Chapter 8 – Rehabilitation
Section A: The Language of Exercise and Rehabilitation
John D. Childs, MPT, MBA, OCS, CSCS James J. Irrgang, PhD, PT, ATC
Rehabilitation involves procedures designed to minimize impairments, functional limitations, and disability after injury or illness. In sports medicine, rehabilitation includes procedures designed to restore athletes to their previous level of function within the shortest time possible. Rehabilitation begins immediately after injury and culminates in return to sport or return to the highest functional level possible based on the nature and severity of the injury. For the athlete, rehabilitation frequently consists of a combination of various physical agents and therapeutic exercise techniques aimed at minimizing the impairments, functional limitations, and disability associated with the injury. Knowledge of the theoretical principles, indications and contraindications, and proper application of each technique is necessary to maximize the potential for return to sport and to minimize the risk for reinjury.
Disablement
In rehabilitation of the athlete, it is useful to consider the model of disablement proposed by Nagi.
[ 45 ] In this model, an active pathologic process is the interruption of or interference with normal processes in the body. Impairment is the loss of or abnormality in structure or function at the organ or system level. Impairments are consequences of the pathologic process and may be manifested as signs or symptoms. Signs are those findings perceived by the clinician during examination
(e.g., decreased knee range of motion, knee joint laxity). Symptoms are manifestations of the pathologic process that are perceived by the athlete and reported to the clinician during the examination (e.g., giving way of the knee during physical activity). Functional limitations are those limitations that are imposed on performance at the level of the whole organism or person. In essence, they are the functional consequences of the pathologic process and subsequent impairments.
Disability is a limitation in performance of socially defined roles and tasks within a sociocultural and physical environment that is a consequence of the athlete's functional limitations.
To illustrate the disablement process, consider the athlete who suffers a knee injury resulting in a torn anterior cruciate ligament. The active pathologic process in this case is disruption of the anterior cruciate ligament. The physical impairments associated with this injury may include pain, swelling, loss of motion and strength, and laxity. The resulting functional limitations from this injury may be the inability to run and perform cutting and pivoting maneuvers. The resulting disability experienced by the athlete may be the inability to perform in sports that require cutting and pivoting. Rehabilitation of this athlete should ultimately address the disability or inability to participate in sporting activities. To accomplish this, the rehabilitation program may initially need to address the physical impairments (pain, swelling, instability, limited range of motion, weakness, laxity, and loss of proprioception) resulting from the injury. As the physical impairments improve,
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rehabilitation then focuses on reducing the functional limitations experienced by the athlete. This includes activities to improve the athlete's ability to run, cut, and pivot without symptoms. The final phase of rehabilitation addresses the disability experienced by the athlete. This includes functional training activities that allow the athlete to resume participation in sports that require running, cutting, and pivoting.
In rehabilitation of an athlete, it is useful to consider this model of disablement.
Rehabilitation should not only focus on the physical impairments experienced by the athlete but also address the functional limitations and disability the athlete experiences.
Goal of Rehabilitation
The ultimate goal of rehabilitation after athletic injury is to eliminate or to minimize the disability experienced by the athlete. For this goal to be accomplished, the physical therapist or athletic trainer will focus on eliminating or minimizing the athlete's physical impairments and functional limitations. This requires restoration of symptom-free motion and function to allow individuals to return to their previous level of activity in the shortest time possible.
Specific goals in the rehabilitation program depend on the phase of rehabilitation.
They include limiting inflammation; decreasing pain and swelling; improving joint mobility and flexibility; improving muscle strength, endurance, and power; improving cardiovascular endurance; and promoting coordination. The rehabilitation program must be appropriately designed to meet each of these goals. Furthermore, the athlete's program must be progressed as successive goals are accomplished.
Development and progression of the athlete's rehabilitation program depend on the physical therapist's and athletic trainer's clinical decision-making and problemsolving skills. The physical therapist and athletic trainer must closely evaluate and monitor the impairments and functional limitations demonstrated by the athlete.
Interventions
Rehabilitation requires athletic trainers and physical therapists to have basic knowledge of the effects of therapeutic exercise and physical agents. The purpose, indications, contraindications, and precautions for the use of these procedures must be known. Athletic trainers and physical therapists must be able to relate the effects of physical agents and therapeutic exercise to the rehabilitation goals for the athlete.
Establishment of appropriate goals during rehabilitation depends on the ability to assess the extent of injury and functional status of the injured athlete. An understanding of disease and the healing process is necessary to ensure appropriate rehabilitation. Anatomy, kinesiology, and biomechanics must also be considered in the development of a rehabilitation program.
Assuming a thorough clinical examination has been performed, physical therapists and athletic trainers can choose from a number of potential interventions in their armamentarium to address an athlete's impairments and functional limitations. These include various physical agents, therapeutic exercise (e.g., range of motion and
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stretching, resistance exercise, functional training), and education of the patient. The choice of intervention and the specific parameters associated with the intervention should be based on the best available evidence in peer-reviewed literature. The remainder of this chapter is limited to the use of therapeutic exercise to eliminate or to minimize impairments, functional limitations, and disability in athletes. In addition, we review basic principles and considerations for the use of each intervention.
Therapeutic Exercise
Therapeutic exercise is defined as those movements that are designed to eliminate or to minimize the athlete's physical impairments, functional limitations, and disability.
Therapeutic exercise can be used to maintain or to improve range of motion, muscle function, and proprioception. A therapeutic exercise program should be individually designed to address physical impairments, functional limitations, and disability experienced by the athlete. A therapeutic exercise program must consider the nature and severity of the injury or illness, the purpose of the exercise, the sequence and progression of the exercise, and the contraindications and precautions. In addition, the intensity, frequency, and duration of the exercise must be appropriate for the stage of inflammation, healing, and conditioning. Therapeutic exercise may take one of several forms, including range of motion and stretching exercise, resistance exercise, neuromuscular training, and functional training.
Range of Motion
The range of motion available at a particular joint is determined by the configuration of the joint surfaces as well as surrounding soft tissue structures, such as the capsule, ligament, muscle, tendon, fascia, and skin. The range of motion available at a particular joint is termed joint range.
[ 32 ] Joint range is measured in degrees with a goniometer. Muscle range is related to the functional excursion produced by muscles that cross the joint.
[ 32 ] The functional excursion of a muscle is the distance that it is capable of lengthening and shortening. For a one-joint muscle, the functional excursion is directly influenced by the joint that the muscle crosses. A one-joint muscle is expected to shorten and lengthen sufficiently to permit full active range of motion at the joint that it crosses. The functional excursion of a multijoint muscle exceeds the joint range of any one of the joints that it crosses. A multijoint muscle cannot lengthen or shorten sufficiently to permit the simultaneous extreme range of motion at all the joints that it crosses, however. For example, the hamstrings cannot lengthen sufficiently to permit simultaneous full hip flexion and full knee extension.
In this position, the hamstrings are said to be passively insufficient. In the passive insufficient position, further motion is limited by tension in the musculotendinous unit. Similarly, the hamstrings cannot shorten sufficiently to permit simultaneous full active knee flexion and hip extension. In this position, the hamstrings are said to be actively insufficient. In the active insufficient position, the muscle fibers cannot shorten any further and are ineffective in generating additional tension.
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Assessment of active range of motion indicates the individual's ability and willingness to perform the movement requested, the range of motion available, and the muscle function. Limited active range of motion may be due to pain, limited muscle function, or limited passive movement. If there are contraindications or restrictions to assessment of active motion, one should assess passive motion.
Passive motion is assessed as long as there are no contraindications or restrictions to assessment of passive motion. If there are contraindications or restrictions to assessment of passive motion, the physical therapist or athletic trainer should wait for tissue healing to occur before either active or passive motion is assessed.
Assessment of passive motion should include assessment of joint mobility. Causes of limited passive motion include limited joint play, musculotendinous shortening, limited scar mobility, capsuloligamentous adhesions and tightness, internal derangement of the joint, and bony block to motion. The cause of the limited passive motion must be determined so that appropriate treatment can be rendered to improve passive motion. Although the specifics of assessment of motion are beyond the scope of this discussion, some basic principles need to be understood.
Mechanical Characteristics of Connective Tissue and Muscle.
To increase motion, the properties of the tissue that limits the motion must be considered. These tissues are traditionally divided into noncontractile and contractile tissues. Noncontractile tissues are the ligaments, capsule, fascia, and connective tissue components of muscle and skin. Contractile tissues are the muscle, tendon, and tendinous insertion to bone.
The material strength of tissue is its ability to resist load or stress. Stress is defined as force per unit of cross-sectional area and can be tensile, compressive, or shearing.
Strain is defined as the deformation that occurs in response to stress. It is typically expressed as the percentage of elongation (i.e., change in length divided by original length). The mechanical properties of tissue are often plotted in a stress-strain curve that relates strain as a function of stress for a given tissue ( Fig. 8A-1 ). The toe region occurs at the beginning of the stress-strain curve. This is the region where little force is required to elongate the tissue. This probably represents straightening of the wavy pattern of connective tissue fibers. The elastic range consists of that area of the stress-strain curve in which the tissue returns to its original size and shape when the stress is removed. The upper end of the elastic range is termed the elastic limit. This is the point beyond which the tissue will not return to its original size or shape when the stress is removed. The plastic range of the stress-strain curve represents the range beyond the elastic limit that results in permanent elongation when the stress is removed. The upper end of the plastic range is associated with failure of the tissue. Sequential failure of collagen fibers in tendon occurs between
4% and 8% strain. Frank failure of the tissue occurs beyond 8% to 10% strain of the collagen fibers.
