CHRONOBIOLOGICAL EFFECTS ON MAXIMAL AEROBIC EXERCISE PERFORMANCE AND CONCOMITANT PHYSIOLOGICAL RESPONSES 349

Abstract

It has been established that resting physiological variables, as well as work performance, are subject to circadian variation. The purpose of the present study was to determine whether biorhythms were evident for maximal aerobic performance, and/or selected physiological responses to maximal exercise. Ten healthy, untrained males (21.1 ± 3.0 yrs, 80.2 ± 8.3 kg, 179.1 ± 54 cm) served as subjects for the study. In a randomized manner, each subject performed a graded maximal exercise test on a cycle ergometer at 0800, 1200, 1600, and 2000 h. Maximal exercise performance(time to exhaustion) as well as peak oxygen consumption (VO2), minute ventilation (VE), heart rate (HR), blood pressure (BP), rectal temperature(Tre), and plasma lactate (HLa) response were measured at each session. Comparisons for each variable across the 4 time points were performed with 1 way repeated measures ANOVA. Results indicated that maximal exercise performance was similar (p=0.96) at all time intervals. No significant chronobiological effect on HR was identified. Nonsignificant (p>0.05) increases in peak VO2 (9.4%) and VE (10.8%) were detected at 2000 compared to 0800 h. Peak BP was found to be significantly (p<0.05) less at 0800 h than at all other times of day tested. Tre at exhaustion was significantly (p<0.05) influenced by chronobiological fluctuation; 0800 less than 1200, 1600, and 2000 h; 1200 less than 2000 h. Significant(p<0.05) biorhythmic influences upon HLa response to exercise were noted; 0800 less than 2000 h. The data presented here suggest that while maximal aerobic exercise performance is resistant to time of day effects, certain physiological variables (BP, Tre, and HLa) are sensitive to biorhythmic influences.