EMG activity during the extension actions of the leg muscles was recorded from the vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) of the right leg by pairs of bipolar surface electrodes (Blue Sensor N-00-S, Medicotest) with a distance between the electrode’s centers of 22 mm. After careful preparation of the skin (shaving, abrasion, and cleaning with alcohol), electrode pairs were placed longitudinally on the middle portion of the
muscles. EMG signals were recorded at a sampling rate of 1 kHz with a Muscle Tester ME3000 (Mega Electronics Ltd.) (bandwidth of 8–500 Hz/3 dB and a common mode rejection ratio > 100 dB). To
facilitate and normalize the analysis, the knee movement was divided into four intervals of 22.5. The parameters analyzed in the present study corresponded to the first interval of the movement of the dynamic contractions (from 90 to 112.5 of knee movement) for the VM and VL and to the fourth interval (from 157.5 to 180) for the BF, where those muscles had their maximal activation. An average of the sEMG parameters obtained from the VM and VL was calculated as a more representative index of muscle extension.