Morning to evening changes in the electrical and mechanical properties of human soleus motor units activated by H reflex and M wave

Laboratoire INSERM ERM 207 Motricité Plasticité, Faculté des Sciences du Sport, Université de Bourgogne, BP 27 877, 21078, Dijon Cedex, France.
Arbeitsphysiologie (Impact Factor: 2.3). 11/2005; 95(4):377-81. DOI: 10.1007/s00421-005-0023-6
Source: PubMed

ABSTRACT The aim of the present study was to compare the relative contribution of the soleus motor units (MUs) activated by H and M waves to the plantar-flexion torque in the morning and in the evening. Twelve healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 and 08:00 h and between 17:00 and 19:00 h. Plantar-flexion torque and concomitant electromyographic activity of soleus muscle were assessed under voluntary and evoked conditions. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae and associated soleus EMG in the evening as compared with the morning. The mean values of MVC ranged from 131.6+/-9.6 N m in the morning to 125.1+/-9.0 N m in the evening. Peak-to-peak values of soleus H (max) and M (max) potentials were comparable in the morning and in the evening (2.97 vs 3.18 mV and 7.95 vs 7.44 mV for H (max) and M (max), respectively). The H (max)/M (max) ratio was not modified between the two experimental test sessions (34.8 vs 41.3%). The peak amplitude of the twitch produced by the H (max) wave (Pt (H max)) decreased significantly. When estimating the mechanical contribution to (Pt (H max)) of the slowest and fastest-twitch MUs reflexively and directly activated, we observed that the contribution of the slowest MUs did not change while those of the fastest decreased significantly in the evening. To conclude, a weaker reflex twitch torque caused by higher fatigue state of the MUs directly activated by the M wave which accompanied H (max) in the evening may be regarded as a possible explanation of the weaker plantar-flexion torque production in the evening.

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Available from: Julien Gondin, Aug 29, 2015
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    • "Since the late 1960s, isokinetic dynamometers demonstrated their practical value, utility and effectiveness in connection with muscle rehabilitation, training and testing in both research and clinical settings (Baltzopoulos and Brodie, 1989; Kraemer et al., 2006). Dynamometric investigations have improved our understanding of neuromuscular function (Duclay et al., 2009), adaptations to interventions (Alfredson et al., 1998b; Horstmann et al., 2012) and fluctuations in muscle performance as a function of time of day (Castaingts et al., 2004; Guette et al., 2005). In isometric, isokinetic or isotonic-based research studies, dynamometers are commonly employed to capture EMG signals during plantar-flexion MVIC trials for signal normalization of the triceps surae muscle group (Cresswell et al., 1995; Gerdle and Fugl-Meyer, 1992; Hubley-Kozey and Earl, 2000; Kay and Blazevich, 2009; Pinniger, 2003). "
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