Abstract
To understand the functional difference between dominant and non-dominant limbs in human upright standing, we analyzed electromyographic (EMG) activities while subjects stood on rocking platforms with various sizes. EMG activities were recorded from muscles of ankle and knee joints of both limbs. Subjects were instructed to stand on the rocking platforms so that they rocked in the saggital plane. Movements of the platforms, equivalent to fore and back movements of the subjects, were recorded by a force plate (center of pressure, COP). Mean EMG amplitudes of ankle extensors (m. triceps surae, GS) and flexor (m. tibialis anterior, TA) were higher in the non-dominant side than in the dominant side. Nevertheless mean EMG amplitudes of knee joint muscles were rather complicated; some muscles of the dominant side could show lower amplitude than those of the non-dominant side. As the radius of the rocking platform decreased, the ratio of mean EMG amplitudes of dominant and non-dominant muscle pairs (dominant-ratio) increased, and the correlation coefficient of these muscle pairs increased. Cross correlation analysis of the COP and EMG changes showed that non-dominant side muscles strongly correlated with the COP when subjects stood on the rocking platform with the largest radius. It was supposed that in a condition where subjects easily kept standing, non-dominant limb muscles were primarily used to control the COP, but dominant and non-dominant muscle pairs were used synchronously when it was difficult to keep standing. [J Physiol Sci. 2006;56 Suppl:S191]
