Journal of Sport Rehabilitation, 1996, 5, 13-24 63 1996 Human Kinetics Publishers, Inc.

Clinical Rationale for Closed Kinetic Chain Activities in Functional Testing and Rehabilitation of Ankle Pathologies

Rod A. Harter

Ankle injuries are the most common type of injury in sport worldwide, with ankle sprains accounting for 15% of all injuries. In this paper, the most recent, significant clinical research findings related to closed chain functional testing and rehabilitation of the ankle will be summarized. Biomechanical, physiological, and neurological rationales for integrated utilization of open and closed chain rehabilitation for the ankle will be discussed.

Numerous epidemiological studies have reported ankle injuries to be the most frequent time-loss injury in organized sport worldwide, with ankle sprains accounting for more than 15% of all injuries sustained (4,14,22,38,43). Because of the high morbidity rate of ankle injuries, functional testing and rehabilitative processes for this joint are among the most familiar activities for practitioners of physical medicine.

While most ankle sprains are isolated events that resolve uneventfully, a significant number of ankle injuries result in chronic instability. Chronic ankle instability, associated with residual ligamentous laxity, proprioceptive deficits, and peroneal muscle weakness (5,29,37), has been reported to affect 20 to 40% of individuals who sustain inversion sprains (10, 11, 21, 42).

In 1965, Freeman et al. dichotomized chronic ankle problems as being attributed to either mechanical instability, due to significant lateral ligament laxity, or functional instability, characterized by patients as laxity that allows a "giving way" of the ankle joint, attributed to partial deafferentation of the joint from damage to afferent joint receptors incurred during the ankle sprain (10). These authors concluded that lateral ankle ligament mechanical instability is rarely responsible for functional instability observed at the joint. Their classic work introduced a paradigm that underlies much of the current physical medicine research on the ankle, knee, and shoulder joints.

Some confusion exists regarding the jargon used to describe lower extremity functional testing and rehabilitation. Four key terms worthy of discussion are link system, kinematic chain, kinetic chain, andfunciional ex

Rod A. Harter is with the Department of Exercise and Spo University, Corvallis, OR 97331-3302.

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vationist and founder of the Sierra Club John Muir provided a unique perspective of the link system concept. He wrote, "When we try to pick out anything in the universe, we find it hitched to everything else." It is unlikely he was thinking of closed kinetic chain rehabilitation when he made this observation about 100 years ago, but it does apply to the present discussion. Sport rehabilitation efforts that concentrate on restoring function of a single joint or the muscles of a single body segment in isolation will ultimately fall short. When applied to physical medicine, the link system concept emphasizes the interdependent nature of indi- vidual components (e.g., bones, muscles, tendons, ligaments, and mechanorecep- tors) and their ultimate contribution to the entire system.

Within the study of biomechanics, the kinematic aspects of human move- ment help describe the characteristics of motion and include the form, pattern, and timing of movement without reference to the forces causing the motion. Key components necessary for a kinematic analysis of any rehabilitative exercise include knowledge of body position as well as the linear and/or angular changes in body position that create segmental or whole-body velocities and accelerations (16). In contrast, kinetics is an area of study that involves quantification of the forces that act on the human body or some inert object. A kinetic analysis of a rehabilitative exercise (e.g., toe raises with a 50-kg barbell across the shoulders) would require identification and quantification of the forces that cause or result from motion. In biomechanics and clinical research, kinetic analyses are techni- cally more complex than kinematic analyses since we cannot see forces but can see only the effects of forces (17).

Unfortunately, various published sources freely interchange the terms ki- netic chain and kinematic chain when referring to rehabilitative exercises and functional testing. Since in sport rehabilitation we are commonly interested in both the kinematic and kinetic aspects of the therapeutic activity, one solution is to refer to these activities as either closed chain or open chain phenomena. Regardless of which term is used, the fact remains that each moving body segment in a link system transfers forces to (and receives forces from) adjacent body segments, and, in doing so, affects (and is affected by) the motion of those components (7).

