including tightness of soft-tissue structures such as muscle, tendon, ligament, and joint capsule. Involuntary muscle contraction in the form of spasm can also restrict range. The bony contour of the joint is important in determining the full range of motion. When there is abnormal bone growth around a joint, range can be restricted. In addition, intraarticular loose bodies (e.g., bone or cartilage) and excessive fluid can restrict joint range of motion.
Range of motion varies widely among individuals. Regular activities using a full range of motion will help maintain range, but the maintenance of range of motion is specific to the joints that are used. For instance, an individual can have normal range in one joint but have severely restricted range in another. When connective tissue is not stretched, the collagen component gradually shortens. As a result, the periarticular collagen and the connective tissue of the muscle shorten. Furthermore, immobilization of a muscle in a shortened position also causes a decrease in the muscle length through a decrease in the number of sarcomeres in the muscle (353).
Age and sex also seem to affect range of motion. Women tend to have greater range of motion than men, and young people usually have greater range than the elderly. Tissue temperature is another factor affecting range of motion, with warm tissue having greater distensibility than cool tissue (354,355,356).
Techniques to Assess Range of Motion
Range of motion may be assessed in various ways. Angle measurements can be made with a goniometer, electrogoniometer, or flexometer (357). Flexibility for some movements is also commonly assessed through distance measurements between specific reproducible reference points. One example of this technique would be the assessment of temporomandibular joint motion through measurement of the distance between the upper and lower incisors.
Methods to Improve Range of Motion
TECHNIQUES
Restoration of joint range of motion and soft-tissue extensibility can be achieved through the use of several different stretching
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techniques and modalities. The three general categories of stretching techniques include ballistic, static, and proprioceptive neuromuscular facilitation (PNF) procedures.
Ballistic stretching is characterized by repetitious bouncing movements, where the momentum of a moving body segment is used to generate forces producing a rapid stretch. Fast rates of stretching, as is the case with ballistic stretching, are not advisable, particularly during the early phases of rehabilitation. When fast stretch rates are used, greater tensions are developed, and more energy will be absorbed within the muscle-tendon unit for a given length of stretch (358). As a result, there is a greater risk for injury with this type of stretching. Furthermore, ballistic stretching does not appear to be as effective in enhancing range as other methods of stretching (359,360).
Static stretching involves a slowly applied stretch that is held for several seconds. Proponents of this technique believe that the muscle stretch reflex is minimized through a slow, progressive stretch (361). Static stretching is generally easy to perform, can be done voluntarily or received passively by the individual, and has little associated risk of injury. Although the optimal time to hold a static stretch and number of stretches that should be performed is not known, experimental studies on animals suggest that most stress relaxation takes place during the initial 12 to 18 seconds and that there is little alteration in muscle-tendon unit lengthening after the fourth stretch (358).
Several stretching techniques use the principles of PNF that were developed by Kabat (362) to aid in the rehabilitation of injured World War II veterans. The concept of these stretching techniques is to enhance relaxation of the muscle to be stretched through reciprocal inhibition and the stretch reflex. The two most common PNF stretching techniques are the contract-relax technique and the agonist contract-relax technique. With the former, the muscle is passively stretched, then contracted for 6 to 8 seconds, and then relaxed and passively stretched further to an increased pain-free range. This process is repeated three to six times. Theoretically, the prestretch contraction of the muscle results in inhibition through Golgi tendon organ reflexes.
The agonist contract-relax technique is identical to the contract-relax technique except that the stretch is accompanied by a submaximal contraction of the opposing muscle to the one being stretched. This voluntary contraction of the opposing muscle theoretically results in reciprocal inhibition of the stretched muscle.
When able to participate, the patient can provide valuable feedback to ensure that appropriate positioning is used so that the desired tissues are being stretched. The patient should also understand that some discomfort may be required for adequate stretching, but prolonged poststretching pain is indicative of an overzealous approach. It also seems to be of considerable importance for the patient and therapist to understand that the most rapid gains in range of motion will be achieved through regular stretching. In some cases, the performance of stretching exercises several times each day is desirable, but increases in range of motion can be achieved through three to five sessions per week (359,360).
MODALITIES
Some modalities may be used to enhance range of motion. Because the distensibility of warm tissue is greater than that of cool tissue (354,355,356), heat is commonly used before stretching. Ultrasound is the best therapeutic modality for heating deep-lying tissues (363) and can be used effectively as a prestretching treatment when there are no contraindications for its use. One should also take advantage of the elevation in tissue temperature that can be achieved through exercise. For example, the quadriceps intramuscular temperature can be elevated by 2°C after 10 minutes of cycling at a moderate intensity (Fig. 17-26).
