Effects of dopaminergic medication on upper limb motor function, strength and hand dexterity in people with...

Dopaminergic medications improve motor symptoms and hand dexterity in people with Parkinson's disease (PD). The contribution of altered muscle contractile properties to these functional improvements are not well understood.

To compare the treated (ON) and untreated (OFF) states in people with PD to examine effects of dopaminergic medication on hand dexterity, motor symptom severity, muscle twitch properties and maximal voluntary contraction (MVC).

Sixteen individuals with PD (mean disease duration 6.4 years) completed two sessions: one ON and one OFF dopaminergic medication. Measures included motor symptom severity (MDS-UPDRS III), Grooved Pegboard Test (GPT) time, Purdue Pegboard Test (PPT) peg count, elbow flexion MVC, voluntary activation, and electrically induced twitch properties.

MDS-UPDRS III subscores improved by 27 % ON dopaminergic medication compared to OFF medication, and performance improved on GPT (11 %) and PPT (34 %; p < 0.05). Comparing ON and OFF states, electrically induced contractile properties did not differ, while voluntary elbow flexor MVC increased by 4 %. Normalized MVC was moderately associated with GPT and PPT performance in both ON (GPT: r = -0.48, PPT: r = 0.48) and OFF (GPT: r = -0.61, PPT: r = 0.45) states. Motor symptom severity in the OFF state showed moderate correlations with GPT (r = 0.48) and PPT (r = -0.58), but these associations were not significant in the ON phase (p > 0.05).

Dopaminergic treatment improved motor symptoms, hand dexterity, and strength, without altering electrically induced contractile properties. Improved hand dexterity during treatment appears to be linked to strength gains independent of peripheral muscle changes.