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Evoked H-Reflex and V-Wave Responses During Maximal Isometric, Concentric, and Eccentric Muscle Contraction

Institut National de la Santé et de la Recherche Medicale/Equipe de Recherche Mixte, Faculté des Sciences du Sport, Université de Bourgogne, Dijon, France

Submitted 4 April 2005; accepted in final form 25 July 2005

This study was designed to investigate the modulations of H-reflex and V-wave responses during passive and maximal active dynamic actions. Experiments were performed on 16 healthy males [age: 24 ± 4 (SD) yr]. Maximal H-reflexes (H_max) and M-waves (M_maxR) were evoked at the same muscle length during passive isometric, shortening and lengthening actions and during maximal voluntary isometric, concentric, and eccentric plantar-flexion. In all contraction types, supra-maximal stimulus intensity was used to evoke the superimposed maximal M wave (M_maxA) and V wave (V) of the soleus muscle. At rest, the H_max/M_maxR ratio was significantly reduced during lengthening with respect to isometric and shortening actions (P < 0.05). For each action type, the ratio between H reflex superimposed to the contraction (H_sup) and M_maxA was not different from H_max/M_maxR ratio. When plantar flexors were maximally voluntary activated, the H_sup/M_maxA ratio was still lower during eccentric contraction as compared with isometric and concentric efforts (0.33 ± 0.03 vs. 0.47 ± 0.02 and 0.50 ± 0.03, P < 0.001), whereas V/M_maxA ratios were similar for all contraction types (isometric 0.26 ± 0.02; concentric 0.23 ± 0.03, and eccentric 0.24 ± 0.02; P > 0.05). The V/M_maxA ratio was significantly lower than H_sup/M_maxA during isometric and concentric MVC (P < 0.001). No difference was observed between V/M_maxA and H_sup/M_maxA ratios during eccentric efforts. The H-reflex modulations, present during lengthening actions, were mainly attributed to presynaptic inhibition of Ia afferents and to homosynaptic postactivation depression. Results on V wave and H reflex suggest that during eccentric MVC, the spinal loop is specifically modulated by the supra-spinal centers and/or neural mechanisms at spinal level.

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