RESUMO
The purpose of this study is to investigate significance of transient decrease in sustained tension preceding rapid muscle contraction in elbow flexor muscles.<BR>Before rapid voluntary contraction, steady forces below 20% of the maximum contraction were maintained, and each transient decreas was detected by using high sensitive strain gauge (FD pick-up) with EMG of brachial biceps and triceps muscles. And girth and length changes of the biceps brachii muscle with the tension decrease were detected by using rubber strain-gauge method and X-ray technique, respectively.<BR>The following results were obtained<BR>1) The transient decrease of steady forces were observed during the premotion silent period. Amount and duration of the transient tension decrease were below 20% of each steady force and 100 ms, respectively.<BR>2) Amount of the transient tension decrease inversely correlated to time to half Pmax on the rapid tension development. (p<0.001)<BR>3) Amount of the transient tension decrease was significantly coefficient with decrement of girth of upper arm. (p<0.001)<BR>4) A distance between two Cu wire apexes inserted into biceps brachii muscle shortened with increment of muscle force.<BR>These results suggest that before rapid muscle contraction stretch of biceps brachii muscle transiently occure, and that the stretch accelerate the following shortning velocity of the muscle via a stretch reflex.