Low-intensity activity breaks combined with alternate day interval training mitigate cardiovascular effects of sedentary behavior

This study aimed to determine whether interrupting prolonged sitting with brief bouts of light-intensity activity (ISIT), undertaking structured high-intensity interval training (HIIT), or the combination of both interventions would elicit greater cardiometabolic benefits. Seventeen healthy adults (22–50 yr) were recruited to undertake three 2-wk interventions in a random order: 1) HIIT (6 HIIT sessions þ <5,000 steps following the session and on the next day), 2) ISIT (2.5-min light-intensity walking every hour for 12 h/day on weekdays), and 3) HIIT þ ISIT. Participants underwent a 6-day lead-in phase prior to each condition (days 1–3: normal activity, days 4–6 sedentary: <5,000 steps/day). Pre- and postassessments included glycemic control (2-h postprandial glucose), endothelial function via flow-mediated dilation (FMD), cardiorespiratory fitness, and body composition. Changes in primary and secondary outcomes were assessed via repeated measures ANOVA. Eleven participants completed all conditions (8 female, 33 ± 5 yr, 23 ± 4 kg/m², habitual activity 7,156 ± 2,272 steps/day). FMD significantly improved following HIIT þ ISIT when compared with ISIT (þ 1.04 ± 1.20%, P ¼ 0.02), but there were no differences when ISIT was directly compared with HIIT. Cardiorespiratory fitness improved significantly following HIIT þ ISIT when compared with ISIT (þ 1.88 ± 2.03 mL/kg/min, P ¼ 0.01), but there were no differences when ISIT alone was compared with HIIT. There were no significant differences between groups for outcomes related to glucose control or body composition. HIIT þ ISIT elicits greater improvements in cardiovascular outcomes when compared with ISIT but not HIIT. The benefits of structured exercise, such as HIIT, may go beyond those achieved by limiting sedentary behavior alone. NEW & NOTEWORTHY Although the adverse health effects of sedentary behavior are well-recognized, effective strategies for interrupting such behavior remain unclear. This study demonstrates that combining light-intensity activity breaks throughout the day with structured high-intensity exercise every other day can mitigate some of the cardiovascular consequences associated with prolonged sedentary periods in healthy young adults. Furthermore, our findings also suggest that merely incorporating regular breaks of light-intensity activity may not suffice. These results underscore the importance of regular exercise for cardiovascular health amid sedentary lifestyles.