title: Time-of-day effect on the torque and neuromuscular properties of dominant and non-dominant quadriceps femoris.
abstract: 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-to-trough 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 18:00 h. The central activation of the quadriceps muscle of each leg remained unchanged during the day. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24 h 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.
authors.affiliation: Laboratoire INSERM ERM 207 Motricité Plasticité, Faculté des Sciences du Sport, Université de Bourgogne, Dijon, France. marie.guette@u-bourgogne.fr
authors.forename: Marie
authors.initials: M
authors.lastname: Guette
authors.forename: Julien
authors.initials: J
authors.lastname: Gondin
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
mesh_terms: D000328:Adult; D001831:Body Temperature; D002940:Circadian Rhythm / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D013848:Thigh / Q000033:anatomy & histology*; D013997:Time Factors; D019415:Torque