Functional exercise is by no means a new concept, and a brief historical digression is essential for perspective. In 1979, Knight (27) described an eight- component model of ' 'total injury rehabilitation. ' ' He suggested that each phase was a vital aspect necessary for complete rehabilitation and advised that the process should proceed in the following sequence in order to develop or maintain each component: (a) intact articulations and muscles, (b) pain-free joints and muscles, (c) joint flexibility, (d) muscular strength, (e) muscular endurance, (f) muscular speed, (g) integrated and coordinated movement (skill patterns), and (h) cardiovascular endurance (27).

That same year, Knight (26) also introduced a modification of the classic progressive resistance exercise protocol published by Delorme (8). Knight termed his modification daily adjustable progressive resistance exercise, and this widely adopted model allows for diurnal variations in an athlete's physiological and psychological status during both closed and open chain rehabilitative activities.

Kegerreis (24) described a "progressive reorientation" of an injured athlete into his or her sport as a process of meeting individual needs and goals. Kegerreis et al. (25) defined the term functional progression as a planned, progressively

Ankle Pathologies 15

more difficult sequence of exercises that enable the acquisition or reacquisition of skills required for safe and effective athletic performance. To apply the concept of functional progression, the clinician analyzes the types and magnitudes of physiological stress that an athlete will encounter upon return to sport and designs a graduated rehabilitation program based on these specific requirements.

Debate continues about the superiority of closed chain over open chain rehabilitative activities. In truth, both open and closed chain techniques have their place in clinical practice, and the following sections will address the benefits and limitations of each.

Benefits and Limitations of Open Chain Ankle Rehabilitation

Open chain rehabilitative activities are highly specific to the intended target tissue. Whether the activity is joint mobilization for ligamentous structures, proprioceptive neuromuscular facilitation (PNF) for improving range of motion and strength, or progressive resistance exercise applied manually or with external resistance to overload an isolated muscle or muscle group, the focus is isolation. Open chain rehabilitation may involve uniplanar or multiplanar motions, as controlled by the clinician. Open chain activities can also be used to build athlete1 patient-clinician rapport and promote compliance through the use of manual therapeutic procedures.

Application of open chain rehabilitation techniques in the lower leg permits isolation of individual muscles. Rehabilitative exercises using isokinetic dyna- mometry provide information about the specific characteristics of the force- velocity curve and permit quantification of the force or torque generated at every angle of movement, the amount of mechanical work and power generated, and the nature of the relationship between the agonist and antagonist muscles (39). Furthermore, open chain isokinetic exercise allows for the study of individual muscles or muscle groups and facilitates comparisons between the involved and contralateral normal limbs.

The major limitation of open chain rehabilitation, in general or specific to the ankle joint, is the artificial nature of many of the activities and exercises. While these techniques (e.g., PNF patterns or progressive resistance exercises) will improve the targeted deficit, the principle of specific adaptation to imposed demands (SAID) suggests that transfer of these improved neurophysiological capabilities to activities of daily living and sport is less than optimal. For optimal results, open chain rehabilitation activities should be combined with a program of more functional, closed chain ankle rehabilitation techniques.

Benefits and Limitations of Closed Chain Ankle Rehabilitation

The benefits of closed chain rehabilitative activities, discussed in greater detail elsewhere in this special issue, include (a) increased joint compressive forces leading to increased joint stability, (b) increased muscle coactivation, (c) de- creased joint shear forces, and (d) utilization of the SAID principle (33).

While increased agonist/antagonist muscle coactivation has been shown to

16 Harter

decrease joint shear forces (33), rehabilitative exercises that elicit high levels of antagonist cocontraction are biomechanically inefficient (49). Suppose that a particular ankle rehabilitation exercise can be performed with a plantar flexion torque of 100 N . m. The most efficient way to accomplish this movement is to use agonist activity (plantar flexor muscles only). However, in the presence of antagonist muscle coactivation that results in a dorsiflexion torque of 30 N . m, an agonist plantar flexion torque of 130 N . m is required to accomplish the task. The greater the amount of cocontraction, the greater the amount of work the agonist muscles must do to accomplish the same result.

Winter (48) noted that agonist/antagonist cocontractions occur in patients with a variety of pathologies, specifically in cases of spastic cerebral palsy and hemiplegia. To a lesser extent, agonistlantagonist coactivation also occurs during normal movements when joint stabilization is required, for example, at the ankle joint during locomotion or at the knee joint during a 1-RM squat exercise. While muscle coactivation during closed chain rehabilitation activities is generally desired for reducing joint shear forces and helping to protect healing soft tissues, the clinician needs to be aware of the mechanical inefficiency of such movements.

