Journal of the American Academy of Orthopaedic Surgeons 412 Orthopaedic surgeons are intimately involved in the rehabilitation pro- cess, in that they establish the ana- tomic diagnosis of the injury, deter- mine the timing of entrance into and exit from the rehabilitation program, and select the modalities and exer- cises that are used. Even though they usually do not physically demon- strate or personally supervise the exercises, they must understand the basic concepts underlying the vari- ous types of exercises and the timing of exercise progressions, in order to effectively communicate with the physical therapists and coordinate the best program for the individual patient’s needs. Most current rehabilitation pro- grams emphasize functional resto- ration of the injured part, which requires not only repair and healing of injured tissues but also restoration of correct positioning and move- ment of joints as well as activation of muscles in the proper sequence so as to achieve normal function. Closed- chain protocols have been advocated in rehabilitation because they have characteristics that encourage more complete functional restoration. These exercises have been used extensively for anterior cruciate ligament (ACL) injuries as a major component of “accelerated” knee rehabilitation, as well as for rehabilitation of patients with patellofemoral and shoulder injuries. Despite increasing usage, there is still controversy about what closed- chain exercises are and how and when to use them. Neither is there a common understanding of what defines a closed-chain exercise, how closed-chain exercises promote functional restoration, and what the best closed-chain exercises are for different stages of the rehabilitation process. To be able to appropriately prescribe and utilize these tech- niques, the physician must first un- derstand the underlying physiology and biomechanics of closed-chain rehabilitation. Definitions The human body produces motions and performs complex skills through sequential activation of muscles and movement of body segments, or links. 1,2 This link activation, which may be activity- or sport-specific, is termed a “kinetic chain.” There are two broad-based classes of kinetic chains—”open,” in which the termi- nal link of the chain is not loaded and is freely movable (mobile end, no load [MNL]), and “closed,” in which the terminal link is con- strained or immovable due to a fixed position or large load (fixed end, external load [FEL]). The mo- tion of the foot of a kicking leg is an example of an MNL kinetic chain. A pure FEL kinetic chain is exempli- fied by a fixed foot during a squat exercise. Force generation, force distribution, joint motion, muscle ac- tivation, and resultant tissue stress can be quite different in the two classes. Dr. Kibler is Medical Director, Lexington Sports Medicine Center, Lexington, Ky. Mr. Livingston is Clinical Specialist, Lexington Sports Medicine Center. Reprint requests: Dr. Kibler, Lexington Sports Medicine Center, 1221 South Broadway, Lexington, KY 40504. Copyright 2001 by the American Academy of Orthopaedic Surgeons. Abstract Closed-chain exercise protocols are used extensively in rehabilitation of knee injuries and are increasingly used in rehabilitation of shoulder injuries. They are felt to be preferable to other exercise programs in that they simulate normal physiologic and biomechanical functions, create little shear stress across injured or healing joints, and reproduce proprioceptive stimuli. Because of these advantages, they may be used early in rehabilitation and have been inte- gral parts of “accelerated” rehabilitation programs. The authors review the important components of a closed-chain rehabilitation program and provide examples of specific exercises that are used for rehabilitation of knee and shoul- der injuries. J Am Acad Orthop Surg 2001;9:412-421 Closed-Chain Rehabilitation for Upper and Lower Extremities W. Ben Kibler, MD, and Beven Livingston, MS, PT W. Ben Kibler, MD, and Beven Livingston, MS, PT Vol 9, No 6, November/December 2001 413 Steindler 2 was the first to de- scribe the differences in muscle activation and joint motion that occur when the distal end of the arm or leg in a kinetic chain meets considerable resistance compared with when it is freely movable. His definition of a closed-chain condi- tion required that the foot or hand meet enough resistance to prohibit or restrain its free motion, and that the resultant extremity muscle acti- vation was sequential from distal to proximal in the extremity. Physical therapy protocols have been developed to take advantage of the force-generation and loading characteristics of closed-chain exer- cises. There has been wide variety in their application, but in general, closed-chain protocols include a progression of exercises that are based on application of a load to the