Effect of Repeated Eight-Minute Muscle Loading on the Angle of Straight-Leg Raising

Transcription

1 Effect of Repeated Eight-Minute Muscle Loading on the Angle of Straight-Leg Raising RICHARD W. BOHANNON The right lower extremities of 10 experimental subjects were passively loaded for 8 minutes on three consecutive days to determine the effects of such loading on the angle of straight-leg raising. The angle was determined cinematographically each day after loading for 15 seconds, every 30 seconds thereafter during 8 minutes of loading, and 10 minutes and 24 hours after loading. Twenty-four hours after three days of loading, the straight-leg-raising angle of the Experimental Group was an average of 4.4 degrees greater than it was initially. This increase was not statistically significant. The comparable angle of 10 control subjects increased an average of 0.6 degrees. The 4.4 degree increase suggests that muscle lengthens slowly in response to 8 minutes of stretching applied on three consecutive days. Key Words: Leg, Muscles, Physical therapy. Physical therapists often encounter patients with limitations in joint range of motion (ROM). Limited length of the musculotendinous unit (MTU) crossing a joint is responsible, at least in part, for inadequate ROM in many cases. Although physical therapists often endeavor to increase MTU length through various procedures, little objective data are available to assist the clinician in making knowledgeable decisions about the appropriate intensity, frequency, and duration of treatment for MTU lengthening. A large proportion of the information available has been derived from in vitro studies of animal or cadaver MTUs or their components. At least three conclusions can be drawn from these studies. First, tendons demonstrate immediate lengthening in proportion to the magnitude of loads applied to them. 1 Second, small loads applied to tendons over long periods of time result in greater residual lengthening than do heavy loads applied over shorter periods of time. 1,2 Third, some of the immediate lengthening occurring in muscle fibers 3 or whole muscle 4 during loading is transient and can be attributed to temporary Mr. Bohannon was a graduate student, Division of Physical Therapy, Department of Medical Allied Health, School of Medicine, University of North Carolina, Chapel Hill, NC, when this article was written. He is currently Chief of Physical Therapy, Southeastern Regional Rehabilitation Center, Owen Drive, Fayetteville, NC (USA). This article was submitted May 2, 1983; was with the author for revision six weeks; and was accepted October 24, sarcomere lengthening (changes in actin/myosin overlap). In vitro experiments performed to date have provided some useful information but have fallen short of providing adequate rationale for designing clinical procedures to lengthen "tight" muscles. Such experiments have fallen short because they were performed in vitro and because most were performed on tendons, which are less extensible and, therefore, not representative of whole muscle. 5 Several studies performed on live animals provide further information about the effects of loading on MTUs. These investigations indicate that the number of sarcomeres found longitudinally 6 and the length of the parallel elastic component 7 increase in animal MTUs that have been subjected to long-term loading by positioning in a lengthened state. Although these responses to loading may occur in humans, the amount of lengthening cannot be predicted from experiments on animals. Clinical reports and experiments on human subjects, like experiments on animals, fall short of defining adequate frequencies, intensities, and durations of loading for increasing MTU length. Some clinical reports fall short because they do not specifically address increasing MTU length but, rather, the measured changes in ROM. Among such clinical reports are those of Kottke and associates 8 and Sapega et al 9 who have reported the clinical application of relatively specific low loads for 20 or more minutes to increase ROM. The report of Kottke and associates specifically described the results of 10 representative patients. 8 Sapega et al, on the other hand, offered no objective documentation of the results of their method. 9 Both clinical reports provided insight for clinical practice but lacked the controls required for establishing cause-effect relationships. Some experimental investigators have controlled variables that may influence outcome, but the value of their studies is limited because the loads used in the experiments lacked objectivity, the loads were applied for a very short time, or the measurement techniques used were of questionable validity. An example of limited objectivity would be describing a load only as that resulting in a pulling sensation behind the knee of a subject when the subject undergoes passive straight-leg raising (SLR). 10 In regard to duration, no experiment could be found that used human subjects and documented more than one minute of continual static load application Although one minute of loading may be the duration used by some clinicians, it is shorter than the time suggested by in vitro studies as appropriate and shorter than clinical reports indicate is necessary to achieve optimal results. Previous investigators have used a horizontal reference to measure the angle of SLR, a measurement technique of questionable validity. 10 " 13 Because the validity of this technique for reflecting hamstring MTU length is questionable, I also must question the results of the experiments using Volume 64 / Number 4, April

