intra- and intersession reliability in maximal and ...

Journal of Strength and Conditioning Research Publish Ahead of Print DOI: 10.1519/JSC.0000000000000321

INTRA- AND INTERSESSION RELIABILITY IN MAXIMAL AND EXPLOSIVE ISOMETRIC TORQUE PRODUCTION OF THE ELBOW FLEXORS Running head: Explosive Torque Production of the Elbow Flexors

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Olaf Prieske, Ditmar Wick, Urs Granacher

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Department of Training and Movement Sciences, University of Potsdam, Potsdam, Germany

Manuscript No.: JSCR-08-2994

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Revision No.: 3

Corresponding author:

Prof. Dr. Urs Granacher

Department of Training and Movement Sciences

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Am Neuen Palais 10, Haus 12 D-14469 Potsdam Phone: +49 331 977 1543 Fax: +49 331 977 1263

E-mail: [email protected]

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ABSTRACT The purpose of this study was to assess intra- and intersession reliability of maximal and explosive isometric torque production of the elbow flexors and its respective neuromuscular activation pattern. Subjects (13 men, age 24.8 ± 3.1 years, height 1.9 ± 0.1 m, body mass 83.7 ± 12.7 kg and 5

6 women, 26.5 ± 1.4 years, 1.7 ± 0.1 m, 62.7 ± 7.0 kg) were tested and retested 2-7 days later

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performing unilateral maximal isometric elbow flexions. Absolute (coefficient of variation [CV], test-retest-variability [TRV], Bland-Altman plots with 95% limits of agreement) and relative

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reliability statistics (intraclass-correlation coefficient [ICC]) were calculated for various mechanical (i.e., maximal isometric torque, rate of torque development, impulse) and electromyographical 10

measures (i.e., mean average voltage) at different time intervals relative to onset of torque (i.e., 30, 50, 100, 200, 300, 400, 100-200 ms). ICC values were ≥0.61 for all mechanical and

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electromyographical measures and time intervals indicating good to excellent intra- and intersession reliability. Bland-Altman plots confirmed these findings by showing that only 0-2 (≤13.3%) data points were beyond the limits of agreement. Regarding torque and electromyographic measures, CV (11.9-32.3%) and TRV (18.4-53.8%) values were high during the

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early intervals of torque development (≤100 ms) indicating high variability. During the later intervals (>100 ms), lower CV (i.e., 5.0-29.9%) and TRV values (i.e., 5.4-34.6%) were observed indicating lower variability. The present study revealed that neuromuscular performance during

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explosive torque production of the elbow flexors is reproducible in time intervals >100 ms 20

following onset of isometric actions, whereas during earlier time intervals variability is high. Key Words: maximal isometric contraction, explosive force production, electromyography, test-

retest reliability

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INTRODUCTION 25

In several sports-related activities (e. g., throwing the javelin, shot put) the time for generating maximal force is limited (21). Therefore, the ability to produce force rapidly and also to test force production should be considered as highly important for coaches and researchers. In terms of

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testing, explosive force/torque production (during intact joint actions) can be easily assessed during maximal isometric contractions and are defined as the rate of force/torque development (RTD) (1). In order to accurately document test results and interpret acute and long-term changes

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in performance measures such as RTD, coaches and researchers need reliable testing equipment and procedures (10). A frequently used method in many laboratories, training rooms and clinical facilities for the assessment of rapid force production is isometric testing using isokinetic

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dynamometers (10). In support of this notion, different types of isokinetic devices have been used to assess rate of force development/RTD (1,11,16). However, studies investigating reliability measures in explosive force/torque production with isokinetic testing instruments revealed

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contradictory results (11,16,20).

