Adaptive alterations in muscle synergies during the recovery step compensate for perturbation-induced stability demands in older adults.

backgroundAging is intimately linked to alterations in neuromuscular control, which can severely affect mobility. This study aimed to investigate how muscle synergies in older adults contribute to distinct forms of gait.

methodsWe measured the surface electromyography signals from 14 muscles in the lower limbs and trunk of healthy older adults during mechanically perturbed walking. Muscle weight and temporal activation coefficients for muscle synergies were extracted through a non-negative matrix factorization framework.

resultsFive distinct muscle synergies were identified in each gait pattern. Among these, four muscle synergies observed in the perturbed step and the first recovery step exhibited high similarity to their corresponding patterns in the normal step. Key differences were observed in the first recovery step: a specific muscle synergy pattern dominated by the gluteus medius and tibialis anterior muscles replaced the synergy dominated by the erector spinae in the normal step. The numbers of major activated muscles in the muscle synergy dominated by the vastus medialis and the gluteus medius decreased in the perturbed step, while these numbers increased in the first recovery step. During the transition phase of the stance in the first recovery step, the activation phase of the major synergistic muscles extended.

conclusionsSpecific muscle synergy patterns are associated with balance recovery and stability maintenance. Fractionation and merging of muscle synergies triggered in response to perturbations may relate to functional decline in older adults, serving as a mechanism for remodeling to adapt to changes in limb biomechanics and multiple motor task commands. CLINICAL TRIAL NUMBER: Not applicable.