TECHNICAL NOTE
TECHNICAL REPORT: RELIABILITY AND VALIDITY THE iSAM 9000 ISOKINETIC DYNAMOMETER JULIA C. ORRI1
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GIBSON F. DARDEN2
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Department of Exercise and Sport Science, University of San Francisco, San Francisco, California; 2Department of Health, Physical Education, and Recreation, Coastal Carolina University, Conway, South Carolina
ABSTRACT This study assessed the mechanical reliability and validity of the INRTEK iSAM 9000 isokinetic dynamometer, and compared the obtained torque values of the prototype device with those from a traditional device. Sixty volunteers (40 men and 20 women) were tested at 60° per second for shoulder, knee, and trunk flexion, and extension on both the Cybex 6000 and a new isokinetic dynamometer (iSAM 9000). Intraclass correlation coefficients (ICC) and standard errors of measurement (SEM) revealed a high level of reproducibility and precision in the device’s torque measurements (ICC range = 0.94–0.98; SEM range = 5.2–29.7). Pearson r values revealed very high relationships between the two instruments (set 1: r = 0.84– 0.93; set 2: r = 0.87–0.93; P , 0.05). Significantly higher peak torque for both sets of left and right knee flexion and extension, right shoulder extension and trunk extension was found for the iSAM 9000 compared to the Cybex 6000 (P , 0.05). The strong ICCs and small SEMs support the device’s mechanical reliability and validity. The high correlation coefficients between the prototype dynamometer and the Cybex 6000 support the new device’s validity in the measurement of isokinetic torque. The findings of this study will be used to refine the next generation of the INRTEK isokinetic device with respect to test protocols and the reliability of measuring human muscle performance.
KEY WORDS muscular strength, peak torque, angular velocity, industry, Cybex
INTRODUCTION
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sokinetic dynamometry is a well-accepted method to assess human muscle performance in both clinical and research environments (8,10). Isokinetic strength is the force generated by a muscle at a constant rate of movement, and isokinetic dynamometers provide constant velocity with accommodating resistance throughout a joint’s
ROM. With the combination of isokinetic dynamometers and computer technology, objective measures of muscle function on variables related to torque, power, and endurance can be obtained. These measures are then interpreted as a measure of muscle performance (e.g., average and peak torque, power, endurance, etc.) and can form the basis of preseason screening, identifying injury potential, and setting goals for rehabilitation. Establishing the mechanical reliability and validity of a prototype device is the first step in ensuring the accurate assessment of human muscle performance. The preset angular velocity of the device must be accurate, and the device must measure the torque it is intending to be measuring. Once the device is determined to be mechanically accurate, it is then useful to examine the validity of the device by comparing it to a commercially produced isokinetic dynamometer known to accurately and reliably measure human muscle performance. The importance of establishing the reliability and validity (mechanical and human) of isokinetic dynamometry is demonstrated by multiple reports in the scientific literature (2,3,5,6,15). Recently, there has been a declining market for isokinetic manufacturing and testing based on changes in the health care and insurance industries as well as the expense of equipment (7). In addition, other factors include the space involved with measuring only one joint at a time with separate dynamometers, the relatively time consuming nature of isokinetic testing, concerns relative to sport specificity (11), and the predictive value of isokinetic assessment (4,9). However, one company, INRTEK (Injury Reduction Technology, Inc. Myrtle Beach, SC) recently introduced a prototype isokinetic dynamometer (iSAM 9000) to measure muscle function (flexion and extension) of the shoulder, knee, and trunk in one self-contained unit. This study assessed the mechanical reliability and validity of the new isokinetic device and compared the torque values obtained by the new device with those from a commercially available isokinetic dynamometer, the Cybex 6000 (Cybex, Lumex, Ronkonkoma, NY).
Address correspondence to Julia C. Orri, jorri@usfca.edu.