[ 8 ] This corresponds to 20% to 40% strain of the entire tendon.
[ 48 ]
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Figure 8A-1 Typical stress-strain curve for connective tissue. Toe region represents the region where little stress is required to lengthen the tissue; it probably represents straightening of wavy pattern of collagen fibers. Elastic region is that portion of the curve in which tissue returns to its original length when the stress is removed. Plastic region is that portion of the curve that results in permanent elongation when the stress is removed. (Modified from Kisner C, Colby, LA:
Therapeutic Exercise: Foundations and Techniques, 3rd ed. Philadelphia, FA Davis, 1996.)
Connective tissues are viscoelastic, that is, they exhibit the properties of viscosity and elasticity. Elasticity refers to the tissue's ability to return to its original length when stress is removed. Viscosity refers to a tissue's ability to resist elongation.
Because of the viscoelastic nature of connective tissue, it exhibits the properties of creep, relaxation, and stiffness. Creep is the elongation of tissue that results from constant loading over time ( Fig. 8A-2 ). Creep can be increased by increasing tissue temperature.
[ 37 ] Relaxation is the progressive decrease in internal stress over time as a result of lengthening to a constant strain. Stiffness is the ability of the tissue to resist elongation and is indicated by the slope of the stress-strain curve shown in Figure
8A-1 . Because connective tissue is viscoelastic, stiffness is dependent on the rate of loading. Increased rate of loading is associated with greater stiffness.
Figure 8A-2 Graphic representation of phenomenon of creep. Tissue undergoes gradual elongation over time when subjected to constant stress. (From Irrgang JJ: Rehabilitation. In Fu
FH, Stone DA [eds]: Sports Injuries. Baltimore, Williams & Wilkins, 1995, pp 81-95.)
Lengthening of connective tissue requires plastic deformation that results in gradual rearrangement of the connective tissue. Adequate time must be provided for remodeling to prevent fatigue or rupture of the tissue, or both. Plastic deformation of connective tissue can be maximized by use of the principles of creep, relaxation, and stiffness. To maximize permanent lengthening, low-magnitude forces are applied for prolonged periods. This process can be facilitated by the use of heating modalities and by maintaining the lengthened position during the period of cooling.
[ 37 ]
Brand
[ 6 ] suggested that if a joint is held at its end range for a significant time, “then it will grow.” The amount of time the joint is positioned at its end range is referred to as the total end-range time. Flowers and La-Stayo [ 16 ] provided evidence to support this hypothesis when they demonstrated that passive range of motion at the distal interphalangeal joint was almost doubled in patients with contractures of the distal interphalangeal joint who were casted for 6 days compared with subjects who were casted for only 3 days.
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The mechanical characteristics of contractile tissue must be considered in attempting to increase the functional excursion of muscles. Muscle consists of both contractile and noncontractile components.
[ 55 ] The noncontractile components include the series elastic and the parallel elastic components. The series elastic component is the connective tissue that connects the muscle fiber to bone; the parallel elastic component consists of the connective tissue that surrounds each muscle fiber.
Lengthening of the musculotendinous unit lengthens both the series and the parallel elastic components, producing a sharp rise in tension. As lengthening of the musculotendinous unit continues, mechanical disruption of the cross-bridges begins, as the actin and myosin filaments slide apart and an abrupt lengthening of sarcomere occurs. This is termed sarcomere give.
[ 15 ] Sarcomeres are elastic, and when shortterm stretch is removed, they return to their original length. This implies that shortterm stretching is not effective in increasing the length of the contractile components of a muscle.
Plastic deformation of contractile tissue can be achieved with prolonged immobilization. Prolonged immobilization in the lengthened position results in the addition of sarcomeres and permanent lengthening of the contractile tissues. This occurs to maintain the greatest functional overlap of the actin and myosin filaments.
Prolonged immobilization in the shortened position results in a decreased number of sarcomeres.
[ 58 ][ 62 ]
Techniques to Increase Motion.
Various strategies exist to improve motion. These include active and passive range of motion exercises, stretching and flexibility exercises, joint mobilization and manipulation, and neurophysiologic techniques to stretch muscle. To decide which strategy may be most appropriate, the physical therapist or athletic trainer must assess both active and passive motion.
If joint play is limited, treatment to restore passive motion includes joint mobilization followed by range of motion and stretching exercises for the joint. If passive motion is limited and mobility testing reveals normal joint play, the functional excursion of the musculotendinous unit is assessed. If functional excursion of the musculotendinous unit is limited, neurophysiologic stretching techniques can be incorporated to relax the muscles before elongation. This allows the contractile component to be lengthened more easily.
Range of Motion Exercise
Range of motion exercises are exercises that are performed within the unrestricted range of motion to maintain joint mobility and functional excursion of muscles.
Range of motion exercises can be passive, active assistive, or active. Passive range of motion exercises are movements that are produced by an external force without voluntary muscle effort on the part of the athlete. The external force may be applied by an athletic trainer or therapist, another part of the athlete's body, a machine, or gravity. Passive range of motion exercises are indicated when the athlete is not able to move the body segment voluntarily or when voluntary muscle activity would be
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detrimental to the healing process. Passive range of motion can be used to limit the adverse effects of immobility and to demonstrate motion when teaching other forms of exercise. In addition, passive range of motion techniques may be applied before stretching. Passive range of motion will not prevent muscle atrophy or affect muscle strength or endurance, nor will it improve circulation to the same extent that voluntary, active use of the muscles does. True passive movement may be difficult to obtain when muscles are innervated.
Active range of motion exercises are exercises within an unrestricted range of motion that are produced by active voluntary muscle contraction. Active-assistive exercises combine active voluntary contraction with an outside force to complete motion within the unrestricted range. Both active and active-assistive range of motion exercises are used when the athlete is able to contract the muscles actively to move the segment and when there are no contraindications to active voluntary muscle contraction. Active and active-assistive range of motion exercises can be used (1) to limit the adverse effects of immobility and maintain contractility of muscles, (2) to provide sensory feedback, (3) to provide a stimulus for maintaining integrity of bone, (4) to increase circulation, (5) to improve coordination and motor skills necessary for functional activities, and (6) to improve strength of weak muscles.
Sustained active exercises involving large muscle groups can be used to improve cardiorespiratory function. Active-assistive and active exercises cannot be used to strengthen muscles or to maintain strength of muscles that are already strong, however. Active exercises develop skill and coordination only in the movement patterns used.
Range of motion exercises may be performed in anatomic planes or in combined patterns incorporating movement in several planes simultaneously. Range of motion exercises can also be performed in sport-specific functional patterns. They should be performed within the pain-free range of motion. Motion beyond the available range of motion should not be forced. In general, 5 to 10 repetitions several times per day are adequate to limit the adverse effects of immobility.
The athlete's response to range of motion exercises should be closely monitored and documented. Range of motion exercises are contraindicated when motion is disruptive to the healing process. It is important to recognize signs of excessive exercise if range of motion exercises are performed acutely after injury. These signs are increased pain, swelling, warmth, redness, and loss of motion that persists for more than 1 to 2 hours after the exercise is completed. Range of motion exercises should not be confused with stretching exercises when the treatment goal is to increase range of motion.
Stretching and Flexibility Exercise
Stretching exercises are designed to increase range of motion and lengthen pathologically shortened soft tissue structures. Flexibility is defined as the ability of
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the muscle to relax and yield to a stretching force [ 32 ] ; as such, flexibility exercises are used to increase length of the musculotendinous unit. The term flexibility exercise is often used synonymously with stretching exercise, as is done here unless it is otherwise necessary to make the distinction.
Several general guidelines should be followed to enhance the effectiveness of stretching exercises and to minimize the risk for injury. Before stretching, local application of heat or engagement in light active exercise to elevate body temperature may be beneficial because it increases soft tissue extensibility. Massage and biofeedback may be employed to promote relaxation and to decrease muscle spasm, making it easier to stretch tight muscles. If mobility of a joint surface is limited, mobilization techniques are used before stretching exercises. Athletes should stretch until tightness is first perceived. Stretching exercises should avoid forcing the joint beyond the normal range of motion required for athletic activity.
Stretching exercises should not be performed in the acute stages of healing.
Stretching during this period may jeopardize the healing tissue and aggravate inflammation. During this time, range of motion exercises rather than stretching exercises should be used. Stretching exercises should not cause a persistent increase in pain that lasts longer than 1 to 2 hours. Caution must be used in stretching across the fracture site of a newly united fracture. Stretching exercises should not be used in an attempt to increase motion that is limited by a bony block.
