Neuromuscular Properties and Functional Aspects of Taped Ankles*

Transcription

1 /99/ $02.00/0 THE AMERICAN JOURNAL OF SPORTS MEDICINE, Vol. 27, No American Orthopaedic Society for Sports Medicine Neuromuscular Properties and Functional Aspects of Taped Ankles* Heinz Lohrer, MD, Wilfried Alt, PhD, and Albert Gollhofer, PhD From the Institute of Sport Medicine Frankfurt am Main, Frankfurt, and the Department of Sport Science of Stuttgart University, Stuttgart, Germany ABSTRACT We used electromyographic and goniometric methods to test 40 subjects to describe the neuromuscular and biomechanical adaptation of the ankle with respect to application of two different adhesive tapes and to exercises. The neuromuscular responses to inversion injury simulation, together with the mechanical displacements of the joint complex, were analyzed before and after controlled athletic exercises. The proprioceptive amplification ratio was calculated on the basis of the integrated reflex electromyographic results and on the maximum inversion amplitude. Relevant stability gains were achieved immediately after applying tape. There was reduced tape stability after athletic exercise for one of the two tape materials tested. No further loosening was detected, even after prolonged wearing of tape (24 hours). Compared with the unprotected ankle, the taped ankle had a significant increase in the proprioceptive amplification ratio. Both fatigue and mechanical loosening may be responsible for the significant reduction in this ratio immediately after exercise. After the 24-hour interval, the ratio was increased, which could be explained by physiologic neuromuscular regeneration and mechanical restabilization of the tape itself. The sensitivity of the proprioceptive amplification ratio, both to external stabilization and to internal fatigue, supports its potential value to quantify functional joint stability. No information is yet available regarding the conditions under which neuromuscular mechanisms can effectively protect the capsular and ligamentous structures of the * Presented in part at the 1997 GOTS annual meeting, Munich, Germany, June 1997, where it won the GOTS-Jäger award. Address correspondence and reprint requests to Heinz Lohrer, MD, Institute of Sport Medicine Frankfurt am Main, Otto-Fleck-Schneise 10, D Frakfurt, Germany. Funding for this work was received from commercial parties named in this study. See Acknowledgments for funding information. ankle joint. From a functional point of view, the mechanical limitation of extreme inversion movements of the foot should be a requirement. At the same time, however, a high degree of neuromuscular activation is desirable to protect the joint against inversion injury. So far only limited attempts have been made to examine injury prevention aspects in stable and chronically unstable ankle joints using neurophysiologic methods. 7,29 Three basic types of chronic ankle joint instability may be defined 6 : 1) mechanical damage of the lateral capsular ligamentous structures of the ankle joint due to elongation, partial rupture, or complete rupture; 2) damage or functional disorder of the afferent setup of the joint (proprioception); and 3) weakness of the pronator muscles (peroneus longus and brevis). The studies so far conducted to evaluate these factors have yielded contradictory results. Johnson and Johnson 13 observed no effects on peroneal muscle latencies with external supination of 35. These investigators evaluated three groups of subjects: patients undergoing nonoperative therapy, patients treated surgically, and untreated patients with functional instability. The degree of stress applied to the tested extremity was not reported. In contrast, Karlsson and Andreasson, 14 in a study of 20 patients with unilateral instability, detected a significantly shorter peroneal muscle latency on the healthy side at 30 of inversion. The latency of ms reported for unstable joints is markedly longer compared with values stated in the literature 3,17 and in our own previous studies. 1,2 Although the concept of reaction time used by Karlsson and Andreasson evidently relates to the latency of the polysynaptic reflex, the effects of taping on an unstable ankle joint are interesting only insofar as they shorten the peroneal muscle latency during simulated inversion injuries. The main disadvantage of all studies published so far on proprioceptive behavior after simulated inversion injury is that only neuromuscular pathways (latency), rather than the quantitative and qualitative effects of reflex muscle response, have been taken into account ,20 69