2 the technique.16 By measuring the angle of SLR in relation to the pelvis, I obtained a more valid indication of hamstring MTU length even in the presence of pelvic rotation.16 The practicing clinician needs to know how MTUs respond to durations of loading longer than one minute. The documentations of such responses must be made by a valid and objective method. I chose to document the response of MTUs to a period of loading between those previously tested experimentally and those suggested from in vitro experiments and clinical reports. If I found this period was effective, clinical goals might be accomplished with a limited commitment of time. The specific purpose of this investigation was to determine whether three consecutive days of 8 minutes of loading with the maximum load that subjects could tolerate would lead to a significant increase in the angle of SLR in relation to the pelvis, during the application of the load and at 10 minutes and 24 hours after removing the load. In addition, I sought to determine whether such differences would exceed those that might result from the measuring process alone. I tested the following null hypotheses: 1) no significant differences will exist each day between the angle of SLR in relation to the pelvis of the Experimental Group after 15 seconds of loading and between the same angle relationship at three subsequent times (during 8 minutes of loading and 10 minutes and 24 hours after loading), 2) no significant differences will be found between the SLR angle of the Experimental Group at 15 seconds of loading the first day and all subsequent measurements of the angle on the second and third days, and 3) the SLR angle of the Experimental and Control Groups will not differ significantly at any time. METHOD Subjects Twenty volunteers with dominant right lower extremities (preferred for kicking) participated in the study. The five men and 15 women ranged in age from 21 years to 36 years. All subjects were free of known neurological or orthopedic dysfunction that might influence their response to hamstring MTU loading. None of the subjects was involved in an excercise program to lengthen or strengthen their hamstring 492 Fig. 1. Subject undergoing loading. Note the EMG biofeedback unit on the table, the threepoint splint, the markings on the right pelvis and lower extremity, and the location of straps used to stabilize the left leg. MTUs. Subjects were assigned randomly to an Experimental or Control Group; as a result, two men were in the Experimental Group and three men were in the Control Group. unit to help subjects relax their hamstring muscles during the stretching procedure. Instrumentation I loaded (stretched) the right hamstring MTU of each subject by placing weights in the weight pan of the Elgin table and connecting the cable through the pulley system to a stirrup on the right ankle. This technique allowed transmission of a load from the weight pan to the subject (Fig. 1). Before loading, the left lower extremity of each subject was stabilized to the table by a 15-cm-wide (6-in) strap drawn snugly across the thigh and a 6-cm-wide (2.4in) strap drawn snugly over the lower leg (Fig. 1). This stabilization, which I have already shown cannot prevent pelvic rotation, was performed only in an effort to limit pelvic rotation.16 The right knee of each subject was maintained in extension (to assure SLR) by a threepoint splint (Fig. 1). I used the following equipment: 1) the overhead cable pulley system of a model A-1500 Elgin exercise unit* to stretch subjects* hamstring MTUs; 2) a model DPP 30 Chatillon push/pull gaugef to measure the actual load transmitted from the weight pan to the subject; 3) a model HR16, 16 mm Bolex movie camera to record the angle of SLR in relation to the pelvis during the procedure; 4) a Vanguard Motion Analyzer** to determine the position of the right lower extremity in relation to the pelvis (because my experience with the Vanguard Motion Analyzer** in a previous study had shown it can accurately and precisely determine joint angles16); and 5) a Cyborg J-33 EMG biofeedback Procedure Preliminaries to Experimental Loading * Elgin Exercise Appliance Co, PO Box 108, 1002 E Third St, Sandwich, IL John Chatillon and Sons, Inc, Kew Gardens Rd, Kew Gardens, NY Bolex International SA, Yverdon, Switzerland. ** Vanguard Instrument Corp, Walt Whitman Rd, Melville, NY At least two weeks before the actual experiment, I tested the subjects to de Cyborg Corp, 55 Chapel St, Newton, MA PHYSICAL THERAPY