As discussed previously, the interdependence of the human link system dictates that motion at one body segment will be accompanied by predictable movement at other joints. Davies (7) observed that in the presence of dysfunction associated with an injury, this predictable pattern of movement may not be possible due to pain, effusion, limited range of motion, and/or muscle weakness. These limitations interfere with normal joint motion and muscle activity (via alteration of muscle recruitment patterns), and compensations occur. Davies suggested that if only closed chain exercises are performed, then the segments proximal and distal to the injured link may not display existing deficits, and the injured joint may not be totally rehabilitated. Without performing open chain functional testing to identify the presence of a specific deficit and without subse- quent isolated rehabilitation of the insufficiency, the weak link in the kinetic chain may go undetected and thus uncorrected (7).

The Role of Functional Testing in Ankle Injury Rehabilitation

In 1980, Malone et al. (34) observed that lower extremity rehabilitation is not complete until each muscle of the involved limb has equivalent or greater strength and flexibility than the opposite side. Surprisingly, very few published studies have compared the lower extremities of healthy individuals for bilateral symmetry.

Functional testing has been defined as the maximal performance of an activity or series of activities designed to assess (indirectly) muscular strength and power and to quantify function (1). The key purposes of functional testing are to (a) reveal asymmetries that may predispose an individual to injury, (b) measure progress in rehabilitation objectively, and (c) assess the ability of a body segment to tolerate external forces (1).

Bandy and associates (2) recently determined the reliability and limb sym- metry for five unilateral functional tests of the lower extremities. Testing four different pools of healthy subjects on three separate occasions, these authors reported ipsilateral-contralateral limb differences of less than I%,, indicating

Ankle Pathologies 17

bilateral limb symmetry. Intraclass correlation coefficients were calculated at .94 for the one-legged triple hop, .93 for the one-legged horizontal hop, .92 for the timed one-legged horizontal hop, .90 for the one-legged crossover hop, and .85 for the one-legged vertical hop.

Bandy et al. (2) demonstrated reliability and bilateral symmetry for five different closed chain functional tests, but how specific to the ankle joint complex are these tests? Are they sensitive (valid) measures of ankle joint function? Worrell et al. (50) used three single-leg hop tests to compare the injured versus noninjured limb functional abilities in 22 patients with previous unilateral ankle sprains. The time from ankle injury to testing ranged from 5 weeks to 2 years; 8 patients (36%) had pain and occasional swelling in their injured ankles at the time of testing. The authors found no significant differences between injured and noninjured lower extremity limb function for any of the three tests: single-leg hop for distance, single-leg 6-m hop for time, and 30-m single-leg agility hop. In a separate analysis of the 8 patients with residual ankle pain and swelling with activity, none of the hop tests detected significant functional deficits in the injured limb. Worrell et al. concluded that while their single-leg hop tests were quite reliable, with ICC values ranging from .77 to .99, the tests lacked the sensitivity (validity) to detect functional differences at the ankle. One explanation given for these findings was that compensation provided by the more proximal knee and hip joints was sufficient to mask any strength deficits in the ankle joint complex.

Another explanation of the problem associated with using closed chain tests to evaluate ankle joint function may be found in the proportion of movement goal contributed by the ankle joint musculature. For example, Robertson and Fleming (40) evaluated the kinetics of the hip, knee, and ankle joints during the standing broad jump, a two-legged activity kinematically similar to the single- leg hop for distance test described previously. For the propulsive phase of the standing broad jump, the contributions to total energy by the ankle, hip, and knee joints were 50%, 46%, and 4%, respectively. These same authors estimated that the ankle contributed 36% of the total energy required for the vertical jump, compared to 40% contributed by the hip and 24% by the knee (40).

