BACKGROUND/OBJECTIVES
Circadian physiology has been linked to body weight regulation and obesity. To date, few studies have assessed the association between exercise timing and weight related outcomes. The aim of this secondary analysis was to explore the impact of exercise timing (i.e. 24h clock time of exercise session) on weight loss and components of energy balance.
SUBJECTS/METHODS
Overweight/obese (BMI 25.0–39.9 kg/m2), physically inactive, young adults (~51% female) completed a 10-month supervised exercise program (400 or 600 kcal/session for 5 days/week) or served as non-exercise controls (CON). Participants were categorized based on the time of day in which they completed exercise sessions (Early-Ex: >50% of sessions completed between 7:00–11:59AM; [n=21], Late-Ex: >50% of sessions completed between 3:00–7:00PM; [n=25], Sporadic-Ex: <50% of sessions completed in any time category; [n=24], and CON; [n=18]). Body weight, energy intake (EI; digital photography), and non-exercise physical activity (NEPA; accelerometer) were assessed at baseline, 3.5, 7 and 10 months. Total daily energy expenditure (TDEE; doubly labeled water), was assessed at baseline and 10 months.
RESULTS
At month 10, weight loss was significantly greater in both Early-Ex (−7.2±1.2%; p<0.001) and Sporadic-Ex (−5.5±1.2%; p=0.01) vs CON (+0.5±1.0%), and Early-Ex vs Late-Ex (−2.1±1.0%; p<0.001). There were no between group differences for change in TDEE, EI, and non-exercise energy expenditure (P>0.05). A significant group*time interaction (p=0.02) was observed for NEPA (counts/min), however, after adjusting for multiple comparisons, group effects were no longer significant.
CONCLUSION
Despite minimal differences in components of energy balance, Early-Ex lost significantly more weight compared to Late-Ex. While the mechanisms are unclear, the timing of exercise may be important for body weight regulation.