3 RESEARCH termine the maximum passive SLR load they could tolerate for eight minutes. This load, which was placed in the weight pan of the Elgin table, was documented so that it could be applied during the experimental period as a lengthening and measuring load. Because the load on the weight pan was not the actual load transmitted through the cable of the Elgin table, the Chatillon push/pull gauge was hooked to the cable to measure the actual load for each subject. The angle of SLR in relation to the pelvis during the experiment was determined from markings placed on the right pelvis and lower extremity of each subject. I adapted this manner of marking from Mundale et al 17 and have described my use of it in detail elsewhere. 16 In essence, the marking procedure allows the measurement of the angle between the straight leg and a line perpendicular to the line between the superior and inferior iliac spines. Before each day's loading procedure, I instructed all subjects to neither assist nor resist the pull of the weights during the loading procedure and to maintain their right lower extremity in neutral adduction-abduction. I instructed the subjects in the use of the auditory feedback from the Cyborg J-33 EMG biofeedback unit to indicate the level of electrical activity in their hamstring muscles. I placed EMG biofeedback electrodes on a line midway between the ischial tuberosity and the popliteal space, after reducing skin resistance by shaving, rubbing with an abrasive, and rubbing with alcohol. The threshold of the unit was set to provide auditory feedback with any muscle contraction above the resting level. The level of electrical activity during the experiment was not recorded for statistical assessment. The Bolex camera was set for singleframe filming and positioned perpendicular to the axis of motion of the right lower extremity of the subject. Experimental Loading After completing the preliminary procedures, subjects were divided into Experimental and Control Groups. All subjects had their right lower extremities loaded as previously described with their preestablished maximum loads. I selected 8 minutes of loading for the Experimental Group for four reasons. First, 8 minutes was greater than the Fig. 2. Method for determining hamstring torque. duration that is often applied manually in a clinical setting. Second, this time period was substantially longer than durations of static loading previously tested experimentally. Third, the time was of short enough duration to be tolerated by the experimental subjects. Fourth, if 8 minutes of loading produced significant lengthening, the results would provide justification for the clinical application of loads of durations shorter than the 20 minutes recommended by previous investigators. 8,9 Initial recordings (cinematographic photographs) of the angle of SLR in relation to the pelvis were made 15 seconds after the lower extremity of each experimental subject was loaded and every 30 seconds thereafter until 8 minutes of loading was completed. I knew from a previous study that samplings of the angle at 30-second intervals were adequate to illustrate trends in the angle during loading. 16 The right lower extremity of each experimental subject was then allowed to rest on the table for 10 minutes. After 10 minutes of rest, the right lower extremity was again loaded for 15 seconds, and another photograph was taken to establish a 10- minute residual measurement of the angle. Twenty-four hours later, the lower extremity was again loaded, and a photograph taken after 15 seconds to establish a 24-hour residual measurement. This procedure was repeated 24 hours and 48 hours after the first day of loading. The first photograph taken on the second and third days (15 seconds after loading) served as both the initial measurement of those days and as the 24- hour residual measurement for the previous day. Subjects in the Control Group were loaded for photography in the same manner as those in the Experimental Group. They did not, however, undergo 8 minutes of loading. Instead, the right lower extremity of the control subjects rested on the table during the time that the experimental subjects had the load applied for stretching. Therefore, on three days, the Control Group was loaded for 15-seconds initially and for Volume 64 / Number 4, April

4 TABLE 1 Comparison of Experimental and Control Group Subjects a Group Control Experimental Age (yr) 23.4 ± ± 5.0 Mass (kg) 64.3 ± ± 9.4 Cable Load (kg) 6.6 ± ±1.3 Hamstring Muscle Torque (Nm) 44.0 ± ±12.0 Angle of SLR with Pelvis ( ) 79.2 ± ± 8.8 a Measurements of cable load, leg angle, and estimates of torque acting on the hamstring muscles are those obtained at the completion of 15 seconds of loading on Day 1 of the study. TABLE 2 Means and Standard Deviations of the Angle of Straight-Leg Raise in Relation to Pelvis Over Time Group Experimental Control Time a 15 sec (initial) 8 min 10-min residual 24-hr residual 15 sec (initial) 8 min 10-min residual 24-hr residual Day ± ± ± ± ± ± ± ± 7.9 Angle ( ) Day ± ± ± ± ± 7, ± ± ± 8.0 Day ± ± ± ± ± ± ± ± 9.0 a The 24-hour measurement time of each day is equivalent to the 15-second measurement time of the following day. 15 seconds at 8 minutes, and 10 minutes, and 24 hours after the loading procedure. Photographs were taken at the end of each 15-second period of loading. Because of the tendency of the angle of SLR (in relation to the pelvis) to increase rapidly during the first seconds of loading as the lengthening load