Several other investigators have calculated the relative contribution of the ankle joint muscles to vertical jump height, with values ranging from 22 to 40% of the total energy (19, 32, 40). These values are presented in Table 1. The ideal closed chain test of ankle joint functional ability would require the ankle musculature to generate 100% of the energy needed to accomplish the task. By definition, closed kinetic chain activity produces motion in other, more proximal joints in the body, and therefore no "pure" closed chain ankle functional test

ntegratedCiosed and Open Chain Ankle Rehabilitation

The recent increased emphasis on the use of closed kinetic chain exercises in sport rehabilitation has generated substantial research interest and a large number of research studies involving closed and open chain activities. Assuming that both types of rehabilitative activities are necessary for total rehabilitation (28), I wiIl present physiological, biomechanical, and neurological rationales for an

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Table 1 Individual Joint Relative Contributions (in percentages) to Vertical Jump Performance

Reference Ankle Knee Hip Other

Robertson & Fleming (1987) 36 24 40 - Hubley & Wells (1983) 23 49 28 - Luhtanen & Komi (1978) 22 56 - 22"

Tncludes 10% attributed to trunk, 10% to arm swing, and 2% to head swing.

integrated open and closed chain rehabilitation program by reviewing recent investigations that have helped provide a greater scientific foundation for ankle joint rehabilitation.

Physiological Rationale

For many years clinicians have sought to maintain or improve the cardiovascular and muscular fitness levels of athletes and patients by prescribing exercises that accommodate for an individual's disability. Non-weight-bearing and partial- weight-bearing activities have been a mainstay in ankle injury rehabilitation protocols for years; however, only recently have exercise physiology research studies addressed the efficacy of these activities through controlled investigations.

Deep water running while wearing a flotation vest has been promoted as an effective method of cardiovascular conditioning for the injured athlete as well as for others who desire a non-weight-bearing, biomechanically specific aerobic workout. Because of its viscosity and the presence of drag forces, water provides a resistance proportional to the effort exerted by the athletelpatient.

Several recent studies have compared the physiological costs and benefits of treadmill and deep water running. Bishop et al. (3) tested well-trained, uninjured runners (5 men and 2 women) and measured several physiological parameters while subjects ran on a treadmill and while they ran in a pool while wearing buoyant vests. Ventilation, oxygen uptake, and respiratory quotient values were significantly higher during treadmill running than during water running, while perceived exertion rating was not significantly different. These authors observed that water running elicited 36% lower metabolic costs than treadmill running despite subjects' efforts to maintain similar levels of exertion in both activities.

Butts et al. (6) compared maximal physiological responses in 12 female and 12 male trained subjects during treadmill running and deep water running with flotation vests. These authors found significantly lower ventilation volumes and heart rates during. maximal water running compared to treadmill running, regardless of gender. Their female subjects' average maximum oxygen consump- tion (V0,max ) during water running was 16% lower than for treadmill running; their male subjects' average V0,max was 10% less during deep water running than treadmill running.

If water running has a lower metabolic cost than treadmill running, yet the subject feels the same level of exertion in both activities, what parameters should

Ankle Pathologies 19

the clinician use to write an appropriate prescription of water rehabilitative exercises for the athlete with a sprained ankle? Wilder et al. (46) required subjects to perform a water running graded exercise test during which the required stride rate was increased gradually from 48 to 104 cycles per minute. To determine the relationship between water running cadence and heart rate, these authors tested 20 subjects (10 male, 10 female) to develop an "environment-specific7' measure of exercise intensity. They reported a strong correlation (r = .73) between their subjects' heart rates and the water running cadence, concluding that cadence may be used as a quantitative measure for exercise prescription for water running.

In a three-way comparison of water running, stationary cycling, and running, Eyestone and associates (9) assessed maximum oxygen consumption (V02max) and 2-mile run performance in trained, healthy subjects. These authors stratified their subjects into experimental groups based on initial 2-mile times, then assigned them to water running, stationary cycling, or overground running training groups. After 6 weeks of performing their assigned mode of aerobic exercise, all groups had small (3 to 5%) yet statistically significant decreases in V02max but no significant changes in 2-mile run times. There were no significant differences in posttreatment V02max among the three experimental groups. Eyestone et al. concluded that runners who cannot run because of bony or soft tissue injury can, for at least 6 weeks, maintain their 2-mile run performance and V02max by substituting either stationary cycling or water running. The results of this study should comfort those athletedpatients who are concerned that cycling or pool running during rehabilitation of a sprained ankle will drastically diminish their aerobic fitness levels.