METHODS
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Experimental Approach to the Problem
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Rationale for the Study. This research was the first of a series of studies to address the mechanical and human reliability of
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dynamometer, designed to test muscular strength using a concentric isokinetic mode of operation (Figure 1). The isokinetic nature of the machine can be confirmed with velocity curve data, plotted using the device position sensor and time (via the computer clock). A certified tachometer was used to measure the speed of the gearbox shaft, and the motor drive frequency was adjusted until 10 RPMs were obtained. The device allows for accommodating resistance, requiring maximal effort exertion, in which subject effort is matched with equal resistance. As a result, the limb moves at a constant speed throughout the full range of motion, which is a unique component of isokinetic assessment (14). Greater effort, and therefore, muscle performance, is accompanied by higher torque curves at a constant velocity (14).
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The position sensor (for movement angle) and load cells (for force) send a voltage to the hardware; this voltage is related to a specific position or force based on calibration plots. Device speed is ultimately controlled by the variable frequency drive (the motor drive), which turns a customdesigned worm gearbox. The gearbox allows the output shaft to turn in either direction up to the speed of the input shaft that is turned by the motor. A unique application of a worm gearbox is used; it has an anti-backdrive feature that does not allow the shaft to turn faster than the set speed (14). Procedures. This study determined the mechanical validity
and reliability of the iSAM 9000. Then, peak torque values (Nm) were compared between the iSAM 9000 and Cybex 6000 for the knee, shoulder, and trunk at 60° per second from two sets of data. By design, this was the only testable speed possible on the iSAM9000 due to the large volume of subjects who were tested annually and the need to produce a cost-effective machine. An additional purpose was to measure the consistency of scores between sets 1 and 2 for the iSAM 9000. Subjects
Forty men and 20 women volunteered for this study. Their mean 6 SD age, body mass, and height were 43.5 6 11.0 yr, 80.5 6 15.8 kg, 174.7 6 9.5 cm, respectively. All subjects completed a health and physical activity questionnaire and were free of musculoskeletal, cardiovascular, and neuromuscular conditions that are contraindications for an isokinetic evaluation. Participants gave written informed consent and the experimental procedures were approved by the Institutional Review Board (IRB) at Coastal Carolina University. Procedures
Figure 1. iSAM9000.
To determine the mechanical reliability of the iSAM 9000, 3 sets of drop tests were performed. Each set consisted of 7 drops of 4.5 kg through 31.8 kg (4.5, 9.1, 13.6, 18.2, 22.7, 27.3, and 31.8 kg) of mass on both the right and left lever arms. One set was done before calibration and 2 sets were performed after calibration. For the drop tests, each mass was placed on the lever arm and the arm was permitted to drop through the range of motion while the computer recorded the measured torque and unfiltered mass. These values were obtained for the 3 sets and entered into an Excel spreadsheet for calculation of the reliability coefficients. The subjects meeting testing criteria received written descriptions of the instrument and how it works (isokinetics, accommodating resistance, maximal effort, general test protocol, etc.) prior to testing. Each participant was asked to report to the testing facility on two separate occasions. Subjects were advised to eat a light meal 2–3 hours prior to testing, avoid heavy exercise the day of testing, and to wear comfortable clothing. Body mass and height were measured at the testing facility. Subjects then reported to the Cybex 6000 or the iSAM 9000 station, depending on their randomly predetermined testing VOLUME 22 | NUMBER 1 | JANUARY 2008 |
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New Isokinetic Strength Testing Device order. Each dynamometer was calibrated prior to the testing day, but no gravity corrections were performed on either device. Verbal instructions and explanation of how the device worked were also given to the subjects before and throughout the test process. Straps were used to stabilize the hips, upper body and legs. The subjects held onto the side stabilization handles during the knee test on both dynamometers. Once the subject was set up for each test, they were given at least 3 familiarization, or warm-up, repetitions consisting of graded effort, including submaximal and maximal effort repetitions. After 15 sec of rest, they performed 5 maximal test repetitions at 60° per second through a full ROM. Subjects were instructed to push and pull as hard as they could against the device throughout the full ROM. Verbal encouragement (‘‘push, pull’’) was consistent for both devices. A second set was performed after a 60 second rest period. The testing order was as follows: right knee, left knee (Figure 2), left shoulder, right shoulder (Figure 3), and trunk (Figure 4). On the iSAM 9000 shoulder test, the subject began with their hand at side hip level prior to flexing;140–150°, while the starting position for the trunk test required the subject to stand straight and subsequently bend at the waist to about 90° of
Figure 2. Knee test.
