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 yr). Maximal H-reflexes (Hmax) and M-waves (MmaxR) 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 (MmaxA) and V-wave (V) of the soleus muscle. At rest, the Hmax/MmaxR 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 (Hsup) and MmaxA was not different from Hmax/MmaxR ratio. When plantar flexors were maximally voluntary activated, the Hsup/MmaxA ratio was still lower during eccentric contraction as compared to isometric and concentric efforts (0.33 ± 0.03 versus 0.47 ± 0.02 and 0.50 ± 0.03, P<0.001), while V/MmaxA 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/MmaxA ratio was significantly lower than Hsup/MmaxA during isometric and concentric MVC (P<0.001). No difference was observed between V/MmaxA and Hsup/MmaxA ratios during eccentric efforts. The H-reflex modulations, present during lengthening actions, were mainly attributed to presynaptic inhibition of Ia afferents and to homosynaptic post activation 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.