Performance fatigability on a constant-load dynamic task is greater in females with moderate-severity Parkinson's disease than healthy-aging controls.

Parkinson's disease (PD) is a neurodegenerative disorder associated with self-reported fatigue. While fatigue is a disabling symptom, performance fatigability, a decline in strength or power during sustained tasks, remains poorly understood, particularly during isotonic (constant-load) contractions, which are encountered in everyday activities. We assessed performance fatigability and recovery in people with PD compared to healthy-aging controls. Fifteen females with PD and 14 healthy-aging controls underwent neuromuscular testing of knee extensors using dynamometry. Participants then performed repeated maximal-effort isotonic knee extensions at a 20 % maximum voluntary contraction (MVC) load until peak power declined 40 %. Performance fatigability was assessed by repetitions to task failure, with recovery tracked for 10 min afterwards. Despite no baseline differences in neuromuscular performance, PD achieved ∼58 % fewer repetitions to failure. Immediately post-task failure, compared to controls, PD exhibited less fatigue-induced impairments in MVC torque, voluntary activation, and quadriceps electromyographic (EMG) activity, but similar impairment of twitch torque. For power and twitch torque, PD and controls recovered similarly, whereas PD recovered sooner for MVC torque and quadriceps EMG. Isotonic performance fatigability differs subtly between PD and healthy controls, providing novel insights into the physical manifestations of fatigue in PD and potential implications for understanding disease progression and management.