Changes in activity in triceps surae muscles during prolonged isometric contractions / 体力科学

ABSTRACT

In order to examine muscle activities, surface electromyo-grams (EMGs) were recorded from the triceps surae muscles (lateral gastrocnemius LG, medial gastrocnemius MG, soleus SOL) during prolonged isometric contractions at 20°of ankle joint angle under constant load (10% MVC) . The results were summarized as follows;<BR>1) EMG recordings were obtained which showed complementary activity in each muscle in the time course. Changes in activity was found between whole muscles in the synergist of triceps surae muscles.<BR>2) Muscle activity most frequently took the form of MG+SOL, followed by MG acting alone and SOL acting alone. Ta/Ts value (the ratio of total activity period and total silent period on EMG activity) showed 4.0 in MG and SOL. In contrast, it showed 0.3 in the LG.<BR>3) In the latter half of all exercise times, frequent changes in activity were shown, and Ta/Ts value increased in the gastrocnemius muscle and decreased in the soleus muscle. These results indicate that frequent changes in activity in the latter half were caused by the reduc tion in Ts in the gastrocnemius muscle, and the reduction in Ta in the soleus muscle.<BR>4) Mean integrated EMGs increased significantly in the middle and latter phases in each burst activity, but those in the latter phase did not increase compared to those in the middle phase. These results suggest that the rotation of activity between muscles may have occured before the remarkable increase of EMG activity with fatigue.