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Figure 17-26. Effect of leg cycling at different intensities and durations on intramuscular temperature of the quadriceps at a depth of 3 cm. The mean resting value is represented at R. (With permission from Hoffman MD, Williams CA, Lind AR. Changes in isometric function following rhythmic exercise. Eur J Appl Physiol 1985;54:177–183.) |
Simultaneous stretching and brief application of fluorimethane spray (stretch and spray) or passage of ice along the course of the muscle being stretched has also been advocated as a means to enhance the stretch of muscles (364). When an active trigger point is present, stretching may be enhanced by injection of a small amount of local anesthetic into the trigger point before stretching. The reader is referred elsewhere (364) for a description of the techniques for stretch and spray and trigger point injections.
PROPRIOCEPTION
Importance
Proprioceptive organs provide the central nervous system with information about the position and movement of body parts. Recent work has demonstrated the importance of proprioceptive sensation in the rehabilitation after injuries, and in understanding the etiologies and predisposing factors to injuries and reinjuries.
Decreased joint proprioception has been observed in patients with osteoarthritis, rheumatoid arthritis, and Charcot's disease and is believed to influence the progressive joint deterioration with these disorders (365,366). The risk of falling may also relate to proprioception as measures of postural sway have been demonstrated to relate to the falling risk (367,368,369,370).
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Much of the work demonstrating the importance of proprioception in rehabilitation comes from the sports medicine literature. The importance of improving proprioception has been demonstrated by the finding of a significantly greater risk of sustaining an ankle injury during soccer among players with abnormal proprioceptive testing compared with those players with normal values (371). The successful return to sport after a ligament injury may be even more dependent on proprioception than on ligament tension (372).
Factors Affecting Proprioception
Sensation of the position and movement of a joint arise from afferent information originating from muscles, joint capsules, ligaments, and skin. As a result, injuries or disease to these structures may affect proprioception. For instance, reduced proprioception has been shown to be associated with knee (373) and ankle (374,375,376) ligament injuries, rheumatoid arthritis (377), and osteoarthritis (365). The importance of muscle receptors in proprioception has been demonstrated through the finding of impaired reproduction of joint angle after fatiguing contractions of the associated muscles (378).
Disease of the neurologic system may also affect proprioception. Diabetics with cutaneous sensory neuropathy have been shown to have a significant loss of ankle joint proprioception (379). Decreases in proprioception have also been found with increasing age (365,377,380,381) and may be part of the normal aging process.
Techniques to Assess Proprioception
Methods for accurate and objective assessment of joint movement and position perception have not been adequately developed for widespread clinical use. The most common clinical method of evaluating proprioception is a nonquantitative test of joint position perception consisting of the subject verbally describing the joint position after the examiner passively moves the segment into one of two or more predetermined positions (382). Another nonquantitative testing technique used in the clinical setting involves testing the ability of a person to return a joint to a predetermined joint position.
In the research setting, a number of techniques have been used in the evaluation of proprioception. These research techniques include using an isokinetic dynamometer to quantify angles during reproduction of a predetermined joint position (383,384), matching of joint position with the side contralateral to the one being passively moved or positioned (385,386,387), and measurement of joint movement perception threshold (379,383,388). Although not exclusively a measure of proprioception, other techniques that may provide related information about balance and coordination include measures of postural sway (389,390) and responses to perturbations that create sway (391).
Techniques to Improve Proprioception
Proprioceptive exercises are performed with the goal of reducing the proprioceptive deficits that may have resulted through injury or disease. There is some evidence for the effectiveness of proprioceptive exercises in that it has been shown that the proprioceptive deficits present after ligament injuries can be reduced (392,393,394).
Classic lower-extremity proprioceptive exercises have used the tilt (teeter or wobble) board. Unidirectional boards may be used initially, followed by multidirectional boards. More functionally specific proprioceptive exercises can also be developed. These activities may include backward and sideways walking and running, or other agility drills.
It should also be noted that elastic bandaging (365) has been shown to improve position sense in those with impaired proprioception. This may be achieved through enhancement of the activity of the skin proprioceptors.
THE EXERCISE PRESCRIPTION
General Considerations
The exercise prescription should be a systematic and individualized recommendation about physical activity for development and maintenance of health and fitness and/or treatment of specific conditions. Regardless of the individual's age, functional capacity, or medical conditions, the exercise prescription should include information about the mode, intensity, duration, frequency, and rate of progression of physical activity. Each exercise session should also use an appropriate warm-up and cool-down period, which could include flexibility exercises. Individualization of the exercise prescription is based on considerations of the individual's health history, cardiac risk factors, behavioral characteristics, personal goals, exercise preferences, and specific exercise needs.
The specific purpose of an exercise program will depend on the individual. However, exercise goals generally include (a) to counteract the detrimental physiologic effects of previous sedentary living or a transient period of reduced activity associated with disease or injury, and (b) to optimize functional capacity within the physical limitations of medical conditions that may be present. In addition, valuable clinical information for the ongoing treatment of a patient can frequently be elicited through exercise training programs.
