Age-related differences in proactive and reactive neuromechanics throughout the time course of walking balance perturbations.

We examined whether age-related differences in proactive and reactive distal leg muscle neuromechanics exist and their effects on whole body instability during treadmill-induced perturbations in walking. Fifteen younger adults (22.3 ± 3.3 years) and 15 older adults (73.6 ± 5.5 years) participated. In all, we delivered eight combinations of perturbation side (right/left), direction (anterior/posterior), and anticipation (yes/no), each repeated twice and delivered in a fully randomized order as participants walked at their preferred speed. Older adults habitually exhibited greater generalized anticipatory control and lesser stability than younger adults, evidenced via greater antagonist coactivation and larger transverse plane angular momentum, respectively. However, older adults failed to supplement their generalized anticipatory control with proactive neuromechanical adjustments when perturbations were anticipated. Indeed, only younger adults deployed direction-specific proactive adjustments preceding anticipated perturbations. Older adults also deployed larger reactive responses and exhibited greater instability than younger adults during perturbation recovery, particularly when unanticipated. Taken together, our results show that older adults fail to deploy proactive adjustments and deploy larger but less effective reactive responses to walking balance perturbations. These results have very specific implications for the design and implementation of interventions to improve older adults' ability to prepare for and respond to walking balance challenges and mitigate falls in their communities.NEW & NOTEWORTHY This is the first study to combine electromyography and dynamic ultrasound imaging to investigate local distal leg proactive and reactive neuromechanics, and their role in governing instability, in the context of walking balance perturbations. Older adults do not supplement their generalized anticipatory control with proactive adjustments and exhibit larger, but less effective, reactive responses than younger adults. These results can inform the design and implementation of interventions to improve older adults' balance and mitigate falls.