Sedentary behaviour, but not moderate-to-vigorous physical activity, is associated with respiratory responses to acute psychological stress

Background: Acute psychological stress induces respiratory responses, and stress-induced respiratory changes can be used to non-invasively reflect metabolic regulation. Respiratory and cardiovascular responses to stress are both driven by sympathetic mechanisms. Higher volumes of sedentary behaviour and lower volumes of physical activity are associated with elevated sympathetic tone and larger cardiovascular responses to stress. The aim of this study was to test whether these associations translate to measures of respiratory stress reactivity.Methods: Daily hours of sedentary behaviour (thigh-mounted activPAL) and moderate-to-vigorous physical ac-tivity (MVPA; wrist-mounted ActiGraph) were assessed across seven days. Breath-by-breath respiratory (e.g., breathing frequency [BF], end-tidal carbon dioxide partial pressure [PetCO2], carbon dioxide output [VCO2] and respiratory exchange ratio [RER]) responses to an 8-min Paced Auditory Serial Addition Test were then measured using a Cortex MetaLyzer3B.Results: Healthy participants (N = 61, mean age +/- SD = 25.7 +/- 8.9 years) recorded high volumes of sedentary behaviour (9.96 +/- 1.48 h/day) and MVPA (1.70 +/- 0.71 h/day). In adjusted models (with the inclusion of sedentary behaviour, MVPA, and other a priori selected covariates) hours of daily sedentary behaviour were associated with baseline to stress changes in BF (B = 0.695, 95% CI = 0.281 - 1.109, p = .014), VT (B =-0.042, 95% CI =-0.058 - -0.026, p = .014), PetCO2 (B =-0.537, 95% CI =-0.829 - -0.245, p = .014), VCO2 (B =-0.008, 95% CI =-0.014 --0.003, p = .030), and RER (B =-0.013, 95% CI =-0.021 --0.005, p = .022). Daily hours of MVPA were not linked with respiratory responses to stress.Discussion: Sedentary behaviour, but not MVPA, is associated with respiratory stress reactivity. Future work should untangle the underlying mechanisms of these findings and explore the consequences for cardiometabolic disease.