Figure 3. Shoulder test.
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Figure 4. Back test.
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during flexion and extension of the knee, shoulder, and trunk for men and women combined. Correlations were very high for each set (set 1: r = 0.84–0.93; set 2: r = 0.87–0.93), representing 71–86% of the variance between the 2 devices (P , 0.05). When the data for men and women were analyzed separately, the correlations remained very high for the men for all exercises (r = 0.83–0.93). For the women, all correlations were significant with the exception of right and left shoulder flexion and left shoulder extension (P . 0.05) (Table 4). The data for mean peak torque (Nm) for Cybex 6000 and iSAM 9000 are presented in Table 5. All subjects obtained significantly higher peak torque values during the second set, regardless of device, except for right and left shoulder extension, right knee extension (Cybex), and trunk flexion
For the tests performed on the Cybex 6000, hard copies of the force curve graphs and numeric peak torque (single best) were printed out. If a subject had a ‘‘false start’’ due to device sensitivity, the repetition data were omitted. Peak torque data (not compared to body weight) were entered into a master spreadsheet (Microsoft Excel). On the iSAM 9000 tests, the peak torque data were printed out and visually inspected for accuracy and true effort. Obvious ‘‘impact artifacts’’ were adjusted by using the highest ‘‘true’’ peak torque. The artifact was readily identifiable by the immediate vertical spike, with no sustained torque. TABLE 1. Mechanical reliability and validity for tests 1 and 2 (iSAM). Reliability was determined using intraclass correlation coTest 1 efficients (ICC). The standard error of measurement (SEM) Mass ea Mass total Arm length Calc torque (kg) (kg) (m) (Nm) was calculated for each ICC. The Pearson product moment Right arm correlation coefficient (r), was 4.6 4.6 0.71 32.1 calculated to determine the rela4.5 9.1 0.71 63.6 tionship between the peak tor4.6 13.8 0.71 95.9 4.6 18.4 0.71 128.2 que measurements obtained by 4.6 23.1 0.71 160.5 the iSAM 9000, and the Cybex 4.5 27.6 0.71 192.0 6000. Independent Student 4.6 32.2 0.71 224.2 t-tests were performed to deterLeft arm mine mean peak torque differ4.6 4.6 0.71 32.1 4.5 9.1 0.71 63.6 ences between the two devices. 4.6 13.8 0.71 95.9 A priori statistical power was 0.8. 4.6 18.4 0.71 128.2 All data were analyzed using 4.6 23.1 0.71 160.5 SPSS v. 8.0 (Chicago, IL). A 0.05 4.5 27.6 0.71 192.0 level of significance was set and 4.6 32.2 0.71 224.2 all data are presented as mean 6 Test 2 SD unless noted.
RESULTS Table 1 shows the mechanical reliability and validity for tests 1 and 2 for the iSAM. Table 2 shows the reliability correlation coefficients and ICC’s for the comparisons between sets 1 and 2 on the iSAM 9000. Both the ICCs and Pearson r’s were very high (r = 0.94–0.98) (P , 0.05). Table 3 shows the results of the Pearson product moment correlations for Cybex 6000 and iSAM 9000 peak torques
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Measured torque (Nm) 32.3 65.2 99.2 131.1 165.3 192.8 225.7 31.6 64.9 100.5 131.5 164.5 197.8 229.5
Right arm 4.6 4.5 4.6 4.6 4.6 4.5 4.6
4.6 9.1 13.8 18.4 23.1 27.6 32.2
0.71 0.71 0.71 0.71 0.71 0.71 0.71
32.1 63.6 95.9 128.2 160.5 192.0 224.2
32.3 66.6 100.9 132.5 166.2 198.1 222.5
4.6 4.5 4.6 4.6 4.6 4.5 4.6
4.6 9.1 13.8 18.4 23.1 27.6 32.2
0.71 0.71 0.71 0.71 0.71 0.71 0.71
32.1 63.6 95.9 128.2 160.5 192.0 224.2
31.6 65.6 100.1 131.8 164.3 199.3 229.5
Left arm
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TABLE 2. Reliability (intraclass coefficients) for sets 1 and 2 (iSAM). Test
ICC
SEM 1
SEM 2
Right knee flexion Right knee extension Left knee flexion Left knee extension Right shoulder flexion Right shoulder extension Left shoulder flexion Left shoulder extension Trunk flexion Trunk extension
0.94 0.96 0.95 0.95 0.94 0.98 0.95 0.94 0.96 0.94
11.12 14.48 12.27 15.03 6.34 5.79 5.16 9.17 17.69 29.72
10.99 13.92 12.63 14.75 6.27 5.87 5.19 8.93 18.35 29.09
difference in right versus left-side comparisons on the Cybex 6000 was found for shoulder extension set 1 (62.9 6 20.9 ft-lb vs 60.0 6 19.3 ft-lb) (P , 0.05). For the iSAM 9000, significant differences were found between the right and left knee and shoulder for all paired comparisons (P , 0.05).