Stretching exercises may be performed actively or passively. During passive stretching, the stretch is produced by forces external to the body. The external force can be applied manually or mechanically. Manual passive stretching exercises are performed by the physical therapist or athletic trainer. Passive mechanical stretching is performed by use of a mechanical device to apply a low (5- to 10-pound) external load to the shortened tissues. Passive mechanical stretching may be performed with the use of ankle weights or other mechanical equipment. In active stretching, the stretching force is created by active voluntary contraction of the athlete's muscles.
Active stretching allows incorporation of the neurophysiologic principles of stretching, which are discussed later.
Stretching exercises may be cyclic or prolonged. Cyclic stretching refers to a stretch that is maintained for a short time (i.e., less than 10 seconds) but performed for many repetitions. Prolonged stretching, on the other hand, consists of low-load stretches that are maintained for longer times for a fewer number of repetitions. The length of a prolonged stretch is variable and may range from 30 seconds or more to several hours, depending on the patient's level of tolerance. The total end-range times for repeated cyclic and prolonged stretches may be similar. Prolonged stretching may result in greater permanent lengthening of contractile and noncontractile tissues; however, cyclic stretching may be better tolerated by the athlete.
Stretching exercises can also be performed statically or ballistically. A slow static stretch is less likely to elicit a stretch reflex response. Ballistic stretching refers to a high-intensity, short-duration stretch that results in rapid lengthening of the muscle,
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which in turn stimulates the muscle spindle and facilitates a stretch reflex. The musculotendinous unit is susceptible to microtrauma with ballistic stretching.
Ballistic stretching may be beneficial immediately before engaging in exercise, but it should be performed only after a warm-up that includes slow static stretching.
When the athlete demonstrates limited range of motion in the subacute or chronic phases of healing, stretching exercises are indicated to regain the motion that is necessary for athletic activity. Stretching exercises can also be used to correct muscle imbalances that result when a muscle group is tight and its opposing muscle group is weak. In general, the tight muscle group should be stretched before strengthening exercises are performed to improve strength of the opposite muscle group. Stretching exercises may also be indicated before activity as a warm-up and after activity as a cool-down. Proper warm-up and cool-down minimize the risk for musculotendinous injuries associated with physical activity and sports.
Physiologic Motion and Accessory Motion
To understand the principles related to joint mobilization, it is necessary to understand the distinction between physiologic motion and accessory motion.
Physiologic motion is the angular displacement of a bone about its axis of rotation, referred to as swing. Physiologic motion is also referred to as osteokinematics.
These are movements that the patient can perform under voluntary muscle control
(i.e., flexion-extension, abduction-adduction, and internal-external rotation).
Accessory motions are the component movements necessary for physiologic motion.
These are not under voluntary control. These movements consist of rolling, gliding, compression, distraction, and spin. Accessory motion is also referred to as arthrokinematics.
[ 63 ]
Rolling occurs when new points on one surface meet new points on an opposing surface, much like a tire rolling along the road ( Fig. 8A-3 B ). Rolling of the joint surface always occurs in the same direction as the swing of the bone. During normal movement of a joint, rolling does not occur in isolation. Rolling is accompanied by gliding of the joint surfaces to prevent the convex joint surface from rolling off the concave surface. Gliding of the joint surface involves contact of the same point on one surface with new points on the opposing surface, much like a locked tire sliding over a road ( Fig. 8A-3 A ). The direction of gliding depends on the shape of the articular surface. Convex joint surfaces glide in the direction opposite the swing of the bone, whereas concave joint surfaces glide in the same direction as the swing of the bone. Normal joint motion combines both rolling and gliding of the joint surfaces. Joint mobilization techniques are designed to restore the normal gliding of joint surfaces that is necessary for physiologic motion.
Figure 8A-3 A, Representation of gliding. The same point on one surface comes into contact with new points on the opposing surface. B, Representation of rolling. New points on one surface contact the new points on opposing surface. (Modified from Kisner C, Colby LA:
Therapeutic Exercise: Foundations and Techniques, 3rd ed. Philadelphia, FA Davis, 1996.)
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Joint Mobilization
Joint mobilization is a manual therapy technique comprising a continuum of skilled passive movements to the joints and related soft tissues that are applied at varying speeds and amplitudes, including a small-amplitude, high-velocity therapeutic movement.
[ 24 ]
Joint mobilization is used to reduce pain and to restore accessory joint motion (joint play) of a hypomobile joint. Restoring normal joint play is necessary to restore full physiologic motion of the joint. Joint mobilization by use of sustained movements increases the extensibility of tight capsules and ligaments that limit mobility of the joint surfaces. Joint mobilization can also be used to reduce pain and spasm. These techniques are typically small-amplitude, oscillatory motions that stimulate joint mechanoreceptors to inhibit the perception of pain. Joint mobilization techniques may also reduce pain by stimulating movement of synovial fluid and preventing fluid stasis.
Proper application of joint mobilization techniques requires grading of the forces that are used. The Maitland or Australian system
[ 41 ]
uses oscillatory techniques.
Techniques are graded I through V. Grade I oscillations are small-amplitude movements at the beginning of the available range of motion. Grade II oscillations are large-amplitude motions performed within the available range but not up to the motion barrier. Grade III oscillations are large-amplitude motions performed up to and beyond the motion barrier. Grade IV oscillatory movements are small movements performed at and beyond the motion barrier. Grade V mobilization is a high-velocity small-amplitude motion that is used to restore the final few degrees of motion of the joint, to alter positional relationships, to break adhesions, or to stimulate joint receptors, which in turn reduces pain. Grade V mobilization is synonymous with manipulation of a joint ( Fig. 8A-4 ).
Figure 8A-4 Grading system for joint mobilization/manipulation. A, Normal range of motion
(ROM) available for a given joint. B, ROM available for a joint with restricted motion. The motion barrier represents resistance to motion engaged near the end of the motion. Motion beyond the motion barrier is achieved with overpressure. C, Grade I motion—small-amplitude movement at the beginning of the range. D, Grade II motion—large-amplitude motion within the available range but not up to the motion barrier. E, Grade III motion—large-amplitude movement up to and beyond the motion barrier. F, Grade IV motion—small-amplitude motion at and beyond the motion barrier. G, Grade V motion—high-velocity, small-amplitude motion performed beyond the motion barrier. (From Irrgang JJ: Rehabilitation. In Fu FH, Stone DA
[eds] Sports Injuries. Baltimore, Williams & Wilkins, 1995, pp 81-95.)
The Kaltenborn or Norwegian system uses sustained mobilization techniques.
[ 29 ] This system has three grades of motion. Grade I motion, also called piccolo motion, separates the joint surfaces just enough to equalize intra-articular and atmospheric
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pressure and is typically used to decrease pain. Grade II motion, or slack technique, removes the slack from the capsule and surrounding ligaments and can be used as a trial treatment to increase range of motion in the subacute stage of inflammation.
Grade III motion, or stretch technique, uses sufficient force to stretch joint structures to improve mobility.
Proper application of joint mobilization techniques requires a thorough examination of the involved joint to determine what tissues are limiting motion as well as the stage of inflammation. The mobilizing force should be correlated with the sequence of pain to resistance of motion. Pain that occurs before resistance to motion is reached indicates an acute condition. Mobilization for acute conditions consists of grade I or grade II oscillating techniques to decrease pain and maintain joint play.
Pain synchronous with resistance to motion indicates a subacute condition. A trial of gentle stretching is used for subacute conditions. Maitland or Kaltenborn grade II mobilization techniques are appropriate for subacute conditions. Pain engaged after resistance to motion has been encountered is indicative of a chronic condition.
Vigorous stretching is indicated for chronic conditions. Joint mobilization techniques for chronic conditions include primarily Maitland grade III or grade IV or Kaltenborn grade III techniques.
When joint mobilization is performed, the athlete should be positioned to promote relaxation and stabilization of the part to be mobilized. Mobilization is initially performed with the joint in the position in which the capsule has the greatest amount of laxity. This position generally occurs in the middle of the available range of motion. As range of motion improves, joint mobilization techniques can be performed in the restricted position. Forces should be applied as close to the opposing joint surfaces as possible. The area of contact with the hand should be as large as possible to improve the patient's comfort. The force of the mobilization technique is graded according to the stage of the condition and the intended goals of treatment as described before.
The direction of movement is dictated by the direction of the restricted motion and the shape of the joint surface. The treatment plane is a plane perpendicular to a line from the axis of rotation to the center of the concave joint surface ( Fig. 8A-5 ).
When joint surfaces are distracted, the force should be applied perpendicular to the treatment plane. With gliding joint surfaces, the forces should be applied parallel to the treatment plane, using the convex-concave rule. According to the convexconcave rule, concave joint surfaces should be glided in the direction of the limited swing of the bone, whereas convex surfaces should be glided in the direction opposite the limited swing of the bone. In performing joint mobilization techniques, angular motion of the bone should be minimized. Angular motion during gliding of joint surfaces may result in compression of the joint surfaces, which may damage the articular surface.
Figure 8A-5 Treatment plane (T.P.) is a line perpendicular to the line drawn from the axis of rotation for a joint to the center of a concave joint surface. Forces to distract the joint are applied perpendicular to the treatment plane. Forces to glide the joint are applied parallel to the treatment
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plane. (Modified from Kisner C, Colby LA: Therapeutic Exercise: Foundations and Techniques,
3rd ed. Philadelphia, FA Davis, 1996.)
