The types of exercise selected for a resistance training program are contingent on many factors, including the cause and extent of primary and secondary impairments. Deficits in muscle performance, the stage of tissue healing, the condition of joints and their tolerance to compression and movement, the general abilities (physical and cognitive) of the patient, the availability of equipment, and of course, the patient's goals and the intended functional outcomes of the program must be considered. A therapist has an array of exercises from which to choose to design a resistance exercise program to meet the individual needs of each patient. There is no one best form or type of resistance training. Prior to selecting specific types of resistance exercise for a patient's rehabilitation program, a therapist may want to consider the questions listed in Box 6.6.
BOX 6.6 Selecting Types of Resistance Exercise: Questions to Consider
Based on the results of your examination and evaluation, what are the type and extent of the deficits in muscle performance?
Based on the underlying pathology causing the deficits in muscle performance or the stage of tissue healing, what types of resistance exercise would be more appropriate or effective than another?
What are the goals and anticipated functional outcomes of the resistance training program?
Which types of resistance exercise are more compatible with the desired goals?
Are there any restrictions on how the patient is permitted or able to be positioned during exercise?
Is weight bearing contraindicated, restricted, or fully permissible?
Is there hypomobility of affected or adjacent joints (due to pain or contracture) that could affect how the patient is positioned during resistance exercise?
Is there a portion of the ROM in which the patient cannot safely or comfortably perform resistance exercises due to hypermobility?
Are there cardiovascular or respiratory impairments that could affect positioning during exercise?
Will the patient be expected to perform the exercises independently using mechanical resistance, or would manual resistance applied by the therapist be more appropriate at this point in the rehabilitation program?
What types of equipment will be available or needed for exercises?
Application of the SAID principle based on the concept of specificity of training is key to making sound exercise decisions. In addition to selecting the appropriate types of exercise, a therapist must also make decisions about the intensity, volume, order, frequency, rest interval, and other factors discussed in the previous section of this chapter for effective progression of resistance training. Table 6.6 summarizes general guidelines for progression of exercise.
TABLE 6.6Progression of a Resistance Training Program: Factors for Consideration ||Download (.pdf) TABLE 6.6 Progression of a Resistance Training Program: Factors for Consideration
|Factors ||Progression |
|Intensity (exercise load) || |
Submaximal → maximal (or near-maximal)
Low-load → high-load
|Body position (nonweight- bearing or weight-bearing) ||Variable: depending on pathology and impairments, weight-bearing restrictions (pain, swelling, instability) and goals of the rehabilitation program |
|Repetitions and sets ||Low volume → high volume |
|Frequency ||Variable: depends on intensity and volume of exercise |
|Type of muscle contraction || |
Static → dynamic
Concentric and eccentric: variable progression
|Range of motion || |
Short arc → full arc
Stable portion of range → unstable portion of range
|Plane of movement ||Uniplanar → multiplanar |
|Velocity of movement ||Slow → fast velocities |
|Neuromuscular control ||Proximal → distal control |
|Functional movement patterns || |
Simple → complex
Single joint → multijoint
Proximal control → distal control
The types of exercise presented in this section are static (isometric) and dynamic, concentric and eccentric, isokinetic, and open-chain and closed-chain exercise, as well as manual and mechanical and constant and variable resistance exercises. The benefits, limitations, and applications of each of these forms of resistance exercise are analyzed and discussed. When available, supporting evidence from the scientific literature is summarized.
Manual and Mechanical Resistance Exercise
From a broad perspective, a load can be applied to a contracting muscle in two ways: manually or mechanically. The benefits and limitations of these two forms of resistance training are summarized in a later section of this chapter (see Boxes 6.14 and 6.15).
Manual Resistance Exercise
Manual resistance exercise is a type of active-resistive exercise in which resistance is provided by a therapist or other health professional. A patient can be taught how to apply self-resistance to selected muscle groups. Although the amount of resistance cannot be measured quantitatively, this technique is useful in the early stages of an exercise program when the muscle to be strengthened is weak and can overcome only minimal to moderate resistance. It is also useful when the range of joint movements needs to be carefully controlled. The amount of resistance given is limited only by the strength of the therapist.
NOTE: Techniques for application of manual resistance exercises in anatomical planes and diagonal patterns are presented in later sections of this chapter.
Mechanical Resistance Exercise
Mechanical resistance exercise is a form of active-resistive exercise in which resistance is applied through the use of equipment or mechanical apparatus. The amount of resistance can be measured quantitatively and incrementally progressed over time. It is also useful when the amount of resistance necessary is greater than what the therapist can apply manually.
NOTE: Systems and regimens of resistance training that involve the use of mechanical resistance, such as progressive resistive exercise (PRE), circuit weight training, and velocity spectrum rehabilitation, and the advantages and disadvantages of various types of resistance equipment are addressed later in this chapter.
Isometric Exercise (Static Exercise)
Isometric exercise is a static form of exercise in which a muscle contracts and produces force without an appreciable change in the length of the muscle and without visible joint motion.182,210 Although there is no mechanical work done (force × distance), a measurable amount of tension and force output are produced by the muscle.Sources of resistance for isometric exercise include holding against a force applied manually, holding a weight in a particular position, maintaining a position against the resistance of body weight, or pushing or pulling an immovable object.
During the 1950s and 1960s, isometric resistance training became popular as an alternative to dynamic resistance exercise and initially was thought to be a more effective and efficient method of muscle strengthening. Isometric strength gains of 5% per week were reported when healthy subjects performed a single, near-maximal isometric contraction everyday over a 6-week period.133 However, replications of this study called into question some of the original findings, particularly the rapid rate of strength gain.
Repetitive isometric contractions, for example a set of 20 per day, held for 6 seconds each against near-maximal resistance has since been shown to be a more effective method to improve isometric strength. A cross-exercise effect (a limited increase in strength of the contralateral, unexercised muscle group), as the result of transfer of training, also has been observed with maximum isometric training.67
Rationale for Use of Isometric Exercise
The need for static strength and endurance is apparent in almost all aspects of control of the body during functional activities. Loss of static muscle strength occurs rapidly with immobilization and disuse, with estimates from 8% per week187 to as much as 5% per day.208 these two aspects of static muscle performance, it has been suggested that muscular endurance plays a more important role than muscle strength in maintaining sufficient postural stability and in preventing injury during daily living tasks.192 For example, the postural muscles of the trunk and lower extremities must contract isometrically to hold the body erect against gravity and provide a background of stability for balance and functional movements in an upright position. Dynamic stability of joints is achieved by activating and maintaining a low level of co-contraction—that is, concurrent isometric contractions of antagonist muscles that surround joints.195 The importance of isometric strength and endurance in the elbow, wrist, and finger musculature, for example, is apparent when a person holds and carries a heavy object for an extended period of time.
With these examples in mind, there can be no doubt that isometric exercises are an important part of a rehabilitation program designed to improve functional abilities. The rationale and indications for isometric exercise in rehabilitation are summarized in Box 6.7.
BOX 6.7 Isometric Exercise: Summary of Rationale and Indications
To minimize muscle atrophy when joint movement is not possible owing to external immobilization (casts, splints, skeletal traction)
To activate muscles (facilitate muscle firing) to begin to re-establish neuromuscular control but protect healing tissues when joint movement is not advisable after soft tissue injury or surgery
To develop postural or joint stability
To improve muscle strength when use of dynamic resistance exercise could compromise joint integrity or cause joint pain
To develop static muscle strength at particular points in the ROM consistent with specific task-related needs
Types of Isometric Exercise
Several forms of isometric exercise with varying degrees of resistance and intensity of muscle contractions serve different purposes during successive phases of rehabilitation. All but one type (muscle setting) incorporate some form of significant resistance and, therefore, are used to improve static strength or develop sustained muscular control (endurance). Because no appreciable resistance is applied, muscle setting technically is not a form of resistance exercise but is included in this discussion to show a continuum of isometric exercise that can be used for multifaceted goals in a rehabilitation program.
Muscle-setting exercises. Setting exercises involve low-intensity isometric contractions performed against little to no resistance. They are used to decrease muscle pain and spasm and to promote relaxation and circulation after injury to soft tissues during the acute stage of healing. Two common examples of muscle setting are of the quadriceps and gluteal muscles.
Because muscle setting is performed against no appreciable resistance, it does not improve muscle strength except in very weak muscles. However, setting exercises can retard muscle atrophy and maintain mobility between muscle fibers when immobilization of a muscle is necessary to protect healing tissues during the very early phase of rehabilitation.
Stabilization exercises. This form of isometric exercise is used to develop a submaximal but sustained level of co-contraction to improve postural stability or dynamic stability of a joint by means of midrange isometric contractions against resistance in antigravity positions and in weight-bearing postures if weight bearing is permissible.195 Body weight or manual resistance typically is the source of resistance.
Various terms are used to describe stabilization exercises. They include rhythmic stabilization and alternating isometrics, two techniques associated with proprioceptive neuromuscular facilitation (PNF) described later in the chapter.220,288 Stabilization exercises that focus on trunk/postural control are referred to by a variety of descriptors including dynamic, core, and segmental stabilization exercises. Applications of these exercises are addressed in Chapter 16. Equipment, such as the BodyBlade® (see Fig 6.50) and stability balls are designed for dynamic stabilization exercises.
Multiple-angle isometrics. This term refers to a system of isometric exercise in which resistance is applied, manually or mechanically, at multiple joint positions within the available ROM.57 This approach is used when the goal of exercise is to improve strength throughout the ROM when joint motion is permissible but dynamic resistance exercise is painful or inadvisable.
Characteristics and Effects of Isometric Training
Effective use of isometric exercise in a resistance training program is founded on an understanding of its characteristics and its limitations.
Intensity of muscle contraction. The amount of tension that can be generated during an isometric muscle contraction depends in part on joint position and the length of the muscle at the time of contraction.285 It is sufficient to use an exercise intensity (load) of at least 60% of a muscle's maximum voluntary contraction (MVC) to improve strength.162,285 The amount of resistance against which the muscle is able to hold varies and needs to be adjusted at different points in the range. Resistance must be progressively increased to continue to overload the muscle as it becomes stronger.
