Interventional studies on sedentary behaviour (SB) and cardiac health are missing. Therefore, this study investigates the effects of reducing SB on cardiac structure and function in inactive and sedentary adults with metabolic syndrome.

In this randomized controlled trial, the intervention group (n = 33) aimed at reducing SB by 1 h/d for 6 months. The control group (n = 31) continued their SB and physical activity (PA) as usual. All participants wore accelerometers throughout the study. Echocardiography was performed at rest and during incremental exercise tests before and after the intervention.

No intervention effects were observed in any echocardiographic variables between the randomized groups. However, when participants were regrouped into a less sedentary (mean SB reduction 60 min/d) or a continuously sedentary group, based on their actual measured behaviour change, left ventricular (LV) mass index and end-diastolic diameter decreased more in the less sedentary than in the continuously sedentary group (group x time P = 0.045 and 0.020, respectively). Moreover, LV global longitudinal strain during exercise improved in the less sedentary group compared to the continuously sedentary group. Among all participants, the change in light PA was correlated inversely with the change in LV mass index (r = –0.32, P = 0.026), and the change in standing time was correlated with the change in the early diastolic flow velocity / lateral mitral annular velocity (E/e’) ratio (r = 0.28, P = 0.048).

A 6-month intervention aimed at reducing SB did not affect cardiac structure or function. However, in participants with successful SB reduction and increased light PA regardless of original randomization, LV mass index may have decreased, and LV function during exercise may have improved.