title: Diurnal variation in maximal and submaximal strength, power and neural activation of leg extensors in men: multiple sampling across two consecutive days.
abstract: This study aimed to compare day-to-day repeatability of diurnal variation in strength and power. Thirty-two men were measured at four time points (07 : 00 - 08 : 00, 12 : 00 - 13 : 00, 17 : 00 - 18 : 00, and 20 : 30 - 21 : 30 h) throughout two consecutive days (day 1 and day 2). Power during loaded squat jumps, torque and EMG during maximal (MVC) and submaximal (MVC40) voluntary isometric knee extension contractions were measured. The EMG/torque ratio during MVC and MVC40 was calculated to evaluate neuromuscular efficiency. A significant time-of-day effect with repeatable diurnal patterns was found in power. In MVC, a significant time-of-day effect was present on day 2, whereas day 1 showed a typical but nonsignificant diurnal pattern. EMG and antagonist co-activation during MVC remained statistically unaltered, whereas neuromuscular efficiency improved from day 1 to day 2. A similar trend was observed in MVC40 neuromuscular efficiency with significant time-of-day and day-to-day effects. Unaltered agonist and antagonist activity during MVC suggests that modification at the muscular level was the primary source for the diurnal variation in peak torque. A learning effect seemed to affect data in MVC40. In conclusion, the second consecutive test day showed typical diurnal variation in both maximum strength and power with no day-to-day effect of cumulative fatigue.
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland. milan.sedliak@sport.jyu.fi
authors.forename: M
authors.initials: M
authors.lastname: Sedliak
authors.forename: T
authors.initials: T
authors.lastname: Finni
authors.forename: S
authors.initials: S
authors.lastname: Cheng
authors.forename: T
authors.initials: T
authors.lastname: Haikarainen
authors.forename: K
authors.initials: K
authors.lastname: Häkkinen
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D019415:Torque