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 to healthy peers. Methods: Changes in maximal voluntary activation (ΔVA, central fatigue) and potentiated twitch force (ΔQtw,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 (FBF), and quadriceps electromyography (EMG) were measured during a fatiguing exercise (85% of peak power output (PPO)). For a specific comparison, on another day, CTRLs repeat the fatiguing test matching the time to failure (TTF) and PPO of PDs. Results: At 85% of PPO (PD = 21 ± 7 W; CTRL = 37 ± 22 W), both groups have similar TTF (~5.9 min), pulmonary gas exchange, FBF, and EMG. After this exercise, the maximal voluntary contraction force (MVC) and Qtwpot decreased equally in both groups (-16%, p = 0.483; -43%, p = 0.932), while VA decreased in PD compared to CTRL (-3.8% Vs -1.1%, p = 0.040). At the same PPO and TTF of PDs (21 W; 5.4 min), CTRLs showed a constant drop in MVC, and Qtwpot (-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). Conclusion: In PDs, central NF seems exacerbated by the fatiguing task which, however, does not alter peripheral fatigue. This, besides the TTF like CTRLs, suggests that physical activity may limit NF and counterbalance PD-induced degeneration through peripheral adaptations.