When performing isometric exercises, to avoid potential injury to the contracting muscle, apply and release the resistance gradually. This helps to grade the muscle tension and ensures that the muscle contraction is pain-free. It also minimizes the risk of uncontrolled joint movement.
Duration of muscle activation. To achieve adaptive changes in static muscle performance, an isometric contraction should be held for 6 seconds and no more than 10 seconds because muscle fatigue develops rapidly. This allows sufficient time for peak tension to develop and for metabolic changes to occur in the muscle.133,192 A 10-second contraction allows a 2-second rise time, a 6-second hold time, and a 2-second fall time.57
Repetitive contractions. Use of repetitive contractions, held for 6 to 10 seconds each, decreases muscle cramping and increases the effectiveness of the isometric regimen.
Joint angle and mode specificity. Gains in muscle strength occur only at or closely adjacent to the training angle.161,162,285 Physiological overflow is minimal, occurring no more than 10° in either direction from the training angle.162 Therefore, when performing multiple-angle isometrics, resistance at four to six points in the ROM typically is recommended. Additionally, isometric resistance training is mode-specific, causing increases in static strength with little to no impact on dynamic strength (concentric or eccentric).
Sources of resistance. It is possible to perform a variety of isometric exercises with or without equipment. For example, multiple-angle isometrics can be carried out against manual resistance or by simply having the patient push against an immovable object, such as a door frame or a wall.
Equipment designed for dynamic exercise can be adapted for isometric exercise. A weight-pulley system that provides resistance greater than the force-generating capacity of a muscle leads to a resisted isometric exercise. Most isokinetic devices can be set up with the velocity set at 0°/sec at multiple joint angles for isometric resistance at multiple points in the ROM.
PRECAUTION: Breath-holding commonly occurs during isometric exercise, particularly when performed against substantial resistance. This is likely to cause a pressor response as the result of the Valsalva maneuver, causing a rapid increase in blood pressure.94 Rhythmic breathing, emphasizing exhalation during the contraction, should always be performed during isometric exercise to minimize this response.
CONTRAINDICATION: High-intensity isometric exercises may be contraindicated for patients with a history of cardiac or vascular disorders.
Dynamic Exercise: Concentric and Eccentric
A dynamic muscle contraction causes joint movement and excursion of a body segment as the muscle contracts and shortens (concentric muscle action) or lengthens under tension (eccentric muscle action). As represented in Figure 6.7, the term concentric exercise refers to a form of dynamic muscle loading in which tension in a muscle develops and physical shortening of the muscle occurs as an external force (resistance) is overcome, as when lifting a weight. In contrast, eccentric exercise involves dynamic loading of a muscle beyond its force-producing capacity, causing physical lengthening of the muscle as it attempts to control the load, as when lowering a weight.
(A) Concentric and (B) eccentric strengthening of the elbow flexors occurs as a weight is lifted and lowered.
During concentric and eccentric exercise, resistance can be applied in several ways: (1) constant resistance, such as body weight, a free weight, or a simple weight-pulley system; (2) a weight machine that provides variable resistance; or (3) an isokinetic device that controls the velocity of limb movement.
NOTE: Although the term isotonic (meaning equal tension) has been used frequently to describe a resisted, dynamic muscle contraction, application of this terminology is incorrect. In fact, when a body segment moves through its available range, the tension that the muscle is capable of generating varies through the range as the muscle shortens or lengthens. This is due to the changing length-tension relationship of the muscle and the changing torque of the load.182,210,248 Therefore, in this textbook "isotonic" is not used to describe dynamic resistance exercise.
Rationale for Use of Concentric and Eccentric Exercise
Both concentric and eccentric exercises have distinct value in rehabilitation and conditioning programs. Concentric muscle contractions accelerate body segments, whereas eccentric contractions decelerate body segments (e.g., during sudden changes of direction or momentum). Eccentric contractions also act as a source of shock absorption during high-impact activities.63,175
A combination of concentric and eccentric muscle action is evident in countless tasks of daily life, such as walking up and down inclines, ascending and descending stairs, rising from a chair and sitting back down, or picking up or setting down an object. Hence, it is advisable to incorporate a variety of concentric and eccentric resistance exercises in a rehabilitation progression for patients with impaired muscle performance to improve muscle strength, power, or endurance and to meet functional demands.
Special Considerations for Eccentric Training
Eccentric training, in particular, is considered an essential component of rehabilitation programs following musculoskeletal injury or surgery and in conditioning programs to reduce the risk of injury or reinjury associated with activities that involve high-intensity deceleration, quick changes of direction, or repetitive eccentric muscle contractions.175,213,254 Eccentric training also is thought to improve sport-related physical performance.10,175
Traditionally, regimens of exercise that emphasize high-intensity, eccentric loading, such as eccentric isokinetic training or plyometric training (see Chapter 23) have been initiated during the advanced phase of rehabilitation to prepare a patient for high-demand sports or work-related activities.175 Recently, however, progressive eccentric training early in the rehabilitation process has been advocated to more effectively reduce deficits in strength and physical performance that often persist following a musculoskeletal injury or surgery. However, the safety of early implementation of eccentric resistance exercise must first be examined.
FOCUS ON EVIDENCE
Gerber and colleagues111 conducted a randomized, prospective clinical trial to determine the safety and effects of a gradually progressed, eccentric exercise program initiated during the early phase of rehabilitation (approximately 2 to 3 weeks postoperatively) following arthroscopically assisted anterior cruciate ligament (ACL) reconstruction. All participants in the study began a 15-week traditional, but "accelerated" (early weight bearing and ROM) exercise program immediately after surgery. After the first 2 to 3 postoperative weeks, in addition to continuing the traditional program, half of the participants (experimental group) performed 12 weeks of gradually progressed, lower extremity training on a motorized eccentric ergometer. During that 12-week time period, the control group followed the same graduated program on a standard exercise cycle that provided only concentric resistance. During cycling knee ROM was limited to the 20° to 60° range of knee flexion in both groups to protect the healing ACL graft.
Knee effusion and stability and knee and thigh pain were measured preoperatively and at 15 and 26 weeks postoperatively. Quadriceps strength and one aspect of physical performance (distance of a single-leg long jump) were measured prior to surgery and again at 26 weeks after surgery. Results of the study indicated that there were no significant differences in knee or thigh pain and knee effusion and stability between groups at any point during the investigation. It is also important to note that quadriceps strength and physical performance improved significantly in the eccentric training group but not in the control group. This study demonstrated that the addition of progressively graduated eccentric resistance training during early rehabilitation following ACL reconstruction was safe and effective in reducing strength deficits and improving physical performance.
The results of a one-year follow-up study by Gerber and colleagues112 involving 80% of the original study participants demonstrated that quadriceps strength and physical performance continued to be superior in the eccentric training group than in the group that participated in the traditional program.
Characteristics and Effects of Concentric and Eccentric Exercise
A summary of the characteristics and effects of eccentric versus concentric resistance exercise is noted in Box 6.8.
BOX 6.8 Eccentric Versus Concentric Exercise: Summary of Characteristics
Greater loads can be controlled with eccentric than concentric exercise.
Training-induced gains in muscle strength and mass are greater with maximum-effort eccentric training than maximum-effort concentric training.
Adaptations associated with eccentric training are more mode- and velocity-specific than adaptations as the result of concentric training.
Eccentric muscle contractions are more efficient metabolically and generate less fatigue than concentric contractions.
Following unaccustomed, high-intensity eccentric exercise, there is greater incidence and severity delayed-onset muscle soreness than after concentric exercise.
Exercise load and strength gains. A maximum concentric contraction produces less force than a maximum eccentric contraction under the same conditions (see Fig. 6.6). In other words, greater loads can be lowered than lifted. This difference in the magnitude of loads that can be controlled by concentric versus eccentric muscle contractions may be associated with the contributions of the contractile and noncontractile components of muscle. When a load is lowered during an eccentric exercise, the force exerted by the load is controlled not only by the active, contractile components of muscle but also by the noncontractile connective tissue in and around the muscle. In contrast, when a weight is lifted during concentric exercise, only the contractile components of the muscle lift the load.63
With a concentric contraction, greater numbers of motor units must be recruited to control the same load compared to an eccentric contraction, suggesting that concentric exercise has less mechanical efficiency than eccentric exercise.63,78 Consequently, it requires more effort by a patient to control the same load during concentric exercise than during eccentric exercise. As a result, when a weight is lifted and lowered, maximum resistance during the concentric phase of an exercise does not provide a maximum load during the eccentric phase.
If a resistance exercise program involves maximum effort during eccentric and concentric exercise and if the exercise load is increased gradually, eccentric training increases eccentric strength over the duration of a program to a greater degree than concentric training increases concentric strength. This may occur because greater loads can be used for eccentric than concentric training.232
Given that eccentric exercise requires recruitment of fewer motor units to control a load than concentric exercise, when a muscle is very weak—less than a fair (3/5) muscle grade—active eccentric muscle contractions against no external resistance (other than gravity) can be used to generate active muscle contractions and develop a beginning level of strength and neuromuscular control. In other words, in the presence of substantial muscle weakness, it may be easier to control lowering a limb against gravity than lifting the limb.
PRECAUTION: There is greater stress on the cardiovascular system (i.e., increased heart rate and arterial blood pressure) during eccentric exercise than during concentric exercise,63 possibly because greater loads can be used for eccentric training. This underscores the need for rhythmic breathing during high-intensity exercise. (Refer to a later section of this chapter for additional information on cardiovascular precautions.)
Velocity of exercise. The velocity at which concentric or eccentric exercises are performed directly affects the force-generating capacity of the neuromuscular unit.53,78 At slow velocities with a maximum load, an eccentric contraction generates greater tension than a concentric contraction. At slow velocities, therefore, a greater load (weight) can be lowered (with control) than lifted. As the velocity of exercise increases, concentric contraction tension rapidly and consistently decreases, whereas eccentric contraction forces increase slightly but then rapidly reach a plateau under maximum load conditions (see Fig. 6.6).
