Surface electromyography (EMG)

Muscle activity was monitored by EMG (myon 320, myon AG, Zurich, Switzerland) during the MVIC, PRT, and SWE measurements. After standard skin preparation, surface electrodes (Blue Sensor N, Ambu A/S, Ballerup, Denmark) were placed on the muscle belly of the VL, according to SENIAM recommendations (Hermens et al. 1999). The sample rate was 2000 Hz. EMG signals of the MVIC measurements were high-pass filtered (10 Hz, Butterworth) and the root-mean square (RMS, 50 ms window) values were calculated. The mean of 500 ms (± 250 ms around the peak value) was calculated around the maximum value. During the passive measurements we monitored the live EMG signal for activity. If signal changes were observed, the trial was repeated. Furthermore, a post-hoc analysis was performed for the PRT and SWE to ensure that the subject was relaxed, i.e. did not show EMG activity exceeding 5% of MVIC, if we could detect changes in the raw EMG signal during analyzing process (Gajdosik et al. 2005; Kato et al. 2010). In these cases, the EMG signal was high-pass filtered (10 Hz, Butterworth) and the root-mean square (RMS, 50 ms window) values were calculated.