Abstract
Passive movements are empirically known to be effective for the functional restoration of weakened muscles. In simple reaction time (RT) studies of normal subjects, electromyographic reaction time (EMG-RT) of the prime mover muscle is faster during passive movement in the same direction as the active movement than during passive movement in the opposite direction, of which phenomenon is referred to as “direction specificity”. A recent study has shown that vocal RT of slow reactors are fast and that of fast reactors are slow during passive movements, compared to vocal RT at static posture, implying that passive movements increase one's arousal level.
In this study, we examined EMG-RT of the biceps brachii muscle for elbow flexion in ten normal subjects, six patients with Parkinson's disease (PD) and twelve patients with spinocerebellar degenerations (SCD) under three conditions; at static posture of elbow flexion 60° (STAT), and during passive elbow flexion ranged from 20° to 100° (PFLX) and passive elbow extension ranged from 100° to 20° (PERT) with angular velocity of 20°/sec.
Compared to STAT condition, EMG-RT was fast during PFLX and slow during PEXT in the normal and PD groups. However, in SCD group, EMG-RTs of both PFLX and PEXT were slower than EMG-RT of STAT. EMG-RT of PFLX was faster than that of PEXT in the three groups.
The direction specificity of passive movements was well preserved in PD and SCD groups. EMG-RTs during each passive movement were slower than EMG-RT at static posture in SCD group, but not in PD group. The result in SCD group could not be interpreted by model that passive movements increase one's arousal level, suggesting the abnormality of arousal response induced by passive movements in patients with SCD.
