Utilization and significance of girth changes in human muscles following contraction: A case of handgrip / 体力科学

ABSTRACT

To clarify length changes of human muscle, forearm girth was recorded during various handgrips by using the rubber-strain-gauge method.<BR>Subjects quickly lifted loads of 10, 20, 30% of the maximum grip strength (MVC) at a distance of 2 cm, and/or lifted and lowered those loads with the rhythm of 1 Hz.<BR>In isometric condition, handgrip was performed with muscle strength for several seconds in the same conditions as the above. Fatiguing successive contraction was performed with muscle strength of 30% MVC for a few minutes.<BR>1) During ballistic contraction of forearm flexors, differences between the onsets of its discharge and the increase in forearm girth were about 20 ms in all conditions. The increase in forearm girth occurred prior to the onset of the rise in the loads, and its extent depended on the loads.<BR>2) In repetitive handgrips, changes of forearm girth in the muscle contraction phase were similar to those of the ballistic contractions. In the muscle relaxation, recovery of forearm girth to its resting level was delayed with increase of the loads.<BR>3) Forearm girth during successive contraction for a short time remained at an approximately steady level, while its extent depended on the muscle strength. During fatiguing successive contraction, forearm girth gradually increased with an increase in muscle discharge.<BR>These results suggest that length change in human muscle occures during muscle contraction in isometric conditions. Furthermore, this method is useful for the study of the human muscle shortening and lengthening, as to the muscle activity of concentric conditions and muscle relaxation process, even when there is no agreement of force-EMG relation.