Reproducibility for isometric and isokinetic maximum knee ... - IOS Press

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Isokinetics and Exercise Science 20 (2012) 149–153 DOI 10.3233/IES-2012-0451 IOS Press

Reproducibility for isometric and isokinetic maximum knee flexion and extension measurements using the IsoMed 2000-dynamometer Johannes Dirnberger∗ , Hans-Peter Wiesinger, Alexander Kösters and Erich Müller Department of Sport Science and Kinesiology, Christian Doppler Laboratory, University of Salzburg, Hallein-Salzburg, Austria

Abstract. The present study was conducted to evaluate the relative and absolute reproducibility of the IsoMed 2000-dynamometer in measuring Peak Torque (PT) during maximum isometric and isokinetic (60 and 120◦ /s) knee flexion and extension. Thirty four physically active male subjects (mean age: 23.2 years) were measured in three sessions (T1–T3), 48–72 h apart. Repeated measures analysis of variance (ANOVA) with Bonferroni post hoc adjustments revealed significant systematic errors for isokinetic flexion measurements with mean values on the second and third visit being around 3–5% higher than the corresponding values obtained in the first visit. Intraclass correlation coefficients (ICC 2,1) of 0.90–0.98 and 0.94–0.98 combined with values of standard error of measurement (SEM) of 5.5–9.1 and 4.0–9.0 Nm were found for T1–T2 and T2–T3, respectively. Based on the systematic errors found for flexor measurements and a clear improvement in reproducibility parameters from T1–T2 to T2–T3 for nearly all measurements, we recommend the use of a familiarisation session prior to actual testing. Keywords: Reproducibility, isometric and isokinetic maximum strength testing, knee flexion and extension, IsoMed 2000dynamometer

1. Introduction Since the introduction of the concept in the 1960’s isokinetic dynamometry has become a well-accepted method and benchmark for assessing human muscle function [1]. The clinical applicability of this method derives to a significant extent from the acceptable reproducibility of the obtained strength scores. Past research into the issue of reproducibility focused on the use of different instruments and the testing of knee muscles in physically active adult subjects. Different isokinetic devices such as the Biodex [2–6], Cybex [3,7–11], KinCom [12–17] or Lido were used. ∗ Address for correspondence: Johannes Dirnberger, Department of Sport Science and Kinesiology, University of Salzburg, 49 Rifer Schlossallee, Hallein-Salzburg, 5020, Austria. Tel.: +43 0 660 549 4195; Fax: +43 0 662 6389 4881; E-mail: johannes.dirnberger@sbg. ac.at.

Generally, the results of these studies indicate good to excellent intraclass correlation coefficients (ICC) above 0.80 (relative reproducibility) and SEM values and coefficient of variation (CV) below 10% (absolute reproducibility). However, some of these dynamometers are no longer commercially available while other are constantly upgraded. There are also new isokinetic devices such as the IsoMed 2000. Even though several scientific studies have used the latter to assess maximum knee muscle performance [20–22] there is only one study relating to its reproducibility. This study has reported excellent relative reproducibility (ICC > 0.90) and acceptable measures of absolute reproducibility (SEM < 20 Nm) for measuring the PT during maximum discrete concentric and eccentric knee extension of physically active young men. However, reproducibility results cannot be generalised and should be regarded as specific to the device, protocol, and subject group used for testing.

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J. Dirnberger et al. / Reproducibility for isometric and isokinetic maximum knee flexion and extension measurements