Biomechanical Rationale

When a clinician is developing either a strength development or rehabilitation program for the 12 muscles that cross the ankle joint, knowledge of the individual contribution of each muscle to the total force created is important. If we assume that muscles in the same tibial compartment, for example, the evertors, share in the development of muscular force, they likely do so in proportion to their cross- sectional area. The physiological cross-sectional area (PCA) of a muscle is a value calculated from the mass, length, and density (a constant value) of the muscle fibers (49). Wickiewicz et al. (45) measured muscle mass, fiber lengths, and angle of pennation in three cadavers and calculated the PCA of lower extremity muscles acting at the ankle, knee, and hip.

The potential for a given muscle to create force is related directly to its cross-sectional area. In general, stress values measured during isometric testing range from 20 to 100 N/cm2, and higher values have been measured in pennate muscles (49). If the clinician knows the type of muscle (parallel or pennate fibered) and the relative size of a muscle, then its contribution to the total amount of stress (force per unit of cross-sectional area) produced during human movement can be estimated. Table 2 contains the relative PCAs of 9 of the 12 muscles that cross the ankle joint, with the soleus (41%) and gastrocnemius (22%) comprising nearly two-thirds of the totalcross-sectional area of all 12 muscles (45). Knowing the PCA of the soleus and gastrocnemius muscles, the clinician can .design a rehabilitation program that involves plantar flexion resistance exercises with the knee flexed to facilitate activity in the larger soleus and with the knee extended to

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Table 2 Absolute and Relative Physiological Cross-Sectional Areas (PCA) of Muscles Crossing the Ankle Joint

Muscle Absolute PCA (cm2) Relative PCA (%)

Soleus Gastrocnemius Tibialis posterior Peroneus brevis Flexor hallucis longus Tibialis anterior Extensor digitorum longus Flexor digitorum longus Extensor hallucis longus

Note. Adapted from Wickiewicz et al. (1983) and Winter (1990). "Data not available.

facilitate gastrocnemius activity. In closed chain rehabilitation activities, agonistl antagonist coactivation is often a desired outcome, and knowledge of the PCAs of the muscles involved helps the clinician select exercises and provides greater insight regarding the agonistlantagonist strength ratios of the ankle musculature.

Neurological Rationale

Given the frequency of ankle injuries, it should come as no surprise that the first theories relating to the importance of peripheral feedback to normal function involved the ankle joint. Freeman et al. (1 1) described chronic ankle instability following a sprain as being attributed to either mechanical or functional instability. They defined mechanical instability as the condition in which the ankle joint ligaments have been disrupted and permit pathological motion. In contrast, these authors theorized that functional instability was caused not by a lack of ligamen- tous tissue integrity but by what they termed articular deafferentation of the ankle joint (1 1).

Nearly 3 decades ago, Freeman and Wyke (12) found three different types of mechanoreceptors in the ankle ligaments and joint capsules of cats. While mechanoreceptors have since been identified in human tibiofemoral (41) and glenohumeral joints (44), their presence in the human ankle joint has been confirmed only recently (35).

Recent electromyographic (EMG) studies have provided contradictory re- sults regarding the theorized presence of mechanoreceptors in the ankle joint. Konradsen and Ravn (29) compared peroneal muscle reaction time to sudden inversion to 30" in 15 subjects with functionally unstable ankles and 15 subjects with no history of ankle sprains. They found statistically significant differences in peroneal brevis (22% latency) and peroneus longus (26% latency) reaction times between their subjects who had functionally unstable ankles and those who did not. The neurophysiological significance of peroneal muscle latencies of this magnitude was not discussed by the authors and requires further investigation.

Ankle Pathologies 21

Johnson and Johnson (23) also assessed the latency between a sudden unexpected inversion to 35" and the onset of peroneal muscle activity. Three experimental groups were tested: 7 subjects who underwent nonsurgical treatment and rehabilitation, 6 subjects who rehabilitated following surgery to correct ankle instability, and 11 subjects with injury-free ankles. No significant differences were found among the three groups, with the normal ankles having the longest average peroneal reaction times, followed by the surgically treated and nonsurgi- cally treated ankle sprains. The small sample size and large individual subject differences in this study resulted in low statistical power (.30) and raised the possibility of a Type I1 error. However, the likelihood of a Type I1 error is diminished by the fact that the results are in agreement with two previous studies that compared differences in peroneal onset latency between injured and the contralateral normal ankles (20, 36).