distal end of an extremity that does not move freely due to either posi- tioning (e.g., on a wall or on the ground [Fig. 1]) or the load charac- teristics (e.g., axially applied heavy load). Subsequent joint motion takes place in multiple planes while the limb is supporting weight. These conditions differentiate these exer- cises from “open chain” exercises, such as knee extensions, trunk ex- tensions against gravity, and isolated rotator cuff exercises with tubing or weights. Dillman et al 3 described condi- tions that define closed-chain exer- cises. They realized that the effect of the exercise on joint positions and muscle activations is the critical point in defining a closed-chain exercise. They felt that closed-chain exercises have to include relatively small joint movements, low joint accelerations, large resistance forces, joint compression, decreased joint shear, stimulation of joint pro- prioception, and enhanced dynamic stabilization through muscle coac- tivation. They also recognized that the amount of load at the terminal end of the extremity is as important as the motion of the extremity. Even if the distal end of the extrem- ity is somewhat mobile, a large enough load can still create physio- logic conditions that replicate closed-chain characteristics. This enlarged the concept of a closed- chain exercise from being only an FEL activity to include mobile end–external load (MEL) activities as well, making it more applicable to the upper extremity. For exam- ple, a military press (an MEL exer- cise) can have closed-chain effects similar to those of a pushup (an FEL exercise). This concept has been validated by Blackard et al, 4 who found that there was no differ- ence in muscle activation between equivalently loaded upper-extremity exercises with either fixed or mobile ends. They concluded that external loading characteristics were more important than arm motion in de- scribing and simulating human activity. Lephart and Henry 5 modified the MEL condition to include two differ- ent external load conditions—axial load (e.g., military press) and rotary load (e.g., arm rotations with dumb- bells). This helped to define types of exercises but did not change the con- cept that closed-chain joint loading and muscle activation characteristics can be obtained with a movable dis- tal end. However, it enlarged the scope of the types of exercises that can be employed in a closed-chain rehabilitation program. Livingston 6 developed an opera- tional definition to guide implemen- tation of closed-chain exercises and to determine whether exercises have the characteristics described by Dillman et al. 3 As Livingston de- fines closed-chain rehabilitation exercises, the activities require a sequential combination of joint motions; the distal end of the kinetic chain meets considerable resistance (MEL or FEL conditions); and move- ment of the individual joints of the kinetic chain sequence and transla- tion of their instant centers of rota- tion occur in a predictable manner determined by the distribution of forces throughout the chain. This definition implies control by the physician or therapist of (1) extrem- ity position, (2) distal segment mo- tion and position, (3) application of forces and loads, and (4) movement of the entire extremity. Physiology and Biomechanics of Closed- Chain Rehabilitation Most lower-extremity occupational and athletic activities involve kinetic chain activity. The large majority of these activities start with the feet on the ground, which gives a base of stability, allows generation of a ground-reaction force, and initiates a sequence of segment activity to provide optimal position and mo- tion for the distal aspect of the ter- minal segment in the chain. 1,6 Force production is governed by the “summation of speed” principle, in Figure 1 Positioning for early-stage lower- extremity exercises. With one-leg support, notice hip-trunk extension posture. The arms may be used to help balance the trunk initially. Closed-Chain Rehabilitation Journal of the American Academy of Orthopaedic Surgeons 414 which the total energy or force in a kinetic chain is summated from the contributions of individual seg- ments. 1 Kinetic-chain segment motions and positions are created by mus- cle activation patterns. Length- dependent patterns operate locally around a joint, using co-contraction force couples to control joint per- turbations. Force-dependent pat- terns harmonize segment motions by operating around two or more joints and using agonist-antagonist force couples to generate or trans- fer force. 7 These two types of mus- cle activations result in coordinated segment motions that allow kinetic- chain activity to produce the de- sired forces needed for occupa- tional or athletic purposes. The resultant synergistic patterns create postural stability throughout the entire extremity while allowing voluntary muscle activity at the distal segment. 