Effects of aging and exercise on dynamic postural control: Analysis of muscle synergies

This study aims to investigate human motor control mechanisms providing coordination of voluntary dynamic movements under the effects of "natural aging" and "participation in regular exercise". Electrophysiological activities of selected lower extremity muscles and ground reaction forces are recorded simultaneously by surface electromyography and force platform, respectively during "voluntary body sway" (VBS). The healthy older physically active group (master athletes) and the healthy sedentary groups (young and older) are included to the study. Principal Component Analysis is used to determine the number of muscle modes and the composition of muscle modes i.e., reciprocal or co-activation contraction patterns. Synergy index is calculated with the Uncontrolled Manifold (UCM) Hypothesis. The results of the UCM analysis for the dominant side are for the first time compared with the non-dominant side. The main findings of the study: there was no age or exercise effect i) on the number of muscle modes (the same for all groups) and ii) on contraction pattern (reciprocal pattern for all groups), iii) the young sedentary group had lower values for UCM variance components than the older groups, probably depending on experiencing the lowest task difficulty, iv) synergy index was highest for older sedentary group, and lowest for master athletes, v) older sedentary group showed less flexible, more rigid motor control strategies, vi) UCM variance components and synergy index values were different in the multi-muscle coordination of dominant and non-dominant lower extremity. Re-examining the VBS movement by dividing it into phases was recommended to reach more detailed information about muscle synergy patterns. It was revealed that the differences in multi-muscle coordination between dominant and non-dominant limbs should not be neglected.