Time‐of‐Day Effects on Myoelectric and Mechanical Properties of Muscle During Maximal and Prolonged Isokinetic Exercise

Abstract

The aim of this study was to examine the time-of-day (TOD) effects in myoelectric and mechanical properties of muscle during a maximal and prolonged isokinetic exercise. Twelve male subjects were asked to perform 50 maximal voluntary contractions (MVC) of the knee extensor muscles at a constant angular velocity of 2.09 rad . sec(-1), at 06 : 00 and 18 : 00 h. Torque and electromyographic (EMG) parameters were recorded for each contraction, and the ratio between these values was calculated to evaluate variations of the neuromuscular efficiency (NME) with fatigue and with TOD. The results indicated that maximal torque values (T(45)Max) was significantly higher (7.73%) in the evening than in the morning (p<0.003). The diurnal variation in torque decrease was used to define two phases. During the first phase (1st to the 26th repetition), torque values decreased fast and values were higher in the evening than in the morning, and during the second phase (27th to the 50th repetition), torque decreased slightly and reached a floor value that appeared constant with TOD. The EMG parameters (Root Mean Square; RMS) were modified with fatigue, but were not TOD dependent. The NME decrease-significantly with fatigue, showing that peripheral factors were mainly involved in the torque decrease. Furthermore, NME decrease was greater at 18 : 00 than at 06 : 00 h for the vastus medialis (p<0.05) and the vastus lateralis muscles (p<0.002), and this occurred during the first fatigue phase of the exercise. In conclusion, the diurnal variation of the muscle fatigue observed during a maximal and prolonged isokinetic exercise seems to reflect on the muscle, with a greater contractile capacity but a higher fatigability in the evening compared to the morning.

Time of day has no effect on maximal aerobic and peak power

“…2,3,15 However, diurnal variation in muscle function has previously been reported. Peak muscular torque 29,30 and fatigability 31 increase throughout the day. Nerve conduction velocity also increases throughout the day 32 and time to peak and relaxation times decrease by 8.3% and 10.7%, respectively, 30 making for better muscle properties in the late afternoon than in the early morning.…”

Sports performance: is there evidence that the body clock plays a role?

“…Examples include peak force of leg and back muscles (Coldwells et al 1994;Guette et al 2005;Nicolas et al 2005Nicolas et al , 2008aSedliak et al 2007;Souissi et al 2004;Wyse et al 1994) and of arm muscles (Gauthier et al 1996;Nicolas et al 2008b), maximal anaerobic power output (Kin-Isler 2006;Souissi et al 2007) and performance in broad and vertical jumps (Reilly and Down 1992). When rhythmic changes have been characterised from at least six measures obtained at equally spaced intervals throughout the 24 h, the peaks in performance are located from about 15:30 to 20:30 hours, with amplitudes ranging from 2 to 11% of the daily mean (summarised in Reilly 2007).…”

Effects of time of day on resistance exercise-induced anabolic signaling in skeletal muscle

“…It must, however, be noted that their study was not primarily designed to address the effect of time of day. Hence, the acute loadings and biopsy samplings were not scheduled to early morning and late afternoon hours, when diurnal minimum and maximum in neuromuscular performance is typically found, respectively (12,26,32,33,35). Furthermore, early morning and late afternoon hours are also when hormonal signalling is dramatically different (e.g., cortisol to testosterone ratio -for a review see (16)).…”