Risk Stratification
A concern in advising middle-aged and older people is the risk of sudden cardiac death or other cardiac complications associated with exercise. The incidence of sudden death with exercise is low, but when it occurs in those more than 35 years of age, it is usually related to a combination of coronary artery disease and vigorous exercise (395). It is important to note that the benefits of exercise conditioning outweigh the small risk of sudden cardiac death or other cardiac complications (93,396,397). Furthermore, regular exercise may help protect against sudden death or myocardial infarction from strenuous physical activities (58,63,93,396).
Risk stratification assists in the decision about how to proceed in developing an exercise program. This is performed through a clinical evaluation that includes identification of the presence of coronary risk factors. The coronary artery disease risk factor thresholds are displayed in Table 17-7. Those younger individuals (men <45 years of age, women <55 years of age) who are asymptomatic and meet no more than one risk factor threshold from Table 17-7 are considered at low risk. Those older individuals (men ≥45 years of age, women ≥55 years of age) or those who meet the threshold for two or more risk factors from Table 17-7 are considered at moderate risk. Individuals with one or more signs/symptoms from Table 17-8 or with known cardiovascular, pulmonary, or metabolic disease are considered at high risk.
Those at low risk can begin moderate (intensities of 40% to 60% of V·O2max) or vigorous (intensities greater than 60% of V·O2max) exercise programs without the need for further assessment (Table 17-9).
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Those at moderate risk are not thought to require further assessment before starting a moderate exercise program, but they should have a medical examination and exercise test before beginning a vigorous exercise program. Those at high risk should have a medical examination and exercise test before starting a moderate or vigorous exercise program.
TABLE 17-7. Coronary Artery Disease Risk Factor Thresholds |
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For those who have recently experienced a cardiac event, participation in a supervised exercise program within a cardiac rehabilitation program is an effective and safe way of initiating an exercise program and then progressing to an aerobic-intensity threshold (398). Surveys indicate low morbidity and mortality rates associated with supervised exercise programs (399,400,401,402). A 1986 report derived from a survey among 167 supervised rehabilitation exercise centers (400) indicated a rate of cardiac arrest of one per 112,000 patient-hours, a rate of nonfatal myocardial infarction of one per 294,000 patient-hours, and a mortality rate of one per 784,000 patient-hours. A more recent study published in 1998 from a 16-year assessment within one center indicated that the rate of adverse events had not increased substantially despite inclusion of more higher-risk patients in cardiac rehabilitation programs (402).
In children and young adults, deaths associated with physical activities are uncommon, but when they occur, they are generally related to congenital heart disease or acquired myocarditis (93,403). Individuals with known congenital heart disease should generally be encouraged to remain physically active but refrain from vigorous and competitive athletics (93). Screening for detection of cardiac abnormalities in healthy young people before participation in sports appears to be of limited value (403).
TABLE 17-8. Major Signs or Symptoms Suggestive of Cardiovascular and Pulmonary Disease |
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Injury and Illness Precautions
It is important that exercise programs be designed to avoid inducing or exacerbating health problems. Although any exercise carries some risk of injury, the risk can be extremely minimal through individualization of the exercise prescription. An increased
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risk of musculoskeletal injury is associated with weight-bearing activities, high exercise intensities and volume, previous history of injury, biomechanical abnormalities, and a rapid increase in exercise participation. Injury risk can be minimized by avoidance of weight-bearing activities in those predisposed to musculoskeletal injuries because of obesity, previous injury or biomechanical abnormalities. Selection of appropriate footwear and gradual increases in physical activity are also important to minimizing injury.
TABLE 17-9. Recommendations for Medical Examination and Clinical Exercise Testing Prior to Exercise Participation |
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The effect of exercise on immune function is not completely understood. There is some evidence that regular aerobic exercise enhances immune function but that strenuous exercise may transiently impair immune status (179,180,181,182,183). Furthermore, the effect of exercise on the progression of existing infectious diseases like viral respiratory infections is not well understood. Myocarditis can develop when individuals continue to exercise in the presence of such illnesses. Therefore, strenuous exercise should usually be avoided in the presence of fever or myalgia.
Environmental Factors
Hot and/or humid conditions can increase the health risk associated with exercise. In extreme conditions of exercise and environmental heat stress, competition for blood flow between muscle and cutaneous vascular beds can lead to reduced ability to exercise and/or thermoregulate. Serious heat disorders with exercise are more common in competitive events, where the drive to perform well can override normal signals to stop or decrease work levels. Because of the potential health hazards of exercise performed in hot/humid environmental conditions, some organizations or groups cancel events or release warnings regarding activity participation based on environmental conditions. When participating in activities performed in a hot environment, people should monitor their ability to respond physiologically to the combined stressors. Heart rate tracks upward and rating of perceived effort typically rises in relation to the body heat load. Thus, these parameters can provide important feedback in regulating work level in a hot environment (74,77).
