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 < 1V)),
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