The specific aim of the present study, which ties in with the study mentioned above [23], was therefore to examine the reproducibility of the IsoMed 2000 in measuring PT during isometric and reciprocal concentric isokinetic knee flexion and extension. The testing protocol that has been selected for evaluation is an integral component of the standard performance diagnosis currently administered for athletes of the Austri¨ an Football Association (OFB) at the Olympic Center Salzburg-Rif. 2. Method 2.1. Subjects The sample consisted of physically active healthy male college students (n = 34) ranging in age from 18 to 30 years (mean ± SD, age: 23.2 ± 2.9 years, height: 179.5 ± 6.6 cm, weight: 75.9 ± 7.0 kg) with no previous experience in isokinetic exercise or prior history of orthopaedic knee pathology. Subjects were asked to maintain their regular physical activity levels during the study period without carrying out weight training of their lower extremities. The research protocol complied with the Declaration of Helsinki and was approved by the local Research Ethics Board (Department of Sport Science and Kinesiology, University of Salzburg). All subjects signed a written statement of informed consent before participating in the study. 2.2. Instruments An IsoMed 2000-dynamometer (D&R Ferstl GmbH, Hemau, Germany) combined with the manufacturer’s unilateral knee attachment was used for all tests. Immediately before each session, the device was calibrated according to the manufacturer’s specifications. For all post test data acquisition, the manufacturer’s computer software IsoMed analyze V.1.0.5 was utilized. 2.3. Testing Subjects participated in three identical sessions, 48– 72 h apart. In an attempt to reduce possible effects of diurnal influences and inter-tester variability, sessions were conducted during the same time of the day (± 1 h) and by the same examiner. Prior to testing, subjects accomplished 10 minutes of cycling on a stationary Kettler ergorace ergometer (Heinz Kettler GmbH and Co. KG, Ense-Parsit, Ger-

many) at a sub-maximal intensity of 1.5 W/kgBW and a pedal rate of 70 rpm. Following this general warm-up period, subjects were positioned on the IsoMed 2000dynamometer chair with the hip joint at about 75◦ (0◦ = full extension) and the popliteal fossa of tested leg ending up with the frontal edge of the seat. Stabilisation was achieved by adjustable straps and pads secured at the shoulders, chest, hip, and right femur and by instructing subjects to grip the side handles situated right lateral to the hip. The lateral femoral epicondyle was used as a bony landmark for matching the knee’s anatomical axis of rotation with the mechanical axis of the dynamometer. By means of a strap, the distal shin pad of the dynamometer lever arm was attached approximately 2–3 cm superior to the lateral malleolus at a position of 90◦ knee flexion. After fixation, the weight of the tested leg resting in a relaxed state at terminal extension was measured and gravity adjustment was made using the integrated software. In order to minimize possible force oscillation, a threshold force requirement of 50 N was chosen. To ensure similar conditions on each of the testing sessions, individual settings were recorded and saved by the integrated IsoMed 2000 software. Isometric and isokinetic (60 and 120◦ /s) maximum strength of the right knee flexor and extensor muscle group were tested with a rest period of two minutes between single tests. The order of testing was random for each subject and maintained the same for all sessions. For isometric flexion and extension measurements, the knee joint was fixed at 85 and 95◦ , respectively. As we had observed a change in the knee angle of about 5◦ in past tests during maximum effort due to deformation of the calf (flexion) and shin pad (extension), we estimated these settings appropriate to represent an actual knee angle of about 90◦ during contraction. Prior to testing, subjects performed two sub-maximal practice trials as a specific warm-up and to get acquainted with the requirements of the test. Between warm-up and testing, there was a rest period of 1 minute, in which subjects were asked to develop their maximum force rapidly and then to resist for about 3 seconds in the subsequent test. Each test consisted of 3 maximum repetitions separated by 1 minute. Isokinetic measurements were taken at two angular velocities: 60 and 120◦/s. Range of motion (ROM) was set to reach from 10–90◦ with a fast acceleration setting at the beginning and a hard deceleration cushion at the end of the movement. Subjects were asked to perform 6 moderate and 2 sub-maximal practice trials prior to testing. The following rest period of 1 minute was used


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Table 1 Group means and standard deviations for single-session Peak Torque (Nm) measurements as well as main effect p-values for comparison of sessions T1

Mean ± SD T2

T3

Main effect p-value

ISO FLEX EXT

121.9 ± 28.5 235.7 ± 49.6

125.2 ± 31.0 236.5 ± 50.4

125.8 ± 31.0 238.5 ± 52.1

0.084 0.473

60◦ /s FLEX EXT

120.9 ± 26.1∗ 220.1 ± 42.4

126.9 ± 28.7 222.9 ± 42.1

125.8 ± 27.4 222.8 ± 42.5

0.003 0.259

120◦ /s FLEX EXT

109.1 ± 23.9∗ 195.5 ± 36.9

114.0 ± 24.9 198.0 ± 36.4

113.3 ± 25.7 195.9 ± 37.6

0.002 0.192

SD: standard deviation; T: testing session; PT: Peak Torque; ∗ : p < 0.05, significantly lower than sessions 2 and 3. ISO: isometric; FLEX: flexion; EXT: extension.