1,2,8 These synergis- tic patterns include increased acti- vation of biarticular muscles (i.e., hamstrings, quadriceps) by mon- articular muscles (i.e., gluteus medius, soleus) 9 and coordination of arm and scapular movements to produce glenohumeral stability through the range of motion, al- lowing maximum arm motion. 10 They are highly dependent on joint- and angle-specific proprio- ceptive feedback. 11 In the leg, the hamstrings act as part of a length-dependent force cou- ple to control anterior tibial transla- tion. 8 They also work as part of a force-dependent pattern to coordi- nate hip and knee motion, 1 stabilize the hip, and transfer loads up and down the leg. 9 In the shoulder, the rotator cuff acts as part of a length- dependent force couple to increase glenohumeral concavity and com- pression, 10 but also works as part of a force-dependent pattern to link trunk extension, scapular rotation, and arm internal rotation. 8,10 Closed-chain exercise protocols have characteristics that simulate these biomechanical and physiolog- ic requirements. Mechanically, they initiate joint movements from the ground or a base of support, em- phasize sequential control of seg- ment position or motion, place the segments in functionally correct positions, and control the transfer of generated loads. Physiologically, they utilize both length-dependent and activity-specific force-dependent activation patterns, emphasize position-specific proprioceptive feedback to initiate and control acti- vation, and can use the more versa- tile MEL configuration to achieve FEL muscle activation (Fig. 2). Closed-chain exercises have also been shown to be protective for healing and repaired tissues. They produce minimal translation, shear, and distraction forces due to the compressive nature of the applied load and the greater control of the resultant motions. 5,6,9,12,13 This con- fers a margin of safety that allows shorter periods of complete immo- bilization, earlier initiation of reha- bilitation, and resultant “accelerated” protocols. 12-14 Because closed-chain exercises emphasize and produce patterns of A B Figure 2 Intermediate-stage lower-extremity exercises. A, Use of a sliding board for an MEL exercise to balance the body over a moving leg. The patient slides side to side and pushes off each edge. B, Use of a Fitter involves the same principles as use of a sliding board, but there is a more unstable base due to its rounded edges, therefore presenting more of a proprioceptive challenge. W. Ben Kibler, MD, and Beven Livingston, MS, PT Vol 9, No 6, November/December 2001 415 motions and muscle activations, they may not maximally rehabilitate all of the individual muscles or achieve normal motion of all of the joints in the relevant kinetic chain. This is due to both muscle-activation substitutions and alterations that allow approximations of the normal patterns and to individual character- istics of muscle activation. Some muscles, such as the deltoid, upper trapezius, gluteus medius, and gas- trocnemius, are more resistant to inhibition and alteration in injury or fatigue situations; others, such as the serratus anterior, lower trapezius, supraspinatus, and vastus medialis obliquus (VMO), are easily fatigued and inhibited, and tend to “drop out” from the activation patterns. Clinical examples of these alter- ations include hip abductors and extensors substituting for knee ex- tensors in gait after ACL recon- struction, 15 the upper trapezius substituting for the lower trapezius in acromial elevation, 10,16 and the deltoid substituting for the supra- spinatus in arm elevation. In these situations, the desired kinetic-chain function (walking or arm elevation) may be accomplished, but activa- tion of important muscles is not. Rehabilitation strategies can be developed to maximize activation of the inhibited muscles while still utilizing a closed-chain framework. This involves placing the extremity in a closed-chain position, empha- sizing the normal activation pat- tern, and progressively “unmask- ing” the target muscle by eliminat- ing the substituting muscle. This process may be called “facilitation of muscle activation.” Role of Closed-Chain Exercises in Rehabilitation Closed-chain rehabilitation protocols have beneficial characteristics that are associated with functional physi- ology and biomechanics. They may be utilized early in the rehabilitation sequence to protect the injured area and to prepare the entire kinetic chain for function. They are the foun- dation for some rehabilitation pro- grams. However, they must be mon- itored to ensure that all muscles are being appropriately activated. These protocols can be used in both MEL and FEL configurations for knee and shoulder rehabilitation (Figs. 3-7). Different levels of exercises may be used in the early (acute or healing) phase, the intermediate (recovery) phase, and the late (functional) phase of rehabilitation, 6,7 depending on the degree of tissue healing, the possible positions of the extremity, and the amount of load and the range of motion that are allowed. Knee and Leg Rehabilitation Closed-chain rehabilitation tech- niques have been utilized to accel- erate and improve functional re- storation after ACL injury and reconstruction. 