2 70 Lohrer et al. American Journal of Sports Medicine The purpose of this study was to investigate the sensitivity of functional joint stability to ankle taping and to athletic exercise. A complex parameter was defined quantifying reflex-induced neuromuscular activation in relation to the maximum inversion amplitude of the ankle joint after controlled mechanical stimulus. MATERIALS AND METHODS Study Subjects and Inclusion Criteria The study group consisted of 40 volunteers (18 men and 22 women). These 40 subjects were randomly assigned to two study groups (Table 1). Group 1 was tested with one kind of tape and group 2 was tested with another. Only stable ankle joints (as determined by clinical examination) with no history of injury were admitted to the study. All subjects were first informed about the study procedure and the possible risks associated with the study. All volunteers gave their written consent to participate. Figure 1. The taping technique used. A, the crossed dorsoventral and mediolateral straps. B, technique completed by a figure-of-8 (gray strips). Materials Tape. Two tape materials from different manufacturers were tested comparatively. Group 1 was tested with Leukotape (3.75 cm wide) (Beiersdorf Medical, Hamburg, Germany) and group 2 with 3M-tape (3.8 cm wide) (3M Medica, St. Paul, Minnesota). The tape was applied using a standardized technique described by Montag and Asmussen. 21 The application of the tape starts with six crossed dorsoventral and mediolateral straps (Fig. 1A). A figureof-8 completes the procedure (Fig. 1B). Inversion Tilt Platform. Neuromuscular and mechanical parameters were recorded using a measuring device that could induce controlled ankle inversion movements. 26 From an initial relaxed stance, a mechanical stimulus was applied of 15 of plantar flexion and 30 of inversion (Fig. 2). The right foot was loaded with at least 90% body weight; the amount of weight was controlled visually with a load cell under the left foot. Goniometers. Angular movement in the ankle joint was detected with strain-gauge twinaxial goniometers (Penny & Giles, Blackwood, United Kingdom) (accuracy, 0.1 ). The sagittal angle excursions and the Achilles tendon angle 22 were recorded continuously at a sampling rate of 1000 Hz. The goniometer was fixed directly to the skin at the midline of the dorsal aspect of the Achilles tendon and TABLE 1 Descriptions of the Two Study Groups Descriptive factor Group 1 (tape 1) Group 2 (tape 2) Sex Men 10 8 Women Mean age (years) 23.6 (19 31) 24.5 (18 29) (range) Mean weight (kg) (range) 67.9 (61 74) 69.5 (63 78) Mean height (cm) (range) 168 ( ) 173 ( ) Figure 2. After online load checking, an inversion injury is simulated by sudden release of movement, comprising 30 of inversion combined with 15 of plantar flexion. the calcaneus. The positions of the electrodes and goniometers were marked with a water-resistant pen to ensure exact reapplication after 24 hours. Electrodes. Bipolar surface EMG data were sampled from the tibialis anterior, peroneus longus, gastrocnemius medialis, and vastus medialis muscles as described previously. 11 The skin was cleaned and slightly rubbed with sand paper. Silver-silver chloride surface electrodes (Hellige, Freiburg, Germany), equipped with contact gel, were placed over the muscle bellies. Electrical resistance between the two electrodes was measured, and only values less than 5 k were accepted. Experimental Procedure Initially, a range of motion test and five sprain simulations were performed to record the individual standard values. Time and measurement conditions of this procedure were controlled accurately. For the range of motion test, the maximum motion amplitudes for dorsal exten-

3 Vol. 27, No. 1, 1999 Neuromuscular Properties and Functional Aspects of Taped Ankles 71 sion-plantar flexion and for inversion-eversion were determined by strain-gauge twinaxial goniometers. The knee joint was flexed 90 and active movements into the respective terminal ankle joint positions were measured. Then the tape was applied to the right ankle. Five simulated inversions were then executed and athletic exercise was performed with 10 minutes of treadmill running (10 km/ hr) and 2 minutes of slope jumping using four 15 sloped lateral surfaces. The device used was designed with four sloped platforms ( meters) arranged to the borders of one flat central platform ( meters) elevated 15 cm from the ground (Fig. 3). Optical signals were used to record the jump direction, which was displayed on a monitor via a computer. Exercise-induced changes were then monitored during five sprain simulations. The exercise phase of 10 minutes on the treadmill and 2 minutes of slope jumping was then repeated, followed by five further sprain simulations. Finally, the active range of motion test was again performed. After exactly marking the positions of the surface electrodes, we removed them. After this, the subjects left the experimental laboratory for 24 hours. Subjects were told to avoid athletic or other activities involving movements exceeding normal everyday activity. After 24 hours the goniometers and surface electrodes were applied once more to their previously marked positions and five sprain simulations and the active range of motion test were performed. After we removed the ankle tape, the measurements were repeated during sprain simulations and the range of motion test. Signal Processing The electrophysiologic signals were first amplified (1000- fold), filtered (0.5 khz low-pass; 10 Hz high-pass), and stored together with the signals of the electrogoniometers and the trigger signals (signals from the measuring platform) at a frequency of 1 khz per measuring channel on a personal computer system for later analysis. Before further processing, the raw EMG signals had to be rectified and averaged. This was necessary to ensure high reliability of the recordings. 