Plantar Flexion Torque as a Function of Time of Day

Abstract

The possible peripheral and/or central origin in the mechanisms responsible for day-time fluctuation in maximal torque of the triceps surae muscle were investigated with a special emphasis on antagonist muscle coactivation. Eleven 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 h and 08:00 h in the morning and between 17:00 h and 19:00 h in the evening. To investigate peripheral mechanisms, the posterior tibial nerve was stimulated at rest, using percutaneous electrical stimuli, to evoke single twitch, double twitch, and maximal tetanic contraction (100 Hz). Maximal voluntary contraction of the plantar flexors was also assessed by means of the relative electromyographic activity of respective agonist and antagonist muscles (soleus, gastrocnemius medialis, gastrocnemius lateralis, and tibialis anterior). A double twitch was delivered during maximal voluntary plantar flexion to record muscle activation (i.e., interpolated twitch technique). The coactivation level of the tibialis anterior muscle during plantar flexion was calculated. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae in the evening as compared with the morning (-7.0 %; p < 0.05). Concerning the central command, when extrapolated by the twitch interpolation technique, the decrease in mean activation level of -6.8 % was consistent with the fluctuation in torque (-7.0 %). Soleus muscle electromyographic activity (normalized to the M-wave) showed a significant decline (21.6 %; p < 0.001). Moreover, individual changes in MVC percentage were significantly related to those of normalized electromyographic activity of the soleus muscle (r = 0.688; p < 0.01). Thus, it indicated that the subject's capacity to activate the soleus muscle was affected by the time of day. The coactivation level in the tibialis anterior muscle during plantar flexion did not change significantly in the evening. Concerning peripheral mechanisms, we observed a decrease in maximal M-wave amplitude for soleus and gastrocnemii, associated with unchanged single twitch and tetanus torque. To conclude, impairment in soleus muscle central command seemed to be the mechanism in the origin of torque failure. Such information would be of importance in the investigation of day-time fluctuations in complex motor task performances implicating the triceps surae muscle.

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

“…In agreement with the previous study (Guette et al 2005b), we observed a lower MVC torque and concomitant soleus muscle EMG ratio that was associated with a constant peak-twitch torque at M max . The present findings point to a nochange in the efficiency of the reflex transmission between Ia spindle afferent input and soleus a-motoneuron pool according to the time of the day.…”

“…Nevertheless, studies concerning plantar flexor muscles (Castaingts et al 2004;Guette et al 2005b) are less consistent. In fact, in voluntary submaximal conditions, Castaingts et al (2004) described a lower neuromuscular efficiency (i.e.…”

“…the ratio between force and activity of the muscle) in the evening as compared with the morning. Moreover, Guette et al (2005b) reported a decline in maximal voluntary plantar flexion torque in the evening. These latter studies were conducted in the condition of usual daily living which corresponded to the combination of the endogenous (body clock controlled) and exogenous (under influence of environment and life style) components of the circadian rhythm.…”

Human circadian rhythms and exercise: Significance and application in real-life situations

“…The difference between the peaks and nadirs in fitness indices is up to about 20%, except for flexibility, which shows a larger difference with its lowest value at midnight. Two notable reports 31,32) have investigated the circadian rhythms of muscle strength. In these reports, maximal voluntary plantar flexion torque was 5-7% higher in the morning than in the evening.…”

“…To elucidate the mechanisms, the test session of those studies included measurements during tetanic contractions using the electrical stimulation technique. The authors suggested that possible mechanisms underlying the decreased plantar flexion torque in the evening might be a decrement in soleus muscle central command 31) and higher fatigue state in the fastest-twitch motor units in the weight-bearing soleus muscle 32) . As these studies did not strictly control the subjects' behavior, results may differ by employing a "constant routine" protocol.…”