A common error made by some weightlifters during high-intensity resistance training is to assume that if a weight is lifted quickly (concentric contraction) and lowered slowly (eccentric contraction), the slow eccentric contraction generates greater tension. In fact, if the load is constant, less tension is generated during the eccentric than the concentric phase. The only way to develop greater tension is to increase the weight of the applied load during the eccentric phase of each exercise cycle. This usually requires assistance from an exercise partner to help lift the load during each concentric contraction. This is a highly intense form of exercise and should be undertaken only by healthy individuals training for high-demand sports or weight lifting competition. This technique is not appropriate for individuals recovering from musculoskeletal injuries.
Energy expenditure. Against similar exercise loads, eccentric exercise is more efficient at a metabolic level than concentric exercise232 —that is, eccentric muscle contractions consume less oxygen and energy stores than concentric contractions.41 Therefore, the use of eccentric activities such as downhill running may improve muscular endurance more efficiently than similar concentric activities because muscle fatigue occurs less quickly with eccentric exercise.63,232
Specificity of training. Opinions and results of studies vary on whether the effects of training with concentric and eccentric contractions in the exercised muscle group are mode-specific. Although there is substantial evidence to support specificity of training,11,24,80,205,240,275 there is also some evidence to suggest that training in one mode leads to strength gains, though less significant, in the another mode.85 For the most part, however, eccentric training is more mode-specific than concentric training.232 Eccentric exercise also appears to be more velocity-specific than concentric exercise.232 Therefore, because transfer of training is quite limited, selection of exercises that simulate the functional movements needed by a patient is always a prudent choice.
Cross-training effect. Both concentric283 and eccentric284 training have been shown to cause a cross-training effect—that is, a slight increase in strength occurs over time in the same muscle group of the opposite, unexercised extremity. This effect, sometimes referred to as cross-exercise, also occurs with high-intensity exercise that involves a combination of concentric and eccentric contractions (lifting and lowering a weight).
This effect in the unexercised muscle group may be caused by repeated contractions of the unexercised extremity in an attempt to stabilize the body during high-effort exercise. Although cross-training is an interesting phenomenon, there is no evidence to suggest that a cross-training effect has a positive impact on a patient's functional capabilities.
Exercise-induced muscle soreness. Repeated and rapidly progressed, high-intensity eccentric muscle contractions are associated with a significantly higher incidence and severity of delayed-onset muscle soreness (DOMS) than occurs with high-intensity concentric exercise.16,43,106,212 Why DOMS occurs more readily with eccentric exercise is speculative, possibly the result of greater damage to muscle and connective tissue when heavy loads are controlled and lowered.16,43 It also has been suggested that the higher incidence of DOMS associated with unaccustomed, high-intensity eccentric exercise may adversely affect the training-induced gains in muscle strength.63,80,106
It should be noted that there is at least limited evidence to suggest that if the intensity and volume of concentric and eccentric exercise are equal, there is no significant difference in the degree of DOMS after exercise.100 Further, if the intensity and volume of eccentric exercise is progressed gradually, DOMS does not occur.111
Dynamic Exercise: Constant and Variable Resistance
The most common system of resistance training used with dynamic exercise against constant or variable resistance is progressive resistance exercise (PRE). A later section of this chapter, which covers systems of training using mechanical resistance, addresses PRE.
Dynamic Exercise: Constant External Resistance
Dynamic exercise against constant external resistance (DCER) is a form of resistance training in which a limb moves through a ROM against a constant external load,168 provided by free weights such as a handheld or cuff weight, torque arm units (Fig. 6.8 A), weight machines, or weight-pulley systems.
(A) N-K Exercise Unit with torque arm and interchangeable weights provides constant external resistance. (Courtesy of N-K Products Company, Soquel, CA.); (B) Cybex/Eagle Fitness Systems shoulder press provides variable resistance throughout the range of motion. (Courtesy of Cybex, Division of Lumex, Ronkonkoma, NY.)
This terminology—DCER exercise—is used in lieu of the term "isotonic (equal tension)" exercise because although the load (weight) selected does not change, the torque imposed by the weight and the tension generated by the muscle both change throughout the range of movement.182,248 If the imposed load is less than the torque generated by the muscle, the muscle contracts concentrically and accelerates the load; if the load exceeds the muscle's torque production, the muscle contracts eccentrically to decelerate the load (see Fig. 6.7)
DCER exercise has an inherent limitation. When lifting or lowering a constant load, the contracting muscle is challenged maximally at only one point in the ROM in which the maximum torque of the resistance matches the maximum torque output of the muscle. A therapist needs to be aware of the changing torque of the exercise and the changing length-tension relationship of the muscle and modify body position and resistance accordingly to match where in the range the maximum load needs to be applied (see Figs. 6.46 and 6.47). Despite this limitation, DCER exercise has been and continues to be a mainstay of rehabilitation and fitness programs for effective muscle loading and subsequent training-induced improvements in muscle performance.
Variable Resistance Exercise
Variable resistance exercise, a form of dynamic exercise, addresses the primary limitation of dynamic exercise against a constant external load (DCER exercises). Specially designed resistance equipment imposes varying levels of resistance to the contracting muscles to load the muscles more effectively at multiple points in the ROM. The resistance is altered throughout the range by means of a weight-cable system that moves over an asymmetrically shaped cam, by a lever arm system (Fig. 6.8 B), or by hydraulic or pneumatic mechanisms.249 How effectively this equipment varies the resistance to match muscle torque curves is questionable.
Dynamic exercise with elastic resistance products (bands and tubing) also can be thought of, in the broadest sense, as variable resistance exercise because of the inherent properties of the elastic material and its response to stretch.146,152,243 (Refer to the final section of this chapter for additional information on exercise with elastic resistance devices.)
NOTE: When dynamic exercise is performed against manual resistance, a skilled therapist can vary the load applied to the contracting muscle throughout the ROM. The therapist adjusts the resistance based on the patient's response so the muscle is appropriately loaded at multiple portions of the ROM.
Special Considerations for DCER and Variable Resistance Exercise
Excursion of limb movement. During either DCER or variable resistance exercise, the excursion of limb movement is controlled exclusively by the patient (with the exception of exercising on resistance equipment that has a range-limiting device). When free weights, weight-pulley systems, and elastic devices are used, stabilizing muscles are recruited, in addition to the targeted muscle group, to control the arc and direction of limb movement.
Velocity of exercise. Although most daily living, occupational, and sport activities occur at medium to fast velocities of limb movement, exercises must be performed at a relatively slow-velocity to avoid momentum and uncontrolled movements, which could jeopardize the safety of the patient. (As a point of reference, dynamic exercise with a free weight typically is performed at about 60°/sec.57) Consequently, the training-induced improvements in muscle strength that occur only at slow velocities may not prepare the patient for activities that require rapid bursts of strength or quick changes of direction.
Hydraulic and pneumatic variable resistance equipment and elastic resistance products do allow safe, moderate- to high-velocity resistance training.
Isokinetic exercise is a form of dynamic exercise in which the velocity of muscle shortening or lengthening and the angular limb velocity is predetermined and held constant by a rate-limiting device known as an isokinetic dynamometer (Fig. 6.9).57,83,138,200 The term isokinetic refers to movement that occurs at an equal (constant) velocity. Unlike DCER exercise in which a specific weight (amount of resistance) is selected and superimposed on the contracting muscle, in isokinetic resistance training the velocity of limb movement—not the load—is manipulated. The force encountered by the muscle depends on the extent of force applied to the equipment.5,138
Biodex isokinetic dynamometer is used for testing and training. (Courtesy of Biodex Medical Systems, Inc., Shirley, NY.)
Isokinetic exercise is also called accommodating resistance exercise.138 Theoretically, if an individual is putting forth a maximum effort during each repetition of exercise, the contracting muscle produces variable but maximum force output, consistent with the muscle's variable tension-generating capabilities at all portions in the range of movement, not at only one small portion of the range as occurs with DCER training. Although early advocates of isokinetic training suggested it was superior to resistance training with free weights or weight-pulley systems, this claim has not been well supported by evidence. Today, use of isokinetic training is regarded as one of many tools that can be integrated into the later stages of rehabilitation.5
Characteristics of Isokinetic Training
A brief overview of the key characteristics of isokinetic exercise is addressed in this section. For more detailed information on isokinetic testing and training, a number of resources are available.5,57,81,83,122
Constant velocity. Fundamental to the concept of isokinetic exercise is that the velocity of muscle shortening or lengthening is preset and controlled by the unit and remains constant throughout the ROM.
Range and selection of training velocities. Isokinetic training affords a wide range of exercise velocities in rehabilitation from very slow to fast velocities. Current dynamometers manipulate the velocity of limb movement from 0°/sec (isometric mode) up to 500°/sec. As shown in Table 6.7, these training velocities are classified as slow, medium, and fast. This range theoretically provides a mechanism by which a patient can prepare for the demands of functional activities that occur at a range of velocities of limb movement.
TABLE 6.7Classification of Velocity of Training in Concentric Isokinetic Exercises* ||Download (.pdf) TABLE 6.7 Classification of Velocity of Training in Concentric Isokinetic Exercises*
|Classification ||Angular Velocity |
|Isometric ||0°/sec |
|Slow ||30°–60°/sec |
|Medium ||60°–180°or 240°/sec |
|Fast ||180 or°240°–360°/sec and above** |
Selection of training velocities should be as specific as possible to the demands of the anticipated functional tasks. The faster training velocities appear to be similar to or approaching the velocities of limb movements inherent in some functional motor skills such as walking or lifting.5,299 For example, the average angular velocity of the lower extremity during walking has been calculated at 230° to 240°/sec.5,57,299 Notwithstanding, the velocity of limb movements during many functional activities far exceeds the fastest training velocities available.