The importance of fluid intake during sustained exercise should be emphasized. Anyone planning to compete in an endurance-type activity combined with heat stress should undergo heat acclimation before competition. Daily exercise in the heat for 7 to 10 days will significantly improve ability to thermoregulate (74). Some of the physiologic adjustments with acclimation include improved sweating (earlier onset and increased capacity), decreased loss of electrolytes, and increased blood volume. As a consequence of acclimation, physiologic strain during exercise combined with heat is reduced, as evidenced by a lower heart rate and core temperature (74). A position statement issued by the American College of Sports Medicine on preventing heat problems with distance running serves as a useful guide for avoiding heat-related problems with exercise (404).
In extremely cold environments, it is important to provide protection against hypothermia and cold injuries to exposed skin. Appropriate clothing and protection of the hands and face can allow comfortable continuation of exercise under quite extreme conditions.
Concerns regarding the safety of exercise at altitude have been raised, especially for patients with ischemic heart disease (405,406). Typically, work capacity is reduced at high altitudes due to lower oxygen availability. This effect is seen starting at about 1,500 m and is reduced further about 6% to 10% per additional 1,000 m of ascent. Most resort areas and major highways are located at less than 4,000 m. Minimal information is available regarding the safety of exercise at altitude for patients with cardiopulmonary diseases, although it appears that exercise is safe for many cardiac patients, at least up to moderate altitudes (405). Because work capacity often is reduced at altitude, the amount of absolute work that can be performed at a prescribed index of myocardial work (i.e., rate-pressure product) will be lower at high altitude than at sea level. Because of the impact on work capacity, heart rate and perceived effort provide better indices to gauge work level than absolute work units. Because of the improved oxygen-carrying capacity brought on during the first few days of exposure to altitude, vigorous physical activities should be delayed on immediately arriving at high altitudes.
Safety issues regarding exercise combined with air pollution have been raised. As reviewed elsewhere (74,406), minimal information is available regarding the impact of many air pollutants on work tolerance or cardiovascular responses to exercise. Because air pollutants can impact on oxygen-carrying capacity and lung function, communities often issue ozone alerts when the ozone level reaches a critical threshold. These alerts often advise people, especially those with coronary artery and pulmonary diseases, to avoid outdoor exercise. The long-term health effects of repeated exercise combined with air pollution remain unclear.
Other environmental factors may also impact certain types of exercise. For instance, uneven or soft terrain and the presence of wind may substantially increase physiologic demands (407,408) and require that absolute work rates be adjusted downward. For some individuals it is important to also consider the risk of falling presented by the exercise environment.
Equipment
A multitude of devices are on the market for use in strength and aerobic training. Special devices are also available for stretching and proprioceptive exercises. Special exercise equipment items are often used in the clinical setting and may be quite advantageous under some circumstances. Nevertheless, it is generally desirable to develop exercise programs that can be continued by the patient outside the clinical setting. This frequently means developing exercise programs that are not reliant on special equipment. For strength training this may mean that exercises need to be designed that use body weight, readily available items found at home, or elastic tubing as the resistive force. Maintenance and development of aerobic conditioning can also be achieved through many different modes of exercise. When walking and running are appropriate options for an individual, these modes of exercise can certainly be as beneficial as other forms of exercise (202) and do not require any special equipment. Viable alternatives for some individuals may include the use of community resources or purchase of exercise equipment for use at home.
Compliance
Exercise requires participation by the individual performing the exercise. This is sometimes a challenging concept to overcome when working with some patients who have grown accustomed to the classical medical model of passively accepting the treatment provided by their clinicians. Instilling an understanding of the concept that the individual needs to be a participant in the exercise program, along with a basic understanding of exercise, is critically important for success of the exercise program.
Often patients do not understand the differences between stretching and strengthening, and between exercises to develop strength and those to develop aerobic capacity. For
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strength gains to occur, it is important for the patient to understand that the muscles need to be voluntarily contracted against resistance. Whether the exercise is for strengthening, aerobic conditioning, or stretching, patients need to realize that some discomfort is required for success, but they should also recognize the difference between an appropriate level of discomfort and signals of overzealousness.
When exercise is initiated too aggressively, the transient exacerbation of symptoms or delayed-onset muscle soreness may be discouraging to the patient. Postexercise cryotherapy to local areas of inflammation may control exacerbations of symptoms. Restriction in the use of exercises involving eccentric contractions may also limit the development of delayed-onset muscle soreness.