Oscillatory joint mobilization techniques are performed at a rate of 1 or 2 cycles/second for 1 to 2 minutes. Sustained joint mobilization techniques are sustained for 5 to 15 seconds and repeated 10 times. Joint mobility and range of motion are assessed at the completion of joint mobilization. The athlete should also perform range of motion and stretching exercises as a follow-up treatment to joint mobilization. The athlete should be warned that it is common to experience some increase in soreness; however, this should subside within several hours.
Joint mobilization techniques should be used only when mobility testing reveals decreased joint play. Joint mobilization is contraindicated with hypermobile joints.
Joint mobilization techniques that stretch the joint capsule are contraindicated during the period of active inflammation. During this period, joint mobilization will aggravate inflammation. Joint mobilization is also contraindicated in the presence of a large joint effusion in which the capsule is already stretched because of distention of the joint. Use of mobilization techniques after fractures should be delayed until there is radiographic evidence of union.
Neurophysiologic Stretching
The neurophysiologic properties of contractile tissue must also be considered in attempting to increase range of motion limited by musculotendinous structures. The muscle spindle is a sensory organ sensitive to muscle lengthening. Quick stretching of the muscle results in lengthening of the muscle spindle and initiation of the monosynaptic stretch reflex. Consequently, sudden or ballistic stretching of musculotendinous units may cause the muscle to contract while it is being lengthened, thus resulting in increased soreness after ballistic stretching.
Another sensory organ, the Golgi tendon organ, is found in the musculotendinous junction; it is sensitive to tension caused by passive stretching or active contraction of the musculotendinous unit. Excessive musculotendinous tension causes the Golgi tendon organ to discharge, inhibiting contraction. Reciprocal inhibition occurs when the opposing muscle is inhibited as a muscle contracts.
These neurophysiologic principles can be incorporated to relax muscles before elongation, allowing the contractile component to be lengthened more easily; however, they generally do not result in a permanent increase in length. Examples of neurophysiologic stretching are contract-relax and contract-relax-contract techniques.
Contract-relax stretching techniques involve isometric contraction of the tight muscle followed by lengthening of the muscle. The prestretch contraction of the
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short muscle results in autogenic inhibition of the muscle as the Golgi tendon organ is stimulated, allowing the shortened muscle to lengthen. As an example, a contractrelax stretching technique for the hamstrings incorporates contraction of the hamstrings by simultaneous hip extension and knee flexion followed by passive lengthening of the hamstrings after the contraction.
Contract-relax-contract stretching techniques incorporate an isometric contraction of the tight muscle followed by relaxation and contraction of the opposing muscle while the tight muscle is lengthened. Contract-relax-contract stretching techniques combine autogenic inhibition with the principle of reciprocal inhibition. Reciprocal inhibition results in inhibition of the antagonist muscle when the agonist is contracted. As an example, a contract-relax-contract technique to lengthen the hamstrings incorporates contraction of the hamstrings by simultaneous hip extension and knee flexion followed by relaxation of the muscle and contraction of the quadriceps and hip flexors while the hamstrings are lengthened.
Muscle Function
Rehabilitation of athletes frequently incorporates resisted exercises to address impairments of muscle performance, such as strength, work, power, and endurance.
These terms are often misused when they are applied to exercise and muscle performance. Strength is defined as the maximal amount of force a muscle can generate for a given type and speed of contraction.
[ 32 ][ 34 ] Force is an action that tends to change the state of rest or motion of matter.
[ 34 ][ 44 ] It is a linear quantity measure that is measured in newtons. When a muscle exerts force on the skeleton, it produces rotation about an axis.
[ 34 ][ 44 ] Torque is a rotational measure and is equal to the product of the force multiplied by the perpendicular distance from the line of action of the force to the axis of rotation. In assessing strength or force generated by a muscle acting on the bony skeleton, one is measuring torque.
Work, power, and endurance are often included in the discussion of strength. Work is force expressed through a distance with no limitation on time.
[ 34 ] For linear motion, work is the product of force multiplied by distance; for rotational movements, work is equal to the product of torque multiplied by distance. Power is the rate of doing work or work per unit of time.
[ 34 ] It can also be expressed as a product of force times velocity. Power should not be confused with torque generated at a high-contractile velocity. Maximal power is generated at intermediate contractile velocities.
[ 34 ]
Endurance is the ability of a muscle or muscle group to generate force or work over time without fatigue. Muscle endurance can be quantified as the length of time that a contraction can be maintained or as the number of repetitions that can be performed at particular force or power level through a specified range of motion.
[ 32 ] As endurance improves, the muscle is capable of performing a greater number of contractions or holding against a load for a longer time.
Strength versus Endurance Exercises
Strength training exercises are designed to increase the maximal force that a muscle can generate. Traditionally, strength training involves heavy-resistance, low-
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repetition exercise. The definition of heavy resistance varies for individuals and from muscle group to muscle group. In general, heavy resistance is considered to mean the amount of weight that can be lifted for 6 to 12 repetitions before fatigue develops. Strength training exercises using heavy resistance are typically performed for 6 to 12 repetitions.
Response to strength training includes hypertrophy of muscle fibers. The increased cross-sectional area of muscle fibers is related to increased contractile protein and the number of fibrils within the muscle fiber as well as to increased density of the capillary bed surrounding individual muscle fibers. Hypertrophy may also be related to an increase in the connective tissue component of muscle. Heavy-resistance training appears to hypertrophy fast-twitch (type II) muscle fibers selectively.
Hyperplasia is an increase in the number of muscle fibers that results from longitudinal splitting of muscle fibers. Hyperplasia has been observed in laboratory animals exposed to heavy-resistance exercise [ 21 ][ 22 ][ 23 ] ; however, hyperplasia is controversial in humans. In response to strength training, individuals are able to recruit an increased number of motor units. Improved generation of muscle force may also be related to improved recruitment and synchronization of motor units.
This may explain increases in strength early in the training program in the absence of hypertrophy. Biochemical changes associated with strengthening are small and inconsistent.
Endurance training makes use of low- to moderate-resistance high-repetition exercises. Endurance training results in peripheral and central adaptations that improve an individual's ability to sustain work. The peripheral adaptations are localized to the muscle or muscles involved in the endurance training exercises. The peripheral responses generally improve oxidative capacity of the muscle fiber. This is a result of an increased concentration of myoglobin within the muscle fibers.
Increased myoglobin concentration aids in the delivery of oxygen from the cell membrane to mitochondria. Endurance training also improves oxidation of carbohydrates and fats within the muscle fiber. This is the result of an increase in the size, number, and membrane surface area of mitochondria as well as of an increase in the concentration and activity of oxidative enzymes. The intramuscular stores of adenosine triphosphate and creatine phosphate also increase with endurance training.
There appears to be selective hypertrophy of slow-twitch (type I) muscle fibers; however, this may be modified by the intensity of the endurance exercise. Highintensity endurance training (>90%) results in improved endurance capabilities in type II fibers.
[ 20 ][ 25 ] Anaerobic glycolysis is not appreciably affected by endurance training.
Cardiovascular responses to endurance training occur if the training stimulus is sufficient. In general, the cardiovascular response to endurance training is increased cardiac output related to increased stroke volume. Resting heart rate and heart rate at a given workload decrease in response to endurance training.
Factors That Influence Muscle Strength
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Strength of normal muscle is influenced by several factors. The amount of force that a muscle can generate is related to its cross-sectional size. Length of the muscle also influences force generation. According to the length-tension relationship, muscle can generate maximal force at its resting length. This is the position at which there is a maximal number of cross-bridges between the actin and myosin filaments. As the muscle shortens, greater overlap of the actin-myosin filaments results in a decreased number of cross-bridges. Because of this, the force that a muscle can generate in a shortened position is decreased. The contractile force generated by a muscle also decreases as the muscle is lengthened beyond its resting position. There is increased force, however, because of passive lengthening of the connective tissue. Therefore, the total force produced by the musculotendinous unit (including both contractile and noncontractile forces) increases as the muscle lengthens ( Fig. 8A-6 ).
Figure 8A-6 Relationship of contractile and noncontractile tension to total tension of a muscle.
Contractile tension is greatest at the resting length for a muscle. As the muscle is shortened or lengthened, contractile tension decreases. Noncontractile tension increases as the muscle is lengthened. Total tension produced by a muscle is the sum of contractile and noncontractile tension. (From Irrgang JJ: Rehabilitation. In Fu FH, Stone DA [eds]: Sports Injuries.
Baltimore, Williams & Wilkins, 1995, pp 81-95.)
The number of motor units recruited also influences the level of force generated.
The level of force increases as the number of motor units recruited increases.
According to Henneman's size principle, small motoneurons are recruited before large motoneurons. Small motoneurons innervate slow-twitch (type I) muscle fibers.
These fibers produce low levels of force and are resistant to fatigue. Large motoneurons innervate fast-twitch (type II) muscle fibers. Fast-twitch muscle fibers produce high levels of force, but they fatigue rapidly. Because small motoneurons are recruited before large motoneurons, activities involving low levels of muscle tension are produced primarily by slow-twitch muscle fibers. As force requirements increase, progressively more fast-twitch fibers are recruited.
