A ground-based comparison of the Muscle Atrophy Research and Exercise System (MARES) and a commercially available isokinetic dynamometer

Abstract

IntroductionInternational Space Station (ISS) crewmembers perform muscle strength and endurance testing pre- and postflight to assess the physiologic adaptations associated with long-duration exposure to microgravity. However, a reliable and standardized method to document strength changes in-flight has not been established. To address this issue, a proprietary dynamometer, the Muscle Atrophy Research and Exercise System (MARES) has been developed and flown aboard the ISS. The aims of this ground-based investigation were to: (1) evaluate the test–retest reliability of MARES and (2) determine its agreement with a commercially available isokinetic dynamometer previously used for pre- and postflight medical testing. MethodsSix males (179.5±4.7cm; 82.0±8.7kg; 31.3±4.0yr) and four females (163.2±7.3cm; 63.2±1.9kg; 32.3±6.8yr) completed two testing sessions on a HUMAC NORM isokinetic dynamometer (NORM) and two sessions on MARES using a randomized, counterbalanced, cross-over design. Peak torque values at 60° and 180°s−1 were calculated from five maximal repetitions of knee extension (KE) and knee flexion (KF) for each session. Total work at 180°s−1 was determined from the area under the torque versus displacement curve during 20 maximal repetitions of KE and KF. ResultsIntraclass correlation coefficients were relatively high for both devices (0.90–0.99). Only one dependent measure, KE peak torque at 60°s−1 exhibited good concordance between devices (ρ=0.92) and a small average difference (0.9±17.3Nm). ConclusionMARES demonstrated acceptable test–retest reliability and thus should serve as a good tool to monitor in-flight strength changes. However, due to poor agreement with NORM, it is not advisable to compare absolute values obtained on these devices.