Another important concept for the patient to understand is that the desired changes resulting from an exercise program may not occur in a few days or even a few weeks. The patient must commit to a regular and consistent exercise routine for success. Adherence to a supervised exercise program depends on the personality characteristics of the patient, various aspects of the rehabilitation setting, and the quality of the relationship developed between the patient and clinicians (409). Motivation of the patient is an essential element to success. Education and goal setting play an important role in developing and maintaining motivation. After completion of a supervised exercise program, compliance may be improved through regular follow-up appointments. During these visits the exercise program may be modified and advanced as appropriate.
Health benefits associated with physical activity are largely dependent on long-term adherence to regular participation. Unfortunately, many people who initiate an exercise program do not continue long-term. Drop-out rates from supervised programs remain high and are even higher for individuals after leaving a supervised program.
Approximately one in four adults report no leisure-time activity, and an additional one-third do not get enough physical activity to obtain health benefits (93). Most teenagers do not participate in vigorous activities, and about 50% do not participate in physical education classes at school (93,96). Sedentary living is more common among Americans who have less education and are economically or socially disadvantaged (93,410). To achieve the exercise objectives established in the Healthy People 2010 Program, considerable change in physical activity participation is needed. Although there are indications of improved public awareness of the benefits associated with regular physical activity, this awareness has not yet translated into substantial improvement in physical activity levels among those who are sedentary (411,412,413,414). The recent release of the surgeon general's report on physical activity emphasizes the importance of increasing physical activity levels among all Americans (415).
In implementing exercise programs for long-term compliance, it is important that individuals find physical activities that they are willing to undertake on a regular basis. The appropriate mode of activity, intensity, frequency, and duration to recommend is best determined by learning the individual's exercise preferences (93).
For many people, encouraging them to build greater physical activity into their normal “routines†and/or to participate in sport activities may be more effective in increasing habitual physical activity than encouraging participation in more traditional aerobic modes such as running or ergometry. Sport activities are more enjoyable for some and may thereby lead to better compliance. Electing to perform home activities in a manner more conducive to health benefits (e.g., using a walk-behind mower rather than a rider mower, taking the stairs rather than the elevator) is a convenient and inexpensive way to increase physical activity levels (93,416). When combined with a walk/jog or some other type of exercise program, recreational and home activities can add welcome variety and thereby enhance compliance to a regular program of exercise.
Attitudinal and behavioral factors within different population subgroups (ethnic background, socioeconomic status, gender, age, disease) can influence motivation for, and ability to sustain, physical activities (93,417,418,419). If an individual perceives that a recommended physical activity is inappropriate because of age, gender, or some other factor, the person is likely to be more resistant to accepting advice.
Compliance with a regular program of physical activity is most likely if the individual perceives a benefit, the activity is enjoyable or acceptable, the individual feels safe and competent with the activity, the activity is convenient or fits into the daily schedule, costs are minimal, negative perceptions are minimized, and the individual recognizes the benefit of performing daily activities in ways that incorporate more physical activity (93). Further work is required to develop better strategies for improving exercise compliance, especially among subpopulations where physical activity participation is low, such as those who are socioeconomically deprived (93,412,413).
EXERCISE PRESCRIPTION IN SPECIAL POPULATIONS
Considerations in Chronic Disease States
Exercise is an important component of the management of many medical and disabling conditions. Additionally, many of the individuals treated in the rehabilitation setting with exercise will have concomitant medical conditions or disabilities that will affect the design of an exercise program and their responses and adaptations to exercise. Special considerations in the design of exercise programs are often required when disease or disability is present.
The interaction between exercise and the given medical condition is important to understand so that the potential adverse effects of exercise may be avoided. In general, the exercise program must not interfere with the standard medical treatment of a disease state and must be individualized in accordance with the presence and severity of the medical condition. Considerations relative to some of the common medical conditions and disabilities encountered in the rehabilitation setting are discussed later. The reader is also referred to relevant chapters in this text covering some of these disease states.
CARDIAC DISEASE
Cardiac disease is a common condition among individuals treated in the rehabilitation setting. Although exercise can generally be performed by those individuals with cardiovascular disease, it is important to recognize the presence and extent of disease before initiating exercise. This knowledge allows the development of a safe exercise program for the individual. Risk stratification (discussed earlier) assists in the process of developing a safe exercise program.
The general guidelines for aerobic exercise already discussed are applicable for patients with stable cardiac disease. For patients with ischemic changes, angina, or arrhythmias during exercise, exercise at an intensity of 10 to 15 beats per minute below the ischemic, angina, and dysrhythmic thresholds should be prescribed. When an individual is at high risk for cardiac events during exercise (Table 17-10), a more cautious approach is warranted with regard to the exercise intensity and level of supervision, and electrocardiographic and
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blood pressure monitoring should be considered. Gradual and prolonged cool-downs are particularly important in the population with known cardiac disease for reducing the risk of arrhythmias and postexercise hypotension from blood pooling in the lower extremities.
