title: Effect of time of day on aerobic and anaerobic responses to high-intensity exercise.
abstract: This study evaluated the effect of time of day on performance of high-intensity, constant-power cycle ergometry by both men and women. Subjects performed all-out cycle ergometer tests in the morning and in the afternoon in randomized order. For all tests, work rate was a constant 5.0 W.kg-1 (women, n = 6) or 6.0 W.kg-1 (men, n = 8). Total work performed was 9.6% greater in the afternoon (mean +/- SE, 348.8 +/- 40.6 J.kg-1) compared to the morning (318.2 +/- 39.5 J.kg-1). The greater amount of work in the afternoon was associated with a 5.1% higher aerobic power and a 5.6% larger anaerobic contribution. There was no interaction between gender and the effect of time of day on the aerobic or anaerobic contributions. These results provide evidence of a circadian rhythm in aerobic and anaerobic responses to high-intensity short-duration exercise, in women as well as in men.
authors.affiliation: Department of Kinesiology, University of North Texas, Denton 76203-3857.
authors.forename: D W
authors.initials: DW
authors.lastname: Hill
authors.forename: D O
authors.initials: DO
authors.lastname: Borden
authors.forename: K M
authors.initials: KM
authors.lastname: Darnaby
authors.forename: D N
authors.initials: DN
authors.lastname: Hendricks
authors.forename: C M
authors.initials: CM
authors.lastname: Hill
mesh_terms: D000054:Acceleration; D000332:Aerobiosis / Q000502:physiology; D000693:Anaerobiosis / Q000502:physiology; D000704:Analysis of Variance; D002940:Circadian Rhythm; D004734:Energy Metabolism / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012737:Sex Factors; D014937:Work / Q000502:physiology