The training velocities selected also may be based on the mode of exercise (concentric or eccentric) to be performed. As noted in Table 6.7, the range of training velocities advocated for concentric exercise is substantially greater than for eccentric training.5,83,122
Reciprocal versus isolated muscle training. Use of reciprocal training of agonist and antagonist muscles emphasizing quick reversals of motion is possible on an isokinetic dynamometer. For example, the training parameter can be set so the patient performs concentric contraction of the quadriceps followed by concentric contraction of the hamstrings. An alternative approach is to target the same muscle in the concentric mode, followed by the eccentric mode, thus strengthening only one muscle group at a time.298 Both of these approaches have merit.
Specificity of training. Isokinetic training for the most part is velocity-specific,24,122,149 with only limited evidence of significant overflow from one training velocity to another.143,273 Evidence of mode-specificity (concentric vs. eccentric) with isokinetic exercise is less clear.12,83,121,205,240
Because isokinetic exercise tends to be velocity-specific, patients typically exercise at several velocities (between 90° and 360°/sec) using a system of training known as velocity spectrum rehabilitation.5,57,83 (This approach to isokinetic training is discussed later in this chapter.)
Compressive forces on joints. During concentric exercise, as force output decreases, the compressive forces across the moving joint are less at faster angular velocities than at slow velocities.5,57,81,83
Accommodation to fatigue. Because the resistance encountered is directly proportional to the force applied to the resistance arm of the isokinetic unit, as the contracting muscle fatigues, a patient is still able to perform additional repetitions even though the force output of the muscle temporarily diminishes.
Accommodation to a painful arc. If a patient experiences transient pain at some portion of the arc of motion during exercise, isokinetic training accommodates for the painful arc. The patient simply pushes less vigorously against the resistance arm to move without pain through that portion of the range. If a patient needs to stop a resisted motion because of sudden onset of pain, the resistance is eliminated as soon as the patient stops pushing against the torque arm of the dynamometer.
Training Effects and Carryover to Function
Numerous studies have shown that isokinetic training is effective for improving one or more of the parameters of muscle performance (strength, power, and muscular endurance).12,24,83,143,193,205 In contrast, only a limited number of studies have investigated the relationship between isokinetic training and improvement in the performance of functional skills. Two such studies indicated that the use of high-velocity concentric and eccentric isokinetic training was associated with enhanced performance (increased velocity of a tennis serve and throwing a ball).85,201
Limitations in carryover. Several factors inherent in the design of most types of isokinetic equipment may limit the extent to which isokinetic training carries over to improvements in functional performance. Although isokinetic training affords a spectrum of velocities for training, the velocity of limb movement during many daily living and sport-related activities far exceeds the maximum velocity settings available on isokinetic equipment. In addition, limb movements during most functional tasks occur at multiple velocities, not at a constant velocity, depending on the conditions of the task.
Furthermore, isokinetic exercise usually isolates a single muscle or opposing muscle groups, involves movement of a single joint, is uniplanar, and does not involve weight bearing. Although isolation of a single muscle can be beneficial in remediating strength deficits in specific muscle groups, most functional activities require contractions of multiple muscle groups and movement of multiple joints in several planes of motion, some in weight-bearing positions. It is important to note, however, that some of these limitations can be addressed by adapting the setup of the equipment to allow multi-axis movements in diagonal planes or multi-joint resisted movements with the addition of an attachment for closed-chain training.
Special Considerations for Isokinetic Training
Availability of Equipment
From a pragmatic perspective, one limitation of isokinetic exercise is that a patient can incorporate this form of exercise into a rehabilitation program only by going to a facility where the equipment is available. In addition, a patient must be given assistance to set up the equipment and often requires supervision during exercise. These considerations contribute to high costs for the patient enrolled in a long-term rehabilitation program.
The setups recommended in the product manuals often must be altered to ensure that the exercise occurs in a position that is safe for a particular joint. For example, even though a manufacturer may describe a 90°/90° position of the shoulder and elbow for strengthening the shoulder rotators, exercising with the arm at the side may be a safer, more comfortable position.
Initiation and Progression of Isokinetic Training During Rehabilitation
Isokinetic training typically is begun in the later stages of rehabilitation, when active motion through the full (or partial) ROM is pain-free. Suggested guidelines for implementation and progression are summarized in Box 6.9.5,57,83,122
BOX 6.9 Progression of Isokinetic Training for Rehabilitation
Initially, to keep resistance low, submaximal isokinetic exercise is implemented before maximal effort isokinetic exercise.
Short-arc movements are used before full-arc motions, when necessary, to avoid movement in an unstable or painful portion of the range.
Slow to medium training velocities (60°–180°/sec) are incorporated into the exercise program before progressing to faster velocities.
Maximal concentric contractions at various velocities are performed before introducing eccentric isokinetic exercises for the following reasons.
Concentric isokinetic exercise is easier to learn and is fully under the control of the patient.
During eccentric isokinetic exercise, the velocity of movement of the resistance arm is robotically controlled by the dynamometer, not the patient.
Open-Chain and Closed-Chain Exercise
In clinical practice and in the rehabilitation literature, functional activities and exercises commonly are categorized as having weight-bearing or nonweight-bearing characteristics. Another frequently used method of classifying movements and exercises is based on "open or closed kinetic chain" and "open or closed kinematic chain" concepts. These concepts, which were introduced during the 1950s and 1960s in the human biomechanics and kinesiology literature by Steindler256 and Brunnstrom,32 respectively, were proposed to describe how segments (structures) and motions of the body are linked and how muscle recruitment changes with different types of movement and in response to different loading conditions in the environment.
In his analysis of human motion, Steindler256 proposed that the term "open kinetic chain" applies to completely unrestricted movement in space of a peripheral segment of the body, as in waving the hand or swinging the leg. In contrast, he suggested that during closed kinetic chain movements the peripheral segment meets with "considerable external resistance." He stated that if the terminal segment remains fixed, the encountered resistance moves the proximal segments over the stationary distal segments. Steindler also noted that a closed kinetic chain motion in one joint is accompanied by motions of adjacent joints that occur in reasonably predictable patterns.
Both Steindler and Brunnstrom pointed out that the action of a muscle changes when the distal segment is free to move versus when it is fixed in place. For example, in an open chain the tibialis posterior muscle functions to invert and plantarflex the foot and ankle. In contrast, during the stance phase of gait (during loading), when the foot is planted on the ground, the tibialis posterior contracts to decelerate pronation of the subtalar joint and supinate the foot to externally rotate the lower leg during mid and terminal stance.
During the late 1980s and early 1990s, clinicians and researchers in rehabilitation, who were becoming familiar with the open and closed kinetic (or kinematic) chain approach to classifying human motion, began to describe exercises based on these concepts.221,230,274
Controversy and Inconsistency in Use of Open-Chain and Closed-Chain Terminology
Although use of open- and closed-chain terminology to describe exercises has become prevalent in clinical practice and in the rehabilitation literature, a lack of consensus has emerged about how—or even if—this terminology should be used and what constitutes an open-chain versus a closed-chain exercise.25,71,72,124,251,291
One source of inconsistency is whether weight bearing is an inherent component of closed kinetic chain motions. Steindler256 did not specify that weight bearing must occur for a motion to be categorized as closed kinetic chain, but many of his examples of closed-chain movements, particularly in the lower extremities, involved weight bearing. In the rehabilitation literature, descriptions of a closed kinetic chain often do61,101—but sometimes do not127,251—include weight bearing as a necessary element. One resource suggested that all weight-bearing exercises involve some elements of closed-chain motions, but not all closed-chain exercises are performed in weight-bearing positions.251
Another point of ambiguity is whether the distal segment must be absolutely fixed in place to a surface and not moving on a surface to be classified as a closed-chain motion. Steindler256 described this as one of the conditions of a closed kinetic chain motion. However, another condition in his description of closed-chain motions is that if the "considerable external resistance" is overcome, it results in movement of the peripheral segment. Examples Steindler cited were pushing a cart away from the body and lifting a load. Consequently, some investigators have identified a bench press exercise, a seated or reclining leg press exercise, or cycling as closed-chain exercises because they involve pushing motions and axial loading.25,60 If these exercises fit under the closed-chain umbrella, does an exercise in which the distal segment slides across the support surface also qualify as a closed-chain motion? Opinion is divided.
Lifting a handheld weight or pushing against the force arm of an isokinetic dynamometer are consistently cited in the literature as examples of open-chain exercises.* Although there is no axial loading in these exercises, considering Steindler's condition for closed-chain motion just discussed, should these exercises more correctly be classified as closed-chain rather than open-chain exercises in that the distal segment is overcoming considerable external resistance? Again, there continues to be no consensus.
Given the complexity of human movement, it is not surprising that a single classification system cannot adequately group the multitude of movements found in functional activities and therapeutic exercise interventions.
Alternatives to Open-Chain and Closed-Chain Terminology
To address the unresolved issues associated with open-chain and closed-chain terminology, several authors have offered alternative or additional terms to classify exercises. One suggestion is to use the terms, "distally fixated" and "nondistally fixated" in lieu of closed-chain and open-chain.204 Another suggestion is to add a category dubbed partial kinetic chain291 to describe exercises in which the distal segment (hand or foot) meets resistance but is not absolutely stationary, such as using a leg press machine, stepping machine, or slide board. The term closed kinetic chain is then reserved for instances when the terminal segment does not move.
To avoid use of the open- or closed-chain terminology, another classification system categorizes exercises as either joint isolation exercises (movement of only one joint segment) or kinetic chain exercises (simultaneous movement of multiple segments that are linked).159,221 Boundaries of movement of the peripheral segment (movable or stationary) or loading conditions (weight-bearing or nonweight-bearing) are not parameters of this terminology. However, other, more complex classification systems do take these conditions into account.72,181
An additional option is to describe the specific conditions of exercises. Using this approach, most open-chain exercises could be described as single-joint weight-bearing exercises, and most closed-chain exercises would be identified as multiple-joint weight-bearing exercises.131
Despite the suggested alternative terminology, open- and closed-chain terminology continues to be widely used in practice settings and in the literature.† Therefore, recognizing the many inconsistencies and shortcomings of the kinetic or kinematic chain terminology and that many exercises and functional activities involve a combination of open- and closed-chain motions, the authors of this textbook have elected to continue to use open- and closed-chain terminology to describe exercises.