to instruct subjects to push (extension)/pull (flexion) as fast as possible throughout the entire range of motion in the subsequent test. Testing itself consisted of 5 reciprocal maximum flexion-extension cycles. Isometric and isokinetic testing was introduced by giving the verbal countdown “[. . . ] concentrate, 3–2– 1–go [. . . ]”. Additionally, strong verbal encouragement and visual online feedback were provided during testing to ensure maximum effort.

ferences and individual mean values with significant correlations indicating heteroscedasticity [4,9]. As all data turned out to be homoscedastic, absolute reproducibility was evaluated using the standard error of measurement (SEM) according to the formula SEM = SD × (1 − ICC) [13,14,25–27]. All statistics were performed using SPSS V.17.0 (SPSS Inc., Chicago, Illinois, USA) and Microsoft Excel 2003 (Microsoft Corp., Redmont, Washington, USA). Level of significance was set at α < 0.05.

2.4. Statistical analysis Gravity corrected PT (Nm), defined as the maximum torque value throughout repetitions for each movement type and velocity, was chosen as criterion measure of maximum strength performance. Descriptive statistics were used to calculate means and standard deviations for each testing session. Repeated measures analysis of variance (ANOVA) with Bonferroni post hoc adjustments were performed to determine whether there were any significant changes in group mean values between testing sessions (systematic errors). Further reproducibility calculations were conducted comparing consecutive pairs of sessions (T1–T2; T2– T3). Relative reproducibility was determined using the intraclass correlation coefficient (ICC 2,1). In line with the recommendations of Vincent [24], an ICC over 0.9 was considered as high, between 0.8 and 0.9 as moderate, and below 0.8 as low. The decision for choosing an adequate measure of absolute reproducibility was based on presence or absence of heteroscedasticity relating to the increase in the amount of random error as the measured values increase [25]. Heteroscedasticity was determined by examining the Pearson’s correlation coefficient (r) between individual absolute dif-

3. Results Significant systematic errors (all p < 0.05) were seen for isokinetic flexion measurements with mean values on the second and third sessions being around 3–5% higher than corresponding values on the preceding first visit (Table 1). Regarding relative and absolute reproducibility, overall high ICC values of 0.902–0.977 and 0.941– 0.975 (all p < 0.05) with corresponding measures of SEM of 5.5–9.1 and 4.0–9.0 Nm were found for T1–T2 and T2–T3, respectively (Table 2). All data turned out to be homoscedastic (all p > 0.05). However, T1–T2 comparison of isokinetic flexion and extension measurements at 60◦ /s showed a tendency to heteroscedasticity with Pearson’s correlation coefficients of 0.32 and 0.31 and corresponding p-values of 0.07 and 0.08, respectively. 4. Discussion The present study was conducted to evaluate reproducibility of findings retrieved from the IsoMed 2000-

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J. Dirnberger et al. / Reproducibility for isometric and isokinetic maximum knee flexion and extension measurements Table 2 Relative (ICC) and absolute (SEM) reproducibility statistics for test-retest comparison of Peak Torque (Nm) measurements ICC (2,1) T1–T2 T2–T3

95% CI T1–T2

T2–T3

SEM (Nm) T1–T2 T2–T3

ISO FLEX EXT

0.924 0.966

0.941 0.969

0.852–0.961 0.933–0.983

0.886–0.970 0.939–0.984

8.2 9.1

7.5 9.0

60◦ /s FLEX EXT

0.902 0.963

0.957 0.972

0.758–0.956 0.928–0.982

0.916–0.978 0.945–0.986

8.6 8.1

5.8 7.0

120◦ /s FLEX EXT

0.929 0.977

0.975 0.975

0.805–0.969 0.954–0.989

0.950–0.987 0.951–0.988

6.5 5.5

4.0 5.8

ICC: intraclass correlation coefficient; CI: confidence interval; SEM: standard error of measurement; T: testing session; ISO: isometric; FLEX: flexion; EXT: extension.

