Abstract
The purpose of this research is to understand the mechanism of multi-joint movement in bifunctional muscles, especially the difference in muscular activity ratio of different parts. In ten healthy adults (six men, four women), muscular activity of rectus femoris (RF) among bifunctional muscles was investigated during four trial exercises; ①knee extension, ②hip flexion, ③knee joint and hip joint total flexion, and ④knee joint and hip joint total extension. The surface electromyogram of RF of four parts from proximal electrode to the most distal electrode was measured using electromyography, and the rate of the muscular activity was compared among trial exercises and parts of electrodes. In the central electrode position where a muscle cross-section area serves as the maximum, no difference in muscular activity was seen among the trial exercises. Moreover, when RF played only a cooperative role like during exercises ① and ②, the muscular activity was hardly changed by the parts of the same muscle. During exercise ④, however, in the proximal electrode near a hip joint, muscular activity became small, and became large in the distal electrode near a knee joint. During exercise ③, the reverse phenomenon happened. The results suggest that, in bifunctional muscles which achieve a cooperative action and antagonism action of two adjoining joints simultaneously, the mechanism similar to reciprocal innervation may exist in its muscle.