When neuromuscular control is discussed as it relates to ankle functional testing and rehabilitation, several terms must first be defined. For discussion purposes, proprioception is the cumulative neural input to the central nervous system from mechanoreceptors located in muscles, tendons, ligaments, joint capsules, and the skin (47). Kinesthesia is the conscious awareness of joint position and movement resulting from proprioceptive input to the system (13).

There currently are three main clinical measures of kinesthesia associated with ankle joint rehabilitation: postural balance, ankle joint position sense, and threshold to detection of passive motion (31). Postural balance, a closed chain activity that has drawn the most research attention of these three parameters, can be defined as the subject's capacity to maintain the center of gravity (more correctly, the line of gravity) within the base of support during single-limb or double-limb stance (47).

In addition to assessing peroneal latency, Konradsen and Ravn (29) also evaluated postural balance during single-limb stance in their study. They reported greater postural sway in their subjects with ankle functional instability than in subjects with normal ankles. This finding is supported by previous studies em- ploying a similarly modified Romberg test (10, 30).

Goldie et al. (15) evaluated postural balance during single-legged stance following unilateral ankle inversion sprains in 24 balance-trained and 24 untrained subjects. Testing was conducted during four single-legged stance experimental conditions: injured leg with eyes open, injured leg with eyes closed, noninjured leg with eyes open, and noninjured leg with eyes closed. Goldie and associates found postural balance to be significantly worse in the untrained subjects' injured legs compared to their noninjured legs for both the eyes open and eyes closed conditions. No significant postural balance deficits were found in the group who underwent balance retraining. Based on these findings, the authors strongly recommended that rehabilitation following inversion ankle sprains include bal- ance retraining to reduce the risk of reinjury.

Unfortunately, Goldie et al. (15) provided no guidelines for the number of proprioceptive retraining sessions required to eliminate postural balance deficits. While their trained subjects performed an average of 32 balance training sessions, these subjects experienced a wide range of practice, anywhere from. 2 to 140 sessions. Eighty-three percent of the trained group participated in at least 10 balance practice exercises using wobble-board type devices.

More recently, Hoffman and Payne (18) used a force platform to quantify

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the effects of a postural balance training program in 28 healthy subjects. These authors observed significant decreases in postural sway in both the anterior- posterior and medial-lateral directions in their group that trained using a BAPS board 3 days a week for 10 weeks. While the efficacy of this paradigm has not yet been proven on subjects with ankle sprains, their data suggest that clinicians should use a minimum of 30 balance practice sessions over 10 weeks in an effort to improve postural balance.

Summary

The challenges facing clinicians who rehabilitate ankle sprains haven't changed much since the days of Hippocrates, who wrote, "Healing is a matter of time, but also is a matter of opportunity." What have changed, however, are the means to overcome those challenges and the ability to provide the most appropriate circumstances in which healing can occur.

The goals of this paper have been to provide a concise review of the current research related to rehabilitation of ankle joint injuries and to create a stronger scientific foundation for what is done in the clinical setting. The three main tenets of sports medicine are injury prevention, treatment, and rehabilitation, and with regard to the ankle joint, great progress has been made in each dimension. Critical thinking and the ability to implement current research findings into clinical practice remain as trademarks of clinician excellence.

References

1. Bandy, W.D. Functional rehabilitation of the athlete. Orthop. Phys. Ther. Clin. North Am. 1 :269-281, 1992.

2. Bandy, W.D., K.R. Rusche, and F.Y. Tekulve. Reliability and limb symmetry for five unilateral functional tests of the lower extremities. Isokinet. Exerc. Sci. 4:108- 111, 1994.

3. Bishop, P.A., S. Frazier, J. Smith, and D. Jacobs. Physiologic responses to treadmill and water running. Phys. Sportsmed. 17:87-94, February 1989.

4. Blyth, C.S., and F.O. Mueller. An Epidemiologic Study of High School Football Injuries in North Carolina, 1968-1972. Washington, DC: Consumer Product Safety Commission, 1974, pp. 72-84.