12-14 These tech- niques create weight-bearing forces across the joint that increase local agonist-antagonist muscle coactiva- tion, decrease joint shear, minimize joint displacement and ACL strain, and reproduce proprioceptive stim- uli. In addition, they activate the kinetic chains of weight bearing, running, and jumping. This repro- duces the normal biomechanics of the entire leg, allowing hip-muscle activation to increase quadriceps and hamstring force output by transferring muscle work to these biarticular muscles 9 and by creating a hip moment that is a major con- tributor to the knee moment. 15 Hip- muscle activation and work output create load-absorbing capacity that can compensate for a low load- absorbing capacity in the knee so that the entire leg functions at an acceptable level early in rehabilita- tion. 15 Closed-chain exercises also reproduce the physiologic length- dependent patterns for hip- and knee-joint stability, as well as force- dependent patterns of coordination of hip, knee, and ankle joint motion. The effect that closed-chain exercises have on the entire kinetic chain is more functionally important than the effect on the knee joint alone. Closed-chain techniques are also useful in rehabilitation of the patient with patellofemoral pain, largely due to the same factors of joint position control, larger im- provements in the strength of the entire kinetic chain, and alteration of the magnitude and position of applied forces. Increased total leg stiffness, with resultant knee joint control, is achieved by activating the hip muscles concurrently with the knee muscles. 9,17 Closed-chain exercises have been shown to pro- duce greater improvements in quadriceps strength and leg perfor- mance than open-chain exercises. 18 Closed-chain exercises produce lower patellofemoral joint stresses in the functionally and sympto- matically important arc of motion from extension to 45 degrees of flex- ion than do open-chain exercises. 19 Lower-extremity closed-chain exercises are largely FEL, with the foot on the ground in the early reha- bilitation stages. Most protocols emphasize early, if not immediate, weight bearing on the affected ex- tremity. The leg may be supported, but controlled range of motion and compression loading of the joint are encouraged. Initially, the patient is in a two-legged support stance, but may be moved into a one-legged support stance as healing progresses. Rhythmic motion patterns of flexion/ extension and lateral movement are used. Early emphasis is placed on achievement and maintenance of a position of 0 degrees of hip exten- sion and neutral pelvic tilt to allow maximum hip-muscle activation. Most leg exercises should proceed from this “ideal” position. Closed chain–based protocols advocated for rehabilitation of ACL and patellofemoral injuries 12-14,17 Closed-Chain Rehabilitation Journal of the American Academy of Orthopaedic Surgeons 416 are similar in their early stages, but differ in the intermediate and re- covery stages (from 3 weeks to 3 months). Common characteristics include progressive compression loading of the joint, controlled increase in range of motion, main- tenance of functional posture of the knee and leg, and emphasis on early return to functional activities, such as running, weight lifting, and mild cutting. Some of the more commonly advocated closed-chain exercises in the intermediate and recovery stages include the two-legged squat with increasing resistance, the one- legged squat with support, and the step up–step down maneuver—all of which are FEL exercises. Exam- ples of MEL exercises include slid- A B D E C Figure 3 Exercises to increase quadriceps activation. A and B, Hip extension and foot-flat in step down–pull up exercise acti- vates the quadriceps eccentrically and con- centrically. Hip control is maintained by activation of hip extensors and abductors. Notice VMO activation in left leg. C, Slant board use in a step down–pull up exercise. Quadriceps activation is greater. D and E, Hip extension and hip and pelvis rotation. The trunk and hip are rotated around the planted leg. Notice VMO activation. W. Ben Kibler, MD, and Beven Livingston, MS, PT Vol 9, No 6, November/December 2001 417 ing on a smooth surface (Fig. 2, A) or using a Fitter device (Fitter International, Calgary, Alberta, Canada) with a rounded-edge sup- port surface (Fig. 2, B) and trampo- line bounding. The range of possi- ble exercises