In addition, there is a void in the literature regarding intra- and intersession reliability of electromyographic (EMG) data assessed during maximal isometric contractions. In fact, this is 40

particularly prevalent for the early part of the force/torque-time curve. Further, studies

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investigating reliability of mechanical (i.e., force/torque signal) and electrophysiological (i.e., EMG signal) parameters during maximal isometric contractions primarily focused on lower limb muscles (12,20). Thus, the purpose of this study was to assess absolute and relative test-retest reliability (i.e., intra- and intersession comparison) for different mechanical (e.g., RTD) and 45

electrophysiological measures (e.g., maximal EMG amplitude) during maximal voluntary isometric contraction of the elbow flexors on an isokinetic device with special emphasis on the early part of the torque-time curve. Basically, today’s isokinetic devices (e.g, Isomed 2000 [D&R Ferstl GmbH, Hemau, Germany], Biodex System 3 [Biodex Medical Systems, Shirley, NY, USA] or Con-Trex MJ

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4 [Physiomed Elektromedizin AG, Schnaittach/Laipersdorf, Germany]) show high functional and 50

technical standards revealing similarities in construction, application, testing accuracy and possibilities (5,11,14–16). Thus, the results of the present study will not be solely applicable to specific laboratory conditions but can be translated to general testing situations when the goal is to assess maximal and explosive torque production in different populations using isokinetic devices. Based on the results of this study, coaches and practitioners will be provided with useful information regarding the interpretation of training-induced changes in explosive torque

METHODS Experimental Approach to the Problem

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production in particular during the early part of the torque time curve.

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A single-group, repeated measure design was used to assess absolute (e.g., coefficient of variation) and relative reliability (e.g., intraclass-correlation coefficient) for mechanical and

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electrophysiological measures during maximal isometric contractions of the upper limbs with an isokinetic dynamometer. Each participant was tested on two different occasions separated by at

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least 48 hours and a maximum of 7 days (mean 4.4 ± 1.5). This time interval was chosen because studies related to test-retest reliability regarding maximal isometric contraction have been 65

confined to this window (11–13,16,20). All participants were kindly asked to refrain from any strenuous exercise/work out within a time period of 48 h before the tests. In addition, each

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participant was asked to reappear at the same time of day for the second test and to keep their diet constant over the experimental period to rule out diurnal and nutrition specific variability (10). For each session, the experimental procedure included the performance of a series of

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maximal isometric contractions of the dominant elbow flexors on an isokinetic dynamometer. Isometric testing is a very common method for the assessment of explosive torque production (10) and is thus appropriate for the analysis of different mechanical and electrophysiological measures during the early part of the torque-time curve. Parameters of absolute and relative reliability were calculated for both, EMG and torque-time curve measures.

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Subjects With reference to the study of Mirkov et al. (13), an a priori power analysis (6) with an assumed type 1 error of 0.05 and a type 2 error rate of 0.10 (90% statistical power) was conducted, which revealed that 17 persons would be sufficient to test intersession reliability of RTD. Finally, 13 healthy male (age 24.8 ± 3.1 years, height 1.9 ± 0.1 m, body mass 83.7 ± 12.7 kg) and 6 female

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subjects (age 26.5 ± 1.4 years, height 1.7 ± 0.1 m, body mass 62.7 ± 7.0 kg) volunteered to

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participate in this study. All participants were right-hand-dominant (according to the lateral

preference inventory (4)) exercise science students and/or recreational athletes (e.g., running or

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rowing). All subjects perfomed at least 3 hours of sports activities per week on a regular basis. None had any history of musculoskeletal, neurological, or orthopedic disorder that might have 85

affected their ability to execute the experimental protocol. All participants gave their written

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informed consent before the start of the study. Data acquisition took place between November and December 2011. Local ethical permission was given, and all experiments were conducted according to the declaration of Helsinki.

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Procedures

Measurement of Maximal Isometric Torque Maximal isometric torque of the elbow flexors was measured using a motorized isokinetic dynamometer (IsoMed2000®, D&R Ferstl GmbH, Hemau, Germany). The maximum error of the

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torque sensor was < 0.2%. After individual adjustment, the participants were seated in a rigid chair of the isokinetic device, with the hip angle adjusted at 66° and the knee angle at 90° for

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proper alignment of the dynamometer’s range of motion. Straps attached to the isokinetic system firmly fixed the upper body and the hip. The dominant right forearm was attached to the lever arm of the dynamometer, while the upper arm was placed on an arm support unit. The individual positioning for each subject was documented so that it was similar during both test occasions. Tests of maximal isometric contractions were performed during static elbow flexion at an elbow