5. Bosien, W.R., L.S. Staples, and S. Russell. Residual disability following acute ankle sprains. J. Bone Joint Surg. 37A: 1237-1243, 1955.

6. Butts, N.K., M. Tucker, and C. Greening. Physiologic responses to maximal treadmill and deep water running in men and women. Am. J. Sports Med. 19:612-614, 1991.

7. Davies, G.J. The need for critical thinking in rehabilitation. J. Sport Rehabil. 4:l-22, 1995.

8. Delorme, T.L. Restoration of muscle power by heavy resistance exercises. J. Bone Joint Surg. 27-A:645-667, 1945.

9. Eyestone, E.D., G. Fellingham, J. George, and A.G. Fisher. Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. Am. J. Sports Med. 21 :41-44, 1993.

10. Freeman, M.A.R. Treatment of ruptures of the lateral ligament of the ankle. J. Bone Joint Surg. 37-A:661-668, 1965.

Ankle Pathologies 23

11. Freeman, M.A.R., M.R.E. Dean, and I.W.F. Hanharn. The etiology and prevention of functional instability of the foot. J. Bone Joint Surg. 47B:678-685, 1965.

12. Freeman, M.A.R., and B. Wyke. The innervation of the ankle joint: An anatomical and histological study of the cat. Acta Anat. 68:321-334, 1967.

13. Garn, S.N., and R.A. Newton. Kinesthetic awareness in subjects with multiple ankle sprains. Phys. Ther. 68: 1667-1671, 1988.

14. Ganick, J.G. The frequency of injury, mechanism of injury, and epidemiology of ankle sprains. Am. J. Sports Med. 5:241-242, 1977.

15. Goldie, P.A., O.M. Evans, and T.M. Bach. Postural control following inversion injuries to the ankle. Arch. Phys. Med. Rehabil. 75:969-975, 1994.

16. Hall, S.J. Basic Biomechanics (2nd ed.). St. Louis: Mosby, 1995, pp. 3-13. 17. Hamill, J., and K.M. Knutzen. Biomechanical Basis of Human Movement. Baltimore:

Williams & Wilkins, 1995, pp. 8-10. 18. Hoffman, M., and V.G. Payne. The effects of proprioceptive ankle disk training on

healthy subjects. J. Orthop. Sports Phys. Ther. 21:90-93, 1995. 19. Hubley, C.L., and R.P. Wells. A work-energy approach to determine individual joint

contributions to vertical jump performance. Eur. J. Appl. Physiol. 50:247-254, 1983. 20. Isakov, E., J. Mizrahi, P. Solzi, Z. Suzak, and M. Lotem. Response of peroneal

muscles to sudden inversion of the ankle during standing. Int. J . Sport Biomech. 2: 100-109, 1986.

21. Itay, S., A. Ganel, H. Horoszowski, and I. Farine. Clinical and functional status following lateral ankle sprains. Orthop. Rev. 11:73-76, 1982.

22. Jakobsen, B.W., A.B. Nielsen, and J. Yde. Epidemiology and traumatology of injuries in track athletes. Scand. J. Med. Sci. Sports 3:57-61, 1992.

23. Johnson, M.B., and C.L. Johnson. Electromyographic response of peroneal muscles in surgical and nonsurgical injured ankles during sudden inversion. J. Orthop. Sports Phys. Ther. 18:497-501, 1993.

24. Kegerreis, S. The construction and implementation of functional progressions as a component of athletic rehabilitation. J. Orthop. Sports Phys. Ther. 5:14-19, 1983.

25. Kegerreis, S., T. Malone, and J. McCarroll. Functional progressions: An aid to athletic rehabilitation. Phys. Sportsmed. 12:67-71, December 1984.

26. Knight, K.L. Knee rehabilitation using a daily adjustable progressive resistance exer- cise technique. Am. J. Sports Med. 6:134-140, 1979.

27. Knight, K.L. Total injury rehabilitation. Phys. Sportsmed. 7: 11 1, August 1979. 28. Knight, K.L. Guidelines for rehabilitation of sports injuries. Clin. Sports Med. 4:405-

416, 1985. 29. Konradsen, L., and J.B. Ravn. Prolonged peroneal reaction time in ankle instability.

