Electrical and mechanical H_max-to-M_maxratio in power- and endurance-trained athletes

Abstract

The aim of this study was to compare the mechanical and electromyographic (EMG) characteristics of soleus motor units activated during maximal H reflex and direct M response among subjects with different histories of physical activity. Power-trained athletes produced stronger twitches, with a higher rate of twitch tension buildup and relaxation, than their endurance counterparts for both maximal H-reflex and maximal M-wave responses. The maximal H-reflex-to-maximal M-wave ratios for both force output (twitch) and EMG wave amplitude were significantly lower in power-trained than endurance-trained athletes. However, power-trained athletes exhibited a significantly greater twitch-to-EMG ratio for the reflexly activated motor units with respect to the entire motor pool, whereas endurance-trained athletes had comparable twitch-to-EMG ratios for both reflexly and directly activated units. Power training increases the force output of the whole ensemble of the motor units, thereby compensating for the lower efficacy of the reflex transmission between Ia spindle afferent input and soleus alpha-motoneuron. On the other hand, the lower level of force evoked by the reflexly activated units in endurance-trained athletes is associated with a greater motor pool reflex excitability. Therefore, endurance-trained athletes produce the necessary force by recruitment of more slow-twitch units than do other subjects for comparable levels of force and type of task.

Unilateral Reference Values for Hoffmann’s Reflex in Patients with Suspected Lumbosacral Radiculopathies

“…Thus, both the H-reflex amplitude and the M-wave amplitude will decrease upon atrophy of the soleus-gastronemius or the development of a lesion in the efferent pathway of the peripheral nervous system. The M-wave is related to direct activation of all motor neuron pool innervated axons [15], while the H-wave is related to transmission of sig- nals between Ia fibers and α-motor neurons (mainly slow-twitch motor units) [15]. Therefore, although the H/M ratio is generally considered an index representing the level of reflex excitability of the motor pool [1,8], a decreased H/M ratio may instead indicate proximal lesions, such as lesions at Ia afferent fibers proximal to ganglion or conduction blocks at proximal efferent fibers.…”

“…The sample size of our study was small and may be insufficient to establish valid reference values. We assessed H-wave profile parameters with the conventional clinical protocol [12], so the standing and dynamic methods were not investigated [15]. Furthermore, the sensitivity and specificity of our unilateral H-reflex reference values for the diagnosis of lumbosacral radiculopathy were not investigated in this study and need to be determined in the future.…”

Maturation-related differences in neuromuscular fatigue after a short-term maximal run

“…Assuming that the bigger H max /M max ratio is associated with the greater percentage of low-threshold motor units [32], the observed post-fatigue differences in the metabolic and neuromuscular characteristics between the studied groups could be explained to some extent by the maturation-related decrease in the relative proportion of more aerobic lowthreshold muscle fibres [33]. Overall, the present results support the previous outcomes that because of their lower anaerobic capacity children are less capable of pushing their neuromuscular system to the same degree as more matured athletes [34].…”

New evidence of corticospinal network modulation induced by motor imagery

“…In session 3, FCR H max were first measured, as they provided a sufficient associated M wave to H wave (M atH ) to ensure similar stimulation conditions throughout the experiment (Grosprêtre and Martin 2012 (Maffiuletti et al 2001) or H1 (Katz and Pierrot-Deseilligny 1998), was measured in SOL (intensity range: 10 -40 mA). At this intensity, PNS minimizes the risk of an antidromic collision between alpha motoneuron axon and reflex volley that could interfere with a presynaptic conditioning maneuver.…”