Sex-independent and dependent effects of older age on cycle-to-cycle variability of muscle activation during gait

Background Older age is associated with higher stride time variability in female and male gait, which may have a neuromuscular origin. We sought to determine how older age and sex affect muscle activation variability during gait, and how these patterns relate to stride time variability. Methods Ninety-three adults (51 females; aged 20–82 years) completed six gait trials at their self-selected speed. Cycle-to-cycle variabilities (CCVs) were calculated for stride time, and for amplitude of electromyography (EMG) of the rectus femoris (RF), tibialis anterior (TA), and gastrocnemius lateralis (GL) recorded over different gait phases. Statistical models tested for Age × Sex × Muscle effects and for relationships between EMG CCVs and stride time CCVs. Results Significant Age and Age × Muscle effects on EMG CCV were observed in several phases of gait (p < .05), where each year of age was associated with 0.11–0.18% higher EMG CCV, generally in the RF. A significant Age × Sex × Muscle effect on EMG CCV at mid-stance (p < .05) indicated that, in females, each year of age was associated with 0.11% lower GL CCV. Significant but low strength correlations (ρ = 0.298–0.351) were found between EMG CCV and stride time CCV. Conclusions Associations between older age and higher muscle activation variability were generally sex-independent. A sex-dependency in GL activation variability may contribute to gait instability in aging females. Individual variabilities of muscle activation were not strongly related to stride time variability.