TABLE 17-10. Characteristics of Cardiac Patients Associated with High Risk |
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Resistance training can be performed by most patients with stable cardiac disease as long as a significant dynamic work component is involved. Exclusion criteria for resistance training include congestive heart failure, severe valvular disease, poor left ventricular function, uncontrolled dysrhythmias, and peak exercise capacity under 5 METs (96). When exercise intensity monitoring is warranted, the rate-pressure product may be a better indicator of ischemic threshold during resistance exercise than heart rate. For an accurate determination of the rate-pressure product, blood pressure needs to be taken while the muscular contractions are performed, since blood pressure decreases rapidly on release of the resistive load.
DIABETES
The diabetic individual can present many challenges in developing an exercise program. Problems associated with diabetes include cardiovascular disease, peripheral neuropathy, peripheral vascular disease, autonomic dysfunction, renal disease, and retinopathy. Because of the high risk of cardiovascular disease in diabetics, exercise testing before the initiation of an exercise program is advisable (96).
The most common problem experienced by exercising diabetics is hypoglycemia. This can result from the presence of too much insulin, or accelerated absorption of insulin from the injection point. This is most likely to occur when short-acting insulin is used and injected near the active muscle mass. It is therefore important that type 1 (insulin-dependent or juvenile-onset) diabetics be under adequate regulation before initiating an exercise program. Table 17-11 lists recommendations that have been provided to minimize the risk of hypoglycemic events among diabetics. An important component of the exercise prescription for the diabetic involves education on these precautions.
It is recommended that the diabetic be attentive to the importance of using proper footwear and the practice of good foot hygiene. It should be recognized that diabetics on β-blocking agents may be unable to experience hypoglycemic symptoms and/or angina. Additionally, it is important for the diabetic to take precautions to avoid hyperthermia that may result from impaired sweating.
TABLE 17-11. Recommended Precautions for Diabetics to Minimize the Risk of Hypoglycemic Reactions Associated with Exercise |
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The general exercise guidelines for aerobic exercise discussed earlier are applicable for the diabetic individual. However, it is important to recognize that the use of heart rate for establishing exercise intensity may be inappropriate for those diabetics with autonomic neuropathy and chronotropic insufficiency. In these cases, the use of perceived exertion to establish intensity may be more appropriate. The recommended mode of exercise also requires some consideration. Avoidance of weight-bearing activities in order to minimize foot irritation is important for obese diabetics. Also, those with advanced retinopathy should not use exercise modes that cause excessive jarring or a marked increase in blood pressure.
OBESITY
Weight loss is achieved through a negative caloric balance. This is best accomplished from a combination of reduced caloric intake and increased caloric expenditure (141). Exercise increases overall energy expenditure, and so is recommended as a component of the treatment of obesity.
Individuals who are overweight are generally sedentary and are likely to have negative connotations about exercise. Exploration of these individuals' history with exercise is important in developing future exercise compliance. Other problems associated with exercise in obesity include muscle soreness and orthopedic injury. As a result, aerobic exercise programs for obese individuals should use activities that minimize joint stress, such as walking, cycling, rowing, stair climbing, and exercise in water.
ARTHRITIS
The exercise program for individuals with arthritis must be adjusted depending on the state of the disease. When the disease activity is high in those with rheumatoid arthritis, activity may need to be minimized to avoid tissue damage. The use of short-duration, frequent sessions may be tolerated and allow one to minimize the adverse effects of inactivity and maintain range of motion even during high disease activity. Non-weight-bearing and low-impact activities are recommended to limit joint stress. Swimming and cycling may be the best-tolerated exercise
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modes by those with arthritis. Resistance training and range-of-motion activities are also particularly important to optimize joint stability and movement patterns.
PERIPHERAL VASCULAR DISEASE
Peripheral arteriosclerosis is associated with hypertension and hyperlipidemia, and is frequently observed in patients with coronary artery disease, cerebrovascular disease, and diabetes. Because of the common association of peripheral arteriosclerosis with coronary artery disease, these patients are generally advised to undergo exercise testing before initiating an exercise program. A discontinuous testing protocol will likely optimize the testing results. Because of the limitations caused by leg discomfort with treadmill or cycle ergometry testing, arm ergometry may be required to achieve adequate myocardial stress.
Walking is the preferred mode of exercise training for induction of functional changes, but non-weight-bearing activities may be better tolerated initially by these patients. Exercise sessions should use interval training at intensities that elicit the most leg discomfort tolerable to the patient. Initially, the sessions should be 20 to 30 minutes twice a day, and progress to 40 to 60 minutes in one session each day. As functional capacity improves, the exercise intensity should be increased so that central cardiovascular adaptations are more likely to be induced.
SPINAL CORD INJURY
Spinal cord injury affects exercise capacity through its alteration of the amount of functioning muscle mass, and through compromise of the autonomic nervous system affecting cardioacceleration, blood flow redistribution, and thermoregulation. These issues are important from the standpoint of exercise capacity, potential training adaptations, and safety during exercise.
