Time-of-day effect on the torque and neuromuscular properties of dominant and non-dominant quadriceps femoris

The study was conducted first, to determine the possibility of a dichotomy between circadian rhythm of maximal torque production of the knee extensors of the dominant and non-dominant legs, and second, to determine whether the possible dichotomy could be linked to a change in the downward drive of the central nervous system and/or to phenomena prevailing at the muscular level. The dominant leg was defined as the one with which subjects spontaneously kick a football. Tests were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. To distinguish the neural and Muscular mechanisms that influence Muscle strength, the electromyographic and mechanical muscle responses associated with electrically evoked and/or voluntary contractions of the human quadriceps and semi-tendinosus muscles for each leg were recorded and compared. The main finding was an absence of interaction between time-of-day and dominance effects on the torque associated with maximal voluntary contraction (MVC) of both quadriceps. A significant time-of-day effect on MVC torque of the knee extensors was observed for the dominant and non-dominant legs when the data were collapsed, with highest values occurring at 18:00 h (p < 0.01). From cosinor analysis, a circadian rhythm was documented (p < 0.001) with the peak (acrophase) estimated at 18: 18 +/- 00: 12 h and amplitude (one-half the peak-totrough variation) of 3.3 +/- 1.1%. Independent of the leg tested, peripheral mechanisms demonstrated a significant time-of-day effect (p < 0.05) on the peak-torque of the single and doublet stimulations, with maximal levels attained at 18:00h. The central activation of the quadriceps muscle of each leg remained unchanged during the clay. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24h period, and that the changes are linked to modifications prevailing at the muscular, rather than the neural, level. The similar rhythmicity observed in this Study between the dominant and non-dominant legs provides evidence that it is not essential to test both legs when simple motor tasks are investigated as a function of the time of day.