Acute Metabolic Responses to Breaking Up Sedentary Time in Older Adults.

reserve). Metabolic flexibility was determined by combining hourly measurements of respiratory exchange ratio (RER) and plasma insulin levels (T0-T8). Meals (consumed after T0 and T4) were standardized for the day before and during the experiment day. Mixed linear models included fixed effects (condition, time and condition x time) and random effects (time, condition, participant). Break30 exhibited a greater variance in RER throughout the day compared to noBreak whereas no difference was observed for insulin. Significant condition-by-time interactions were observed for RER at T4 (noBreak=0.83±0.04, Break30=0.86±0.04, Break60=0.83±0.04, p=0.035) and T7 (noBreak=0.87±0.04, Break30=0.90±0.05, Break60=0.89±0.05; p=0.002). A significant interaction was also observed for non‑esterified fatty acid concentrations at T5 (noBreak=0.251 ± 0.042 mmol/L, Break30=0.393 ± 0.042 mmol/L, Break60=0.373 ± 0.042 mmol/L; p=0.041). Compared with prolonged sedentary behavior, interrupting sitting every 30 or 60 minutes appears to induce acute alteration in substrate oxidation. Further studies are needed to confirm these results and to evaluate potential long‑term adaptations.