Changes in corticomotor pathway excitability after exercise training in Parkinson's disease

Abstract

Background: Altered corticospinal excitability in Parkinson's disease (PD) is related to many of the motor signs.

Objective: We examined whether the recruitment properties of the corticospinal pathway to hand muscles are changed after 8 weeks of specialized upper limbs exercise in PD.

Methods: Seven PD subjects were enrolled. Upper limb exercise was achieved by using a specially designed device. The input-output (I-O) curves were obtained by transcranial magnetic stimulation (TMS). The conduction of peripheral axons and H reflex was also recorded. UPDRS scale, part-III motor examination was used to assess the motor symptom. Clinical and neurophysiological data were obtained before and after 2-month exercise training.

Results: After 2-month exercise training, the UPDRS score was significantly improved. Threshold, slope, and V50 (i.e., the stimulus intensity required to obtain a response 50% of the maximum) of the I-O curve were unchanged, whereas the plateau value was significantly higher.

Conclusions: Exercise training affects the larger motoneurons, that is those activated at higher TMS stimulation intensity. These motoneurones are related to the large, type II motor units. Clinical improvement after exercise may depend upon restoration of the recruitment of the large motor unit, i.e., those necessary to perform rapid and strong movements, known to be deficient in PD.

Keywords: Aerobic exercise; Input-output curve; Motor unit; Parkinson disease; Transcranial magnetic stimulation.