overcame the pull of gravity, the documentation of this angle was only recorded after 15 seconds of loading. I used this procedure to measure the SLR angle of both the experimental and control subjects. The results of testing the Control Group helped to clarify the magnitude of changes in the angle of SLR associated with the measuring procedure itself and that associated with the eight minutes of loading. Cinematographic photographs were analyzed on the Vanguard Motion Analyzer. This analysis provided documentation of the angle of SLR in relation to the pelvis for both groups. The first frame of film taken of each subject after 15 seconds of loading was also used to estimate the torque required to stretch the hamstring MTU at the beginning of the passive SLR procedure. I calculated estimations of this torque because they provided a better estimate of actual load on the hamstring MTU than the cable load. I calculated torque using measurements from the film and estimates of limb segment mass and center of mass that were calculated previously by other investigators (Fig. 2). 18,19 Analysis of Data I compared various characteristics of the Experimental and Control Groups by computing t tests of the difference between independent means to establish the comparability of the groups. I used an experimental design, a split-plot factorial analysis of variance (ANOVA) for repeated measures, to determine the effects of grouping, treatment day, and measurement time variables on the angle of SLR as well as the interaction between the variables. 20 This analysis was performed with a BMDP-81 computer program. 21 I performed planned comparisons thereafter to determine if specific intercell differences were statistically significant. RESULTS The group means for age, weight, and cable load, 15-second (initial) hamstring Fig. 3. Mean angle of straight-leg raising in relation to the pelvis during the experimental procedure. 494 PHYSICAL THERAPY

5 torque, and the initial angle of SLR did not differ significantly by t tests for independent means. Comparisons between groups were therefore considered valid (Tab. 1). The angle of SLR of each group demonstrated similar patterns of change from day to day (Fig. 3 and Tab. 2). In the Experimental Group, the mean daily increase in the angle after 8 minutes of loading was 3.7 (±0.4) degrees; the average daily increase in the angle 10 minutes after the 8-minute loading was 2.6 (±0.6) degrees; twentyfour hours after each day's 8-minute loading period the mean increase over the previous day's initial angle was 1.5 (±0.7) degrees; and the mean angle was greater at all later times than on the first day after 15 seconds (initial) of loading. The mean increase was greatest at 8 minutes of loading on the third day (7.1 ). Twenty-four hours after the last of three daily treatment sessions, consisting of stretching for 8 minutes, the mean overall increase in the angle of SLR, in relation to the pelvis, was 4.4 (±5.6) degrees. The Control Group also demonstrated some increases in the angle with successive measurements. These increases were not as consistent, however, and were less than those of the Experimental Group. The mean increase in the angle of the Experimental Group on the final test (24 hours after the third treatment) was more than seven times that demonstrated by the Control Group (4.4 vs 0.6 ). The statistical procedures failed to demonstrate any of the changes described above as significant. None of the null hypotheses could be rejected. The split-plot ANOVA demonstrated the only significant effects to be those of day (p <.01) and measurement time (p < ) (Tab. 3). The only interaction demonstrated to be significant was that between time and group (p <.02). The significant effect of time provided the possibility that significant differences might occur over time in the Experimental Group. This possibility was not confirmed by additional statistical comparisons. That is, the differences in the measured angles of SLR between the Experimental and Control Group were not statistically significant. DISCUSSION The small increases in the angle of SLR occurring during the 8-minute loading period not only lacked significance, but were also largely lost after 24 TABLE 3 Analysis of Variance Summary Table Source of Variance Mean Group (A) Day(B) AB Time (C) AC BC ABC SS df hours, suggesting that the increases were the result of temporary increases in sarcomere length. 3, 4 The mean daily increase in the SLR angle (3.7 ) in the Experimental Group was less than the mean daily increase in the angle of SLR reported by Tanigawa (4.5 ) 10 but was larger than the mean daily increase reported by Hartley-O'Brien (2.8 ). 12 The differences in daily duration, frequency, and intensity of loading and differences in the method of measuring used by the various investigators, probably account for these differences in results. As the angle of SLR had not plateaued within the 8-minute period of loading used in this study, daily increases in the angle may have been greater if the loading time had been prolonged to 20 or more minutes as suggested by previous clinical reports. 