DISCUSSION
The primary findings of the paper were that the prototype isokinetic dynamometer is a mechanically valid and reliable instrument in measuring torque at an angular velocity of 60 degrees per second. Additionally, the torque values obtained by the iSAM 9000 were in reasonably good agreement with the Cybex 6000 isokinetic dynamometer. The very high correlation coefficients for validity (r = 0.84–0.93) and ICC = intraclass correlation; SEM = standard error of reliability (r = 0.94–0.98) suggest that both devices are measurement from sets 1 and 2. comparable at a testing velocity of 60° per second. However, lower correlations were found between the machines for women during the shoulder flexion and extension exercises. In the direct comparisons between the two devices, the iSAM 9000 gave significantly higher peak torque values for all (iSAM 9000) (P , 0.05). For direct device comparisons, the measurements except left shoulder flexion and extension and iSAM 9000 obtained significantly higher peak torque values trunk flexion, compared to the Cybex 6000. These differences compared to the Cybex 6000 for both sets of left and right were found despite similar ROM between the devices and knee flexion and extension, right shoulder extension and lack of gravity correction procedure on either device prior to trunk extension (P , 0.05). Both men and women had higher testing. To help keep ROM consistent at the extremes of values on the iSAM 9000 compared to the Cybex 6000 for flexion and extension, the seat was lowered on the iSAM 9000 the same exercises. The Cybex 6000 obtained higher peak during the shoulder test. The higher peak torque on the iSAM torque values for trunk flexion, compared to the iSAM 9000 9000 may be explained by the stabilization protocol used (P , 0.05). on this device. During the testing on Cybex 6000, a crossThe right and left side comparisons for knee and shoulder strapping procedure was used to stabilize the upper body, flexion and extension on the Cybex 6000 and iSAM 9000 are which due to design, was not available on the iSAM 9000. presented in Tables 6 and 7, respectively. The only significant As a result, the subjects’ use of their upper body during the knee and shoulder measurements could have potentially TABLE 3. Pearson product moment correlations for Cybex 6000 peak torque and accounted for the increase in iSAM peak torque (60° per second) (sets 1 and 2). peak torque values seen on the Right Left iSAM 9000 and points to the importance of consistent stanTest Set 1 Set 2 Set 1 Set 2 dardization of stabilization procedures during isokinetic r r2 r r2 r r2 Knee r r2 assessment. This was especially Flexion 0.89* 0.79 0.92* 0.85 0.92* 0.85 0.91* 0.83 evident during the shoulder Extension 0.89* 0.79 0.89* 0.79 0.93* 0.86 0.93* 0.86 extension testing. The inability Shoulder to stabilize the subjects adeFlexion 0.83* 0.69 0.83* 0.69 0.86* 0.74 0.90* 0.81 Extension 0.93* 0.86 0.90* 0.81 0.90* 0.81 0.87* 0.76 quately may have helped contribute to the higher torque Trunk Set 1 Set 2 values obtained on the iSAM 9000. The significantly higher Flexion .89* .79 .87* .76 Extension .84* .71 .87* .76 values obtained during set 2 of most tests on both devices *Significant correlation between iSAM 9000 and Cybex 6000 (P , 0.05). could be explained by a learning N = 60. effect with the testing procedure and device. This was