Characteristics of Open-Chain and Closed-Chain Exercises
The following operational definitions and characteristics of open- and closed-chain exercises are presented for clarity and as the basis for the discussion of open- and closed-chain exercises described throughout this textbook. The parameters of the definitions are those most frequently noted in the current literature. Common characteristics of open- and closed-chain exercises are compared in Table 6.8.
TABLE 6.8Characteristics of Open-Chain and Closed-Chain Exercises ||Download (.pdf) TABLE 6.8 Characteristics of Open-Chain and Closed-Chain Exercises
|Open-Chain Exercises ||Closed-Chain Exercises |
|Distal segment moves in space. ||Distal segment remains in contact with or stationary (fixed in place) on support surface. |
|Independent joint movement; no predictable joint motion in adjacent joints. ||Interdependent joint movements; relatively predictable movement patterns in adjacent joints. |
|Movement of body segments only distal to the moving joint. ||Movement of body segments may occur distal and/or proximal to the moving joint. |
|Muscle activation occurs predominantly in the prime mover and is isolated to muscles of the moving joint. ||Muscle activation occurs in multiple muscle groups, both distal and proximal to the moving joint. |
|Typically performed in nonweight-bearing positions. ||Typically but not always performed in weight-bearing positions. |
|Resistance is applied to the moving distal segment. ||Resistance is applied simultaneously to multiple moving segments. |
|Use of external rotary loading. ||Use of axial loading. |
|External stabilization (manually or with equipment) usually required. ||Internal stabilization by means of muscle action, joint compression and congruency, and postural control. |
Open-chain exercises involve motions in which the distal segment (hand or foot) is free to move in space, without necessarily causing simultaneous motions at adjacent joints.60,84,86,101,159 Limb movement only occurs distal to the moving joint, and muscle activation occurs in the muscles that cross the moving joint. For example, during knee flexion in an open-chain exercise (Fig. 6.10), the action of the hamstrings is independent of recruitment of other hip or ankle musculature. Open-chain exercises also are typically performed in nonweight-bearing positions.61,101,197,301 In addition, during resistance training, the exercise load (resistance) is applied to the moving distal segment.
Open-chain resisted knee flexion.
Closed-chain exercises involve motions in which the body moves on a distal segment that is fixed or stabilized on a support surface. Movement at one joint causes simultaneous motions at distal as well as proximal joints in a relatively predictable manner. For example, when performing a bilateral short-arc squatting motion (mini-squat) (Fig. 6.11) and then returning to an erect position, as the knees flex and extend, the hips and ankles move in predictable patterns.
Bilateral closed-chain resisted hip and knee flexion/extension.
Closed-chain exercises typically are performed in weight-bearing positions.60,85,101,127,197,301 Examples in the upper extremities include balance activities in quadruped, press-ups from a chair, wall push-offs, or prone push-ups; examples in the lower extremities include lunges, squats, step-up or step-down exercises, or heel rises to name a few.
NOTE: In this textbook, as in some other publications,84,86,127,262 inclusive in the scope of closed-chain exercises are weight-bearing activities in which the distal segment moves but remains in contact with the support surface, as when using a bicycle, cross-country ski machine, or stair-stepping machine. In the upper extremities a few nonweight-bearing activities qualify as closed-chain exercises, such as pull-ups on a trapeze in bed or chin-ups at an overhead bar.
Rationale for Use of Open-Chain and Closed-Chain Exercises
The rationale for selecting open- or closed-chain exercises is based on the goals of an individualized rehabilitation program and a critical analysis of the potential benefits and limitations inherent in either form of exercise. Because functional activities involve many combinations and considerable variations of open- and closed-chain motions, inclusion and integration of task-specific open-chain and closed-chain exercises into a rehabilitation or conditioning program is both appropriate and prudent.
FOCUS ON EVIDENCE
Although often suggested, there is no evidence to support the global assumption that closed-chain exercises are "more functional" than open-chain exercises. A review of the literature by Davies58 indicated there is a substantial body of evidence that both open- and closed-chain exercises are effective for reducing deficits in muscle performance in the upper and lower extremities. However, of the studies reviewed, very few randomized, controlled trials demonstrated that these improvements in muscle performance were associated with a reduction of functional limitations or improvement in physical performance.
A summary of the benefits and limitations of open- and closed-chain exercises and the rationale for their use follows. Whenever possible, presumed benefits and limitations or comparisons of both forms of exercise are analyzed in light of existing scientific evidence. Some of the reported benefits and limitations are supported by evidence, whereas others are often founded on opinion or anecdotal reports. Evidence is presented as available.
NOTE: Most reports and investigations comparing or analyzing open- or closed-chain exercises have focused on the knee, in particular the ACL or patellofemoral joint. Far fewer articles have addressed the application or impact of open- and closed-chain exercises on the upper extremities.
Isolation of Muscle Groups
Open-chain testing and training identifies strength deficits and improves muscle performance of individual muscles or muscle groups more effectively than closed-chain exercises. The possible occurrence of substitute motions that compensate for and mask strength deficits of individual muscles is greater with closed-chain exercise than open-chain exercise.
FOCUS ON EVIDENCE
In a study of the effectiveness of a closed-chain-only resistance training program after ACL reconstruction, residual muscle weakness of the quadriceps femoris was identified.250 The investigators suggested that this residual strength deficit, which altered gait, might have been avoided with the inclusion of open-chain quadriceps training in the postoperative rehabilitation program.
During open-chain resisted exercises a greater level of control is possible with a single moving joint than with multiple moving joints as occurs during closed-chain training. With open-chain exercises, stabilization is usually applied externally by a therapist's manual contacts or with belts or straps. In contrast, during closed-chain exercises the patient most often uses muscular stabilization to control joints or structures proximal and distal to the targeted joint. The greater levels of control afforded by open-chain training are particularly advantageous during the early phases of rehabilitation.
Almost all muscle contractions have a compressive component that approximates the joint surfaces and provides stability to the joint whether in open- or closed-chain situations.182,210,248 Joint approximation also occurs during weight bearing and is associated with lower levels of shear forces at a moving joint. This has been demonstrated at the knee (decreased anterior or posterior tibiofemoral translation)300,301 and possibly at the glenohumeral joint.281 The joint approximation that occurs with the axial loading and weight bearing during closed-chain exercises is thought to cause an increase in joint congruency, which in turn contributes to stability.60,84
Co-activation and Dynamic Stabilization
Because most closed-chain exercises are performed in weight-bearing positions, it has been assumed and commonly reported in the neurorehabilitation literature that closed-chain exercises stimulate joint and muscle mechanoreceptors, facilitate co-activation of agonists and antagonists (co-contraction), and consequently promote dynamic stability.220,264,279 During a standing squat, for example, the quadriceps and hamstrings are thought to contract concurrently to control the knee and hip, respectively. In studies of lower extremity closed-chain exercises and activity of the knee musculature, this assumption has been supported30,50,292 and refuted.87
In the upper extremity, closed-chain exercises in weight-bearing positions are also thought to cause co-activation of the scapular and glenohumeral stabilizers and, therefore, to improve dynamic stability of the shoulder complex.84,291 The assumption seems plausible, but evidence of co-contraction of muscles of the shoulder girdle during weight-bearing exercises, such as a prone push-up or a press-up from a chair, is limited,176 making it difficult for clinicians to draw conclusions or make evidence-based decisions.
There is also some thought that co-activation (co-contraction) of agonist and antagonist muscle groups may occur with selected open-chain exercises. Exercise interventions—such as alternating isometrics associated with PNF,220,264,279 some stretch-shortening drills performed in nonweight-bearing positions,293 use of a BodyBlade® (see Fig. 6.50), and high-velocity isokinetic training—may stimulate co-activation of muscle groups to promote dynamic stability. However, evidence of this possibility is limited.
In some studies of open-chain, high-velocity, concentric isokinetic training of knee musculature,77,123 co-activation of agonist and antagonist muscle groups was noted briefly at the end the range of knee extension. Investigators speculated that the knee flexors fired and contracted eccentrically at the end of the range of knee extension to decelerate the limb just before contact was made with the ROM stop. However in another study, there was no evidence of co-activation of knee musculature or decreased anterior tibial translation with maximum effort, slow-velocity (60°/sec), open-chain training.173
PRECAUTION: High-load, open-chain exercise may have an adverse effect on unstable, injured, or recently repaired joints, as demonstrated in the ACL-deficient knee.87,150,292,300
Proprioception, Kinesthesia, Neuromuscular Control, and Balance
Conscious awareness of joint position or movement is one of the foundations of motor learning during the early phase of training for neuromuscular control of functional movements. After soft tissue or joint injury, proprioception and kines-thesia are disrupted and alter neuromuscular control. Reestablishing the effective, efficient use of sensory information to initiate and control movement is a high priority in rehabilitation.180 Studies of the ACL-reconstructed knee have shown that proprioception and kinesthesia do improve after rehabilitation.19,178
It is thought that closed-chain training provides greater proprioceptive and kinesthetic feedback than open-chain training. Theoretically, because multiple muscle groups that cross multiple joints are activated during closed-chain exercise, more sensory receptors in more muscles and intra-articular and extra-articular structures are activated to control motion than during open-chain exercises. The weight-bearing element (axial loading) of closed-chain exercises, which causes joint approximation, is believed to stimulate mechanoreceptors in muscles and in and around joints to enhance sensory input for the control of movement.*
FOCUS ON EVIDENCE
Despite the assumption that joint position or movement sense is enhanced to a greater extent under closed-chain than open-chain conditions, the evidence is mixed. The results of one study179 indicated that in patients with unstable shoulders kinesthesia improved to a greater extent with a program of closed-chain and open-chain exercises compared to a program of only open-chain exercises. In contrast, in a comparison of the ability to detect knee position during closed-chain versus open-chain conditions, no significant difference was reported.268
Lastly, closed-chain positioning is the obvious choice to improve balance and postural control in the upright position. Balance training is believed to be an essential element of the comprehensive rehabilitation of patients after musculoskeletal injuries or surgery, particularly in the lower extremities, to restore functional abilities and reduce the risk of re-injury.155 Activities and parameters to challenge the body's balance mechanisms are discussed in Chapter 8.
