踵部挙上動作時の姿勢調節にかかわる下腿筋群の活動様式

Abstract

The purpose of the present study was to reveal the functional significance of the pretibial (TA) muscle EMG activities prior to voluntary soleus (Sol) contraction while standing. In addition, we have tried to improve understanding of segmental mechanisms involved in the anticipatory postural adjustment by means of H reflex technique. The results obtained from the present study were as follows: 1) The TA activities preceding voluntary Sol contractions were highly reproducible. 2) If the subject performed forward lean of his body voluntarily during the foreperiod, the TA activity were reduced or almost ceased according to degrees of forward lean of the body. This result was thought to indicate that the TA activities are related to the anticipatory postural adjustment and the lean of the body forward direction. 3) We compared the differences between two types of motor tasks. One of them was required to contract the Sol in a few seconds (UH task), and the other was required to relax the Sol as soon as possible after rising on their toe tips (UD task). In the UH task, the duration of the TA activities increased and the appearance of the Sol activities delayed. 4) The TA and the Sol H reflexes were changed in amplitude parallel according to the EMG activity of the homonymous muscles. Thus, they were reciprocally organized such as facilitation of TA H reflex and inhibition of the Sol H reflex were observed during TA activity, and vice versa during Sol activity. These results strongly suggest that the organization of the segmental motor systems during driving phase of the postural adjustment were reciprocally controlled. 5) The peak times of TA facilitation and Sol inhibition were differentially appeared, and the latter always preceded.