Effects of acute muscle fatigue on postural control in healthy adults and persons with Parkinson's disease

Falls are one of the most disabling features of aging and are increasingly common in persons with balance-impairments such as Parkinson's disease (PD). Falls can cause physical injuries such as fractures and/or head injuries leading to functional incapacity, increased risk of nursing home admission, and higher mortality rate. Acute muscle fatigue has been shown to exacerbate fall-correlated end-points such as postural control in healthy young and elderly individuals. The majority of studies investigating these effects, however, have focused on static stance postural control, or tasks that fail to incorporate more functional movements such as those requiring components of anticipatory and reactive postural control. The purpose of this study was to document the effects of acute lower extremity muscle fatigue on anticipatory and reactive postural control in persons with PD and to compare those results to the impact of fatigue on healthy elderly and young populations. Additionally, this investigation sought to gain insight into the chronology for postural control recovery following acute muscle fatigue. This dissertation has yielded a background on acute muscle fatigue, followed by a systematic review of the evidence on the effects of muscle fatigue on anticipatory and reactive postural control in healthy older individuals. The focus of the paper then shifts to components of an experimentally designed cohort study examining the effects of acute muscle fatigue on a centrally initiated movement task and a peripherally directed lean-induced fall in persons with PD and neurologically healthy adults. Results indicated that both anticipatory and reactive postural control are altered following acute muscle fatiguing exercise in neurologically healthy young and older adults. Amelioration of fatigue effects is extended beyond 30 minutes for most measures. Recovery occurs more readily for reactive postural control than anticipatory postural control. No statistically significant results were found from fatigue effects on postural control in the full cohort of persons with PD. However, a supplementary analysis revealed that postural control is altered in persons with PD who exercised beyond a minimal threshold of energy expenditure. More research is needed with larger sample sizes and improved construct validity for muscle fatigue in this cohort. The results of this study should serve to heighten awareness regarding the potential negative effects of acute muscle fatigue, including the possibility of falls in clinical and community based exercise settings for older adults at risk for falls.