Carryover to Function and Injury Prevention
As already noted, there is ample evidence to demonstrate that both open- and closed-chain exercises effectively improve muscle strength, power, and endurance.58,60,61 Evidence also suggests that if there is a comparable level of loading (amount of resistance) applied to a muscle group, EMG activity is similar regardless of whether open-chain or closed-chain exercises are performed.25,72
That being said, and consistent with the principles of motor learning and task-specific training, exercises should be incorporated into a rehabilitation program that simulate the desired functions if the selected exercises are to have the most positive impact on functional outcomes.60,124,251,291
FOCUS ON EVIDENCE
In a study of older women, stair-climbing abilities improved to a greater extent in participants who performed lower extremity strengthening exercises while standing (closed-chain exercises) and wearing a weighted backpack than those who performed traditional (open-chain) resistance exercises.52 In another study, squatting exercises while standing, a closed-chain exercise, were shown to enhance performance of a jumping task more effectively than open-chain isokinetic knee extension exercises.17 Closed-chain training, specifically a program of jumping activities, also has been shown to decrease landing forces through the knees and reduce the risk of knee injuries in female athletes.134
Implementation and Progression of Open-Chain and Closed-Chain Exercises
Principles and general guidelines for the implementation and progression of open-chain and closed-chain exercises are similar with respect to variables such as intensity, volume, frequency, and rest intervals. These variables were discussed earlier in the chapter. Relevant features of closed-chain exercises and guidelines for progression are summarized in Table 6.9.
TABLE 6.9Parameters and Progression of Closed-Chain Exercises ||Download (.pdf) TABLE 6.9 Parameters and Progression of Closed-Chain Exercises
|Parameters ||Progression |
|% Body weight || |
Partial → full weight-bearing (LE: aquatic exercise, parallel bars, overhead harnessing; UE: wall push-up → modified prone push-up → prone push-up)
Full weight bearing + additional weight (weighted vest or belt, handheld or cuff weights, elastic resistance)
|Base of support || |
Wide → narrow
Bilateral → unilateral
Fixed on support surface → sliding on support surface
|Support surface || |
Stable → unstable/moving (LE: floor → rocker board, wobble board, sideboard, treadmill) (UE: floor, table or wall → rocker or side board, ball)
Rigid → soft (floor, table → carpet, foam)
Height: ground level → increasing height (Low step → high step)
|Balance || |
With external support → no external support
Eyes open → eyes closed
|Exclusion of limb movement || |
Small → large ranges
Short-arc → full-arc (if appropriate)
|Plane or direction of movement || |
Uniplanar → multiplanar
Anterior → posterior → diagonal (forward walking → retrowalking; forward step-up → backward step-up)
Sagittal → frontal or transverse (forward-backward sliding → side to side sliding; forward or backward step-up → lateral step-up)
|Speed of movement or directional changes ||Slow → fast |
Introduction of Open-Chain Training
Because open-chain training typically is performed in nonweight-bearing postures, it may be the only option when weight bearing is contraindicated or must be significantly restricted or when unloading in a closed-chain position is not possible. Soft tissue pain and swelling or restricted motion of any segment of the chain may also necessitate the use of open-chain exercises at adjacent joints. After a fracture of the tibia, for example, the lower extremity usually is immobilized in a long leg cast, and weight bearing is restricted for at least a few weeks. During this period, hip strengthening exercises in an open-chain manner can still be initiated and gradually progressed until partial weight bearing and closed-chain activities are permissible.
Any activity that involves open-chain motions can be easily replicated with open-chain exercises, first by developing isolated control and strength of the weak musculature and then by combining motions to simulate functional patterns.
Closed-Chain Exercises and Weight-Bearing Restrictions: Use of Unloading
If weight bearing must be restricted, a safe alternative to open-chain exercises may be to perform closed-chain exercises while partial weight bearing on the involved extremity. This is simple to achieve in the upper extremity; but in the lower extremity, because the patient is in an upright position during closed-chain exercises, axial loading in one or both lower extremities must be reduced.
Use of aquatic exercises, as described in Chapter 9, or decreasing the percentage of body weight borne on the involved lower extremity in parallel bars are both feasible unloading strategies even though each has limitations. It is difficult to control the extent of weight bearing when performing closed-chain exercises in parallel bars. In addition, lower limb movements while standing in the parallel bars or in water tend to be slower than what typically occurs during functional tasks. An alternative is the use of a harnessing system to unload the lower extremities.157 This system enables a patient to perform a variety of closed-chain exercises and to begin ambulation on a treadmill at functional speeds early in rehabilitation.
Progression of Closed-Chain Exercises
The parameters and suggestions for progression of closed-chain activities noted in Table 6.9 are not all-inclusive and are flexible. As a rehabilitation program progresses, more advanced forms of closed-chain training, such as plyometric training and agility drills (discussed in Chapter 23), can be introduced.62,86 The selection and progression of activities should always be based on the discretion of the therapist and the patient's functional needs and response to exercise interventions.
General Principles of Resistance Training
The principles of resistance training presented in this section apply to the use of both manual and mechanical resistance exercises for persons of all ages, but these principles are not "set in stone." There are many instances when they may or should be modified based on the judgment of the therapist. Additional guidelines specific to the application of manual resistance exercise, PNF, and mechanical resistance exercise are addressed in later sections of this chapter.
Examination and Evaluation
As with all forms of therapeutic exercise, a comprehensive examination and evaluation is the cornerstone of an individualized resistance training program. Therefore, prior to initiating any form of resistance exercise:
Perform a thorough examination of the patient, including a health history, systems review, and selected tests and measurements.
Determine qualitative and quantitative baselines of strength, muscular endurance, ROM, and overall level of functional performance against which progress can be measured.
Interpret the findings to determine if the use of resistance exercise is appropriate or inappropriate at this time. Some questions that may need to be answered are noted in Box 6.10. Be sure to identify the most functionally relevant impairments, the goals the patient is seeking to achieve, and the expected functional outcomes of the exercise program.
Establish how resistance training will be integrated into the plan of care with other therapeutic exercise interventions, such as stretching, joint mobilization techniques, balance training, and cardiopulmonary conditioning exercises.
Re-evaluate periodically to document progress and determine if and how the dosage of exercises (intensity, volume, frequency, rest) and the types of resistance exercise should be adjusted to continue to challenge the patient.
BOX 6.10 Is Resistance Training Appropriate? Questions to Consider
Were deficits in muscle performance identified? If so, do these deficits appear to be contributing to limitations of functional abilities that you have observed or the patient or family has reported?
Could identified deficits cause future impairment of function?
What is the irritability and current stage of healing of involved tissues?
Is there evidence of tissue swelling?
Is there pain? (At rest or with movement? At what portion of the ROM? In what tissues?)
Are there other deficits (such as impaired mobility, balance, sensation, coordination, or cognition) that are adversely affecting much of the performance?
What are the patient's goals or desired functional outcomes? Are they realistic in light of the findings of the examination?
Given the patient's current status, are resistance exercises indicated? Contraindicated?
Can the identified deficits in muscle performance be eliminated or minimized with resistance exercises?
If a decision is made to prescribe resistance exercises in the treatment plan, what resistance exercises are expected to be most effective?
Should one area of muscle performance be emphasized over another?
Will the patient require supervision or assistance over the course of the exercise program or can the program be carried out independently?
What is the expected frequency and duration of the resistance training program? Will a maintenance program be necessary?
Are there any precautions specific to the patient's physical status, general health, or age that may warrant special consideration?
Preparation for Resistance Exercises
Select and prescribe the forms of resistance exercise that are appropriate and expected to be effective, such as whether to implement manual or mechanical resistance exercises, or both.
If implementing mechanical resistance exercise, determine what equipment is needed and available.
Review the anticipated goals and expected functional outcomes with the patient.
Explain the exercise plan and procedures. Be sure that the patient and/or family understands and gives consent.
Have the patient wear nonrestrictive clothing and supportive shoes appropriate for exercise.
If possible, select a firm but comfortable support surface for exercise.
Demonstrate each exercise and the desired movement pattern.
Implementation of Resistance Exercises
NOTE: These general guidelines apply to the use of dynamic exercises against manual or mechanical resistance. In addition to these guidelines, refer to special considerations and guidelines unique to the application of manual and mechanical resistance exercises in the sections of this chapter that follow.
Prior to initiating resistance exercises, warm-up with light, repetitive, dynamic, site-specific movements without applying resistance. For example, prior to lower extremity resistance exercises, have the patient walk on a treadmill, if possible, for 5 to 10 minutes followed by flexibility exercises for the trunk and lower extremities.
Resistance typically is applied to the distal end of the segment in which the muscle to be strengthened attaches. Distal placement of resistance generates the greatest amount of external torque with the least amount of manual or mechanical resistance (load). For example, to strengthen the anterior deltoid, resistance is applied to the distal humerus as the patient flexes the shoulder (Fig. 6.12).
Resistance may be applied across an intermediate joint if that joint is stable and pain-free and if there is adequate muscle strength supporting the joint. For example, to strengthen the anterior deltoid using mechanical resistance, a handheld weight is a common source of resistance.
Revise the placement of resistance if pressure from the load is uncomfortable for the patient.
Resistance (R) is applied to the distal end of the segment being strengthened. Resistance is applied in the direction opposite to that of limb movement to resist a concentric muscle contraction and in the same direction as limb movement to resist an eccentric contraction.
During concentric exercise resistance is applied in the direction directly opposite to the desired motion, whereas during eccentric exercise resistance is applied in the same direction as the desired motion (see Fig. 6.12).
Stabilization is necessary to avoid unwanted, substitute motions.
For nonweight-bearing resisted exercises, external stabilization of a segment usually is applied at the proximal attachment of the muscle to be strengthened. In the case of the biceps brachii muscle, for example, stabilization should occur at the anterior shoulder as elbow flexion is resisted (Fig. 6.13). Equipment such as belts or straps are effective sources of external stabilization.