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not the case for the mechanical measurement of torque. These TABLE 4. Separate Pearson product moment correlations for Cybex 6000 peak differences were not observed on torque and iSAM peak torque for men and women (60° per second) (sets 1 and 2). the Cybex 6000. Although 83% of the subjects were right-hand Right Left dominant, it is unclear why all of Test Set 1 Set 2 Set 1 Set 2 the iSAM 9000 torque values were lower for the left side, while Right knee M F M F M F M F a similar finding did not hold true for the Cybex 6000. Testing Flexion 0.89* 0.80* 0.92* 0.83* 0.92* 0.77* 0.91* 0.78* Extension 0.89* 0.69* 0.89* 0.73* 0.93* 0.70* 0.93* 0.80* position, data processing, subject Right shoulder fatigue, and specific device dyFlexion 0.83* 0.37 0.83* 0.47* 0.86* 0.44 0.90* 0.60* namics may help explain the Extension 0.93* 0.45* 0.90* 0.57* 0.90* 0.13 0.87* 0.46* discrepancies (13). Other issues Trunk Set 1 Set 2 such as inconsistent verbal cues and subject stabilization may Flexion 0.89* 0.68* 0.87* 0.62* help explain the bilateral differExtension 0.84* 0.78* 0.87* 0.73* ences. Since bilateral imbalances *Significant correlation between iSAM 9000 and Cybex 6000 (P , 0.05). can potentially lead to injury M = male (n = 40), F = female (n = 20). (12), it is important for any isokinetic dynamometer to correctly identify and measure weaker muscle groups. Whether especially true for women during shoulder flexion and the iSAM 9000 exhibits augmented sensitivity in determining extension; nonsignificant differences between the machines bilateral differences over the Cybex 6000, is unclear. were found for set one only. This could also be explained by The validation of a new isokinetic device that is relatively the smaller sample of female subjects. cost and space efficient is promising. Although it was the The bilateral differences observed on the iSAM 9000 tests intention of the company to validate an assessment protocol were surprising. The peak torque values were consistently and that could be achieved in the shortest time possible, some significantly lower for the left side on all tests, although this was concerns that may be addressed in the next generation of the iSAM devices include the ability to reliably measure human muscle performance over a broad range of subjects and TABLE 5. Mean (6SD) peak torque values (Nm) for Cybex 6000 and iSAM. speeds. Specifically, the results of this study can only be genTest Cybex (set 1) Cybex (set 2) iSAM(set 1) iSAM (set 2) eralized to an angular velocity Right knee of 60° per second, which is slow Flexion 109.5 6 29.7 112.6 6 29.5§ 127.9 6 35.6* 136.4 6 35.2†§ compared to typical athletic Extension 160.6 6 45.7 164.4 6 47.0 203.9 6 49.9* 209.2 6 48.0†§ movements seen in throwing Left knee and kicking. Although isokiFlexion 108.1 6 31.3 114.1 6 32.2§ 119.9 6 34.6* 126.7 6 35.6†§ Extension 161.5 6 48.4 165.7 6 48.6§ 196.1 6 48.6* 201.4 6 47.7†§ netic testing speeds are not Right shoulder going to completely replicate Flexion 56.1 6 17.2 57.7 6 18.0§ 57.6 6 18.0 61.1 6 17.8§ those found in sports (14), most Extension 85.8 6 28.3 82.1 6 31.4 89.8 6 29.1* 90.2 6 29.5† studies involving athletes utiLeft shoulder lize faster speeds than 60° per Flexion 55.0 6 16.4 57.5 6 16.1§ 53.7 6 17.2 56.8 6 17.3§ Extension 81.3 6 26.2 81.0 6 26.3 81.2 6 27.1 83.5 6 26.4 second. Wilk et al. (16) found Trunk significant differences at 180° Flexion 234.0 6 75.2* 241.7 6 79.3‡§ 218.3 6 61.7 221.5 6 64.0 per second for the external Extension 214.2 6 85.8 232.2 6 93.2§ 246.7 6 89.3* 259.5 6 87.4†§ rotators of professional baseball *Significantly higher peak torque for iSAM 9000 vs. Cybex 6000 (P , 0.05) (set 1). pitchers and suggested that †Significantly higher peak torque for iSAM 9000 vs. Cybex 6000 (P , 0.05) (set 2). data from this test speed be ‡Significantly higher peak torque for Cybex 6000 vs. iSAM 9000 (P , 0.05) (set 2). included in a ‘‘muscle perfor§Significantly higher peak torque for set 2 compared to set 1 (intra-machine) (P , 0.05). mance profile.’’ Moreover, test speeds of 450° per second have VOLUME 22 | NUMBER 1 | JANUARY 2008 |
