Varying pulse duration from 0.05 to 1 ms induces an increase in the H_max and H_M5% amplitude, and a decrease in M_Hmax amplitude (Figure 3). This agrees with previous work reporting a leftward shift of the H-reflex RC relative to M-wave RC (Panizza et al. 1989; Lagerquist and Collins, 2008) and supports differences in the biophysical properties of axons involved in the H reflex and M wave (Lin et al., 2002). In contrast with the absence of a pulse-duration effect on H_MAX in the soleus (Lagerquist & Collins, 2008), we observed an increase in H_MAXamplitude with the increase in pulse duration, as also reported in the FCR (Panizza et al., 1989). This can reflect the decrease in M_Hmax, which indirectly reflects the magnitude of the antidromic volley, as its decreased amplitude with the increase in pulse duration may reduce collisions between orthodromic and antidromic volleys (Schieppati, 1987). However, only a very weak negative association between the H_max amplitude and the M_Hmax was observed when data from both groups and the three pulse durations were pooled (r² = 0.11, p = 0.005), indicating that H_max may not primarily depend on the M_Hmax. Although the group I volley (Ia and Ib) induced by the stimulus is dominated by the monosynaptic Ia volley, the disynaptic Ib pathway from the Golgi tendon organ likely limits the amplitude of the H reflex (Marchand-Pauvert et al., 2002). Expecting similar biophysical properties between Ia and Ib afferents, the magnitude of the inhibition induced by Ib afferent stimulation should follow the recruitment of Ia afferents, therefore being greater for long pulse duration. This could counteract the lesser antidromic volley for long pulse duration, thereby contributing to the only weak relation between H_max and M_Hmax. Yet, this remains speculative and further studies are required to unravel the mechanisms of action that limit H_max amplitude and the influence of pulse duration on H_max.