dynamometer in measuring PT during maximum isometric and isokinetic (60 and 120◦/s) knee flexion and extension of physically active adult men. Analyzed data revealed the following major observations: by trend significant (isometric) and significant (isokinetic) systematic errors were seen for flexion measurements with mean values of the second and third session being around 3–5% higher than corresponding measures of the first session. On the contrary, no significant change in mean values was observed for extension measurements. A similar pattern with stable results for isokinetic extension, but significant improvements for isokinetic flexion (+6–8%) from the first to the succeeding two testing sessions was also seen by Impelizzeri et al. [9]. Regarding reproducibility at T1–T2, for all measurements, even for isokinetic flexion measurements, excellent ICC values of 0.90–0.98 (relative reproducibility) combined with acceptable values of SEM ranging between 5.5 and 9.1 Nm (absolute reproducibility) were found. However, relative and absolute reproducibility for extension were clearly stronger compared to corresponding flexion measurements, with the exception of absolute reproducibility for isometric measurements. Comparison of reproducibility results of T1–T2 to corresponding results found at T2–T3 for most instances shows a clear improvement to ICC values of 0.95–0.98 and SEM values of 4.0–9.0 Nm. This especially was seen for flexion measurements. Only reproducibility for isokinetic extension at 120◦ /s, which had already shown a rather high level at T1–T2, experienced a slight decrease. Whereas relative reproducibility, similar to T1–T2, remained stronger for extension measurements, absolute reproducibility, in contrast to T1–T2, was consistently found to be slightly weaker for extension than for corresponding flexion measurements.

These observations indicate a practice based improvement during T1–T2, especially occurring with respect to flexion measurements. According to Impellizzeri et al. [9], this development could be due to biomechanical factors: the seated position does not respect the typical length-tension relationship of the hamstrings during daily activities like walking or running. Consequently, due to the unaccustomed length of the hamstring muscles, practice prior to testing would be needed to get subjects familiar to the testing protocol. Indeed, most of the subjects commented that they found it more difficult and unfamiliar to develop maximum force during flexion measurements on the first visit than on the succeeding visits. Additionally, solely during isometric flexion contractions on the first visit, some of the subjects actually suffered from short termed muscle cramps, so that single repetitions had to be repeated. As a consequence of these observations the use of a pre-test or familiarisation session to allow subjects to become acquainted to the testing protocol, particularly regarding flexion measurements, is recommended. Inconsistent results have been found in former studies regarding a comparison between reproducibility results for velocities. Brown et al. [2] determined reproducibility for measurements over a broad range of velocities ranging from 60 to 450◦ /s; No clear velocity-dependent dominance within flexion measurements could be found, whereas reproducibility results for extension measurements in most instances turned out to be slightly stronger for the slower velocities. Impellizzeri et al. [9] found stronger reproducibility results at 60 than at 120◦ /s for both flexion and extension. On the other hand, Kues et al. [15] determined reproducibility for extension measurements at velocities of 0–400◦/s and indicated an opposite trend with reproducibility becoming stronger with increasing veloci-


ties. Similar patterns were also seen by Li et al. [10], as well as Dirnberger et al. [23], for measurements at 60 and 120◦ /s. The current study supports the findings of Kues et al. [15], Li et al. [10], and Dirnberger et al. [23] with reproducibility in most instances being slightly stronger for the higher velocities. Reproducibility was slightly lower than at corresponding measures at 60◦ /s only in some of the isometric measurements at T1–T2. According to Li et al. [10], and Kues et al. [15], a reason for reproducibility getting stronger with increasing velocities could be due to the amount of time subjects had to perform maximum effort, which is less at higher velocities. Possibly, subjects were more likely to be consistent in effort and maintain maximum force throughout the contraction at the higher velocity.

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Acknowledgements The Authors would like to thank all subjects who volunteered to take part in the study. References [1] [2] [3]

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