Sedentary time (ST) increases obesity risk. In lab studies, interrupting ST improves acute metabolic outcomes, but it's unknown what factors predict who will best respond to this type of intervention and if multi-day in-field ST interruptions influence metabolic responses. We investigated in-lab and in-field metabolic responses to ST interruptions, and if moderate-to-vigorous physical activity (MVPA) and ST in the prior 3yrs affects these responses.
Youth (N=14, mean age=13.0yr, 35.7% male, 42.9% Hispanic, 71.4% healthy weight) from an observational study had accelerometer-measured MVPA and ST assessed bi-annually for 3yrs. They completed 2 in-lab 3hr oral glucose tolerance tests (OGTT) in random order: sit (3hrs of continuous sitting) and sit+walk (3min of moderate-intensity walking every 30min). Glucose, insulin, and C-peptide were assessed at -10, 0, and every 30min for 3hr. In the week following each OGTT, they wore a continuous glucose monitor and were instructed to perform habitual activity or were prompted by a wrist-worn device to interrupt ST every 30min. Repeated measures ANOVA assessed if condition (sit vs. sit+walk) and MVPA and ST (mean min) in the prior 3yrs predicted in-lab and in-field glucose area under the curve (AUC). Models controlled for sex, baseline age (yr), and Hispanic ethnicity.
In-lab glucose (p=0.06), insulin (p=0.02), and C-peptide AUC (p=0.03) were lower in sit+walk vs. sit condition; however, in-field ST interruptions increased 24-hour glucose AUC (p=0.04). MVPA or ST in the prior 3yrs did not predict in-lab or in-field metabolic responses to ST interruptions.
There are acute beneficial effects of interrupting ST in a controlled setting, but not in a free-living setting. These effects are not influenced by prior behavioral patterns. Future work is needed to optimize ST interruptions in the field and understand what individual-level activity pattern metrics (e.g., breaks in ST) may influence responsiveness to this type of intervention.