Author(s): MENDO, M., GIANLUCA VERNILLO2, EIVIND WANG3, OLE KRISTIAN BERG3, MATHIAS FORSBERG BROBAKKEN3, MANI IZADI3, RONAN SHERMAN3, CHIARA BARBI1, ANDREA PATERNO4, ILARIA ANTONELLA DI VICO1,5, MICHELE TINAZZI1,5, FEDERICO SCHENA1,7 AND MASSIMO VENTURELLI1,6, Institution: UNIVERSITY OF VERONA, Country: ITALY, Abstract-ID: 1549

INTRODUCTION:
Parkinson’s disease (PD) is a neurodegenerative disorder characterized by a typically unilateral onset. Fatigue is a common and debilitating symptom that significantly impairs quality of life in individuals with PD. It represents a complex phenomenon involving both central and peripheral components of the neuromuscular system and manifests as a reduced ability of the muscle to generate force. While most existing studies have focused on fatigue in the lower limbs, little is known about its impact on the upper limbs, despite their crucial role in fine motor control and activities of daily living. Therefore, the present study aims to evaluate the effects of PD-related motor symptoms on upper-limb neuromuscular fatigue in patients with PD. We hypothesized that individuals with PD would exhibit greater neuromuscular fatigue than controls, primarily driven by central mechanisms, and that the more affected limb would show greater fatigue than the less affected limb.
METHODS:
Thirteen individuals with PD (H&Y Scale I-II) and six age-, sex-matched healthy controls were included. Participants performed fatiguing exercise protocols in both limbs corresponding to 60s elbow isometric flexion at 40% of maximal voluntary contraction (MVC) for the most impaired limb followed by time-to-failure task at the same intensity. Fatiguing task performed by controls was matched to the absolute force task as the corresponding patients. In patients, the impaired limb was the dominant limb. MVC, voluntary activation (VA), corticospinal excitability and resting twitch were measured before and immediately after each task via interpolated twitch and transcranial magnetic stimulation.
RESULTS:
A significant main effect of limb side was observed (p = .03), with a greater force decline in the patient’s impaired limb compared with the non-impaired limb. Controls exhibited lower decline of MVC than PD (p = .005). VA decline was (12% and 10%) in PD and controls, respectively. Resting twitch amplitude and TMS-derived measures of corticospinal excitability showed similar time-dependent decreases in both groups (p < .05). Time to task failure was 160±77 s for PD and 180±55 s for controls.
CONCLUSION:
These findings indicate that neuromuscular fatigue is exacerbated in the limb with higher motor symptoms of patients with PD. Central factors (VA) rather than peripheral (resting twitch) are responsible for these limb-specific neuromuscular fatigue patterns, likely due to impaired central motor drive associated with basal ganglia dysfunction. These results suggest that fatigue assessment and rehabilitation strategies in PD should account for limb-specific central fatigue mechanisms.