11 Averaging was performed on the basis of the five simulated inversion movement cycles. Additionally, the absolute angle amplitudes in the plantar flexion and inversion directions and the mean angular velocities were calculated. The integrated EMG activity of the reflex response within the first 100 ms after response onset was determined. The time between the start of the mechanical stimulus and the first EMG response (signal level greater than 0.02 mv) characterized the latency of a specific muscle reflex activity (Fig. 4). The Proprioceptive Amplification Ratio The rationale to calculate the proprioceptive amplification ratio was to extract a measure that comprises both the neuromuscular response activity and the corresponding mechanical displacement. Therefore, the integrated reflex activity of the peroneus muscles was divided by the maximum inversion amplitude reached in the inversion tests and normalized to the trial without tape. Statistical Processing Statistical processing included calculation of the descriptive parameters. The significance of changes was calculated by repeated measures multifactorial analysis of variance (MANOVA) using tape material and time of measurement as factors. In the case of factor significance, a variance analysis on the least square difference (LSD) was employed. RESULTS Range of Motion Test The baseline values (untaped ankle) for active inversion were 22 for group 1 and 23 for group 2 (100%) (Fig. 5). Immediately after applying the tape, the active inversion movement of the ankle joints was reduced to 11 for group 1 (50% of baseline) and 11 for group 2 (48% of baseline). Figure 3. This specific slope-jumping device was used during athletic exercise specifically to stress the tape. Figure 4. Example of calculated parameters: EMG of the peroneus muscle, latency, and integration intervals and inversion angle measured by electrogoniometers during the simulated injury.

4 72 Lohrer et al. American Journal of Sports Medicine Figure 5. Ankle joint mobility (dorsiflexion-plantar flexion and inversion-eversion) during active range of motion (comparative literature data from two studies: Roth et al. 25 and Lüssenhop et al. 19 ). Plantar flexion was reduced from 52 for group 1 and 53 for group 2 (baseline values, 100%) to 33 for group 1 (63% of baseline) and 33 for group 2 (62% of baseline) (Table 2). No impairment of eversion was apparent because of the low absolute values (7 and 6 ). After 20 minutes of exercise, inversion mobility increased to 14 in group 1 (64% of baseline) and 15 in group 2 (65% of baseline). Plantar flexion mobility was 50 in group 1 (96%) and 46 in group 2 (87%). After 24 hours, inversion was 16 in group 1 (73%) and 18 in group 2 (78%). Plantar flexion after 24 hours was 46 in group 1 (88%) and 49 in group 2 (92%). Compared with the unprotected situations, all these tape-induced changes of active inversion were significant (P 0.01). The reduction of plantar flexion was significant only immediately after tape application (P 0.001). No statistically significant differences were detected between the two tape materials. Restriction of Inversion Motion on the Sprain Simulator After the test movement, a mean maximum inversion of 32 (100%) was detected for unprotected joints in both test groups (Fig. 6). After tape application, these values were Figure 6. Effect of tape on Achilles tendon angle (inversion angle) measured by goniometers in standardized sprain simulation (30 of inversion 15 of plantar flexion) before, during, and after athletic exercise, and after 24 hours (mean and standard deviation) (P 0.05). reduced to 18 in both groups (56% of baseline) (P 0.01). After 10 minutes of exercise, inversion was decreased to 21 in group 1 (66%) and 23 in group 2 (72%). After 20 minutes of exercise, the inversion was decreased to 21 in group 1 (66%) and 23 in group 2 (72%). The differences were significant only for group 2 (P 0.05). In the retest 24 hours after the physical exercise, tape 1 showed a trend (P 0.059) toward restabilization to 19 (59%). The respective value for tape 2 was 22 (69%). After the final removal of the tape, the maximum inversion was 29 for group 1 (91%) and 31 for group 2 (97%). The differences from the baseline values were not significant. Compared with the unprotected situation, the peroneal integrated EMG values were 83% for group 1 and 91% for group 2 (Fig. 7). After 20 minutes of exercise, these values were 76% and 86%. And 24 hours later 87% and 91% peroneal activity were achieved. None of these values were significant. After tape removal, initial values were calculated (97% and 100%) again. Before and after applying the tape, the TABLE 2 Active Ankle Joint Mobility (in Degrees) With and Without Tape, Before and After Exercise (Means Standard Deviation) Time of measurement Inversion Eversion Inversion-Eversion range Plantar flexion Dorsiflexion Plantar flexiondorsiflexion range Before applying tape Tape 1 a Tape 2 b After applying tape Tape Tape After 20 minutes of exercise Tape Tape hours after exercise Tape Tape a Tape 1 group based on measurements for 19 subjects. b Tape 2 group based on measurements for 20 subjects.

