Electromyographic and mechanographic investigations in patients with muscular hypotonia, which is, for instance, a side-effect after stereotactic treatment of tremor syndromes, permit the presumption that in this sensomotor open-loop situation the decreased muscular resistance to stretching during isometric contraction (initial stiffness) is caused by changes of muscular innervation pattern. Probably, the innervation pattern during tonic activity is changed by a shift of a more tonic motoneurone behaviour to motoneurone activities with predominantly phasic characteristics. In 17 controls and 4 patients with muscular hypotonia caused by stereotactic lesions of VIM area (treatment of tremor syndromes) the EMG of right and left side forearm flexors (especially the activity of the M. biceps brachii) was investigated by a sophisticated, topographically oriented 16-channel-surface-EMG-technique ("EMG-Mapping") during slight isometric contraction. EMG-Maps of forearm flexors (especially of M. biceps brachii) in patients with centrally evoked muscular hypotonia demonstrate that in these open-loop conditions the motor control is changed. For this the reason could be a shift of the activated motor units from a predominantly static to a more phasic functional behaviour. The latest results on muscular activation processes in cats support this presumption.