Changes in lower extremity muscle coordination over a 30-minute walk do not differ by muscle fatigability

Muscle fatigue, the transient decrease in muscle power, leads to low levels of physical activity and an inability to perform activities of daily living. Altered muscle coordination in response to fatigue may contribute to impaired physical performance. We sought to determine whether lower extremity muscle coordination during gait changes differently depending on susceptibility to fatigue (i.e., fatigability). Thirty-one older adults completed muscle power testing before and after a 30-min walk, with the change in power used to categorize participants as more or less fatigable. We used non-negative matrix factorization to identify muscle modules from electromyography (EMG) from the 2nd minute as our measure of baseline muscle coordination. Changes in muscle coordination were determined by computing the variance in the 30th minute's EMG accounted for by the baseline modules across all muscles (tVAF) and in individual muscles (mVAF). We compared tVAF between the 2nd and 30th minutes of the walk in individuals who were more and less fatigable. We used mVAF to explore the contribution of changes in individual muscle activity to tVAF. There was a decrease in tVAF overall in response to the walk (p < 0.001; 92.3 ± 1.6 % vs. 89.0 ± 4.3 %) but this did not differ between groups (interaction p = 0.66). There were significant associations between mVAF and tVAF for knee extensor, knee flexor, and ankle dorsiflexor muscles. Our results suggest that muscle coordination changes over the course of a walk in older adults but that this change does not differ between more and less fatigable older adults.