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joint angle of 70° (0° corresponds to full extension (9)). Before the test trials started, participants

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6 conducted a 5 min warm up comprising a series of submaximal concentric contractions on the dynamometer (range of motion between 10° and 130°). In order to get accustomed to the testing procedures, a number of submaximal and near-maximal isometric actions was conducted. Next, each subject performed between three and four maximal isometric elbow flexions. For each trial, 105

participants were thoroughly encouraged to act “as forcefully and as fast as possible”. Each maximal contraction was sustained for approximately 3 s. Trials with an identified initial

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countermovement were discarded (visual inspection of the torque-time curve). The raw unfiltered torque signals and all EMG parameters were sampled at 1,500 Hz, analog-to-digital converted

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(TeleMyo 2400R G2 Analog Output Receiver, Noraxon®, USA), and finally stored on a computer running MyoResearch XP Master Edition software (ver. 1.08.17, Noraxon®, USA). All torque signals were individually corrected for the effect of gravity on the forearm.

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Subsequently, torque data were filtered by using a second-order Butterworth low-pass filter with a 15 Hz cut-off frequency (1). Maximal isometric torque (MIT) was defined as the maximal value of the torque time curve. Maximal RTD was defined as the maximal slope of the torque-time curve. Submaximal RTD-values were calculated from the average slope of the initial torque-time

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curve in time periods of 0-30, 0-50, 0-100, 0-200, 0-300, 0-400, and 100-200 ms relative to the onset of torque. Onset of torque was defined as the time point at which torque development exceeded 2.5% of MIT (1). Additionally, contractile impulses determined as the area under the

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torque-time curve (∫torque dt) were derived for the same time intervals. 120

Measurement of Surface EMG Recordings Circular bipolar surface electrodes (Ambu®, type Blue Sensor P-00-S/50, Ag/AgCl, 13.2 mm, center-to-center distance 25 mm, Ballerup, Denmark) were placed over the m. biceps brachii and m. brachioradialis. Electrodes were positioned on the muscle according to the European recommendations for surface electromyography (8). The longitudinal axes of the electrodes were

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in line with the direction of the underlying muscle fibers. Inter-electrode resistance was kept below 5 kΩ by shaving, slightly roughening, degreasing and disinfecting the skin. The location of

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7 the electrodes was marked with permanent ink for identical position on both occasions. The EMG signals were differentially pre-amplified (data), telemetrically transmitted to the TeleMyo receiver station and recorded at the same sampling rate as described above for the dynamometer torque 130

signals (i.e., 1,500 Hz). For later offline analysis, raw signals were digitally high-pass filtered (second-order Butterworth, 5 Hz cut-off frequency) and rectified followed by a moving-root-

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mean-square filter with a time constant of 50 ms (1). After signal processing, a sum score of EMG data for the biceps brachii and the brachioradialis

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muscle was calculated (16). Peak EMG was determined as the highest amplitude within the 3-scontraction interval. Average EMG (mean average voltage [MAV]) was identified for time intervals of 0-30, 0-50, 0-100, 0-200, 0-300, 0-400, and 100-200 ms relative to the onset of torque. MAV was defined as the integrated and filtered EMG signal normalized relative to integration time

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(integrated EMG/integration time). Normalized MAV values were determined as MAV relative to peak EMG. Additionally, the median frequency of the power spectral density within the 3-s140

contraction interval was calculated for the m. biceps brachii and the m. brachioradialis using

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MyoResearch XP Master Edition software. Statistical Analyses

The two trials with the highest MIT in the first session (intrasession comparison) and the trial with the highest MIT in each session (intersession comparison) were used for analyses of absolute and relative reliability. No gender-time interactions occurred for any parameter of intersession

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comparison (except for rate of torque development in the 50 ms time interval after onset of contraction, p < 0.05). Thus, gender-specific results were not presented. Measures of central tendency and spread of data are presented as mean values ± SD. Relative reliability of mechanical and electrophysiological measures were quantitatively assessed with the intraclass correlation