The speed and type of muscle contraction also influence the amount of force that a muscle can generate. During a concentric contraction, the muscle shortens as it contracts, whereas during an eccentric contraction, the muscle lengthens as it contracts. Concentric contractions occur when the internal force created by the muscle is greater than the external resistance that is applied. Conversely, eccentric contractions occur when external resistance overcomes the internal resistance created by the muscle. Concentric contractions are necessary to accelerate the body, and eccentric contractions are necessary for deceleration. For concentric contractions, the torque created by the muscle decreases as the speed of contraction increases. During an eccentric contraction, however, the torque created by the muscle increases as the speed of lengthening increases up to some maximal value (
Fig. 8A-7 ). This is believed to result from facilitation of the stretch reflex and stretching of the connective tissue component within the musculotendinous unit,
15

both of which give rise to increased muscle tension with increased speed of lengthening. A maximal eccentric contraction produces greater force than a maximal isometric contraction, and a maximal isometric contraction produces greater force than a concentric contraction. If performed inappropriately, eccentric exercise is associated with increased muscle soreness and increased injury.
Figure 8A-7 Force-velocity relationship for muscle. For concentric contraction, force decreases as the speed of shortening increases. For eccentric contraction, force increases up to some maximum value as the speed of lengthening increases. (Modified from Curwin S, Stanish WD:
Tendinitis: Its Etiology and Treatment. Lexington, Mass, DC Heath and Co, 1984.)
Stanish and colleagues
[ 57 ]
suggested in 1986 that eccentric exercise should be incorporated into the treatment of tendinitis. Alfredson and coworkers [ 1 ] demonstrated that a greater number of individuals with chronic Achilles tendinitis who completed a 12-week eccentric training program were able to return to their preinjury levels of function compared with control subjects who did not receive eccentric training. The mechanism for the positive effects of eccentric training in the rehabilitation of tendinitis is unclear. It is thought that eccentric training may serve to lengthen the musculotendinous unit, thus decreasing the imposed load during physical activity. Another hypothesis is that eccentric training leads to greater hypertrophy and increased tensile strength of the tendon, thus facilitating the tissue remodeling process after injury.
[ 57 ]
The ability of eccentric training to prevent these types of injuries is not known.
A final factor that can influence the ability of a muscle to generate force is motivation. The individual must be willing and motivated to put forth maximal effort to generate maximal forces.
Techniques to Improve Muscle Function
Exercise to improve muscle function can take one of several forms. These exercises can be classified as static or dynamic exercise. Static exercise is isometric exercise in which no observable joint movement occurs. The length of the muscle appears to be constant; however, there is shortening at the sarcomere level. An isometric contraction occurs when torque produced by the muscle is equal to the external resistance. Dynamic resisted exercise results from voluntary contraction of muscles.
Active resistance exercises are those exercises in which the individual uses voluntary muscle contraction to move against an applied external resistance. Active resistance exercises include isotonic and isokinetic exercises.
Specificity of the exercise must be considered in designing a resistance exercise program. This means that the exercise program must be designed to strengthen the muscle or muscle groups in a manner that is specific to the way the muscle functions
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during activity. The speed of the exercise should match the speed of the functional movement. The resistance exercise program should also reproduce the type of contraction required during function. Isometric exercises are used to develop muscles that stabilize the body or a body segment. Concentric exercises are used to develop muscles that are responsible for acceleration, whereas eccentric exercises are used to develop muscles that are responsible for deceleration of the body.
Specificity of the exercise program should also consider the intensity of force required by the muscles during activity. The exercises should be performed through the entire range of motion in which strength is required.
Isometric Exercises
Isometric exercises are a form of resisted exercise in which the muscle contracts without an appreciable change in the length of the muscle or visible joint motion.
Because isometrics occur in the absence of joint motion, isometric exercises can be used when motion is contraindicated. They are also easy to perform and require little equipment. Until recently, it was thought that isometric exercises develop strength only at the position at which the exercise is performed, and the exercises had to be performed in 15- to 30-degree increments to develop strength throughout the full range of motion. Bandy and Hanten
[ 2 ]
demonstrated that isometric quadriceps exercises result in improvements in strength at angles other than those at which the exercise is performed. Isometric exercises with the muscle in the lengthened position resulted in greater carryover of strength to other angles than did isometric exercises performed with the muscle in the shortened position. Isometric exercises do not significantly improve endurance.
When performing isometric exercises, the athlete is instructed to contract the muscle maximally, holding it for 5 to 10 seconds to allow time for development of peak tension. The isometric exercises should be performed at multiple angles to improve strength throughout the range of motion. Submaximal isometrics can also be used to maintain mobility between muscle fibers during the healing phase and to improve circulation through a muscle pumping effect.
Isotonic Exercises
Isotonic exercises make use of movement against a constant external resistance.
They can be performed manually or mechanically to improve strength, power, and endurance. For improvement of strength, the overload principle must be applied, and the muscle must be progressively loaded by increasing resistance or repetitions to make continued improvements in function. Isotonic exercises include both concentric and eccentric exercises.
In developing an isotonic exercise program, one must consider the load, repetitions, sets, and frequency. Load is the amount of resistance used during the exercise. For improvement of strength, the load must be progressively increased. Repetitions are the number of times an exercise is performed in a given bout. The number of repetitions must be progressively increased to improve endurance. Sets are the number of bouts of repetitions that are performed. Many combinations of sets and
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repetitions can be used to improve strength and endurance. Strength is generally improved by lifting heavy amounts of weight for 3 to 5 sets of 6 to 12 repetitions.
For exercises designed to improve strength, heavy resistance is defined as the amount of weight that can be lifted for 6 to 12 repetitions. As strength improves, the amount of resistance must be progressively increased. For endurance to be increased, multiple high-repetition sets should be performed with light to moderate resistance. Frequency is the number of times the exercises are performed per day or week. Early in rehabilitation, isotonic exercises are usually submaximal and can be performed several times daily. As rehabilitation progresses to reconditioning, the isotonic exercises should become more vigorous, but it should be performed less frequently to allow adequate time for recovery to prevent fatigue. Most heavy resisted exercise programs designed to improve strength are done every other day.
Six weeks may be required for improved strength to be seen.
Variable-resistance exercise machines have been developed in an attempt to provide a variable resistance pattern that matches the torque curves produced by a particular muscle or muscle group. For variable-resistance exercise, the resistance is not accommodating and the speed is not controlled.
Isokinetic Exercises
Another type of resisted exercise that has increased in popularity during the past 20 years is isokinetic exercise. Isokinetic exercise involves movement at a constant speed. During isokinetic exercise, the speed of exercise is typically controlled by an isokinetic dynamometer. Most dynamometers allow concentric and eccentric exercise from 0 to 450 degrees/second. During isokinetic exercise, the resistance is accommodating and proportional to the effort put forth by the athlete. Research indicates that there may be some carryover of training from one speed to another. To ensure improvement in muscle performance across the spectrum of speeds, however, isokinetic training should be performed at a variety of contractile velocities.
[ 9 ]
Ideally, the speed of exercise selected for isokinetic training is comparable to the speed of movement required during function. The angular velocity during function typically exceeds the speed of movement permitted by the isokinetic dynamometer, however. Caution must be used in performing isokinetic exercise to ensure that further inflammation or injury does not occur. Inappropriate use of isokinetic exercise can be detrimental. During the earlier phases of rehabilitation, isokinetic exercise should be submaximal. Maximal isokinetic exercise should be reserved for the final stages of rehabilitation. Isokinetic testing has been used to measure muscle performance and to determine when an athlete is ready to return to full activity.
There is little scientific evidence to validate the use of isokinetic testing for predicting the ability to return to athletic function, however.
Intensity of Resistance Exercise
The intensity of exercise depends on the stage of inflammation and healing as well as on the goals of the exercise program. In general, submaximal exercises are used to increase muscle endurance. They are emphasized during the early stages of
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rehabilitation to protect healing tissues and to avoid pain and further aggravation of the injury. Exercises with maximal resistance are used in the later stage of rehabilitation when the goal is to recondition the athlete to improve strength and power.
Several specific exercise regimens to improve strength have been proposed.
DeLorme and Watkins
[ 11 ]
proposed a technique of progressive resistance exercises that begins by establishing a 10-repetition maximal weight. This is defined as the amount of weight that can be lifted precisely 10 times; it is usually established by trial and error. In the scheme proposed by DeLorme, 3 sets of 10 repetitions are performed. The first set is against half of the 10-repetition maximal weight. The second set is against three quarters of the 10-repetition maximal weight, and the third set is against the full 10-repetition maximal weight. A new 10-repetition maximal weight is determined each week. The method proposed by DeLorme builds in a gradual warm-up.
The Oxford technique [ 67 ] is the opposite of the DeLorme method. The first set is performed against the full 10-repetition maximal weight and the third set is performed against half of the 10-repetition maximal weight. This method attempts to accommodate the effects of fatigue; however, warm-up is required before beginning.
Knight [ 33 ] proposed a program of daily adjustable progressive resistance exercises.
