Physical activity intensity and older adolescents’ stress: The ‘STress-Reactivity after Exercise in Senior Secondary EDucation’ (STRESSED) 3-arm randomised controlled trial

Late adolescence (15–19 years) is a period of heightened susceptibility to stress, but regular physical activity may attenuate reactivity to stressors. We aimed to explore the effects of physical activity intensity on older adolescents’ stress-reactivity and self-reported mental health. Three-arm randomised controlled trial in New South Wales, Australia (April–June 2021). Thirty-seven older adolescents (16.1 ± 0.2 years, 59.5 % female) were randomised to: i) non-active control (CON), ii) light-intensity physical activity (LPA), or iii) moderate-to-vigorous-intensity physical activity (MVPA). Physical activity groups participated in 2 x 20-min sessions/week for 6 weeks. Salivary cortisol (sCort) reactivity to induced stress was assessed using the Trier Social Stress Test for Groups and quantified as area under the curve (sCort AUC ; Primary outcome). Secondary outcomes included peak cortisol (sCort Peak ), subjective-reactivity, perceived stress, and non-specific psychological distress. Group differences were assessed using multiple linear regression and quantified using Cohen’s d . No statistically significant effects were observed for sCort AUC or sCort Peak and the pattern of effects for subjective-reactivity was inconsistent. Effects for self-reported mental health were also non-significant (p > .05 for all) but of meaningful magnitude, favouring LPA and MVPA over CON ( d’ s = −0.38 to −0.54). Delivery fidelity was high, satisfaction was moderate-to-high, and there was no evidence of harm. However, recruitment, retention for sCort measures, and adherence were lower than expected. Suboptimal recruitment, retention, and adherence limited our ability to conclude on the effect of physical activity intensity on older adolescents’ sCort-reactivity to induced stress. We observed potentially meaningful effects on self-reported mental health for both physical activity conditions, which could be confirmed in a future powered trial. • The Trier Social Stress Test has never been used in an exercise trial with youth. • Exercise did not appear to influence adolescents’ cortisol-reactivity to a stressor. • Effects on self-reported mental health were not significant but favoured exercise.