During multijoint resisted exercises in weight-bearing postures, the patient must use muscle control (internal stabilization) to hold nonmoving segments in proper alignment.
Stabilization is applied at the proximal attachment of the muscle being strengthened. In this figure, the proximal humerus and scapula are stabilized as elbow flexion is resisted.
Intensity of Exercise/Amount of Resistance
NOTE: The intensity of the exercise (submaximal to near-maximal) must be consistent with the intended goals of resistance training and the type of muscle contraction as well as other aspects of dosage.
Initially, have the patient practice the movement pattern against a minimal load to learn the correct exercise technique.
Have the patient exert a forceful but controlled and pain-free effort. The level of resistance should be such that movements are smooth and nonballistic or tremulous.
Adjust the alignment, stabilization, or the amount of resistance if the patient is unable to complete the available ROM, muscular tremor develops, or substitute motions occur.
Number of Repetitions, Sets, and Rest Intervals
In general, for most adults, use 8 to 12 repetitions of a specific motion against a moderate exercise load. This typically induces expected acute and chronic responses—that is, muscular fatigue and adaptive gains in muscular strength, respectively.
Decrease the amount of resistance if the patient cannot complete 8 to 12 repetitions.
After a brief rest, perform additional repetitions—a second set of 8 to 12 repetitions, if possible.
For progressive overloading, initially increase the number of repetitions or sets; at a later point in the exercise program, gradually increase the resistance.
Verbal or Written Instructions
When teaching an exercise using mechanical resistance or when applying manual resistance, use simple instructions that are easily understood. Do not use medical terminology or jargon. For example, tell the patient to "Bend and straighten your elbow" rather than "Flex and extend your elbow." Be sure that descriptions of resistance exercises to be performed in a home program are written and clearly illustrated.
Assess the patient's responses before, during, and after exercise. It may be advisable to monitor the patient's vital signs. Adhere to relevant precautions discussed in the next section of the chapter.
Cool-down after a series of resistance exercises with rhythmic, unresisted movements, such as arm swinging, walking, or stationary cycling. Gentle stretching is also appropriate after resistance exercise.
Precautions for Resistance Exercise
Regardless of the goals of a resistance exercise program and the types of exercises prescribed and implemented, the exercises must not only be effective but safe. The therapist's interpretation of the examination's findings determines the exercise prescription. Awareness of precautions maximizes patient safety. General precautions for resistance training are summarized in Box 6.11.
BOX 6.11 General Precautions During Resistance Training
Keep the ambient temperature of the exercise setting comfortable for vigorous exercise. Select clothing for exercise that facilitates heat dissipation and does not impede sweat evaporation.
Caution the patient that pain should not occur during exercise.
Do not initiate resistance training at a maximal level of resistance, particularly with eccentric exercise to minimize delayed-onset muscle soreness (DOMS). Use light to moderate exercise during the recovery period.
Avoid use of heavy resistance during exercise for children, older adults, and patients with osteoporosis.
Do not apply resistance across an unstable joint or distal to a fracture site that is not completely healed.
Have the patient avoid breath-holding during resisted exercises to prevent the Valsalva maneuver; emphasize exhalation during exertion.
Avoid uncontrolled, ballistic movements as they compromise safety and effectiveness.
Prevent incorrect or substitute motions by adequate stabilization and an appropriate level of resistance.
Avoid exercises that place excessive, unintended secondary stress on the back.
Be aware of medications a patient is using that can alter acute and chronic responses to exercise.
Avoid cumulative fatigue due to excessive frequency of exercise and the effects of overtraining or overwork by incorporating adequate rest intervals between exercise sessions to allow adequate time for recovery after exercise.
Discontinue exercises if the patient experiences pain, dizziness, or unusual or precipitous shortness of breath.
Additional information about several of these precautions is presented in this section. Special considerations and precautions for children and older adults who participate in weight-training programs are addressed later in the chapter.
The Valsalva maneuver (phenomenon), which is defined as an expiratory effort against a closed glottis, must be avoided during resistance exercise. The Valsalva maneuver is characterized by the following sequence. A deep inspiration is followed by closure of the glottis and contraction of the abdominal muscles. This increases intra-abdominal and intrathoracic pressures, which in turn forces blood from the heart, causing an abrupt, temporary increase in arterial blood pressure.151
During exercise the Valsalva phenomenon occurs most often with high-effort isometric94 and dynamic186 muscle contractions. It has been shown that the rise in blood pressure induced by an isometric muscle contraction is proportional to the percentage of maximum voluntary force exerted.186 During isokinetic (concentric) testing, if a patient exerts maximum effort at increasing velocities, the rise in blood pressure appears to be the same at all velocities of movement despite the fact that the force output of the muscle decreases.76 Although occurrence of the Valsalva phenomenon more often is thought to be associated with isometric94,151 and eccentric63 resistance exercise, a recent study186 indicated that the rise in blood pressure appears to be based more on extent of effort—not strictly on the type (mode) of muscle contraction.
The risk of complications from a rapid rise in blood pressure is particularly high in patients with a history of coronary artery disease, myocardial infarction, cerebrovascular disorders, or hypertension. Also at risk are patients who have undergone neurosurgery or eye surgery or who have inter-vertebral disk pathology. High-risk patients must be monitored closely.
Although resistance training is often recommended for individuals with a history of or who have a high risk for cardiovascular disorders, it is important to distinguish those individuals for whom resistance training is or is not safe and appropriate. In addition to knowledge of screening guidelines for resistance training,7,8 close communication with a patient's physician is essential. After clearance for exercise, low-intensity resistance training (30% to 40% intensity for upper body exercises and 50% to 60% intensity for lower body exercises) typically is recommended.7,8
Prevention During Resistance Exercise
Caution the patient about breath-holding.
Ask the patient to breathe rhythmically, count, or talk during exercise.
Have the patient exhale when lifting and inhale when lowering an exercise load.8
Be certain that high-risk patients avoid high-intensity resistance exercises.
If too much resistance is applied to a contracting muscle during exercise, substitute motions can occur. When muscles are weak because of fatigue, paralysis, or pain, a patient may attempt to carry out the desired movements that the weak muscles normally perform by any means possible.158 For example, if the deltoid or supraspinatus muscles are weak or abduction of the arm is painful, a patient elevates the scapula (shrugs the shoulder) and laterally flexes the trunk to the opposite side to elevate the arm. It may appear that the patient is abducting the arm, but in fact that is not the case. To avoid substitute motions during exercise, an appropriate amount of resistance must be applied, and correct stabilization must be used with manual contacts, equipment, or by means of muscular (internal) stabilization by the patient.
Overtraining and Overwork
Exercise programs in which heavy resistance is applied or exhaustive training is performed repeatedly must be progressed cautiously to avoid a problem known as overtraining or overwork. These terms refer to deterioration in muscle performance and physical capabilities (either temporary or permanent) that can occur in healthy individuals or in patients with certain neuromuscular disorders.
In most instances, the uncomfortable sensation associated with acute muscle fatigue induces an individual to cease exercising. This is not necessarily the case in highly motivated athletes who are said to be overreaching in their training program108 or in patients who may not adequately sense fatigue because of impaired sensation associated with a neuromuscular disorder.219
The term overtraining is commonly used to describe a decline in physical performance in healthy individuals participating in high-intensity, high-volume strength and endurance training programs.108,172 The terms chronic fatigue, staleness, and burnout are also used to describe this phenomenon. When overtraining occurs, the individual progressively fatigues more quickly and requires more time to recover from strenuous exercise because of physiological and psychological factors.
Overtraining is brought on by inadequate rest intervals between exercise sessions, too rapid progression of exercises, and inadequate diet and fluid intake. Fortunately, in healthy individuals, overtraining is a preventable, reversible phenomenon that can be resolved by tapering the training program for a period of time by periodically decreasing the volume and frequency of exercise (periodization).108,167,170,172
The term overwork, sometimes called overwork weakness, refers to progressive deterioration of strength in muscles already weakened by nonprogressive neuromuscular disease.219 This phenomenon was first observed more than 50 years ago in patients recovering from polio who were actively involved in rehabilitation.21 In many instances the decrement in strength that was noted was permanent or prolonged. More recently, overwork weakness has been reported in patients with other nonprogressive neuromuscular diseases, such as Guillain-Barré syndrome.56 Postpolio syndrome is also thought to be related to long-term overuse of weak muscles.98
Overwork weakness has been produced in laboratory animals,129 which provides some insight as to its cause. When strenuous exercise was initiated soon after a peripheral nerve lesion, the return of functional motor strength was retarded. It was suggested that this could be caused by excessive protein breakdown in the denervated muscle.
Prevention is the key to dealing with overwork weakness. Patients in resistance exercise programs who have impaired neuromuscular function or a systemic, metabolic, or inflammatory disease that increases susceptibility to muscle fatigue must be monitored closely, progressed slowly and cautiously, and re-evaluated frequently to determine their response to resistance training. These patients should not exercise to exhaustion and should be given longer and more frequent rest intervals during and between exercise sessions.4,56
Exercise-Induced Muscle Soreness
Almost every individual, unaccustomed to exercise who begins a resistance training program, particularly a program that includes eccentric exercise, experiences muscle soreness. Exercise-induced muscle soreness falls into two categories: acute and delayed onset.