is large, and creativity may be used to match the exercises to the sport or activity demand. In the late stage (after 3 months), emphasis is on functional progres- sions and a mixture of closed- and open-chain exercises. The closed- chain exercises for joint coordina- tion, leg control, and resistance to perturbation should be regarded as a base for the open-chain exercises of jumping rope, cutting, kicking, leg extensions, and leg curls. Facilitation patterns to maximize quadriceps activation and increase knee load-bearing capacity are also employed in the recovery and func- tional stages of rehabilitation. They initially involve active hip extension and quadriceps activation with the foot flat on the floor or stepping off a flat step (Fig. 3, A and B). This FEL pattern reactivates the normal sequencing pattern for the entire leg, but probably does not maximally isolate or activate the quadriceps. The MEL equivalent, using a tram- poline, wobble board, or Fitter, adds an element of increased propriocep- tive feedback. More effective quad- riceps activation in a closed-chain exercise is accomplished by placing the foot on a slant board. Ankle plantar-flexion and slight hip flex- ion decrease hip and ankle activa- tion, but slight knee flexion places more emphasis on quadriceps acti- vation as the patient executes a step up–step down maneuver (Fig. 3, C). Further quadriceps facilitation is accomplished by one-legged stance, hip extension, slight knee flexion, and hip and trunk rotation around the planted leg (Fig. 3, D and E). This FEL exercise promotes maxi- mal electromyographic activity in the VMO. The MEL equivalent uti- lizes a trampoline or wobble board. In summary, closed-chain exer- cises for knee rehabilitation allow early weight bearing, protect the injured or healing area, and prepare the entire extremity for vigorous functional open- or closed-chain athletic activities. They should form the basis for most knee rehabilita- tion protocols, including those for ACL and patellofemoral injuries. The exact sequence and composi- tion of the protocols may be vari- able, but limited outcomes assess- ments indicate a faster return to functional status with protocols in which these types of exercises are emphasized. 12,13 Shoulder and Scapular Rehabilitation On superficial analysis, it would appear that closed-chain rehabilita- tion would have little application for the shoulder and arm. The hand is A B C Figure 4 Early-stage exercises for shoulder and scapular rehabilitation. A, Trunk extension and scapular retraction. The arm may be ele- vated or at the side, depending on healing. Diagonal hip extension and scapular retraction can be done with either a two-legged stance (B) or a one-legged stance. One-legged stance improves hip and pelvis control. Muscle activation goes from the hip through trunk exten- sion to scapular retraction in either stance. C , The modified pushup is an early-stage exercise for lower trapezius–serratus anterior weak- ness. Pushups may also be done with the hands on a table. Closed-Chain Rehabilitation Journal of the American Academy of Orthopaedic Surgeons 418 obviously moving in an open-chain fashion in throwing and serving, and the arm assumes a weight- bearing position only in gymnastics and blocking in football. However, shoulder position, motion, and force transfer fit the physiologic and bio- mechanical requirements of closed- chain activities. In throwing and serving, the scapula and shoulder display intersegmental coordination, with coupled movements that are predictable on the basis of arm posi- tion. 8,10 The shoulder acts as a stable funnel, transferring and regulating forces in the kinetic chain from the legs to the hand. 1,20 The shoulder muscles are activated in mainly co- contraction length-dependent pat- terns to stabilize the joint. 9,10,20,21 Proprioception plays a major role in controlling and activating muscle patterns. 11 In swimming, weight lift- ing, and playing on the offensive or defensive line in football, the hand meets considerable resistance but still moves, creating MEL conditions at the distal end of the extremity. Closed-chain exercises should, therefore, be utilized in shoulder and scapula rehabilitation for func- tional return to most athletic activi- ties from all types of shoulder in- juries. Rehabilitation protocols for tendinitis, postoperative instability, and postoperative labral injuries are basically the same in the acute phase and in the early functional phase. 