Evidence that Neuromuscular Fatigue Is not a Dogma in Patients with Parkinson's Disease

Purpose Given the increased level of fatigue frequently reported by patients with Parkinson's disease (PD), this study investigated the interaction between central and peripheral components of neuromuscular fatigue (NF) in this population compared with healthy peers. Methods Changes in maximal voluntary activation (Delta VA, central fatigue) and potentiated twitch force (Delta Q(tw,pot), peripheral fatigue) pre-post exercise were determined via the interpolated twitch technique in 10 patients with PD and 10 healthy controls (CTRL) matched for age, sex, and physical activity. Pulmonary gas exchange, femoral blood flow, and quadriceps EMG were measured during a fatiguing exercise (85% of peak power output [PPO]). For a specific comparison, on another day, CTRL repeat the fatiguing test matching the time to failure (TTF) and PPO of PD. Results At 85% of PPO (PD, 21 +/- 7 W; CTRL, 37 +/- 22 W), both groups have similar TTF (similar to 5.9 min), pulmonary gas exchange, femoral blood flow, and EMG. After this exercise, the maximal voluntary contraction (MVC) force and Q(twpot) decreased equally in both groups (-16%, P = 0.483; -43%, P = 0.932), whereas VA decreased in PD compared with CTRL (-3.8% vs -1.1%, P = 0.040). At the same PPO and TTF of PD (21 W; 5.4 min), CTRL showed a constant drop in MVC, and Q(twpot) (-14%, P = 0.854; -39%, P = 0.540), instead VA decreased more in PD than in CTRL (-3.8% vs -0.7%, P = 0.028). Conclusions In PD, central NF seems exacerbated by the fatiguing task which, however, does not alter peripheral fatigue. This, besides the TTF like CTRL, suggests that physical activity may limit NF and counterbalance PD-induced degeneration through peripheral adaptations.