Depending on the extent and level of the lesion, spinal cord injury can limit the functional muscle mass to the upper body. This limitation reduces the aerobic demands that can be induced during training. Although it is clear that endurance training with the upper body can enhance peak V·O2 and work capacity during exercise, most or all of the changes will probably come through peripheral rather than central adaptations (197,199). This means that spinal cord injury may prevent or severely limit the ability to achieve central cardiovascular adaptations.
Complete lesions of the spinal cord will also have an effect on the autonomic nervous system. Loss of sympathetic cardiac innervation from lesions above the sixth thoracic level can limit maximal heart rate to 110 to 130 beats per minute (420). Lesions at the cervical and thoracic levels can impair control over regional blood flow during exercise, causing venous blood pooling in the legs and abdomen, and consequently a reduced preloading of the heart. Stroke volume and cardiac output at a given oxygen uptake during exercise tend to be reduced in those with spinal cord injury (421,422). Furthermore, thermoregulatory ability is impaired through loss of sympathetic nervous system control for vasomotor and sudomotor responses in the areas of the insensate skin (423).
Exercise testing before the initiation of an exercise program may have a somewhat greater role in those with spinal cord injury than in the general population. Besides assisting in the recognition of the presence of coronary artery disease, exercise testing in spinal cord injury may assist in ensuring that the individual will not have serious problems with hypotension during exercise. Exercise testing may have additional importance, because classical symptoms of angina pectoris may be absent in quadriplegics, because most of the visceral afferents from the heart enter the spinal cord at the upper thoracic levels. Exercise testing will generally be performed using arm or wheelchair ergometry.
Despite the physiologic limitations, spinal cord-injured people have demonstrated that they can safely participate in many activities, such as long-distance wheelchair propulsion, swimming, kayaking, and cross-country skiing on sit skis. Wheelchair propulsion and wheelchair or arm crank ergometry are common training modes. Recent research has suggested that lower-body compression (424,425,426), functional electrical stimulation of the paralyzed lower limbs (427,428) or supine body position (429) concomitant with upper-body exercise may enhance venous return and cardiac output and provide a greater chance for central training adaptations.
The intensity and duration guidelines for cardiovascular training in the apparently healthy appear to be reasonable for the spinal cord injured (420). Autonomic dysreflexia and hypotension can be serious complications that may present with exercise in this population. The potential thermoregulatory problems of the spinal cord injured should also prompt caution in hot conditions. Nevertheless, the overall risk of serious problems from participating in appropriately structured exercise programs appears to be low for the spinal cord injured.
POSTPOLIOMYELITIS SYNDROME
The fear of increasing muscle weakness from overuse has been a concern about the use of exercise in individuals who have postpolio sequelae. However, it now appears that these individuals can generally exercise without adverse effects. Individuals with postpolio sequelae generally seem to respond to endurance training in a manner similar to healthy adults (430,431,432,433). Likewise, it has been demonstrated that resistance training can enhance strength without complications in individuals with postpolio sequelae (434). Nevertheless, it is recommended that careful individual monitoring, including occasional muscle function tests, be performed during the physical training of individuals with postpolio sequelae (432).
MULTIPLE SCLEROSIS
Concerns about the safety of exercise in those with multiple sclerosis have centered around the potential adverse effects from the autonomic dysfunction that may accompany the disease, and the potential exacerbation of the disease through thermal stress. Unfortunately, very little is known about the effects of multiple sclerosis on the physiologic responses to exercise, or the effects of exercise on the disease process (435,436). There is encouraging evidence that some individuals with multiple sclerosis can perform endurance exercise to levels above the anaerobic threshold without development of significant or persistent neurologic symptoms (437), that aerobic training can induce beneficial cardiovascular adaptations (438), and that strength gains can be achieved through resistance training (439). Nevertheless, until more scientific investigation is completed, a conservative approach to exercise is warranted in the multiple sclerosis patient.
CANCER
Exercise is becoming an accepted component of rehabilitation of patients with cancer. Besides counteracting the effects of inactivity and improving psychological status (440), there is some evidence that immune function may be improved through moderate levels of exercise (179,180,181,182,183).
A number of problems may interfere with the exercise program of individuals with cancer. Cancer treatments may induce cytotoxicity, immunologic suppression, bleeding disorders, and anemia. Some chemotherapeutic agents induce direct
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cardiac or pulmonary damage that affects exercise performance. Difficulties in maintaining nutritional needs, adequate hydration, and electrolyte balance may also be problematic. Other side effects, such as fatigue and infection, may seriously impact exercise programs.