8, 9 The tolerance of the subjects for loading of that duration, however, is unknown. The increases in the angle of SLR in the Control Group of this study indicate that 15 seconds of loading, if repeated, may have a small temporary and insignificant effect on MTU length. This finding would be consistent with those of other investigators who have applied short duration loads repetitively and noted increases in the pelvifemoral angle 15 and the angle of SLR measured against a horizontal reference. 10 The insignificant residual lengthening accomplished in the Experimental Group over the entire 72-hour period of this experiment (mean 4.4 ) and any comparable residual increases in muscle length reported by other investigators are most likely the result of permanent lengthening of the noncontractile elements or the longitudinal addition of sarcomeres or both. 6, 7 The residual gain MS F RESEARCH P in ROM of 4.4 degrees in this study, expressed as a weekly gain, was of the same order of magnitude as the gains reported by others who have studied this problem. Medeiros et al reported that subjects loaded on eight days over an unreported number of weeks gained a total of 5.7 degrees. 15 Tanigawa reported that subjects passively loaded on six days over a three-week period gained a total of 7.1 degrees or about 2.5 degrees a week. 10 Hartley-O'Brien reported that subjects loaded on nine days over a three-week period gained a mean total of 15.4 degrees or 5.1 degrees a week. 12 The mean total gain of the Experimental Group in this Study was considerably less than the gain (21.4 ) calculated by Kottke and associates who studied a series of 10 patients. 8 Within the time span of one week (three days), however, the mean total gain (4.4 ) by the subjects in my experiment exceeded the calculated weekly gain (2.9 ) by the patients of Kottke and associates. If the daily program applied in my experiment had been carried out over a greater number of days, significant increases might have been demonstrated in the angle of SLR. Further studies must be conducted, however, to determine if the treatments are effective in continuing to increase the angle of SLR and to determine how long the effects persist. In comparing the residual increases in ROM in this study with the increases demonstrated by other investigators, two additional points must be considered. First, the greater total gain in ROM reported by some other investigators must be interpreted in light of the method and time of measurement of ROM. By measuring the angle of SLR in relation to the horizontal, Tanigawa 10 Volume 64 / Number 4, April

6 and Hartley-O'Brien 12 obtained greater increases than they would have obtained by measuring against a pelvic reference as I did in my previous study. 16 Furthermore, Tanigawa's reported increase of 7.1 degrees was taken at the end of the last day's treatment rather than one day later, my measurement day for this study. The increase in the angle of SLR (in relation to the pelvis) found in this study at the end of the last day's treatment was also 7.1 degrees. Second, the statistical procedures used to assess the results of this experiment and the sample size should be examined when questioning the usefulness of daily 8-minute loading to achieve a clinical goal. If the results of this study had been used to test the hypotheses that 1) the Experimental Group will demonstrate a significantly greater angle of SLR 24 hours after three consecutive days of 8 minutes of loading than after the initial loading the first day and 2) that the increase in the angle over the same time will be greater for the Experimental than for the Control Group, we would find that t tests confirmed these hypotheses (p <.05). The t test, which is more liberal, has been used by other investigators. Therefore, the reader should remember that the statistical procedure applied, as well as the magnitude of difference, may influence whether results are interpreted as significant. The failure to demonstrate a significant change in the angle of SLR may also have been a function of sample size. If more subjects had been tested, the chance of type II error would have decreased (reducing the possibility that significant results be interpreted as nonsignificant). If the 3 to 4 degrees a week change observed in this experiment and those reported by Kottke and associates are typical, weeks or months may be necessary before sufficient increases can take place in muscle length so that functional differences occur. 