The daily adjustable progressive resistance exercise program attempts to determine objectively when and by how much to increase resistance. Knight originally proposed use of a 6-repetition maximal weight, which is the amount of resistance that can be lifted precisely 6 times. Four sets of exercises are performed. The first set of six repetitions is performed with half of the 6-repetition maximal weight. The second set of 6 repetitions is performed with three quarters of the 6-repetition maximal weight. The third set consists of as many repetitions as possible against the full 6-repetition maximal weight. The number of repetitions performed during the third set is used to determine the resistance for the fourth set. If more than 6 repetitions are performed during the third set, the weight for the fourth set is increased; if 4 or fewer repetitions are performed for the third set, the weight for the fourth set is decreased. The weight is kept the same if 5 or 6 repetitions are performed. The number of repetitions performed during the fourth set determines the amount of weight used for the next session. If 5 or more repetitions are performed during the fourth set, the weight for the next session is increased; if 2 or fewer repetitions are performed for the fourth set, the weight for the next session is decreased. The weight is kept the same if 3 or 4 repetitions are performed.
The methods proposed by DeLorme and Knight and the Oxford technique make use of heavy-resistance, low-repetition exercise in an attempt to increase strength. In this case, heavy resistance is operationally defined as the amount of resistance that can be lifted 6 to 10 times. Heavy-resistance exercise may be inappropriate for the early stages of healing. Heavy resistance may not be tolerated by the joint and the healing structures during this time. Therefore, during the early phases of healing, exercises using submaximal resistance for a greater number of repetitions may be performed.
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We commonly use resistance that can be performed for 30 to 50 repetitions during the early phase of healing. Heavy-resistance exercises are delayed until the athlete enters the reconditioning phase of rehabilitation.
Isotonic exercises can be performed mechanically or manually. Mechanical resisted exercises have several advantages. The amount of resistance and the number of repetitions performed can be used to quantify the patient's baseline level of muscle performance and progression. In addition, athletes can see their progress when they are performing mechanically resisted exercise. This visible progress provides motivation. Resistance applied during mechanically resisted exercises is not limited by the strength of the athletic trainer or therapist. A variety of equipment provides mechanically resisted exercises.
During manually resisted exercises, resistance is applied by the therapist or athletic trainer. Manually resisted exercise can make use of dynamic or static muscle contractions and can be performed in the cardinal planes or in more functional diagonal patterns. Proprioceptive neuromuscular facilitation is a technique of manually resisted exercise that emphasizes movement in diagonal patterns.
Other Issues Related to Strength Training
Open versus Closed Chain Resistance Exercise.
When possible, functional exercise patterns should be used to develop strength. This implies the use of closed chain activities for the lower extremity and open chain activities for the upper extremity. During open chain activities, the distal extent of the extremity is free to move. Movement is produced by contraction of the agonist muscle. During closed chain activities, the distal aspect of the extremity is fixed, and motion occurs simultaneously at all joints that compose the kinetic chain. Movement is produced by co-contraction of muscles. Closed chain exercise simulates functional demands placed on the extremity during a variety of activities. Stability is enhanced as a result of increased joint compression and muscle co-contraction during closed chain activities. Although closed chain exercise may be attractive because of its ability to simulate functional activities, it may not provide an optimal stimulus for strength gains. For example, Ninos and colleagues [ 47 ] found that electromyographic activity of the quadriceps is only 25% to 30% of the electromyographic activity produced during a maximal voluntary isometric contraction when a squat is performed with 25% of body weight applied to the shoulders. Thus, high resistance must be used to increase strength of the quadriceps when performing closed chain exercises for the lower extremity. As noted before, the joint may not tolerate this high level of resistance during the early phases of healing. Strengthening of the quadriceps should therefore make use of a combination of open and closed chain exercises.
Safety.
Several precautions must be observed with respect to the use of resisted exercise in rehabilitation programs for athletes to minimize the risk for injury.
Contraindications to resisted exercise include active inflammation and pain. Use of
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resisted exercise in the presence of active inflammation can lead to further tissue trauma and aggravate pain and swelling. Resisted exercises should be eliminated or reduced if they produce an increase in pain that persists more than several hours after exercise.
One significant precaution in performing resisted exercises is avoidance of a
Valsalva maneuver, which may cause a transient but marked increase in blood pressure that places abnormal stress on the cardiovascular system. Exercise-induced arterial hypertension from the Valsalva maneuver during heavy-resistance exercise may be a risk factor for an acute stroke in healthy young adults.
[ 46 ] During resisted exercise, systolic blood pressure is often in excess of 200 mm Hg, depending on the force and length of the Valsalva maneuver. Narloch and Brandstater [ 46 ] found lower mean blood pressures during execution of the double-leg press at both 85% and
100% of the 1-repetition maximal weight when subjects slowly exhaled during the concentric contraction than when they had a closed glottis. Athletes should thus be warned to avoid use of the Valsalva maneuver. They should specifically be instructed to exhale during the forced phase of the movement, regardless of the movement's direction or anatomic position. In other words, they should exhale during the “sticking phase,” or the most difficult part of the lift. This is known as the principle of biomechanical matching of breathing phases.
[ 66 ]
Prolonged resisted exercises result in local muscle fatigue and total body fatigue.
Local muscle fatigue is a diminished response of a muscle to sustain work. The fatigue may be due to disturbances in the contractile mechanism of the muscle, including decreased energy stores, insufficient oxygen, and lactic acid accumulation.
Local muscle fatigue may also result from inhibitory influences from the central nervous system, pain, and discomfort. Total body fatigue occurs in response to prolonged resisted exercises and may result from decreased blood glucose concentration or depletion of muscle or liver glycogen. No biologic marker of overtraining exists. Adequate time in the training program must be included for recovery from vigorous exercise to avoid fatigue. Recovery is associated with a removal of lactic acid and with replenishment of energy and oxygen stores. Light exercise may facilitate recovery, and recovery after each exercise session is required to improve performance. This requirement has implications for rehabilitation, particularly in the later stages, when the intensity of exercise is increased and more time for recovery is required from session to session.
Resisted exercises may also cause muscle soreness. Immediate muscle soreness develops during or directly after strenuous exercise. It may be related to muscle ischemia or the buildup of metabolites. Muscle soreness of immediate onset generally subsides quickly with rest after exercise. By contrast, delayed-onset muscle soreness develops 24 to 48 hours after vigorous exercise. Numerous causes have been postulated, none satisfactory. Accumulation of lactic acid in the muscle was one of the postulated causes; however, lactic acid is cleared approximately 1 hour after exercise. The reflex pain-spasm theory as proposed by DeVries [ 12 ] held that ischemia produces pain that in turn produces a reflex muscle spasm. A positive feedback loop develops as spasm creates further pain and ischemia. The original
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evidence for this theory included increased electromyographic activity from muscles with delayed muscle soreness; however, this evidence has not been duplicated by others.
Currently, the most plausible explanation for delayed-onset muscle soreness is microscopic tearing of muscle or connective tissue during vigorous exercise.
Disruption of tissue results in inflammation and pain. This theory is supported by the observation that delayed-onset muscle soreness is more common after eccentric exercise. Micro-tearing of muscle and connective tissue may be more pronounced as the muscle lengthens against resistance. Prevention of delayed-onset muscle soreness includes an appropriate period of warm-up and cool-down before and after the resisted exercise. In addition, delayed-onset muscle soreness may be prevented by a gradual progression of the resisted exercise program and the avoidance of the eccentric component of exercise.
The athlete performing resisted exercises must be observed carefully for detection of substitute motions, that is, alternative motions or muscles complete the motion when the prime movers are weak or fatigued. Use of substitute motion allows muscle weakness to persist. Substitute motions can be avoided by using appropriate amounts of resistance and instructing the athletes to perform the exercise precisely.
Proprioception and Neuromuscular Control
Once adequate strength and endurance of the musculature have been established, it is necessary to incorporate activities to improve proprioception and neuromuscular control for improvement of dynamic stability. There has been interest in the role that these factors play in the rehabilitation and prevention of injuries. It has been hypothesized that proprioception is important for providing smooth, coordinated movement as well as protection and dynamic stabilization of joints. Neuromuscular training after injury requires the individual to learn how to recruit muscles with the proper force, timing, and sequence to prevent abnormal joint motion. To understand the role that proprioception and neuromuscular control play in the maintenance of joint integrity, a brief anatomic review is provided.
Anatomic Basis of Neuromuscular Control
Proprioception has been characterized as a specialized variation of touch, including the ability to detect both joint motion and joint position.
[ 40 ] It is important to distinguish this term from kinesthesia, which traditionally refers only to the ability to sense joint motion.
[ 38 ] Proprioception occurs by a complex integration of somatosensory input (both conscious and subconscious) from a variety of mechanoreceptors. It contributes to an athlete's neuromuscular control, which can be defined as the coordination and timing of muscle firing in response to an applied load.
There are basically three classes of peripheral mechanoreceptors that have been delineated in the literature, including muscle receptors, articular (joint) receptors, and cutaneous (skin) receptors.
[ 40 ] These mechanoreceptors, which respond to
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mechanical deformation, signal information about the tissues in which they lie to the central nervous system, modulating the overall state of the neuromuscular system.