5,6 Postoperative rotator cuff protocols should vary with the in- tegrity of the repair, but can also benefit from the proximal activation and low shear characteristics. Just as in knee and leg rehabilitation, closed-chain exercises may be used in the early stages of rehabilitation, and emphasis should be placed on involving all of the joints of the kinetic chain. Early-stage exercises involve not only the scapula but also the hip and trunk. The large extrinsic mus- cles of the shoulder (the latissimus dorsi and pectoralis major) and the muscles that position the scapula (the upper and lower trapezius and serratus anterior) are all attached to the trunk. They provide key stabili- ty and force generation to decrease shoulder load and facilitate rotator cuff activation. Early in rehabilita- tion, when the shoulder muscles are weakest, facilitation needs from proximal muscle activation are at their greatest. Muscle activation patterns to rehabilitate these mus- cles start with stabilization of the hip and trunk, and involve diagonal as well as ipsilateral exercises. Diagonal activations (from left hip to right arm and from right hip to left arm) are important to recreate the rotational activation and control patterns that are used in athletic activities such as throwing and swimming and in daily activities such as reaching and starting a lawn mower. Commonly employed exer- cises to rehabilitate these patterns include trunk extension–scapular retraction (Fig. 4, A) and diagonal hip extension–scapular retraction (Fig. 4, B). These exercises may be done both preoperatively and in the immediately postoperative period. They involve minimal forces at the shoulder and may be done with the arm in a sling or other protective device. Such exercises create a stable posture of the proximal segments that allows accelerated rehabilita- tion of the healing distal tissues. Closed-chain exercises are the most effective method for rehabili- tation of the patient with scapular dyskinesis (alterations in scapular A B C D Figure 5 Intermediate-stage scapular “clock” exercises (arrows indicate direction of scapular motion). A and B, Elevation and depression (12- and 6-o’clock positions, respec- tively). C and D, Retraction and protraction (9- and 3-o’clock positions). W. Ben Kibler, MD, and Beven Livingston, MS, PT Vol 9, No 6, November/December 2001 419 position and motion that are fre- quently associated with shoulder injury and lower trapezius and serratus anterior muscle weak- ness). 5,6,21,22 These alterations are clinically manifested by promi- nence of the inferior medial, entire medial, or superior medial border of the scapula, depending on asso- ciated muscle weakness or inflexi- bility. Weakness of the lower trapezius and serratus anterior is very com- mon, and these muscles are fre- quently difficult to reactivate. Early- stage exercises include modified pushups (Fig. 4, C) and scapular “pinch” retractions—exercises in which the scapulae are retracted to the midline. These initiate scapular control, but do not create forces that protract the scapula or place shear stress on the shoulder joint. Facilita- tion of lower trapezius and serratus anterior activation can be achieved by combined hip-trunk extension and shoulder extension (the “low row” exercise). This exercise may be started in an FEL pattern, with the hand on a wall or table, and then changed to an MEL pattern with the hand on rubber tubing, a ball, or a movable device. Decreasing hip sta- bility by standing on a wobble board or trampoline decreases hip exten- sion and facilitates maximal lower trapezius activation. Intermediate-stage closed-chain exercises include scapular “clock” exercises (Fig. 5), in which the scapula is rotated in elevation and depression (12- and 6-o’clock posi- tions) and retraction and protraction (9- and 3-o’clock positions). Elec- tromyographic studies have demon- strated that these exercises activate scapular stabilizers at moderate lev- els, but do not create shoulder-joint shear by deltoid activation. 6 These can also be done in FEL fashion, with the hand on a wall, or in MEL fashion, with the hand on a ball. Other MEL exercises include “wall washes” (Fig. 6), scapular retraction and shoulder extension, military or bench presses, pushups “with a plus” (performed by arching the back and pushing out farther at the end of the pushup), 23 and dynamic hug exercises. 24 Functional-stage closed-chain scapular exercises include higher- speed scapular protraction and retraction with weights or tubing and medicine-ball drills. These MEL exercises involve hip exten- sion and trunk rotation and provide plyometric-type stretch-shortening cycles to improve power develop- ment. They can be coordinated with more open-chain exercises for rapid hand velocity when appropriate. Rotator cuff rehabilitation with use of closed-chain techniques close- ly simulates normal rotator cuff function. The rotator cuff functions as a compressor cuff when the arm is in the common athletic position of 80 to 105 degrees of elevation, and is maximally activated off a stabilized scapula. 