title: Time-of-day dependence of isokinetic leg strength and associated interday variability.
abstract: The purpose of this study was to assess the interday variability and time-of-day effects on selected isokinetic leg strength indices. Nine adult collegiate sportsmen (mean(s.e.) age 19.6(0.5) years; mean(s.e.) height 1.81(0.02) m; mean(s.e.) body mass 76.5(3.1) kg) completed a series of nine test sessions, organized so that each subject was tested three times within a day (08.00-09.00 hours; 13.00-14.00 hours; 18.00-19.30 hours), on three occasions, each separated by a minimum of 7 days. Gravity-corrected indices of extension peak torque (EPT), flexion peak torque (FPT), and the peak torque ratio (PTR), at contraction velocities of 1.05 rad s-1 and 3.14 rad s-1, were calculated for each subject using an isokinetic dynamometer. Two-way repeated measures analysis of variance of coefficient of variation (V%) scores revealed no significant differences in performance variability across within-subject factors of time-of-day and performance index (P > 0.05). Overall mean(s.e.) V% for scores across experimental conditions were 3.97(0.72)% at 1.05 rad s-1 and 5.98(1.23)% at 3.14 rad s-1, suggesting that similar levels of measurement error occur between 08.00-19.30 hours. One-way repeated measures analysis of variance of absolute strength indices (EPT, FPT and PTR) revealed that significantly higher scores were achieved during session 3 (18.00-19.30 hours), with mean(s.e.) values of 249.1(40.0) N m, 149.0(32.3) N m, 59.5(5.0)% at 1.05 rad s-1, and 172.1(38.7) N m, 121.3(27.7) N m, 71.1(6.2)% at 3.14 rad s-1, respectively (P < 0.05). This finding appears to be consistent with current knowledge about time-of-day effects on the assessment of muscular strength. Thus for stable and maximal values to be obtained during isokinetic leg testing, the use of multiple-trial protocols is recommended, with testing occurring as close to 18.00-19.30 hours as possible. In addition, the observed significant time-of-day effect suggests that appropriate comparison of maximal isokinetic leg strength can only be achieved based on data obtained within 30 min of the same time of day.
authors.affiliation: Division of Sport, Health and Exercise, School of Sciences, Staffordshire University, Stoke-on-Trent, UK.
authors.forename: J P
authors.initials: JP
authors.lastname: Wyse
authors.forename: T H
authors.initials: TH
authors.lastname: Mercer
authors.forename: N P
authors.initials: NP
authors.lastname: Gleeson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002940:Circadian Rhythm / Q000502:physiology*; D002985:Clinical Protocols; D006112:Gravitation; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D016139:Martial Arts / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology; D012399:Rotation; D012420:Running / Q000502:physiology; D012916:Soccer / Q000502:physiology; D013997:Time Factors