Postcontraction depression of reciprocal inhibition in human forearm muscles.
We tested whether a preceding muscle contraction changes reciprocal inhibition (RI) between forearm antagonists. RI was studied in 14 healthy subjects by assessing changes in the H reflex (evoked by median-nerve stimulation) in forearm flexor muscles after conditioning radial-nerve stimulation at 0- and 20-ms intervals. The maximum sizes of the M wave (M(max)) and H reflex (H(max)) were also measured. After a long-lasting maximum voluntary handgrip contraction (mean +/- SEM: 3.9 +/- 0.6 min) of ipsilateral forearm muscles, M(max) and H(max) were unchanged but RI was diminished. After contraction of the contralateral homologous muscles and after contraction elicited by ipsilateral muscle stimulation, RI remained unchanged. These results show that a preceding maximum voluntary contraction (lasting 30 s or more) reduces the activity of the spinal inhibitory interneurons mediating RI. This finding may imply the need to reinterpret results from RI studies in normal subjects and in patients with movement disorders.
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Laboratorio di Neurofisiologia, Istituto di Clinica Neurologica, Università di Milano, Istituto di Ricovero e Cura a Carattere Scientifico Ospedale Maggiore di Milano, Italy. alberto.priori@unimi.it
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Scarlato
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Barbieri
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D000328:Adult; D003213:Conditioning, Psychological; D004558:Electric Stimulation; D004576:Electromyography; D005542:Forearm; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D011826:Radial Nerve / Q000502:physiology; D012016:Reference Values