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TABLE 6. Cybex 6000 peak torque (Nm) bilateral comparisons. Test
Set 1
Knee extension Right 160.6 6 45.7 Left 161.1 6 48.6 Knee flexion Right 109.6 6 29.7 Left 107.9 6 31.4 Shoulder extension Right 85.2 6 28.3* Left 81.3 6 26.2 Shoulder flexion Right 56.0 6 17.3 Left 55.0 6 16.5
Set 2 164.6 6 47.3 165.3 6 48.8 113.4 6 29.8 113.8 6 33.1 82.7 6 27.4 80.4 6 26.8 58.1 6 17.9 56.8 6 16.3
90.1 6 29.8* 83.5 6 26.4 61.1 6 17.9* 56.8 6 17.3
ACKNOWLEDGMENTS
also been advocated for the testing of intercollegiate pitchers (11). Finally, in the rehabilitation setting, higher testing speeds allow the patient to simulate faster joint actions than typically possible from standard exercise devices (1). The application of isokinetic testing in the athletic environment also depends largely on joint and movement specificity. For example, both the iSAM 9000 and Cybex 6000 test pure shoulder flexion and extension in the sagittal plane. Since typical athletic actions involving the shoulder such as throwing require additional torque generated by the internal and external rotators, devices measuring only flexion and extension may only partially identify underlying strengths and weaknesses in the joint. Since using the combination of
TABLE 7. iSAM peak torque (Nm) bilateral comparisons. Set 1
Knee extension Right 204.7 6 49.9* Left 196.0 6 48.6 Knee flexion Right 128.3 6 35.8* Left 119.9 6 34.6 Shoulder extension Right 89.8 6 29.4* Left 81.2 6 27.1 Shoulder flexion Right 57.6 6 18.2* Left 53.7 6 17.2
Set 2 209.6 6 48.2* 201.4 6 47.7 136.7 6 35.5* 126.7 6 35.6
*Significant difference in peak torque between right and left side for each set (P , 0.05).
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PRACTICAL APPLICATIONS The iSAM 9000 allows for accurate and consistent measurement of isokinetic strength in the rehabilitation or athletic setting. In the practical sense, this device will obtain muscle performance measurements comparable to traditional isokinetic devices like the Cybex 6000. This device is contained in one piece and allows the subject to sit upright for the shoulder flexion/extension test. The high reliability values that we report may question the need for performing a second set during testing, which would expedite the testing process. With the reevaluation of the stabilization procedure used during the shoulder testing, less extraneous muscle group involvement may be possible, further enhancing the machine’s effectiveness. In addition, the company has made several steps to expand the capabilities for testing shorter, taller, and heavyset frames (approx. 4#10$ to 6#8$, weighing between 90–360 lbs). A platform will be used, as well as two shorter testing arms for the back adapter to allow proper alignment of shorter heights during back testing. Two lengths of adapters are now available to allow for the shortest and longest arm lengths during shoulder testing. Extender straps are available for wide girths and can be used to lengthen the hip, shoulder, and thigh straps. In conclusion, the results of this study indicate that the iSAM 9000 is a valid and reliable device. The validation of a new isokinetic device that is relatively cost and space efficient is promising. It was the intention of the company to validate an isokinetic assessment protocol that could be achieved in the shortest time possible. The application of and potential for the iSAM 9000 to measure human muscle performance in a broad spectrum of subjects, including testing an increased number of female subjects warrant additional research. Measurement and test protocol issues addressed in this study will need to be addressed in the next generation of this device.
*Significant difference in peak torque between right and left side for each set (P , 0.05).