Afferent signals synapse in the dorsal horn of the spinal cord and then directly, or through interneurons, synapse on alpha motoneuron pools, which relay control information back to the periphery. Afferent information is also processed and modulated at other control centers in the central nervous system (e.g., brain stem, cerebellum, cortex). All three types of mechanoreceptors have an interactive role in the maintenance of joint stability.
Mechanoreceptors have been identified in the ankle, [ 65 ] in the knee, [ 10 ][ 30 ][ 35 ][ 49 ][ 52 ] and in the shoulder.
[ 59 ][ 60 ] Joint receptors are commonly located in the connective tissue of the joint capsule and ligaments. Specifically, they have been identified in the joint capsules, ligaments, menisci, labrum, and fat pads. Four types of joint mechanoreceptors have been described.
[ 28 ][ 65 ]
Type I mechanoreceptors are Ruffinilike receptors that have a low mechanical threshold for activation yet a slow adaptation to the deformation. These characteristics make them uniquely qualified to detect static joint position, amplitude, and velocity of movement. Type II mechanoreceptors are pacinian corpuscle—like receptors that have a low threshold for excitation and adapt rapidly. They are responsible for signaling acceleration and deceleration of the joint. Type III mechanoreceptors are similar to Golgi tendon organs that lie in the musculotendinous unit. They have a high threshold for excitation and are nonadapting. They respond at the extremes of motion and may be responsible for mediating protective reflex arcs. Type IV mechanoreceptors are free nerve endings that convey pain.
Muscle receptors primarily consist of muscle spindles and Golgi tendon organs. The muscle spindle helps regulate the smooth, precise control of muscle activity. Muscle length and velocity of movement are detected by primary and secondary afferent fibers that are intimately entwined in specialized intrafusal muscle fibers (as opposed to the predominant extrafusal fiber type). Primary afferent (type I) fibers sense the degree and rate of stretch in the muscle, whereas secondary afferent (type
II) fibers detect primarily the degree of stretch. This information is relayed to the central nervous system, where it is processed, integrated, and modulated in the spinal cord, brain stem, cerebellum, cortex, and other control centers. Once the information is processed, the appropriate regulatory response is transmitted back to the muscle through efferent alpha and gamma motoneurons that stimulate extrafusal and intrafusal muscle fibers, respectively, helping to maintain precise control of movement. The muscle stretch reflex at the knee is a classic representation of this mechanism occurring at the spinal cord level.
The Golgi tendon organ, on the other hand, responds to increases and decreases in muscle tension by allowing the muscle to stretch and shorten, respectively.
Together, the muscle spindle and Golgi tendon organ assist with the precise regulation of movement. Some investigators have hypothesized that the muscle spindle system may be the most significant component of the neuromuscular system during normal activities of daily living.
[ 17 ][ 18 ][ 42 ][ 43 ]
This is because joint receptors contribute sensory information primarily at the end of the available joint motion,
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positions that do not typically occur during normal activities. The muscle spindle system is persistently active during ambulation, for example, to facilitate smooth limb progression during the gait cycle. Joint receptors are likely to play a much more significant role in athletic performance, however, in which the extremes of joint excursion are more likely to occur.
Function of the Neuromuscular Control Mechanism
Research has demonstrated that mechanoreceptors play an important role in joint stabilization through both feedback and feedforward control paradigms. The feedback mechanisms are mediated by numerous protective reflexes that continuously update muscle activity. For example, slight deformation in the knee ligaments has been demonstrated to evoke a marked increase in activity of muscle spindle afferents, which “set” the joint in its functional context.
[ 28 ] Kim and associates [ 31 ] demonstrated that stimulation of the knee collateral ligaments results in a contraction of muscles about the knee. Furthermore, Solomonow and colleagues [ 56 ] and Buchanan and coworkers [ 7 ] elicited a muscle response with stimulation of the anterior cruciate ligament (ACL) and with an applied varus and valgus load at the knee, respectively. Solomonow and colleagues [ 56 ] described an ACL-hamstring arc in anesthetized cats. High loading of the ACL resulted in increased electromyographic activity in the hamstrings with electrical silence in the quadriceps. The increase in hamstring electromyographic activity was not evident when light to moderate loads were applied to the ACL. It was proposed that this ACL-hamstring reflex arc serves to protect the ACL during high loading conditions. It is unknown whether this reflex arc can protect the joint from injury if high loads are applied rapidly, however.
Under rapid loading conditions, the ligament may be loaded and ruptured before sufficient muscle tension can be generated to protect the ligament. It is likely that similar reflex arcs exist in other joints.
Other proprioceptive reflexes originating from the joint capsule or musculotendinous unit probably exist. This was demonstrated by Solomonow and colleagues, [ 56 ] who reported increased hamstring electromyographic activity in a patient with an ACL-deficient knee during maximal slow-speed isokinetic testing of the quadriceps. The increased electromyographic activity occurred simultaneously with anterior subluxation of the tibia at approximately 40 degrees of knee flexion and was associated with a sharp decrease in quadriceps torque and electromyographic activity. Because the ACL was ruptured, reflex contraction of the hamstrings could not have been mediated by receptors originating in the ACL. It was proposed that this reflex contraction was mediated by receptors in the joint capsule or hamstring muscles. It is likely that similar reflex arcs exist in other areas of the body.
Although feedback mechanisms have traditionally been considered the primary mechanism of neuromuscular control, feedforward mechanisms also play an important role in the maintenance of joint stability. The feedforward mechanism of neuromuscular control is characterized by the use of proprioceptive information in preparation for anticipated loads or activities that will be encountered. This
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mechanism suggests that an internal construct for joint stability is developed that undergoes continuous updates on the basis of previous experience under known conditions. This preparatory information is then coupled with real-time proprioceptive input to generate preprogrammed motor commands to achieve a desired outcome.
[ 13 ][ 19 ][ 36 ]
Several clinical studies have evaluated proprioception in terms of the threshold to detection of passive motion and reproduction of joint position. Barrack and coworkers [ 3 ] demonstrated deficits in the threshold to detection of passive motion in subjects with a unilateral ACL-deficient knee. Lephart and associates [ 39 ] studied the threshold to detection of passive motion in patients who had undergone ACL reconstruction. Testing was performed at 15 degrees and 45 degrees of flexion.
Three trials were performed moving into flexion and extension. The results indicated that threshold to detection of passive motion was less sensitive in the reconstructed knee than in the noninvolved knee. In addition, threshold to detection of passive motion was more sensitive in the reconstructed and normal knee at 15 degrees of flexion compared with 45 degrees of flexion. The enhanced sensitivity to passive motion near full extension may be due to increased stress on the ligament, making it more sensitive to detect motion. Kinesthetic deficits in the shoulder in patients after anterior glenohumeral dislocation were demonstrated by Smith and Brunolli.
[ 54 ] They found deficits in angular reproduction, threshold to detection of motion, and endrange reproduction of joint angle in the shoulder that had been dislocated.
Injury to a joint may result in abnormal sensory feedback and altered neuromuscular control. With a traumatic injury to the knee, for example, it is hypothesized the mechanoreceptors are anatomically disrupted. This causes the joint receptors to aberrantly fire, which leads to impaired neuromuscular control.
[ 40 ] Others suggest that injuries alter joint motion characteristics; thus, the normal coordination of joint receptor firing is interrupted.
[ 26 ]
Evidence for Neuromuscular Training
Fortunately, there is significant redundancy in the relay of afferent information to the central nervous system. Therefore, after acute injury, individuals should theoretically be able to train their neuromuscular control system, with the hope of restoring the system to a more normal state. The terms proprioceptive training and neuromusculartraining are often used interchangeably. We use the term neuromuscular training . Neuromuscular training contributes to the improvement of both proprioception and neuromuscular control.
There is some evidence that neuromuscular training can improve neuromuscular control of abnormal joint motion.
[ 4 ][ 27 ][ 64 ] Ihara and Nakayama [ 27 ] studied the effects of a dynamic joint control training program, in which subjects were instructed to resist randomly applied perturbations of support surfaces with their lower extremities, on hamstring muscle reaction times. Four subjects with chronic knee instability received 3 months of training at a frequency of four times per week and were compared with a control group consisting of five subjects without knee injury who
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did not receive training. Hamstring muscle reaction times were measured indirectly by recording knee flexion movement reaction times and the time to generate peak knee flexion torque in response to passive knee extension motion, provided by a dynamometer. Subjects in the training group exhibited reduced knee flexion movement reaction times and reduced time to generate peak knee flexion torque after training. There were no significant changes in these variables for the control group. In addition, three of the four subjects in the training group were able to return to competitive sports activities after training. The fourth subject was able to return to recreational sports activity.
Beard and colleagues [ 4 ] conducted a double-blind randomized clinical trial to compare the efficacy of two rehabilitative programs for individuals with ACL deficiency. One group received a neuromuscular training program designed to enhance proprioception and to improve hamstring contraction reflexes. This program consisted of perturbation training techniques, cyclical repetitive lower extremity motions emphasizing speed of movement, mini-trampoline activities, and skipping activities. The second group received a standard program of resisted lower extremity strengthening exercises, step-up exercises, and stationary cycling. An indirect measurement of proprioception represented by reflex hamstring contraction latency was recorded before and after the 12-week course of rehabilitation. The
Lysholm Knee Function Scale was used as a self-report measure of knee function.
