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

Objectives: 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. Design and Methods: 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 (sCortAUC; Primary outcome). Secondary outcomes included peak cortisol (sCortPeak), subjective-reactivity, perceived stress, and non-specific psychological distress. Group differences were assessed using multiple linear regression and quantified using Cohen's d. Results: No statistically significant effects were observed for sCortAUC or sCortPeak 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. Conclusion: 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.