Int. J. Sports Med. 12:290-292, 1991. 30. Lentell, G.L., L.L. Katzman, and M.R. Walters. The relationship between muscle

function and ankle instability. J. Orthop. Sports Phys. Ther. 11:605-611, 1990. 3 1. Lephart, S. Reestablishing proprioception, kinesthesia, joint position sense, and neuro-

muscular control in rehabilitation. In Rehabilitation Techniques in Sports Medicine (2nd ed.), W.E. Prentice (Ed.). St. Louis: Mosby, 1994, pp. 118-137.

32. Luhtanen, P., and P.V. Komi. Segmental contribution to forces in vertical jump. Eur. J. Appl. Physiol. 38:181-188, 1978.

33. Lutz, G.E., R.A. Palmatier, K.N. An, and E.Y.S. Chao. Comparison of tibiofemoral joint forces during open-kinetic chain and closed kinetic chain exercises. J. Bone Joint Surg. 75-A:732-739, 1993.

34. Malone, T.R., T.A. Blackburn, and L.A. Wallace. Knee rehabilitation. Phys. Ther. 60: 1602-1609, 1980.

35. Michelson, J.D., and C. Hutchins. Mechanoreceptors in human ankle ligaments. J. Bone Joint Surg. 77-B:219-224, 1995.

36. Nawoczenski, D.A., M.G. Owen, M.L. Ecker, B. Altman, and M. Epler. Objective evaluation of peroneal response to sudden inversion stress. J. Orthop. Sports Phys. Ther. 7: 107-109, 1985.

37. Nitz, A.J., J.J. Dobner, and D. Kersey. Nerve injury and grades I1 and I11 ankle sprains. Am. J. Sports Med. 13:177-182, 1985.

38. Pfeifer, J.P., W. Gast, and W. Pforringer. Traumatology and athletic injuries in basketball. Sportverletz Sportsschaden 6:91-100, 1992.

39. Riera, J., F. Drobnic, P.A. Galilea, and V. Pons. Comparison of two methods for measurement of the extensor muscle dynamic force of the inferior limb: Isokinetic dynamometry and vertical jump tests. Sports Med. Training Rehab. 5:137-143, 1994.

40. Robertson, D.G.E., and D. Fleming. Kinetics of standing broad and vertical jumping. Can. J. Sport Sci. 12:19-23, 1987.

41. Schultz, R.A., D.C. Miller, C.S. Kerr, and. L. Micheli. Mechanoreceptors in human cruciate ligaments: A histological study. J. Bone Joint Surg. 66-A:1072-1076, 1984.

42. Smith, R.W., and S.F. Reischl. Treatment of ankle sprains in young athletes. Am. J. Sports Med. 14:465-471, 1986.

43. Tanvergert, E.M., H.J. Ten Duis, and H.J. Klasen. Trends in sports injuries, 1982-1988: An in-depth study on four types of sport. J. Sports Med. Phys. Fitness 32:214-220, 1992.

44. Vangsness, C.T., M. Ennis, J.G. Taylor, and R. Atkinson. Neural anatomy of the glenohumeral ligaments, labrum, and subacromial bursa. Arthroscopy 1 1 : 180- 184, 1995.

45. Wickiewicz, T.L., R.R. Roy, P.L. Powell, and V.R. Edgerton. Muscle architecture of the human lower limb. Clin. Orthop. 179:275-283, 1983.

46. Wilder, R.P., D. Brennan, and D.E. Schotte. A standard measure for exercise prescrip- tion for aqua running. Am. J. Sports Med. 21:45-47, 1993.

47. Wilkerson, G.B., and A.J. Nitz. Dynamic ankle stability: Mechanical and neuromuscu- lar interrelationships. J. Sport Rehabil. 3:43-57, 1994.

48. Winter, D.A. Energy assessments in pathological gait. Physiotherapy Can. 30:183- 191, 1978.

49. Winter, D.A. Biomechanics and Motor Control of Human Movement (2nd ed.). New York: Wiley, 1990, pp. 68-71.

50. Worrell, T.W., L.D. Booher, and K.M. Hench. Closed kinetic chain assessment follow- ing inversion ankle sprain. J. Sport Rehabil. 3:197-203, 1994.