Acute muscle soreness develops during or directly after strenuous exercise performed to the point of muscle exhaustion.44 This response occurs as a muscle becomes fatigued during acute exercise because of the lack of adequate blood flow and oxygen (ischemia) and a temporary buildup of metabolites, such as lactic acid and potassium, in the exercised muscle.9,44 The sensation is characterized as a feeling of burning or aching in the muscle. It is thought that the noxious metabolic waste products may stimulate free nerve endings and cause pain. The muscle pain experienced during intense exercise is transient and subsides quickly after exercise when adequate blood flow and oxygen are restored to the muscle. An appropriate cool-down period of low-intensity exercise (active recovery) can facilitate this process.51
Delayed-Onset Muscle Soreness
After vigorous and unaccustomed resistance training or any form of muscular overexertion, DOMS, which is noticeable in the muscle belly or at the myotendinous junction,70,104,144 begins to develop approximately 12 to 24 hours after the cessation of exercise. As was already pointed out in the discussion of concentric and eccentric exercise in this chapter, high-intensity eccentric muscle contractions consistently cause the most severe DOMS symptoms.16,63,78,100,104,215 Box 6.12 lists the signs and symptoms over the time course of DOMS. Although the time course varies, the signs and symptoms, which can last up to 10 to 14 days, gradually dissipate.16,78,100
BOX 6.12 Delayed-Onset Muscle Soreness: Clinical Signs and Symptoms
Muscle soreness and aching beginning 12 to 24 hours after exercise, peaking at 48 to 72 hours, and subsiding 2 to 3 days later
Tenderness with palpation throughout the involved muscle belly or at the myotendinous junction
Increased soreness with passive lengthening or active contraction of the involved muscle
Local edema and warmth
Muscle stiffness reflected by spontaneous muscle shortening66 before the onset of pain
Decreased ROM during the time course of muscle soreness
Decreased muscle strength prior to onset of muscle soreness that persists for up to 1 to 2 weeks after soreness has remitted41
Etiology of DOMS. Despite years of research dating back to the early 1900s,142 the underlying mechanisms (mechanical, neural, or/or cellular) of tissue damage associated with DOMS is still unclear.43,196 Several theories have been proposed, and some subsequently have been refuted. Early investigators proposed the metabolic waste accumulation theory, which suggested that both acute and delayed-onset muscle soreness was caused by a buildup of lactic acid in muscle after exercise. Although this is a source of muscle pain with acute exercise, this theory has been disproved as a cause of DOMS.280 Multiple studies have shown that it requires only about 1 hour of recovery after exercise to exhaustion to remove almost all lactic acid from skeletal muscle and blood.104
The muscle spasm theory also was proposed as the cause of DOMS, suggesting that a feedback cycle of pain caused by ischemia and a buildup of metabolic waste products during exercise led to muscle spasm.69 This buildup, it was hypothesized, caused the DOMS sensation and an ongoing reflex pain-spasm cycle that lasted for several days after exercise. The muscle spasm theory has been discounted in subsequent research that showed no increase in EMG activity and, therefore, no evidence of spasm in muscles with delayed soreness.2
Although studies on the specific etiology of DOMS continue, current research seems to suggest that DOMS is linked to some form of contraction-induced, mechanical disruption (microtrauma) of muscle fibers and/or connective tissue in and around muscle that results in degeneration of the tissue.43,106 Evidence of tissue damage such as elevated blood serum levels of creatine kinase, is present for several days after exercise and is accompanied by inflammation and edema.2,105,106
The temporary loss of strength and the perception of soreness or aching associated with DOMS appear to occur independently and follow different time courses. Strength deficits develop prior to the onset of soreness and persist after soreness has remitted.66,212 Thus, force production deficits appear to be the result of muscle damage, possibly myofibrillar damage at the Z bands,43,211 which directly affects the structural integrity of the contractile units of muscle, not neuromuscular inhibition as the result of pain.211,212
Prevention and treatment of DOMS. Prevention and treatment of DOMS at the initiation of an exercise program after a short or long period of inactivity have been either ineffective or, at best, marginally successful. It is a commonly held opinion in clinical and fitness settings that the initial onset of DOMS can be prevented or at least kept to a minimum by progressing the intensity and volume of exercise gradually,48,78 by performing low-intensity warm-up and cool-down activities,68,78,247 or by gently stretching the exercised muscles before and after strenuous exercise.68,247 Although these techniques are regularly advocated and employed, little to no evidence in the literature supports their efficacy in the prevention of DOMS.
There is some evidence to suggest that the use of repetitive concentric exercise prior to DOMS-inducing eccentric exercise does not entirely prevent but does reduce the severity of muscle soreness and other markers of muscle damage.214 Paradoxically, a regular routine of resistance exercise, particularly eccentric exercise, prior to the onset of DOMS or after an initial episode of DOMS has developed and remitted.9,43,44,48 This response is often referred to as the "repeated-bout effect," whereby a bout of eccentric exercise protects the muscle from damage from subsequent bouts of eccentric exercise.196 It may well be that with repeated bouts of the same level of eccentric exercise or activity that caused the initial episode of DOMS, the muscle adapts to the physical stress, resulting in the prevention of additional episodes of DOMS.9,43,175,196
Effective treatment of DOMS, once it has occurred, is continually being sought because, to date, the efficacy of DOMS treatment has been mixed. Evidence shows that continuation of a training program that has induced DOMS does not worsen the muscle damage or slow the recovery process.43,215 Light, high-speed (isokinetic), concentric exercise has been reported to reduce muscle soreness and hasten the remediation of strength deficits associated with DOMS,125 but other reports suggest no significant improvement in strength or relief of muscle soreness with light exercise.74,282
The value of therapeutic modalities and massage techniques also is questionable. Electrical stimulation to reduce soreness has been reported to be effective66,153 and ineffective.282 Although cryotherapy (cold water immersion) after vigorous eccentric exercise reduces signs of muscle damage (creatine kinase activity), it has been reported to have little to no effect on the perpetuation of muscle tenderness or strength deficit.88 Also, there is no significant evidence that postexercise massage, despite its widespread use in sports settings, reduces the signs and symptoms of DOMS.153,272,282 Other treatments, such as hyperbaric oxygen therapy and nutritional supplements (vitamins C and E) also have been shown to have limited benefits.48 However, use of compression sleeves166,171 and topical salicylate creams, which provide an analgesic effect, may also reduce the severity of and hasten the recovery from DOMS-related symptoms.
FOCUS ON EVIDENCE
In a prospective study166,171 of DOMS that was induced by maximal eccentric exercise, the use of a compression sleeve over the exercised muscle group resulted in no increase in circumferential measurements of the upper arm (which could suggest prevention of soft tissue swelling). In participants wearing a sleeve, there was also a more rapid reduction in the perception of muscle soreness and a more rapid amelioration of deficits in peak torque than recovery from DOMS without the use of compression.
In summary, although some interventions for the treatment of DOMS appear to have potential, a definitive treatment has yet to be determined.
When an individual with known (or at high risk for) osteoporosis or osteopenia participates in a resistance exercise program, the risk of pathological fracture must be addressed. Osteoporosis, which is discussed in greater detail in Chapter 11, is a systemic skeletal disease characterized by reduced mineralized bone mass that is associated with an imbalance between bone resorption and bone formation, leading to fragility of bones. In addition to the loss of bone mass, there also is narrowing of the bone shaft and widening of the medullary canal.9,29,82,174
The changes in bone associated with osteoporosis make the bone less able to withstand physical stress. Consequently, bones become highly susceptible to pathological fracture. A pathological fracture (fragility fracture) is a fracture of bone already weakened by disease that occurs as the result of minor stress to the skeletal system.29,82,189,209 Pathological fractures most commonly occur in the vertebrae, hips, wrists, and ribs.82,174 Therefore, to design and implement a safe exercise program, a therapist needs to know if a patient has a history of osteoporosis and, as such, an increased risk of pathological fracture. If there is no known history of osteoporosis, the therapist must be able to recognize those factors that place a patient at risk for osteoporosis.29,54,82,174,189 As noted in Chapter 11, postmenopausal women, for example, are at high risk for primary (type I) osteoporosis. Secondary (type II) osteoporosis is associated with prolonged immobilization or disuse, restricted weight bearing, or extended use of certain medications, such as systemic corticosteroids or immunosuppressants.
Prevention of Pathological Fracture
As noted earlier in the chapter, evidence of the positive osteogenic effects of physical activity that includes resistance training has been determined. Consequently, in addition to aerobic exercises that involve weight-bearing, resistance exercises have become an essential element of rehabilitation and conditioning programs for individuals with or at risk for, osteoporosis.8,9,226,238 Therefore, individuals who are at risk for pathological fracture often engage in resistance training.
Successful, safe resistance training must impose enough load (greater than what regularly occurs with activities of daily living) to achieve the goals of the exercise program (which include increasing bone density in addition to improving muscle performance and functional abilities) but not so heavy a load as to cause a pathological fracture. Guidelines and precautions during resistance training to reduce the risk of pathological fracture for individuals with or at risk for osteoporosis are summarized in Box 6.13.209,226,238
BOX 6.13 Resistance Training Guidelines and Precautions to Reduce the Risk of Pathological Fracture
Intensity of exercise. Avoid high-intensity (high-load), high-volume weight training. Depending on the severity of osteoporosis, begin weight training at a (40% to 60% of 1-RM)), progressing to moderate-intensity (60% to <80% of 1-RM)).
Repetitions and sets. Initially, perform only one set of several exercises 8 to 12 repetitions each for the first 6 to 8 weeks.
Frequency. Perform weight lifting exercises 2 to 3 times per week.
Type of exercise. Integrate weight-bearing activities into resistance training, but use the following precautions:
Avoid high-impact activities such as jumping or hopping. Perform most strengthening exercises in weight-bearing postures that involve low impact, such as lunges or step-ups/step-downs against additional resistance (handheld weights, a weighted vest, or elastic resistance).
Avoid high-velocity movements of the spine or extremities.
Avoid trunk flexion with rotation and end-range resisted flexion of the spine that could place excessive loading on the anterior portion of the vertebrae, potentially resulting in anterior compression fracture, wedging of the vertebral body, and loss of height.
Avoid lower extremity weight-bearing activities that involve torsional movements of the hips, particularly if there is evidence of osteoporosis of the proximal femur.
To avoid loss of balance during lower extremity exercises while standing, have the patient hold onto a stable surface such as a countertop. If the patient is at high risk for falling or has a history of falls, perform exercises in a chair to provide weight bearing through the spine.
In group exercise classes, keep participant-instructor ratios low; for patients at high risk for falling or with a history of previous fracture, consider direct supervision on a one-to-one basis from another trained person.