Effects of fatigue on physical activity and function in patients with Parkinson's disease. 
To characterize the relationships between symptoms of fatigue, physical activity, physical function, and functional capacity in patients with idiopathic PD.  Thirty-seven patients with PD underwent evaluation of physical activity, physical function, functional capacity, and fatigue.  Physical activity and fatigue were measured by standard questionnaires (Godin Leisure Activity Questionnaire, Yale Physical Activity Questionnaire, and Fatigue Severity Scale); physical function was measured by the Up and Go Test and the Six-Minute Walk; and functional capacity was measured by a maximal oxygen uptake exercise test (VO(2max)).  Increased levels of fatigue were associated with decreased levels of leisure physical activity, lower frequency of vigorous physical activity, less time spent moving about performing daily tasks each day, lower diastolic blood pressure and VO(2max), longer Up and Go performance time, and carbidopa-levodopa (CL) use.  A multiple regression analysis was performed to determine factors predicting fatigue (Fatigue Severity Scale).  The Up and Go Test, Leisure Activity Score, CL use, VO(2max), and diastolic blood pressure were the best predictor variables of fatigue.  The Up and Go Test and CL use contributed independently to the model, whereas the other variables appeared to moderate the relationships between these variables.  PD patients with more severe fatigue are more sedentary and have poorer functional capacity and physical function compared with patients with less fatigue.