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coefficient (ICC; two-way random, single measure model) and their respective 95% confidence interval. According to Fleiss’ classification (7), an ICC >0.75 indicates “excellent”, between 0.40 and 0.75 “fair to good” and 100 to 400 ms), CV and TRV amounted to less than 20.0% (except for 175

RTD in the time span of 100-200 ms). Based on dimensionless ratios of the Bland-Altman analysis, the mean bias of MIT, RTD and impulse values was ≤10% (except for RTD at 50 and 100 ms for intrasession and at 50 ms for intersession comparison, respectively). The Bland-Altman plots for

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9 all measures (data not shown) revealed that only 1/19 (5.3%) to 2/19 (10.5%) of the logtransformed data points were beyond the limits of agreement. 180

[insert Table 1, Figure 1] Surface EMG Variables The results for intra- and intersession reliability of EMG measures are shown in Table 2. The TRV

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of peak EMG was 13.9% and 19.4% for intra- and intersession comparison, respectively. During explosive torque production, the mean ICC was higher for MAV than for normalized MAV (Figure 2). Mean CV and mean TRV were also found to be slightly different between MAV and normalized

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MAV (Figure 2). In accordance with the mechanical parameters, CV and TRV were ≤19.5% within and between the sessions during the later phase of RTD (except for values in the time interval of

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100-200 ms, Figure 1. The mean bias of EMG measures was ≤10% (except for MAV at 30 and 50 ms for intrasession comparison). For all EMG variables, zero to only 2/15 (13.3%) of the log190

transformed data points were beyond the limits of agreement of the Bland-Altman analysis (data not shown).

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[insert Table 2, Figure 2]

In terms of power spectral density analysis, the mean bias for all parameters was 100 ms following onset of isometric contraction for intra- and

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intersession comparison. However, during the early part of the torque-time curve (≤ 100 ms),

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variability was high.

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In terms of maximal RTD, our study revealed higher CV values compared to the results found for the knee flexors and extensors (CV ranged from 8.3 to 17.8) (11,20). Methodological reasons (i.e., assessment of different muscle groups) might explain this discrepancy. It can be assumed that 210

knee extensors and flexors are better accustomed to explosive muscle contractions simply

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because they are performed more often in the lower extremities (e.g., acceleration and deceleration during walking, running or jumping) compared to the upper extremities during activities of daily living.

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Relative reliability turned out to be at least fair to good (≥0.47) for both, torque and EMG variables (except for intersession comparison of the median frequency of m. biceps brachii). While our results regarding intra- and intersession reliability for maximal RTD were similar to those that have been reported for knee (11) and elbow extensors/flexors (13), Sleivert and Wenger (16)

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observed poor ICC values for maximal RTD during maximal isometric contractions (ICC, 0.08 to 0.28) of the knee and leg extensors as well as the plantar flexors. However, given that Sleivert and

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Wenger (16) did not report information regarding leg dominance, it can be speculated that limb dominance could influence strength variability. In the present study, all subjects performed elbow flexions with the dominant right arm. In terms of MAV variables, the ICC values showed excellent intra- and intersession reliability (except for the intersession comparison of MAV from 100 to 200 ms). This result was similar to

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those studies that reported excellent intersession reliability for neural activation (12,20) of the lower extremities during maximal isometric contractions in time intervals lasting 0.5 to 6 s. However, these authors did not investigate intersession reliability for the early part of the torquetime curve in the elbow flexors. The results regarding median frequency revealed that the m. brachioradialis showed better intersession reliability in power spectral density compared to the m. biceps brachii. It can be

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speculated that during the present testing procedures, the m. brachioradialis was more readily

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activated (18), whereas the m. biceps brachii showed higher variability of motor unit activation due to higher recruitment thresholds (18). Additionally, small deviations in the tested hand position and/or the direction of torque may also have an influence on the neuromuscular activation level of the m. biceps brachii (19).