8 The clinical experience of many physical therapists may bear this out. The lengthening response of MTUs to loading will probably vary depending on the intensity, frequency, and duration of the loading as well as the particular MTU loaded. Intensity should be documented in experiments of MTU loading in such a way that the results of other experiments can be meaningfully compared. The method used in this study was adequate for documenting gross intensity of loading, but specific measurements of limb mass or the method used by Medeiros et al, 15 and Halkovich et al 14 may provide even greater accuracy. These options would eliminate some of the errors inherent in estimations of center of mass and lower extremity mass, which must be obtained if the amount of torque acting on the hamstring muscle is to be determined. Frequency and duration of loading should also be documented specifically in both experimental and clinical settings. Clinically, the load intensity used to measure MTU length should be kept constant from day to day. Otherwise, day-to-day variations in MTU length may simply reflect differences in the force used to determine ROM. The method used in this experiment allowed a reasonably consistent load application from day to day. This method is also valid and reliable and can be adapted clinically. Whether this method of measurement or others are applied clinically, measurements taken before treatment each day should be recorded as they may provide a better indication of residual lengthening from the previous treatment. Even exercising these precautions, normal interday variation may affect the measurements obtained. 22 Before knowledgeable judgments can be made about the responses of MTUs to loading, experiments such as this will have to be replicated or performed on larger numbers of subjects over longer periods of time. Such experiments should eventually establish critical values for frequency, intensity, and duration in much the same way as critical values are already established for muscle strengthening. CONCLUSIO The hamstring MTUs of 10 young healthy subjects, which were loaded for 8 minutes on three consecutive days with the maximum load that the subjects could tolerate, lengthened only slightly. The angle of SLR (with respect to the pelvis) is indicative of this length and increased only a mean of 4.4 degrees in the 10 subjects, This increase, although over seven times that of a Control Group, was not statistically significant. Even though the size and characteristics of the group studied prohibit bold assumptions, the findings give cause to question the efficacy of daily durations of loading of 8 or fewer minutes. The findings also tend to support the clinical reports and the findings of experiments that suggest that loading for more than 20 minutes should be practiced if adequate soft-tissue lengthening is to occur. Acknowledgments. I thank Dr. David Hollingsworth for his assistance with the statistical analysis and my thesis committee (Ms. Marjory Johnson, Mr. Phil Witt, and Dr. Barney LeVeau) for their review of the paper during various stages of its development. 496 PHYSICAL THERAPY

7 RESEARCH REFERENCES 1. Warren CG, Lehmann JF, Koblanski JN: Elongation of rat tail tendon: Effect of load and temperature. Arch Phys Med Rehabil 51: , Warren CG, Lehmann JF, Koblanski JN: Heat and Stretch procedures: An evaluation using rat tail tendon. Arch Phys Med Rehabil 57: , Griffiths PJ, Guth K, Kuhn HJ, et al: Cross bridge slippage in skinned frog muscle fibers. Biophys Struct Mech 7: , Flitney FW, Hirst DG: Cross-bridge detachment and sarcomere 'give' during stretch of active frog's muscle. J Physiol (Lond) 276: , Halar EM, Stolov WC, Venkatesh B, et al: Gastrocnemius muscle belly and tendon length in stroke patients and able bodied persons. Arch Phys Med Rehabil 59: , Williams PE, Goldspink G: Changes in sarcomere length and physiological properties in immobilized muscle. J Anat 127: , Tadieu C, Tabary JC, Tabary C, et al: Adaption of connective tissue length to immobilization in the lengthened and shortened positions in cat soleus muscle. J Physiol (Paris) 78: , Kottke FJ, Pauley DL, Dtak RA: The rationale for prolonged stretching for correction of shortening of connective tissue. Arch Phys Med Rehabil 47: , Sapega AA, Quedenfeld TC, Moyer RA, et al: Biophysical factors in range of motion exercise. Physician and Sportsmedicine 9:57-65, Tanigawa MC: Comparison of the hold-relax procedure and passive mobilization on increasing muscle length. Phys Ther 52: , Sady SP, Wortman M, Blanke D: Flexibility training: Ballistic, static or proprioceptive neuromuscular facilitation? Arch Phys Med Rehabil 63: , Hartley-O'Brien SJ: Six mobilization exercises for active range of hip flexion. Res Q Exerc Sport 51: , Moore MA, Hutton RS: Electromyographic investigation of muscle stretching techniques. Med Sci Sports Exerc 12: , Halkovich LR, Personius WJ, Clamann HR, et al: Effect of Fluorimethane spray on passive hip flexion. Phys Ther 61: , Medeiros JM, Smidt GL, Burmeister LF, et al: The influence of isometric exercise and passive stretch on hip joint motion. Phys Ther 57: , Bohannon RW: Cinematographic analysis of the passive straight-leg-raising test for hamstring muscle length. Phys Ther 62: , Mundale MD, Hislop HJ, Rabideau RJ, et al: Evaluation of extension of the hip. Arch Phys Med Rehabil 37:75-80, Dempster WT, cited in LeVeau BF (ed): William and Lissner Biomechanics of Human Motion. Philadephia, PA, WB Saunders Co, 1977, pp Braune W, Fischer U, cited in LeVeau BF (ed): William and Lissner Biomechanics of Human Motion. Philadelphia, PA, WB Saunders Co, 1977, p Winer BJ: Statistical Principles in Experimental Analysis. New York, NY, McGraw-Hill Inc, 1971, pp BMDP Statistical Software, ed Berkley, CA, University of California Press, Ekstrand J, Wiktorsson M, Oberg B: Lower extremity goniometric measurements: A study to determine their reliability. Arch Phys Med Rehabil 63: , 1982 Volume 64 / Number 4, April