Plain language summary
Long-term weight management is notoriously difficult, with many people experiencing progressive weight gain throughout adult life. The aim of this study was to assess the acute effects of morning and evening cycling exercise on appetite, post-exercise ad-libitum energy intake, substrate metabolism, voluntary performance, and subjective responses to exercise, in young, healthy males and females. Sixteen healthy participants (eight males and eight females) were recruited to the study. Each participant completed two preliminary trials, followed by two experimental trials which involved exercising at 10:30 or 18:30. Results show that: - post-exercise energy intake was greater after acute cycling exercise performed in the evening compared to the morning, despite no post-exercise differences in subjective appetite. - there wasn’t any difference in exercise performance between morning and evening exercise. - exercise timing did not affect performance during a 15-min all-out performance test. Authors conclude that their findings demonstrate a disconnect between subjective appetite and ad-libitum energy intake but provide some evidence that exercise can offset circadian-related appetite profiles.
Abstract
Exercise is an important component of a weight management strategy. However, little is known about whether circadian variations in physiological and behavioural processes can influence the appetite and energy balance responses to exercise performed at different times of the day. This study compared the effects of morning and evening exercise on appetite, post-exercise energy intake, and voluntary performance. In randomised, counterbalanced order, 16 healthy males and females (n = 8 each) completed two trials, performing morning exercise at 10:30 (AMEx) or evening exercise at 18:30 (PMEx). Exercise consisted of 30 min steady-state cycling (60% V˙ O2peak), and a 15-min performance test. A standardised meal (543 ± 86 kcal) was consumed 2-h before exercise and ad-libitum energy intake was assessed 15 min after exercise, with subjective appetite measured throughout. Absolute ad-libitum energy intake was 152 ± 126 kcal greater during PMEx (P < 0.001), but there was no differences in subjective appetite between trials immediately pre-exercise, or immediately before the post-exercise meal (P ≥ 0.060). Resting energy expenditure (P < 0.01) and carbohydrate oxidation (P < 0.05) were greater during AMEx, but there were no differences in substrate oxidation or energy expenditure during exercise (P ≥ 0.155). Exercise performance was not different between trials (P = 0.628). In conclusion, acute morning and evening exercise prompt similar appetite responses, but post-exercise ad-libitum energy intake is greater following evening exercise. These findings demonstrate discordant responses between subjective appetite and ad-libitum energy intake but suggest that exercise might offset circadian variations in appetite. Longer-term studies are required to determine how exercise timing affects adherence and weight management outcomes to exercise interventions. TRIAL REGISTRATION NCT04742530, February 8, 2021.
Methodological quality
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