PRACTICAL APPLICATIONS

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In summary, the present study proved fair to excellent intra- and intersession reliability in frequently used parameters assessing explosive torque production and its associated neural

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activation (e.g., RTD, MAV) of the elbow flexors using an isokinetic dynamometer. However, inconsistencies in variability were found for intra- and intersession comparison when analyzing mechanical and electrophysiological variables during the early part of the torque-time curve. Consequently, based on the present findings, practitioners and researchers can use the present

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protocol on isokinetic devices to reliably test and interpret acute (e.g., fatigue) and longer lasting (e.g., adaptations to specific training programs/periods) training-induced changes of

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neuromuscular performance during explosive contractions of the upper extremities when time intervals >100 ms are considered. However, changes in mechanical (e.g., RTD) and EMG performance measures (e.g., MAV) of the elbow flexors during time intervals from onset of torque up to 100 ms, have to be interpreted with caution.

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1. Aagaard, P, Simonsen, EB, Andersen, JL, Magnusson, P, and Dyhre-Poulsen, P. Increased rate of force development and neural drive of human skeletal muscle following resistance training. J Appl Physiol 93: 1318–1326, 2002. 2. Atkinson, G and Nevill, AM. Statistical methods for assessing measurement error (reliability) in variables relevant to sports medicine. Sports Med 26: 217–238, 1998. 3. Bland, JM and Altman, DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1: 307–310, 1986. 4. Coren, S. The lateral preference inventory for measurement of handedness, footedness, eyedness, and earedness: Norms for young adults. Bull Psychon Soc 31: 1–3, 1993. 5. Drouin, JM, Valovich-mcLeod, TC, Shultz, SJ, Gansneder, BM, and Perrin, DH. Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity, torque and position measurements. Eurn J Appl Physiol 91: 22–29, 2004. 6. Faul, F, Erdfelder, E, Buchner, A, and Lang, A. Statistical power analyses using G*Power 3.1: Tests for correlation and regression analyses. Behav Res Methods 41: 1149–1160, 2009. 7. Fleiss, JL. Reliability of measurement. The design and analysis of clinical experiments. New York, NY: Wiley, 1986. 8. Hermens, HJ, Merletti, R, Freriks, B. SENIAM: European recommendations for surface electromyography results of the SENIAM project, 2nd edn. Enschede: Roessingh Research and Development, 1999. 9. Komi, PV, Linnamo, V, Silventoinen, P, and Sillanpää, M. Force and EMG power spectrum during eccentric and concentric actions. Med Sci Sports Exerc 32: 1757–1762, 2000. 10. Kraemer, WJ, Ratamess, NA, Fry, AC, and French, DC. Strength training: development and evaluation of methodology. In: Physiological assessment of human fitness. Maud, PJ and Foster, C, eds., 2nd edn. Champaign, IL: Human Kinetics, 2006. pp. 119–150. 11. Maffiuletti, NA, Bizzini, M, Desbrosses, K, Babault, N, and Munzinger, U. Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer. Clin Physiol Funct Imaging 27: 346–353, 2007. 12. McIntosh, KC and Gabriel, DA. Reliability of a simple method for determining muscle fiber conduction velocity. Muscle & Nerve 45: 257–265, 2012. 13. Mirkov, DM, Nedeljkovic, A, Milanovic, S, and Jaric, S. Muscle strength testing: evaluation of tests of explosive force production. Eur J Appl Physiol 91: 147–154, 2004. 14. Muehlbauer, T, Gollhofer, A, and Granacher, U. Association of balance, strength, and power measures in young adults. J Strength Cond Res 27: 582–589, 2013. 15. Mueller, S, Baur, H, Koenig, T, Hirschmueller, A, and Mayer, F. Reproducibility of isokinetic single- and multi-joint strength measurements in healthy and injured athletes. Isokin Exerc Sci 15: 295–302, 2007. 16. Sleivert, GG and Wenger, HA. Reliability of measuring isometric and isokinetic peak torque, rate of torque development, integrated electromyography, and tibial nerve conduction velocity. Arch Phys Med Rehab 75: 1315–1321, 1994. 17. Stokes, M. Reliability and repeatability of methods for measuring muscle in physiotherapy. Physiother Theory Pract 1: 71–76, 1985. 18. Tax, AA, van der Denier Gon, JJ, and Erkelens, CJ. Differences in coordination of elbow flexor muscles in force tasks and in movement tasks. Exp Brain Res 81: 567–572, 1990. 19. ter Haar Romeny, BM, van der Gon, JJ, and Gielen, CC. Relation between location of a motor unit in the human biceps brachii and its critical firing levels for different tasks. Exp Neurol 85: 631–650, 1984.

