Author(s): CHENG, C., LIU, C.Y., CHEN, Y.C., Institution: NATIONAL TAIWAN NORMAL UNIVERSITY, Country: TAIWAN, Abstract-ID: 1359

INTRODUCTION:
Prescribed moderate-intensity aerobic exercise on health issues has been extensively investigated but additional exercise interventions may lead to behavioural compensation (e.g., reducing physical activity at other times). However, it is still unclear whether the timing of exercise can affect physical activity behaviours. This study was to examine the effect of exercise at different times of day on physical activity behaviours over a 72-hour period across exercise and non-exercise days.
METHODS:
22 (20 females) young healthy physically inactive adults (age: 24 ± 5 yr; BMI: 21.8 ± 2.2 kg/m2) were recruited in a randomized crossover study with either 45-min brisk walking in the morning (8:00 ~ 11:00, Mwalk) or in the evening (18:00 ~ 21:00, Ewalk). Heart rate (HR) and rating of perceived exertion (RPE) were measured during exercise. Physical activity levels (i.e., step counts), physical activity intensity, and sedentary behaviours were recorded via a pedometer and an accelerometer over a 72 hours period (the exercise day for 24 hours, EX day; non-exercise day, 24 hours before and after EX day). The habitual physical activity levels were recorded over a period of 7 consecutive days.
RESULTS:
There were no differences in HR (120 ± 25 vs. 119 ± 23 bpm, p = 0.603) and RPE (11 ± 2 vs. 11 ± 2, p = 0.538) during exercise between Mwalk and Ewalk. Compared to habitual physical activity (5406 ± 1306 steps), both Mwalk (12797 ± 3226 steps) and Ewalk (13580 ± 3903 steps) increased physical activity levels on the EX day (p < 0.0001) and there was no difference between 2 trials (p = 0.437). Nonetheless, we did not observe any of behavioural compensation in physical activity levels, physical activity intensity, and sedentary behaviours, as no significant differences were found between Mwalk and Ewalk, regardless of whether it was an exercise day or a non-exercise day (all, p > 0.05).
CONCLUSION:
A 45-min of brisk walk prescribed either in the morning or evening can enhance physical activity levels in physically inactive adults. The timing of brisk walking does not appear to induce behavioural compensation (i.e., reduction of physical activity and/or changes in the pattern of physical activity intensity) across exercise and non-exercise days.