Transient improvement induced by motor fatigue in focal occupational dystonia: the handgrip test.
Muscle fatigue induced by a previous sustained contraction temporarily decreases the motor output, transiently worsening motor performance. Whether muscle fatigue alters motor performance also in dystonia-a disorder whose main pathophysiological abnormality is motor overflow-remains unknown. To assess the effects of muscle fatigue in patients with focal occupational upper limb dystonia, we studied the effect of a previous maximum fatiguing voluntary contraction on motor performance in 10 musicians with focal occupational dystonia, in 3 musicians with hand motor impairment due to non-dystonic disorders, and in 5 normal musicians. The fatiguing task consisted of grasping a spring handgrip as long as possible until the task failed. In dystonic musicians, a fatiguing contraction significantly improved motor performance. The improvement lasted less than 5 minutes and appeared only after fatigue of the affected upper limb. In contrast, in musicians with non-dystonic motor impairment, motor performance remained unchanged or worsened, and normal musician performance consistently worsened.
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Istituto di Clinica Neurologica, Università di Milano, IRCCS Ospedale Maggiore Policlinico, Milano, Italy.
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D000328:Adult; D016022:Case-Control Studies; D020821:Dystonic Disorders / Q000503:physiopathology*; D005260:Female; D018737:Hand Strength; D006801:Humans; D008297:Male; D009069:Movement Disorders / Q000503:physiopathology; D018763:Muscle Fatigue; D009146:Music; D009784:Occupational Diseases / Q000503:physiopathology*