5 Vol. 27, No. 1, 1999 Neuromuscular Properties and Functional Aspects of Taped Ankles 73 Figure 7. Integrated EMG of the peroneus muscle after sudden combined inversion (30 ) and plantar flexion (15 ) relative to the trial without tape. Mean and standard deviation of the two test groups. Figure 8. Average and individual EMG latencies (in milliseconds) of four muscles before and after exercise and after 24 hours (mean of all subjects) (P 0.05). mean latency of the medial vastus muscle was about 4 ms shorter (P 0.01) than for the other muscles (Fig. 8). Proprioceptive Amplification Ratio After tape application the proprioceptive amplification ratio increased to 1.6 (P 0.05) (Fig. 9). After 20 minutes of exercise, the value decreased to 1.2 (P 0.05). After a 24-hour interval, the value increased to 1.5 (P 0.05). The baseline value of 1.0 was calculated after tape was removed. DISCUSSION Figure 9. 95% confidence interval of mean of the proprioceptive amplification ratio. *, P 0.05; **, P Percentage change relative to the initial situation without tape. Note the 0.6 increase in the ratio (50%) by applying tape (after tape). Release of motion in the sagittal plane with simultaneous restriction of inversion would be valuable for a prophylactic brace. In our test, the initial relative restriction of mobility in the active range of motion test after tape application was observed most for inversion, achieving about 65% of baseline (untaped condition). This can be interpreted as evidence that the taping technique used provides the required limitation of functional motion, especially for the inversion component. 21 However, the active plantar flexion range of motion test revealed a considerably smaller decrease in tape-related restriction of motion after only 20 minutes of athletic exercise, with about 90% of baseline being reached. A further loss of tape stability after 24 hours could not be found for either material. The direct relationship between duration of application and loss of stability of taping discussed in the literature could not be demonstrated in this investigation. Indeed, the present study demonstrated a trend toward restabilization 24 hours after tape application; this finding was particularly pronounced for one of the materials tested. This aspect of taping has not been described yet in the literature. In general, range of motion tests are only of limited functional relevance because they are employed on the unloaded foot and in an open kinetic chain position. In this sense, data obtained by functional tilt platform testing are more valuable because the pathophysiologic inversion injury movement is similar. An assessment of external ankle stabilizers based exclusively on range of motion tests is also questionable because it does not adequately take into account the functional unity of mechanical and neurophysiologic action and their relations to the external stimulus. Compared with values found in the literature, 19,25 our findings were similar both for the entire range of motion (dorsal/plantar) and for the corresponding components (plantar flexion, dorsiflexion, inversion and eversion) (Fig. 5). Nevertheless, this mechanical behavior corresponds to the findings observed in complex testing on the sprain simulator, but the loss of stability is less in this more functionally relevant test. The major disadvantage of all studies published so far on proprioceptive behavior after simulated inversion

6 74 Lohrer et al. American Journal of Sports Medicine trauma is the fact that only neuromuscular latencies, but not the quantitative and qualitative effects of reflex muscle response, were taken into account. 13,14,16,20 We can conclude from the latencies of the recorded EMG signals that these must be polysynaptic reflexes. They are necessary for active stabilization of the ankle joint and for stabilization of postural stance. The innervation pattern of the peroneus longus muscle confirms that such proprioceptively induced muscle responses occur with a latency of 60 to 70 ms 4,28 (Fig. 4). Studies on the proprioceptive function of the ankle joint have used methods for the diagnosis of posture (stabilometry) using three-dimensional force measurement platforms. 16,29 Sensory angle perception and reproduction tests in active and passive modes have also been employed. 12,16,17 Proprioceptive deficits in the chronically unstable ankle joint have been demonstrated. 