Electromyographic activity, H-reflex modulation and corticospinal input to forearm motoneurones during active and passive rhythmic movements

Author(s): Riek, S., Bawa, P.

Journal/Book: Hum Movement Sci. 1999; 18: PO Box 211, 1000 AE Amsterdam, Netherlands. Elsevier Science Bv. 307-343.

Abstract: Four subjects produced coordinated movements, consisting of flexion and extension of the wrist in ipsilateral (right wrist only), contralateral (left wrist only), inphase (both wrists in flexion or both in extension) and antiphase (one wrist in flexion, the other in extension) conditions. Electromyographic (EMG) activity was recorded from right wrist flexor and extensor muscles. In one session, transcranial magnetic stimuli (TMS) of the left motor cortex, around threshold intensity, evoked short-latency responses in the right wrist extensors and flexors. In another session, the median nerve at the cubital fossa was stimulated to elicit an H-reflex in the right flexor carpi radialis (rFCR). A movement cycle was divided into 8 segments. In total, 10 identical stimuli were delivered during each segment in each condition, at two movement frequencies. The magnitude of the EMG reponses to TMS was modulated markedly during movements made in the ipsilateral condition, and in both bimanual conditions. EMG activity was greater, and motor-evoked potentials (MEPs) were larger in the antiphase condition than in the inphase condition. When the amplitudes of the MEPs were normalised with respect to background EMG, no significant differences between the bimanual conditions were obtained. For H-reflexes, significant differences between the two bimanual conditions were observed, suggesting differences in levels of excitability of the Ia afferent pathway. These differences were attributed to segmental input associated with changes in muscle length arising from limb movement, and upon descending input to the spinal cord, possibly mediated by Renshaw cell inhibition. During rhythmic passive movement of the right limb, H-reflexes were inhibited and MEPs potentiated in a cyclic fashion. Passive movement of the contralateral left limb resulted in inhibition of both responses.

Note: Article Carson RG, Univ Queensland, Dept Human Movement Studies, Percept & Motor Syst Lab, Brisbane, Qld 4072, AUSTRALIA

Keyword(s): human; voluntary movement; coordination; electromyography; H-reflex; transcranial magnetic stimulation; cylic movement; TRANSCRANIAL MAGNETIC STIMULATION; BIMANUAL COORDINATION; PRESYNAPTIC INHIBITION; VOLUNTARY CONTRACTION; CORTICAL COMMAND; MOTOR CORTEX; DYNAMICS; MUSCLES; HUMANS; LEG

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