Sedentary behaviour and psychobiological reactivity to acute psychological stress

Sedentary behaviour is an emerging risk factor for cardiovascular disease (CVD), but there is a clear gap in the literature with regards to the mechanisms that might underlie this association. Psychobiological stress reactivity testing is a paradigm that could be used to investigate potential mechanisms linking sedentary behaviour with CVD, including those that may not be evident under resting conditions. The pre-existing sedentary behaviour and stress reactivity literature was systematically reviewed (Chapter 2) and it was found that no studies had examined postural and metabolic components of sedentary behaviour in the context of psychobiological stress reactivity. Therefore, Chapters 4 and 5 explored the link between habitual sedentary behaviour (using inclinometry) and psychobiological responses to acute psychological stress. Sedentary behaviour was positively associated with cardiovascular, inflammatory, and cortisol reactivity to stress (Chapter 4). Sedentary behaviour was also related with respiratory responses (as an index of metabolic regulation) to stress (Chapter 5), with hyperventilatory and metabolically dysregulated responses observed in those with higher volumes of sedentary behaviour. Chapter 6 extended the observational findings from Chapters 4 and 5 (focusing on habitual sedentary behaviour) to a randomised crossover trial, which examined whether frequent interruptions to prolonged sitting could impact stress reactivity measures. Breaking up 4 hours of prolonged sitting every 30 minutes with light body-weighted resistance exercise altered cardiovascular, inflammatory, cortisol and respiratory responses to acute psychological stress, relative to 4 hours of uninterrupted prolonged sitting. 

In conclusion, the findings from Chapters 4 and 5 suggest that dysregulated psychobiological stress reactivity is a possible mechanism linking habitual sedentary behaviour with CVD, which therefore helps to fill an important gap in the literature. As shown in Chapter 6, altering psychobiological responses to stress by reducing sedentary behaviour (e.g., by regularly breaking up prolonged sitting) could be a clinically relevant strategy to reduce CVD risk, but further research is needed to explore the longer-term implications of our acute findings.