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References

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20. Viitasalo, JT, Saukkonen, S, and Komi, PV. Reproducibility of measurements of selected neuromuscular performance variables in man. Electromyogr Clin Neurophysiol 20: 487–501, 1980. 21. Zatsiorsky, VM. Biomechanics of strength and strength training. In: Strength and power in sport. Komi, PV, ed., 2nd edn. Oxford, UK: Blackwell, 2003. pp. 439–487.

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Figure Legends: Figure 1: Test-retest variability (TRV) of intrasession (a) and intersession comparison (b) for rate 305

of torque development (RTD), impulse and mean average voltage (MAV). In each parameter TRV was calculated for time intervals of 0-30, 0-50, 0-100, 0-200, 0-300, 0-

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400, and 100-200 ms relative to the onset of torque. Data represent group means ± SD.

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Figure 2: Mean values of test-retest variability (TRV), coefficient of variation (CV) and intraclass correlation coefficient (ICC) for mean average voltage (MAV) and normalized MAV (nMAV), respectively, derived at time intervals of 0-30, 0-50, 0-100, 0-200, 0-300, 0-

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400 and 100-200 ms during intra- and intersession comparison.

Figure 3: Bland-Altman plot comparing the log-transformed median frequency (MDF) displacements of the m. biceps brachii (a, b) and the m. brachioradialis (c, d) during

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intra- (a, c) and intersession testing (b, d) (N = 15). The individual differences of MDF between the intra- and intersession measurements, respectively, are plotted against the associated mean values. Solid lines indicate the average of the differences. Dotted

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lines indicate the limits of agreement corresponding to the mean ± 2SD.

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Table 1: Intraclass correlation coefficients (ICC) and their respective 95% confidence interval (CI), coefficient of variation (CV) and the limits of agreement (LOA) of the Bland-Altman analysis are shown for maximal isometric torque (MIT), rate of torque development (RTD) and impulse calculated for intra- and intersession reliability (N = 19). Intrasession reliability CV

LOA

ICC (95% CI)

CV

LOA

0.99 (0.95-1.00)

2.0

1.02 ×/÷ 1.05

0.99 (0.96-0.99)

4.2

1.02 ×/÷ 1.12

max

0.71 (0.39-0.88)

27.5

1.01 ×/÷ 1.13

0.68 (0.33-0.86)

26.3

0.90 ×/÷ 2.37

30 ms

0.74 (0.45-0.89)

32.3

0.94 ×/÷ 2.09

0.76 (0.47-0.90)

30.2

0.91 ×/÷ 4.14

50 ms

0.80 (0.55-0.92)

25.1

0.87 ×/÷ 4.95

0.80 (0.55-0.92)

23.6

0.85 ×/÷ 4.09

100 ms

0.93 (0.83-0.97)

11.9

0.85 ×/÷ 3.47

0.85 (0.65-0.94)

16.6

0.91 ×/÷ 2.47

200 ms

0.98 (0.96-0.99)

5.1

0.93 ×/÷ 1.94

0.95 (0.88-0.98)

8.8

0.99 ×/÷ 1.36

300 ms

0.98 (0.95-0.99)

5.5

0.98 ×/÷ 1.22

0.96 (0.91-0.99)

7.3

1.02 ×/÷ 1.22

400 ms

0.98 (0.95-0.99)

5.0

1.01 ×/÷ 1.16

0.97 (0.91-0.99)

7.0

1.01 ×/÷ 1.21

100-200 ms

0.77 (0.50-0.91)

25.6

1.01 ×/÷ 1.14

0.72 (0.41-0.88)

29.9

0.96 ×/÷ 2.65

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ICC (95% CI) MIT RTD

Intersession reliability

0.78 (0.52-0.91)

25.5

0.98 ×/÷ 3.08

0.69 (0.36-0.87)

29.3

1.03 ×/÷ 2.40

50 ms

0.79 (0.53-0.91)

25.3

0.93 ×/÷ 2.91

0.76 (0.49-0.90)

