Changes in H reflex and V wave following short-term endurance and strength training

Abstract

This study examined the effects of 3 wk of either endurance or strength training on plasticity of the neural mechanisms involved in the soleus H reflex and V wave. Twenty-five sedentary healthy subjects were randomized into an endurance group (n = 13) or strength group (n = 12). Evoked V-wave, H-reflex, and M-wave recruitment curves, maximal voluntary contraction (MVC), and time-to-task-failure (isometric contraction at 40% MVC) of the plantar flexors were recorded before and after training. Following strength training, MVC of the plantar flexors increased by 14.4 ± 5.2% in the strength group (P < 0.001), whereas time-to-task-failure was prolonged in the endurance group (22.7 ± 17.1%; P < 0.05). The V wave-to-maximal M wave (V/M(max)) ratio increased significantly (55.1 ± 28.3%; P < 0.001) following strength training, but the maximal H wave-to-maximal M wave (H(max)/M(max)) ratio remained unchanged. Conversely, in the endurance group the V/M(max) ratio was not altered, whereas the H(max)/M(max) ratio increased by 30.8 ± 21.7% (P < 0.05). The endurance training group also displayed a reduction in the H-reflex excitability threshold while the H-reflex amplitude on the ascending limb of the recruitment curve increased. Strength training only elicited a significant decrease in H-reflex excitability threshold, while H-reflex amplitudes over the ascending limb remained unchanged. These observations indicate that the H-reflex pathway is strongly involved in the enhanced endurance resistance that occurs following endurance training. On the contrary, the improvements in MVC following strength training are likely attributed to increased descending drive and/or modulation in afferents other than Ia afferents.

Strength training-induced responses in older adults: attenuation of descending neural drive with age

“…Thus, in addition to motoneuron excitability, the maximal firing frequency, as well as the proportion of motoneurons recruited will determine the size of the V-wave, as they will both affect the probability of antidromic collision. Although pre/postsynaptic inhibition may also affect the amplitude of the V-wave, these factors would influence the amplitude of the Hreflex similarly (Zehr 2006;Vila-Cha et al 2012). Interestingly, the reduction in V/M ratio was more than three times larger than the reduction in H/M ratio.…”

“…This discrepancy suggests that the difference in V/M-ratio between young and elderly was mainly caused by the magnitude of efferent motor output, likely reflecting a reduced supraspinal descending drive in elderly. This indicates that the neural function may actually be more altered at supraspinal levels than at spinal levels (Aagaard et al 2002;Vila-Cha et al 2012). Such a central impairment may not immediately lead to a loss of muscle strength, since a gradual loss of motoneurons may be compensated for through axonal sprouting (McNeil et al 2005;Aagaard et al 2010).…”

“…Indeed, this is an important aspect since it also reflects the changes of the fast twitch muscle fibers, which are closely linked to balance adjustments and fall prevention (Hvid et al 2010). The V-wave methodology, an electrophysiological variant of the H-reflex technique, evoked in the triceps surae muscles during maximal muscle contraction has been applied for this frame of testing in several studies (Upton et al 1971;Aagaard et al 2002;Duclay and Martin 2005;Fimland et al 2009;Ekblom 2010;Fimland et al 2010;Fimland et al 2011;Vila-Cha et al 2012). The V-wave is typically normalized to the maximal M-wave (V/M ratio), and its magnitude is suggested to reflect neural drive to the muscle, as well as spinal excitability and pre/ postsynaptic inhibition (Upton et al 1971;Aagaard et al 2002;Aagaard 2003).…”

“…The V-wave is typically normalized to the maximal M-wave (V/M ratio), and its magnitude is suggested to reflect neural drive to the muscle, as well as spinal excitability and pre/ postsynaptic inhibition (Upton et al 1971;Aagaard et al 2002;Aagaard 2003). Although it may be difficult to identify the exact site of the motor system responsible for a difference in V-wave amplitude, it may be used in combination with the H-reflex technique to more specifically determine the sites and mechanisms of neural changes (Aagaard et al 2002;Vila-Cha et al 2012), since the H-reflex is more dependent on motoneuron excitability (Misiaszek 2003;Ekblom 2010;Vila-Cha et al 2012), whereas the V-wave is more sensitive to supraspinal activation of the motoneuron pool. Several studies have, using the V-wave methodology, demonstrated increased descending drive in response to heavy resistance training in young populations (Aagaard et al 2002;Del Balso and Cafarelli 2007;Fimland et al 2009;Ekblom 2010).…”

The H-reflex as an important indicator in kinesiology

“…They observed a 20% increase in the amplitude of the H-reflex following the training. Furthermore, Vila-chã et al [59] compared the effect of a 3-week strength training and endurance training programme. They found that the amplitude of the H-reflex for the soleus muscle increased significantly among those persons who participated in strength training.…”