A premovement silent period does not occur prior to rapid changes of velocity during human limb movements

Surface electromyographic activity (EMG) of the interosseous dorsalis I, the hand extensors and the biceps muscles was analysed in human young normal subjects for the occurrence of a precontraction (PCSP) or a premovement silent period (PMSP) before a sudden increase in tension or rapid change of position after a small isometric contraction or slow isotonic movement. Contrary to the results of Conrad et al. (Exp. Brain Res., 51 (1983) 310-313), in whose experiments the contraction condition changed from isometric to isotonic, a PCSP or PMSP could never be observed in our experiments, where contractions or movements first started at a low force level or with a low speed which had to be changed most rapidly after 2 s and where the recording condition remained strictly either isometric or isotonic. It is concluded that the central nervous system resets the motoneuronal pool activity when the central program is changed from the control of an isometric to the control of an isotonic contraction.