25.4

0.98 ×/÷ 2.68

100 ms

0.88 (0.72-0.95)

16.5

0.92 ×/÷ 3.05

0.79 (0.53-0.91)

20.8

0.92 ×/÷ 2.50

200 ms

0.95 (0.87-0.98)

9.6

0.91 ×/÷ 2.14

0.88 (0.71-0.95)

14.2

0.95 ×/÷ 1.76

300 ms

0.97 (0.93-0.99)

7.1

0.95 ×/÷ 1.52

0.92 (0.82-0.82)

10.8

0.98 ×/÷ 1.47

400 ms

0.98 (0.94-0.99)

6.0

0.97 ×/÷ 1.32

0.94 (0.86-0.98)

9.2

0.99 ×/÷ 1.35

100-200 ms

0.97 (0.92-0.99)

7.1

0.99 ×/÷ 1.23

0.92 (0.81-0.97)

11.2

0.97 ×/÷ 1.54

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impulse 30 ms

CV is displayed in percent (%). LOA is expressed in dimensionless ratio (bias ×/÷ 2SD) after taken antilogs of logtransformed data.

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Table 2: Intraclass correlation coefficients (ICC) and their respective 95% confidence interval (CI), coefficient of variation (CV) and the limits of agreement (LOA) of the Bland-Altman analysis are shown for maximal EMG amplitude (EMGmax), mean average voltage (MAV) and median frequency (MDF) in the biceps brachii (BB) and brachioradialis (BR) muscle calculated for intra- and intersession reliability (N = 15). Intrasession reliability CV

LOA

ICC (95% CI)

CV

LOA

0.88 (0.68-0.96)

11.4

1.07 ×/÷ 1.43

0.75 (0.40-0.91)

16.8

1.03 ×/÷ 1.44

30 ms

0.75 (0.41-0.91)

32.0

0.82 ×/÷ 3.31

0.86 (0.65-0.95)

27.6

1.10 ×/÷ 2.76

50 ms

0.78 (0.47-0.92)

28.2

0.84 ×/÷ 2.84

0.87 (0.66-0.95)

25.4

1.02 ×/÷ 2.50

100 ms

0.85 (0.60-0.95)

20.6

0.94 ×/÷ 2.29

0.90 (0.73-0.97)

17.9

0.99 ×/÷ 1.74

200 ms

0.86 (0.64-0.95)

16.1

0.99 ×/÷ 1.88

0.87 (0.65-0.95)

15.7

0.99 ×/÷ 1.60

300 ms

0.82 (0.54-0.94)

17.0

1.00 ×/÷ 1.85

0.83 (0.57-0.94)

16.5

0.99 ×/÷ 1.54

400 ms

0.86 (0.65-0.95)

13.9

1.04 ×/÷ 1.62

0.84 (0.57-0.94)

15.8

0.99 ×/÷ 1.52

100-200 ms

0.80 (0.52-0.93)

17.0

1.05 ×/÷ 1.87

0.61 (0.15-0.85)

22.7

0.99 ×/÷ 1.78

BB

0.97 (0.90-0.99)

4.6

0.99 ×/÷ 1.14

0.30 (-0.22-0.69)

19.0

1.06 ×/÷ 1.56

BR

0.90 (0.74-0.97)

4.4

1.00 ×/÷ 1.16

0.85 (0.60-0.95)

6.3

1.00 ×/÷ 1.19

TE

EP

C C

MDF

D

ICC (95% CI) EMGmax MAV

Intersession reliability

A

CV is displayed in percent (%). LOA is expressed in dimensionless ratio (bias ×/÷ 2SD) after taken antilogs of logtransformed data.

Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 1a

D

D E

A

A

C C EP

TE

T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 1b

D

D E

A

A

C C EP

TE

T P E C C

Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 2

A

A

C C EP

TE

D

D E T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 3a

A

A

C C EP

TE

D

D E T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 3b

A

A

C C EP

TE

D

D E T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 3c

A

A

C C EP

TE

D

D E T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.

Figure 3d

A

A

C C EP

TE

D

D E T P E C C Copyright Ó Lippincott Williams & Wilkins. All rights reserved.