10,25 The positions advo- cated for maximal isolation of the individual rotator cuff muscles for evaluation and strengthening are not commonly seen in normal serv- ing or throwing and do not allow integration of rotator cuff function with the rest of the kinetic chain. Closed-chain exercises enhance joint compression, activate scapula- and shoulder-coupled motions, control joint position, and stimulate propri- oception. 3-5,10,11,24,25 Because these exercises create low levels of mus- cle activation, they are safer in the early stages of rehabilitation. 6 Early-stage exercises include table pushups and humeral head depressions (Fig. 7, A). When the arm can safely achieve 90 degrees of abduction, intermediate-stage activ- ities include rotator-cuff clock exer- cises, isometric humeral head de- pression with trunk extension and scapular retraction, and pushups, either modified or normal. These create joint compression, work the shoulder muscles in co-contraction at physiologic positions, and reacti- vate normal proprioceptive pat- terns. 25,26 Facilitation of rotator cuff activation is achieved by trunk ex- tension and scapular retraction. This allows optimal positioning of Figure 6 “Wall washes” for scapular rehabilitation. The hand slides on a smooth- surfaced wall. Trunk extension and rotation and scapular motion are emphasized. Closed-Chain Rehabilitation Journal of the American Academy of Orthopaedic Surgeons 420 the muscles to generate force while minimizing length and tension mis- matches. 10,25 Late-stage closed- chain exercises include MEL exer- cises, such as punches with weights (Fig. 7, B and C), standing arm abduction with weights or tubing, and medicine-ball drills. 6,23,25,26 Summary Closed-chain exercise protocols have assumed a large role in functional knee rehabilitation. They have been advocated as being safer and more effective than previously described protocols for both ACL 12-14 and patellofemoral 17,19 rehabilitation, although not all studies demonstrate a clear superiority in outcomes. Closed-chain exercises are also being employed in shoulder rehabilitation protocols, 5,6,24 although no outcomes studies have been reported. Utiliza- tion of these protocols is based on theoretical benefits and anecdotal evidence of more rapid return of shoulder function. On the basis of this information, it appears that closed-chain exercises may increase the effectiveness of both knee and shoulder rehabilitation protocols by simulating normal physiologic activations and biomechanical motions. Because of the utility and increasing use of these exercises, physicians should be familiar with the underlying biomechanics and when it is appropriate to use them. They appear to be effective in the early stages of rehabilitation due to the control of joint motion and tissue loads. There is no clear consensus about a particular set of exercises that should be included in every rehabilitation protocol, although both FEL and MEL exercises can be effective at different stages. The major criterion for including an exercise in a closed-chain protocol is whether it fits the definition 6 and accomplishes the purposes 3,5 of closed-chain activation. Closed-chain exercises and reha- bilitation protocols are not the only techniques for functional rehabilita- tion. A combination of open- and closed-chain exercises will ultimately be necessary to simulate normal functions and optimize the return to activities, especially in throwing, striking, and kicking sports. 5,24 The FEL and MEL exercises provide a stable base and allow shading into MNL exercises that are truly open- chain activities. Closed-chain exercises offer great promise in making rehabilitation more efficacious. Much more atten- tion should be paid to standardizing protocols, validating their direct influence on joint loads and muscle activation, and reporting outcomes studies. Figure 7 Exercises for rotator-cuff rehabilitation. A, Isometric humeral head depression. The resistive weight is set so that the bar does not move. The arm is pulled down with the elbow straight, so that the depression force is concentrated at the shoulder. B and C, Rotator cuff punches with weights. The weight should create a load but allow the arm to be extended. The exercise should start with hip and trunk extension and scapular retraction (B) and then proceed to arm punches at different levels of arm elevation (C). A B C W. Ben Kibler, MD, and Beven Livingston, MS, PT Vol 9, No 6, November/December 2001 421 References 1. Putnam CA: Sequential motions of body segments in striking and throw- ing skills: Descriptions and explana- tions. J Biomech 1993;26:125-135. 2. Steindler A: Kinesiology of the Human Body Under Normal and Pathological Conditions. Springfield, Ill: Charles C Thomas, 1955, pp 63-67. 3. Dillman CJ, Murray TA, Hintermeister RA: Biomechanical differences of open and closed chain exercises with respect to the shoulder. J Sports Rehab 1994;3:228-238. 4. 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