Handgrip Strength Related to Long-Term Electromyography: Application for Assessing Functional Decline in Parkinson Disease

Objective: To determine which clinical measures of physical function (ie, gait, balance, and grip strength) best represent long-term electromyography in persons with Parkinson disease (PD) compared with those without PD. Design: Cross-sectional study. Setting: Local community. Participants: A sample (N=37) of men and women with PD (n = 23) and those without PD (n = 14), living independently at home, older than 50 years of age, from the local community. Interventions: Not applicable. Main Outcome Measures: Measures of gait, balance, and grip strength were completed, and electromyography was examined in biceps brachii, triceps brachii, vastus lateralis, and biceps femoris during a 6.5-hour day. Muscle activity was quantified through burst in electromyography (>2% of the normalized maximum voluntary exertion with a continuous activity period of >0.1s). Stepwise multiple regression models were used to determine the proportion of variance in burst characteristics explained by clinical measures of physical function in PD. Results: Grip strength was the best predictor of muscle activity in persons with PD (R-2=.17-.33; P<04), whereas gait characteristics explained muscle activity in healthy controls (R-2=.40.82; P<.04). Conclusions: Grip strength could serve as an effective clinical assessment tool to determine changes in muscle activity, which is a precursor to functional loss in persons with PD. (C) 2016 by the American Congress of Rehabilitation Medicine