Sex-dependent and sex-independent muscle activation patterns in adult gait as a function of age.

Introduction: Aging leads to poorer neuromuscular control that may impact mobility. However, the specific decades when these changes occur, and whether these time-based changes are sex-specific, are unclear.

Methods: Adults aged 20-82 years (N = 93, 51 females) walked six gait trials at their preferred speed over a 10-m platform. Electromyography (EMG) of the rectus femoris (RF), tibialis anterior (TA), and gastrocnemius lateralis (GL) were measured using wireless surface sensors. Root mean square (RMS) and within-cycle coefficient of variation (CV) values were calculated for several phases of gait. Mixed effect models were conducted to test for Age, Sex, Muscle, and interaction effects, covarying for gait speed and stride length.

Results: A significant Age × Sex × Muscle interaction on RMS at the mid-swing phase was found (p = .036), showing 4.2% higher RF RMS for males (β = 0.42, p = .008) and 3.3% higher GL RMS for females (β = 0.33, p = .038) with each of the three decades investigated. Significant Age × Muscle interactions on GL RMS were found at loading, mid-stance, and over the full gait cycle (ps < .05), with 2.0-4.3% higher values per decade (β = 0.20-0.43, ps < .05). There was generally higher CV with higher age at mid-swing and over the full gait cycle (significant Age effects, ps < .05). Females showed higher CV at loading, mid-stance, and terminal stance (significant Age × Sex effects, ps < .05).

Discussion/conclusion: Results suggest sex-dependent influences of age on muscle recruitment during a few specific phases of gait, and sex-independent influences of age on the recruitment of the ankle musculature, and on the overall gait cycle. These influences may help explain overall increased instability and fall risk in older adults.