Assessment of Anthropometrics, Knee Extensors Maximal Voluntary Isometric Contraction and Rate of Torque Development

Thigh muscle volume was estimated from pre-to-post-training by multiple measurements of skinfolds, circumferences, and diameters of the lower limbs, as detailed elsewhere (Jones and Pearson, 1969). For knee extensor (KE) MVIC participants were seated on an isometric dynamometer (Good Strength, Metitur, Finland) equipped with a cuff (∼2 cm above the lateral malleolus) attached to a strain gauge. Participants stabilized themselves by grasping handles on the side of the chair. Safety belts were strapped across the chest, thighs and hips to avoid displacements. All measurements were taken from the individual’s dominant leg, with the hip and knee angles set at 90° and 70° from full extension, respectively. Each testing session was preceded by a warm-up consisting of several submaximal contractions of the KE muscles at a freely chosen intensity. Thereafter, three, 3 s MVIC trials were performed with rest periods of 2 min between trials. Participants were instructed to extend their knee “as strong and as fast as possible” (Andersen et al., 2010). Online visual feedback of the KE force was provided. The dynamometer force signal was digitized using an acquisition card (Powerlab 16SP, ADInstruments, Australia) and Labchart 7.0 software (ADInstruments, Australia). The sampling frequency was fixed at 2 kHz. The force signal was subsequently multiplied by the lever arm length to obtain knee joint torque. The torque signal was corrected for the effect of gravity on the lower leg (Aagaard et al., 2002). MVIC was therefore defined as the highest peak torque value of the three maximal attempts. The intraclass correlation coefficient (ICC) was 0.84. Rate of torque development (RTD) (Nm s^–1) was defined as the slope of the torque–time curve (i.e., ΔTorque/ΔTime) from 0–200 ms from the onset of torque (Andersen and Aagaard, 2006). Onset of torque was defined as the instant when the knee extensor torque exceeded the baseline by 2.5% of the baseline-to-peak amplitude (Andersen and Aagaard, 2006). The highest value of the three maximal attempts was used for further analysis with a calculated reliability ICC of 0.82. Normalized RTD (RTD_r) was determined as the slope of the moment-time curve when normalized relative to torque (expressed as % torque s^–1 × 100) (Aagaard et al., 2002).