The Effects of Exercise-Induced Ankle Muscle Fatigue on Static Postural Control in Healthy Young Adult Males and Females

Abstract

This thesis describes a series of experiments to investigate sex differences in neuromuscular fatigue mechanisms of the ankle muscles and related postural control changes in healthy young adults. We found that isometric exercise-induced ankle muscle fatigue led not only to significant declines in twitch contractile function and voluntary activation (using twitch interpolation technique, Article 2) but also to significant changes in the center of pressure (COP) sway (backward/right shifts of the COP position and/or increased COP sway velocity) during quiet standing and/or standing forward leaning (FL) task with eyes open and/or eyes closed (Articles 3 and 4). However, we found minor or no significant sex differences in the fatigue mechanisms and fatigue-induced COP sway changes regardless of task difficulty, except for a significant sex X fatigue interaction for COP sway velocity (Article 3). The interaction effect was due to a significant increase in sway velocity in males during the FL task with eyes closed (but not in females), suggesting that males may preferentially rely on ankle control during a relatively challenging task (as compared to females). The general lack of sex differences is not surprising given similar performance and/or perceived fatigability between the sex groups (Articles 2-4), which could be explained by the relatively small differences in contractile function (and/or muscle strength) between males and females for ankle plantar and dorsi flexors compared with other muscle groups. In addition, this thesis involves a scoping review (Article 1), which summarized the broad range of rating of perceived exertion (RPE) values documented in studies observing an effect of muscle fatigue on postural control and suggested the potential effect of various fatigue levels on postural changes. Collectively, these findings advance our understanding of sex-specific fatigue mechanisms and postural control behavior. These findings also indirectly contribute to the understanding of sex differences in injury risks during physically or stability-demanding tasks and sports, as well as to the improvement in the prescription of physical training or rehabilitation exercise.