To remove movement artefacts, the signals were high-pass filtered with a cut-off frequency of 20 Hz (Butterworth fourth-order zero-lag digital filter). The signals were then rectified and expressed as linear envelopes in percent of the maximal value using 10 Hz low-pass Butterworth fourth-order filtering (4). The maximal value was found just before the kicking experiment as the maximal EMG amplitude during 3 maximal contractions. The EMG signals from the maximal voluntary contraction were treated in exactly the same way as the EMG signals obtained during kicking.