After the training, there was improvement in the reflex hamstring contraction latency and self-reported knee functional score in both groups; however, the improvement in the group that received the neuromuscular training was significantly more than the improvement in the group that received the standard training program.
Changes in the reflex hamstring contraction latency were also correlated with the self-reported knee function scores.
Wojtys and colleagues [ 64 ] compared changes in lower extremity muscle function in
32 healthy volunteer subjects who were assigned to an isokinetic training group, an isotonic training group, an agility training group, or a control group. The agility training program consisted of sliding board activities, box jumping, carioca drills (a lateral running drill that incorporates combined crossover steps and side-steps), figure-of-eight running, and backward running. Muscle reaction times of the quadriceps, hamstrings, and gastrocnemius muscles in response to an externally applied anterior tibial translation load as well as the time to generate peak torque for these muscle groups were used as measures of neuromuscular function. The agilitytrained group demonstrated significantly improved reaction times of the quadriceps, hamstrings, and gastrocnemius in response to anterior tibial translation. Perhaps just as important, they found that the reaction time of the medial hamstring and the medial quadriceps muscles in the isokinetic group significantly slowed by 39.1 and
32.4 msec, respectively, after 6 weeks of training. They concluded that isotonic and isokinetic strength training of the lower extremities was not adequate to improve muscle reaction time to anterior tibial translation, but agility exercises did improve this parameter. More research needs to be conducted to substantiate these findings.
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There is evidence to suggest that neuromuscular training is a useful adjunct in rehabilitative programs to return athletes to high levels of physical activity.
Fitzgerald and colleagues [ 14 ] conducted a randomized controlled trial to compare a standard agility training program with an agility training program that was supplemented with a perturbation training program in patients with an ACLdeficient knee that was treated nonoperatively. These individuals were screened on the basis of criteria established by the investigator that could more accurately determine which patients might be candidates for a nonoperative course of treatment. Most of these patients were young, active individuals who tore the ACL during a competitive sport season and wanted to return to play as soon as possible, postponing surgery, if necessary, until after the season was complete. One group of patients was randomized to a standard nonoperative ACL rehabilitation program consisting of open and closed kinetic chain exercises and agility training. The other group was randomized to receive the standard training plus a perturbation training program designed to improve neuromuscular control. Both groups received 12 weeks of rehabilitation. Successful outcome was defined as being able to return to a high level of activity without any episodes of giving way. Subjects in both groups were able to return to premorbid levels of sports activity after training. During a 6month follow-up period, however, a significantly greater number of subjects who received the perturbation training (11 of 12) were able to complete their athletic seasons without experiencing episodes of giving way compared with subjects receiving only the standard training program (7 of 14). In addition, subjects receiving perturbation training maintained higher scores on self-reported and physical performance measures of knee function than did the standard exercise group at 6 months of follow-up. More patients were successful in the group that received the perturbation training than in the group that received the standard training program alone. Fitzgerald and colleagues [ 14 ] hypothesized that the continued ability of the perturbation-trained group to maintain high levels of physical function without experiencing episodes of knee instability may be attributed to the development of adequate lower extremity neuromuscular control mechanisms to maintain dynamic knee stability.
Techniques to Improve Proprioception and Neuromuscular Control
Athletes who have sustained an injury to the stabilizing structures of a joint may need to rely on compensatory neuromuscular mechanisms to maintain dynamic stability. Therefore, rehabilitation should, in part, promote development of these compensatory muscle activity patterns. Although studies seem to be consistent with regard to the muscles involved in the compensatory patterns used after injury to the knee (i.e., quadriceps, hamstrings, and gastrocnemius muscles), there seem to be differences in the way individuals alter the activity of these muscles to maintain joint stability.
[ 53 ] Thus, treatment techniques should be designed to develop individualized compensatory neuromuscular responses to potentially destabilizing loads that may be encountered during functional activities.
Several factors need to be considered in planning interventions that are designed to promote compensatory lower extremity neuromuscular responses. Because
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individuals will encounter a variety of potentially destabilizing forces on the knee during functional activities, it is logical that they be provided with experiences in dealing with these forces during rehabilitation. Treatment techniques should therefore be designed to allow the application of potentially destabilizing loads to the lower extremity in a controlled manner. Another factor to be considered is that destabilizing loads encountered during functional activities usually occur rapidly and without warning, making voluntary neuromuscular responses inadequate for protecting the knee. Treatment techniques should therefore also be designed to promote quick, automatic, protective neuromuscular responses to potentially destabilizing loads by, for example, the application of potentially destabilizing loads to the lower extremity in a quick, random manner during treatment. Finally, it is important to ensure that treatment techniques designed to enhance the development of protective neuromuscular responses to destabilizing loads provide the carryover of learned responses to functional activities. Techniques may be more successful if they are practiced in the context of functional and sport-specific tasks.
Several treatment options are available that have the potential for promoting protective neuromuscular responses in the lower extremity to maintain dynamic stability during physical activity. Balance and agility training techniques, such as shuttle runs, cut and spin drills, cariocas, lateral sliding, and balance boards, can provide the patient with experience in dealing with potentially destabilizing loads on the knee during rehabilitation. Wojtys and colleagues [ 64 ] reported that subjects who underwent 6 weeks of agility training exhibited improved reaction times in the quadriceps, hamstrings, and gastrocnemius muscle in response to unexpected anterior tibial translation. It seems that agility training techniques may enhance protective neuromuscular responses to potentially destabilizing loads on the knee.
Another treatment option for improving neuromuscular control of the lower extremity involves perturbational support surfaces, such as roller boards and tilt boards ( Fig. 8A-8 ). In these techniques, the patient stands on the support surface, on the involved limb, and potentially destabilizing loads are applied to the lower extremity by the therapist through multidirectional perturbations of the roller board or tilt board. The therapist is able to apply the load in a random manner, without warning to the patient, in an attempt to encourage quick, automatic responses to the destabilizing loads. These techniques can also be modified so that patients can experience the perturbations during performance of activity-related tasks, which may also enhance carryover of learned protective responses to functional performance situations. Ihara and Nakayama [ 27 ] and Beard and coworkers [ 4 ] have shown that hamstring reaction time and functional ability were improved after training with these techniques. Fitzgerald and colleagues [ 14 ] reported that ACLdeficient subjects who received perturbation training demonstrated a greater likelihood of success in returning to preinjury-level sports activities than did those subjects who did not receive this type of training as part of the rehabilitation program. These activities generally progress from slow to fast speed, from low to high force, and from controlled to uncontrolled activities. The performance of these activities initially requires the individual's conscious effort. With practice and repetition, however, control of abnormal joint motion should become automatic and
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occur subconsciously. Activities in a neuromuscular training program should also be randomly ordered during training sessions to improve motor learning, thus enhancing long-term carryover.
[ 51 ]
Figure 8A-8 Roller boards (A) and tilt boards (B) can be used to provide a destabilizing force to which the individual must respond.
Neuromuscular control is also important for dynamic joint stability in the upper extremity of the athlete. Reactive neuromuscular training that incorporates principles of proprioceptive neuromuscular facilitation may be used to improve neuromuscular control in the overhead-throwing athlete, for example, who is at risk for shoulder instability. Proprioceptive neuromuscular facilitation patterns include techniques such as rhythmic stabilization, which is the application of skilled input from the clinician to facilitate a desired movement pattern. At the shoulder, this may initially consist of slow, regular perturbations with the joint in the resting position, such as in the plane of the scapula with the shoulder in 30 to 45 degrees of external rotation.
These techniques can be progressed by employing fast, random perturbations with the joint in the provocative position. At the shoulder of the throwing athlete, this might be conducted with the shoulder in 90 degrees of abduction at the end range of external rotation. The athlete's sport should determine specific activities for the upper extremity. Return to throwing for throwing athletes after injury has been described by Pappas and coworkers, [ 50 ] Blackburn and colleagues, [ 5 ] and Wilk and associates.
[ 61 ] Return to throwing should progress from a short-toss program to a long-toss program. Velocity should be increased gradually as tolerated. The functional progression for return to activity must provide the athlete with adequate time to ensure a safe return to sport with minimal risk for reinjury. Further research is required to determine the effectiveness of neuromuscular training for dynamic protection of the injured area.
Summary
We have presented basic guidelines and considerations for rehabilitation of the injured athlete. These principles can be applied to rehabilitation of the common musculo skeletal injuries that occur in athletics. The use of various physical agents and therapeutic exercise in the rehabilitation of the injured athlete has been discussed. Development of a rehabilitation program is a problem-solving process.
This requires thorough evaluation of the athlete for development of goals and a plan of care that addresses the impairments, functional limitations, and disability experienced by the athlete. Rehabilitation of the injured athlete at any point in time may focus on any one area or a combination of these areas. The ultimate goal of rehabilitation of injured athletes is to minimize or to eliminate the disability associated with the injury and to return them to their previous level of sports activity.
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