Observational evidence suggests that a high volume of sedentary behavior (SB) associates with adverse cardiovascular health, yet interventional evidence remains limited. The aim of this doctoral thesis was to investigate the effects of a SB reducing intervention on cardiovascular health.

Sixty-four adults with metabolic syndrome, physical inactivity, and high sedentary time were randomized into the intervention (n=33) and control (n=31) groups. The intervention group aimed at reducing daily SB by 1 h/day for six months, compared to a four-week screening period. The SB was advised to be replaced with other physical activity than exercise training, such as standing up, everyday tasks, and light physical activities. The control group maintained their usual physical activity behavior. All participants wore accelerometers throughout the study to monitor SB and physical activities. The outcomes were maximal cardiorespiratory fitness, and blood pressure and echocardiographic measures at rest and during exercise testing.

The intervention group reduced their SB by 40 min/day and increased moderate-to-vigorous intensity physical activity by 20 min/day, on average, while no statistically significant changes in the control group were observed.

No statistically significant intervention effects on cardiorespiratory fitness or resting or exercise blood pressure and echocardiography were observed. However, among all participants, increased physical activity correlated with improved cardiorespiratory fitness, left ventricular mass index, and submaximal exercise blood pressure and left ventricular global longitudinal strain.

In conclusion, the SB-reducing intervention did not affect the health of the cardiovascular system, although successful SB reduction provided some benefits. Therefore, increasing physical activity is recommended to improve cardiovascular health.