According to the World Health Organization (WHO), chronic diseases are a major global public health concern and the leading cause of mortality worldwide. In the absence of evidence-based actions, the global annual deaths from chronic diseases are projected to rise to 55 million deaths in 2030, accompanied by a substantial increase in socio-economic costs. In this context, the WHO identifies type 2 diabetes mellitus (T2DM) and cardiovascular diseases (CVD) as key chronic conditions of concern related to cardiometabolic health.

Both sedentary behaviour (SB) and physical inactivity have been recognised as interdependent risk factors for the development of T2DM and CVD. SB refers to any waking behaviour, characterised by a low energy expenditure, while being in a sitting or reclining posture, whereas physical inactivity denotes insufficient levels (<150 min per week,) of moderate-to-vigorous physical activity (MVPA). Studies using objective measures have demonstrated that on average Western adults spend 8-12h in SB per day, of which the majority is spent in prolonged sedentary bouts (lasting ≥30 min). In addition, up to 30% of adults worldwide are physically inactive, with higher levels of inactivity in high-income countries. Within this context, it has become evident that excessive prolonged SB, often in combination with physical inactivity, negatively impacts cardiometabolic health, contributing to insulin resistance, increased adiposity, poor lipid profiles and endothelial dysfunction. Given their detrimental effects on T2DM and CVD, strategies aimed at reducing SB and promoting physical activity (PA) warrant further investigation.

Reducing and regularly interrupting SB, even with low-intensity PA, alongside sufficient MVPA, is crucial for maintaining a healthy cardiometabolic profile. Reflecting this, the WHO guidelines advise individuals to engage in 150-300 minutes of moderate-intensity physical activity, 75-150 minutes of vigorous-intensity physical activity, or an equivalent combination each week. Notably, the 2020 WHO guidelines also included recommendations on SB for the first time, emphasizing the importance of limiting sedentary time. The WHO states that replacing SB with physical activity of any intensity can yield health benefits. However, these recommendations remain non-prescriptive and somewhat vague, primarily due to a lack of robust scientific evidence on the optimal frequency, intensity, and duration of PA needed to interrupt sedentary time. The absence of specific guidelines on prolonged SB reflects this evidence gap. To support policy development, well-designed randomised controlled trials are needed to evaluate effective and practical strategies for reducing sedentary time.

So far, the short term cardiometabolic health effects of SB interruptions have been investigated by our research group, laboratory studies of collaborators and other international researchers, demonstrating that; 1) more frequent SB interruptions especially affect glucose metabolism and insulin sensitivity; 2) higher intensity interruptions are associated with cardioprotective adaptations and; 3) longer durations of SB interruptions positively affect lipid metabolism. However, because under real-world conditions frequency, intensity and duration of SB interruptions usually interact, their combined effects on cardiometabolic health need further investigation. Many studies already compared the isolated effects of different SB interruption patterns with respect to frequency, duration and intensity on cardiometabolic health. However, the combined effects of these different approaches matched for energy expenditure are not clear yet. We therefore perform a balanced cross-over study in which the efficacy of distinct activity patterns on cardiometabolic health insulin sensitivity and vascular function) will be compared to a sedentary control condition.

Inclusion Criteria:

• Adults aged 40-70 years
• Sedentary (>9 hours per day)
• < 3 exercise sessions per week

Exclusion Criteria:

• Pregnancy or intend to become pregnant
• Any known contra-indications for physical activity
• >14 alcohol consumptions per week for women and >20 alcohol consumptions per week for men
• Involved in a weight reduction program with an energy restriction diet during the study period
• No consistent body weight over the past month
• Diagnosed with any known cardiometabolic health-related disease