Frequently interrupting prolonged sitting with light body-weighted resistance activity alters psychobiological responses to acute psychological stress: A randomized crossover trial

Background: Uninterrupted prolonged sitting and exaggerated psychobiological reactivity to acute psychological stress are associated with increased risk of cardiovascular disease (CVD). Breaking up prolonged sitting with frequent, short bouts of light intensity physical activity acutely lowers CVD risk markers under resting conditions.

Purpose: To examine whether frequent interruptions to prolonged sitting with body-weighted resistance activity can acutely lower SBP (primary outcome) and other cardiovascular, inflammatory and cortisol (secondary outcomes) responses to acute psychological stress.

Methods: This randomised crossover trial included 17 sedentary participants (9 men; mean ± SD age; 24.0 ± 0.5 years) who completed two conditions: (1) interrupting 4h of sitting with 4-min of light body-weighted resistance activity every 30-min (BREAK), and (2) 4h of uninterrupted sitting (SIT). Following the BREAK and SIT intervention windows, cardiovascular, inflammatory and cortisol markers were measured at rest, during stress tasks (8-min Paced Auditory Serial Addition Test [PASAT] and 3-min Cold Pressor [CP]) and during 45-min recovery periods.

Results: There were main effects of time for cardiovascular parameters (SBP, DBP, HR, cardiac output, and total peripheral resistance [all p<.001]), inflammatory markers (interleukin-6) and cortisol (p<.05) in response to stress. Time-by-condition interaction effects revealed that in the BREAK condition there was lower SBP during immediate recovery from the CP (mean [95% CI]:127.2 [121.3, 133.4] vs 133.4 [125.5, 141.7] mmHg; p=.020), higher concentrations of plasma interleukin-6 45-min post-PASAT (2.70 [1.97, 3.70] vs 1.71 [1.32, 2.22] pg/ml; p=.010), and larger (non-significant) salivary cortisol concentrations 8-min post-CP (6.29 [4.60, 8.58] vs 3.97 [3.16, 4.99] nmol/l; p=.079).

Conclusions: Interrupting prolonged sitting with frequent bouts of light intensity bodyweighted resistance activity alters psychobiological responses to acute psychological stress. Further research should explore the longer-term implications for CVD risk.