Multidimensional Recurrence Quantification Analysis of Multi-muscle Synergy in Elderly during Standing on Slopes

Identifying balance deficits associated with aging is critical to preventing falls in elderly people. The purpose of this study was to investigate the effects of aging on the multi-muscle synergy in lower extremities during standing on sloped surfaces. Eighteen healthy elderly subjects and 18 healthy young subjects were recruited in the experiment. Subjects were required to stand quietly on slopes at 5 different angles for 30 s with and without visual feedback. Surface electromyography signals of muscles in the lower limbs were collected simultaneously during standing. The muscle synergy of synergistic muscles and of antagonistic muscles were quantified by the parameters of multidimensional recurrence quantification analysis (MdRQA). The results showed that the dynamical synergies in synergistic and antagonistic muscle groups were significantly enhanced in elderly group, especially during standing on sloped surfaces (p < 0.05). The MdRQA parameters were significantly increased when standing without visual feedback than with visual feedback (p < 0.05). The aging and the absence of visual feedback led to more deterministic structures in the dynamical coupling of muscle activations, indicating strengthened synergistic contractions of muscles. These changes in elderly may increase the restriction on balance control and reduce the adaptability of motor system to potential external perturbations. This study shed light on the effects of aging on standing balance control and may facilitate to develop novel strategies for evaluation of aging and predication of falls.