We investigated the effects of aging on postural muscles covariate patterns prior to voluntary perturbations. Nine healthy young and nine older subjects were instructed to release a load in a self-paced manner. The results of cross-correlation analyses showed that the average time lag corresponding peak correlation coefficient between trunk flexor and extensor muscles in the older group was significantly shorter, compared to that in the young group. The results of principal component analysis showed that the co-contraction Muscle-modes in the older group were observed more frequently than those in the young group. These results indicate that the older group showed changes in the anticipatory postural muscle co-variation, suggesting the transition from reciprocal to co-activation pattern with aging.
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