Test
strength in multiple planes of movement is a valuable index for predicting injury potential and readiness for return to the industrial or athletic settings, additional research is warranted in this regard. The results point to important implications for isokinetic test protocols. Relevant protocol issues include body stabilization, the use of consistent verbal (or omitted) encouragement, warm-up repetitions, the use of single peak versus average of peak torque measures, and the use of 1 or 2 sets (given the high reliability coefficients between sets 1 and 2). The refinement of test protocols could be addressed for the next generation of the iSAM device and likely enhance the instrument’s effectiveness in its target setting.
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We would like to thank INRTEK and McGuckin and Pyle for their commitment to this study. We would also wish to thank Dave Perrin, Ph.D. and Bruce Gansneder, Ph.D. for their valuable contributions in the preparation of this manuscript.
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Finally, we would like to thank Sue Geesey-Jean for her technical assistance.
7. Greenblatt, D, Diesel, W, and Noakes, TM. Clinical assessment of the low-cost VariCom isokinetic knee exerciser. Med Eng Phys 19: 273–278, 1997.
DISCLOSURES
8. Gulch, RW. Force-velocity relations in human skeletal muscle. Int J Sports Med 15: S2–S10, 1994.
The iSAM dynamometer used for this investigation was donated to the Smith Exercise Science Laboratory at Coastal Carolina University. The authors have no commercial or proprietary interest in this device. The results of the present study do not constitute endorsement of the product by the authors or the NSCA.
9. Mostardi, RA, Noe, DA, Kovacik, MW, and Porterfield, JA. Isokinetic lifting strength and occupational injury. Spine 17: 189–193, 1992. 10. Newman, MA, Tarpenning, KM, and Marino, FE. Relationships between isokinetic knee strength, single-sprint performance, and repeated-sprint ability in football players. J Strength Cond Res 18: 867–872, 2004.
1. Almekinders, LC and Oman, J. Isokinetic muscle testing: is it clinically useful? J Am Acad Orthop Surg 2: 221–225, 1994.
11. Newsham, KR, Keith, CS, Saunders, JE, and Goffinett, AS. Isokinetic profile of baseball pitchers’ internal/external rotation 180, 300, 450 degrees s21. Med Sci Sports Exerc 30: 1489–1495, 1998.
2. Bandy, WD and McLaughlin, S. Intramachine and intermachine reliability for selected dynamic muscle performance tests. J Orthop Sports Phys Ther 18: 609–613, 1993.
12. Niemuth, PE, Johnson, RJ, Myers, MJ, and Thieman, TJ. Hip muscle weakness and overuse injuries in recreational runners. Clin J Sport Med 15: 14–21, 2005.
3. Drouin, JM, Valovich-McLeod, TC, Schultz, SJ, Gansneder, BM, and Perrin, DH. Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity, torque, and position measurements. Eur J Appl Physiol 91: 22–29, 2004.
13. Noffal, GJ. Isokinetic eccentric-to-concentric strength ratios of the shoulder rotator muscles in throwers and nonthrowers. Am J Sports Med 31: 537–541, 2003.
REFERENCES
4. Dueker, JA, Ritchie, SM, Knox, TJ, and Rose, SJ. Isokinetic trunk testing and employment. J Occup Med 36: 42–48, 1994. 5. Farrell, M and Richards, JG. Analysis of the reliability and validity of the kinetic communicator exercise device. Med Sci Sports Exerc 18: 44–49, 1986. 6. Feiring, DC, Ellenbecker, TS, and Derscheid, GL. Test-retest reliability of the Biodex isokinetic dynamometer. J Orthop Sports Phys Ther 11: 298–300, 1990.
14. Perrin, DH. Isokinetic exercise and assessment. Champaign, IL: Human Kinetics. 1993. 15. Taylor, NAS, Saunders, RH, Howick, EI, and Stanley, SN. Static and dynamic assessment of the Biodex dynamometer. Eur J Appl Physiol 62: 180–188, 1991. 16. Wilk, KE, Andrews, JR, Arrigo, CA, Keirns, MA, and Erber, DJ. The strength characteristics of internal and external rotator muscles in professional baseball pitchers. Am J Sports Med 21: 61–66, 1993.
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