6,8,18,29 However, proprioceptive activation by orthotic devices in the ankle joint similar to that occurring in the knee joint 23 has often been postulated, 8,12,27 but has never yet been demonstrated. Konradsen et al. 16 concluded from experiments with regional anesthesia of the ankle joint and foot that the afferent input of the lateral ligaments of the intact ankle joint contributes substantially to the correct stance perception of the ankle joint. Feuerbach et al., 5 on the other hand, could not detect any significant deterioration of proprioception in the ankle joint after local anesthesia of the anterior talofibular and calcaneofibular ligaments. Although selective local anesthesia of individual ligaments cannot be described as methodologically uncomplicated, the investigators concluded that the receptors of the skin, muscles, and other parts of the joint have at least an equivalent influence. Roll et al. 24 confirmed in microgravity experiments that postural regulation occurs on the basis of visual and vestibular influences but also through proprioceptive information from the muscle and skin of the sole of the foot. Lentell et al. 17 demonstrated improved movement perception in the noninjured ankle (kinesthesia) during passive inversion movements compared with the injured side. Konradsen et al. 16 described reduced perception of movement under local anesthesia only for passive motion in healthy subjects. Stance stability was also unchanged under local anesthesia. Clark et al. 3 and Grigg 10 emphasized the major influence of muscles on proprioception. According to these investigators, articular receptors are especially active at the end of a movement. Tropp 29 assumed, on the basis of stabilometric results, that secondary central somatosensory activity is reduced in the unstable joint, which he also regards as a consequence of treatment-related immobilization. Strikingly, these parameters are also altered in the same manner in the healthy, contralateral joint. Generally, however, only unilateral effects have been described after inversion trauma. 13,16,17 The methods described for the evaluation of proprioceptive properties of ankle joints generally do not appear to yield uniform results. Because of the dependency of the reflex response on the initiating movement velocity, 9 reduced EMG potentials are detected, as expected, immediately after applying an orthosis 26 or tape as a response to the induced supination stimulus. The amplitude and velocity of inversion are directly proportional. Therefore, the magnitude of the motor reflex activity can be expressed in relation to the inducing inversion amplitude. With the tape applied, however, the integrated EMG signal reduction is not proportional to the inducing inversion stimulus. Our results showed that the increase in proprioceptive amplification ratio after tape application could be interpreted as a proprioceptively activated effect of tape. The reduction after 20 minutes of exercise might be caused by fatigue and by mechanical loosening of the tape. The increase after 24 hours could be explained by neuromuscular regeneration and restabilization of the tape. The exact baseline value (1.0) was regained immediately after removing the tape, which must be interpreted as evidence that the method was reliable. In the future, all ankle braces used for treatment and prophylaxis should be required to undergo this combined mechanical-neurophysiologic and proprioceptive testing to evaluate their effects in a complex manner. This would allow improved criteria to be developed for individual indications for ankle stabilizers. Studies of this type on chronically unstable joints with and without external supports are required to demonstrate the severity of the proprioceptive deficit as a risk factor of recurrent ankle joint instability compared with uninjured subjects. Intraindividual comparison to the noninjured side should also be investigated in the future. This would provide information as to whether the athletes should be recommended to wear an external support, receive additional neurophysiologic proprioceptive training, or both. CONCLUSION The results obtained in the study confirm that ankle taping is an efficient way to protect the ankle joint from possible injury. This protection is not related to reduced inversion amplitudes alone; the tilting angular velocities are also clearly reduced. This velocity reduction enables the functional reflexes to come into action in time to protect the joint. The observation that both angular amplitude and reflex response are sensitive to the external tape support as well as to fatigue underlines the importance of the proprioceptive amplification ratio. This newly defined measure comprises both electrophysiologic and mechanical aspects of joint stabilization. Thus, it appears logical to use this ratio when functional joint stabilization is to be assessed in further studies. ACKNOWLEDGMENTS This study was supported by the Federal Institute of Sport Science, BISP Cologne, Germany, VF 04/08/02/94 and by Beiersdorf Medical, Hamburg, Germany. The authors express their gratitude to Mr. Juergen Wenzler for his support regarding the technical drawings.

