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: 2.19). 11/2005; 95(4):377-81. DOI: 10.1007/s00421-005-0023-6
Source: PubMed


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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    • "Diurnal rhythms in maximal strength performance (Gauthier et al., 1996; Guette et al., 2005b) or higher in the evening (Callard et al., 2000; Sedliak 1 et al., 2011) when compared to the rest of the day. These controversial results can be partly 2 explained by the fact that EMG data can be affected by the muscle groups examined, as calf 3 muscles seem to have higher EMG in the morning (Guette et al., 2005b; Guette et al 2006). "
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