Author(s): HUTCHINS, K., BRADSHAW, L., DAVIS, M., MACPHERSON, S., DIBNER, C., GONZALEZ, J.T., HAWLEY, J., JOHNSTON, J.D., KOUMANOV, F., MAHER, J., PERKIN, O.J., STOCKS, B.N., THOMPSON, D., TSINTZAS, K., VAN LOON, L.J.C., WHALIN, J.P., WILLIAMS, S., ZIERATH, J.R., BETTS, J.A., Institution: UNIVERSITY OF BATH, Country: UNITED KINGDOM, Abstract-ID: 2677

INTRODUCTION:
Human physiology is regulated by an endogenous timing system that helps coordinate environmental cues and physiological/metabolic processes. Previous research has primarily focused on the effects of light, sleep and nutrition as synchronisers of this timing system. In contrast, the effects of physical activity and exercise have received comparatively little research attention.
METHODS:
In this interim analysis, twelve participants (7 males and 5 females) completed a 37-hour laboratory protocol after adhering to a 1-week of period of standardised sleep-wake timing and light exposure. Participants were randomly assigned to one of three conditions - either continuous rest (CONTROL), morning exercise (EARLY) or evening exercise (LATE). Specifically, following a familiarisation night in the laboratory, the CONTROL group rested for 24 hours (measures starting at 0800 h), whereas the EARLY and LATE groups performed 60-minutes of moderate-vigorous intensity cycling (50 % delta of LT1 and LT2) at either 0800 h or 2000 h, respectively, then rested for the subsequent 23 hours of measurement. All groups received continuous feeding via nasogastric tube for 24 h, prescribed in quantities to meet individual metabolic requirements (as established by indirect calorimetry). In the LATE condition, continuous nutrient delivery commenced at 2000 h, from onset of exercise and continued during the nighttime and following day. In contrast, in the EARLY and CONTROL conditions, continuous feeding began at 0800 h, coinciding with the onset of exercise in the EARLY condition and continued throughout the daytime and nighttime. Substrate oxidation was calculated hourly from indirect calorimetry throughout the wake period, alongside aural temperature every hour during the light phase (0700-2200 h) and every 4 hours during the dark phase (2200-0700 h), with blood pressure measured hourly during waking hours. A repeated measures ANOVA (condition x time) was used to explore patterns within and between experimental conditions.
RESULTS:
Lipid oxidation was significantly higher in the LATE exercise condition compared to EARLY and CONTROL (main effect of condition (p=0.031) but no such differences were evident for carbohydrate oxidation, aural temperature nor blood pressure between groups. Mean ± SD lipid oxidation rates were 0.066 ± 0.023 g·min-1 (CONTROL), 0.066 ± 0.025 g·min-1 (EARLY), and 0.102 ± 0.011 g·min-1 (LATE).
CONCLUSION:
The greater rates of lipid oxidation observed in the LATE condition were especially apparent during the morning after, and may be attributable to a direct effect of having exercised the previous evening (rather than immediately beforehand) and/or due to the differences in feeding pattern relative to daytime measurements that are inherent to this protocol (i.e. continuous delivery of nutrients following exercise during the nighttime as opposed to the daytime).