How does age affect changes in leg muscle activation patterns and leg joint moments during prolonged walking?

The ways in which age affects neuromuscular control in response to walking-related fatigue are poorly understood. Better understanding of the consequences of walking-related fatigue can inform the development of strategies to improve independent mobility for older adults. In this study, we measured leg muscle excitations and net joint moments in younger and older adults during a 30-min walking trial. Twelve leg muscles were monitored, and wavelet transformation and principal component analyses quantified the effects of age and time on muscle excitation patterns. Perceived exertion increased in both age groups, with higher terminal values in older adults. Over the course of prolonged walking, mean EMG frequency and amplitude decreased while EMG intensities in the slower frequency ranges increased for soleus, lateral gastrocnemius, tibialis anterior, peroneus longus, and gluteus maximus muscles. For soleus muscle, a time-dependent decrease in mean frequency was observed only for older adults. We observed a distal-to-proximal redistribution of net joint moments during prolonged walking independent of age; however, older adults walked with greater peak hip joint moments than younger adults. Our results suggest that shank muscles may exhibit higher fatigability during prolonged walking, precipitating an increased demand on proximal leg muscles to power walking. Walking in older adults is often characterized by an increased reliance on proximal leg muscles, which has in turn been implicated in their higher metabolic cost of transport. Accordingly, our collective findings point to neuromuscular changes during prolonged walking that may cause older adults to be more susceptible to walking-related fatigue than younger adults.