The preamplifier was secured on place by attaching it to the corresponding reference electrode. A single 2.5-m long cable connected the preamplifier to the amplifier box. The EMG signal was recorded at the sampling rate of 1000 Hz and (analogically frequency band-pass filtered (effective band width 7–500 Hz), amplified (differential amplifier, CMRR > 110 dB, gain 1000, noise < 1 1-V)), analoque to digital converted (12-bit). The raw EMG signal was converted into averaged EMG in 0.1 s. data epoch, and stored in a PC for later analysis.