TABLE 17-12. Contraindications for Exercising during Pregnancy |
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The general guidelines for aerobic exercise training discussed earlier are appropriate for individuals with cancer, but the intensity should usually be at the lower end of the range. Patients with known or potential malignancies affecting bone, particularly the spine, pelvis, femur, and ribs, should use non-weight-bearing modalities. When the risk of bruising, fractures, and balance problems is increased, resistance exercise should be performed on machines rather than with free weights.
Considerations in Selected Groups within the Able-Bodied Population
Pregnant women, children, and the elderly possess unique physical, physiologic, and behavioral characteristics that need to be considered in the design of exercise programs.
PREGNANCY
Concerns about exercise during pregnancy have related to the competition between the exercising maternal muscle and the fetus for blood flow, oxygen delivery and glucose availability, and issues related to heat dissipation (96). Currently, though, there is no evidence in humans to indicate that healthy pregnant women need to limit their exercise intensity for fear of adverse effects.
TABLE 17-13. Recommendations for Exercise in Pregnancy and Postpartum |
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Contraindications for exercise during pregnancy have been established (Table 17-12). For women who do not have risk factors for adverse maternal or perinatal outcomes, the American College of Obstetrics and Gynecology has provided exercise recommendations (Table 17-13). Within these recommendations, and equipped with the understanding of signs and symptoms for discontinuing exercise (Table 17-14), exercise during pregnancy is felt to be safe.
Those women who exercise regularly and become pregnant can continue their training program. Those beginning a new strenuous exercise program after becoming pregnant are advised to receive physician authorization and begin low-intensity and low-impact or nonimpact activities.
CHILDREN AND ADOLESCENTS
Increasing attention has recently been directed to the rising numbers of overweight and obese children in the United States. This rise has been attributed in part to decreasing levels of physical activity. An important step in reversing this trend in inactivity is provision of positive physical activity/exercise opportunities for children and adolescents. In developing physical activity programs for this group, it is important to consider their maturity levels, skill levels, medical conditions, and prior physical activity experiences. Some general guidelines include (a) providing a variety of activities that exercise all major large muscles; (b) focusing on active, creative, enjoyable play in very young children; (c) encouraging children more than 6 years of age to accumulate a minimum of 30 minutes of at least moderate-intensity activity most, if not all, days of the week; (d) encouraging older children to participate in 20 to 30 minutes of higher-intensity activity at least three times per week for greater benefits; and (e) following a gradual progression in terms of quantity of exercise (96). In addition to immediate health benefits, positive exercise experiences during the younger years may carry over into increased activity in adulthood.
TABLE 17-14. Reasons for Pregnant Women to Discontinue Exercise and Consult a Physician |
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Safety should always be a primary concern in designing exercise programs for children, as they are anatomically, physiologically, and psychologically immature (96). One concern is that overuse injuries and damage to the epiphyseal growth plates may occur if the amount of exercise is excessive or produces acute trauma (443). Ensuring use of appropriate equipment, matching competition according to maturation or skill level, providing adequate skill preparation, and liberalizing rules are methods that may help reduce injuries. Another concern is the reduced ability of children to adapt to extremes in thermal stress. Children are physiologically less tolerant of a high heat load than adults because of a higher threshold for sweating, a lower output of the heat-activated sweat glands, and a slower acclimatization to heat (444). An increased ratio of surface area to body mass could also increase children's susceptibility to hypothermia in a cold environment. Temperature-related problems can be minimized by taking precautions during extremes in environmental temperatures that include limiting strenuous prolonged exercise, providing good hydration, and encouraging appropriate clothing (96).
Children have been shown to respond to resistance-type training with significant strength gains (96,220). In providing safe resistance training programs for prepubescent children, it is important to adhere to guidelines established for this group, including close adult supervision, avoidance of maximal resistance loads, and use of proper lifting techniques (96).
Some children have illnesses or physical challenges that require special guidelines. Some of these guidelines are summarized by the American College of Sports Medicine (96).
ELDERLY
The American College of Sports Medicine has developed general guidelines for aerobic and resistance training in the elderly (96). When designing an exercise program for older adults, the possibility that a latent or active disease process may be present must be considered. Exercise testing should be performed before beginning a vigorous exercise program, as outlined in Table 17-9. The exercise prescription must be individualized based on health status and individual goals.
A conservative approach to exercise is generally warranted in the elderly, since many older persons suffer from a variety of medical problems. Aerobic exercise sessions may initially need to be divided into short bouts, and the mode of exercise should not impose significant joint stress. Because of the variability in maximal heart rate in those more than 65 years of age, the use of age-predicted maximal heart rates for exercise prescriptions is not recommended.
Resistance training can be of considerable benefit to the elderly (445). Like the aerobic exercise prescription, resistance training programs need to be individualized. Resistance training should be initiated with close supervision and minimal resistance.
Maintenance of a functional range of motion is also particularly important for the elderly. As for younger individuals, stretching exercises should be preceded with a warm-up to increase the soft-tissue temperature.
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