7 Vol. 27, No. 1, 1999 Neuromuscular Properties and Functional Aspects of Taped Ankles 75 REFERENCES 1. Alt W, Lohrer H, Gollhofer A: Functional properties of adhesive ankle taping neuromuscular and mechanical effects before and after exercise. Foot Ankle Int, in press, Alt W, Lohrer H, Gollhofer A, et al: Preventive ankle taping Evaluation of mechanical, neuromuscular and thermal effects before and after exercise, in Abrantes JMCS (ed): Proceedings XIV. Symposium on Biomechanics in Sports. Lisboa, Gratica 200, 1996, pp Clark FJ, Grigg P, Chapin JW: The contribution of articular receptors to proprioception with the fingers in humans. J Neurophysiol 61: , Dietz V, Gollhofer A, Horstmann GA, et al: Postural adjustments and gravity. J Physiol 420: 21, Feuerbach JW, Grabiner MD, Koh TJ, et al: Effect of an ankle orthosis and ankle ligament anesthesia on ankle joint proprioception. Am J Sports Med 22: , Freeman MAR, Dean MRE, Hanham IWF: The etiology and prevention of functional instability of the foot. J Bone Joint Surg 47B: , Gleitz M, Rupp S, Hess T, et al: Einflu des Reflextrainings auf die Stabilisierung chronisch instalbiler Sprunggelenke. Orthopädische Praxis 30: , Glick JM, Gordon RB, Nishimoto D: The prevention and treatment of ankle injuries. Am J Sports Med 4: , Gollhofer A, Strass D, Kryöläinen H, et al: Neuromuscular control mechanisms as a function of variable load conditions [abstract]. Int J Sports Med 12: 92, Grigg P: Peripheral neural mechanisms in proprioception. J Sport Rehabil 3: 2 17, Horstmann GA, Gollhofer A, Dietz V: Reproducibility and adaptation of the EMG responses of the lower leg following perturbations of upright stance. Electroencephalogr Clin Neurophysiol 70: , Jerosch J, Bischof M: Der Einflu der Propriozeptivität auf die funktionelle Stabilität des oberen Sprunggelenks unter besonderer Berücksichtigung von Stabilisierungshilfen. Sportverletz Sportschaden 8: , Johnson MB, Johnson CL: Electromyographic response of peroneal muscles in surgical and nonsurgical injured ankles during sudden inversion. J Orthop Sports Phys Ther 18: , Karlsson J, Andreasson GO: The effect of external ankle support in chronic lateral ankle joint instability. An electromyographic study. Am J Sports Med 20: , Konradsen L, Ravn JB: Prolonged peroneal reaction time in ankle instability. Int J Sports Med 12: , Konradsen L, Ravn JB, Sørensen AI: Proprioception at the ankle: The effect of anaesthetic blockade of ligament receptors. J Bone Joint Surg 75B: , Lentell G, Baas B, Lopez D, et al: The contributions of proprioceptive deficits, muscle function and anatomic laxity to functional instability of the ankle. J Orthop Sports Phys Ther 21: , Löfvenberg R, Kärrholm J, Sundelin G, et al: Prolonged reaction time in patients with chronic lateral instability of the ankle. Am J Sports Med 23: , Lüssenhop S, Bruns J, Scherlitz J: Der Einflu von Sprunggelenkorthesen auf Rotation und Plantar-/Dorsalflexion des oberen Sprunggelenks. Orthopädie-Technik 46: , Lynch SA, Eklund U, Gottlieb D, et al: Electromyographic latency changes in the ankle musculature during inversion moments. Am J Sports Med 24: , Montag HJ, Asmussen PD: Taping Seminar. Balingen, Perimed-spitta Medizinische Verlagsgesellschaft, Nigg BM, Morlock M: The influence of lateral heel flare of running shoes on pronation and impact forces. Med Sci Sports Exerc 19: , Perlau R, Frank C, Fick G: The effect of elastic bandages on human knee proprioception in the uninjured population. Am J Sports Med 23: , Roll JP, Popov K, Gurfinkel V, et al: Sensorimotor and perceptual function of muscle proprioception in microgravity. J Vestib Res 3: , Roth AJ, Anders J, Venbrocks R, et al: Diagnostische Bedeutung der Sprunggelenkbeweglichkeit im Sport. Orthopädische Praxis 30: , Scheuffelen Ch, Gollhofer A, Lohrer H: Neuartige funktionelle Untersuchungen zum Stabilisierungsverhalten von Sprunggelenksorthesen. Sportverletz Sportschaden 7: 30 36, Surve I, Schwellnus MP, Noakes T, et al: A fivefold reduction in the incidence of recurrent ankle sprains in soccer players using the Sport- Stirrup orthosis. Am J Sports Med 22: , Thonnard JL, Plaghki L, Willams P, et al: La pathogénie de l entors de la cheville. Test d une hypothèse. Medica Physica 9: , Tropp H: Pronator muscle weakness in functional instability of the ankle joint. Int J Sports Med 7: , 1986