Different Contraction Pattern of Lower Leg Muscle Fiber between Swaying and Tiptoe Standing in Human Upright Posture

Abstract

In recent studies, it is shown that gastrocnemius (GAS) muscle fiber movements in upright standing were paradoxical as compared to the movement of whole muscle length depended on the ankle joint movement. We hypothesized these muscle fiber movement depend on the position of the center of mass (COM) relative to the center of rotation of the ankle joint. The purpose of this study was to examine the change of muscle fiber length in GAS and tibialis anterior (TA) muscles while upright standing postures: swaying anterior-posterior and standing tiptoe-heel. Ultrasonography of the GAS and TA was recorded to detect the change of muscle fiber length in vivo. The center of pressure and the ankle joint angular displacements were recorded to use as visual feedback signals in two postural tasks.