Does the exercise environment matter? Indoor versus outdoor aerobic exercise for adolescents with subthreshold...

Aerobic exercise, defined as rhythmic and continuous physical activity performed at moderate intensity to improve cardiorespiratory fitness, is widely recognised as an effective non-pharmacological intervention for improving the mental health of adolescents with subthreshold depression. However, whether the environment in which exercise is performed-such as indoor versus outdoor settings-modulates its psychological benefits remains insufficiently understood, as empirical evidence is still scarce. This study aims to compare the psychological effects of aerobic exercise conducted in different environmental contexts among adolescents with subthreshold depression and to identify which exercise setting may provide greater therapeutic advantages.

This assessor-blinded, two-arm, parallel-group randomised controlled trial will recruit adolescents who meet standardised subthreshold depression screening criteria. Participants will be randomly assigned to the indoor aerobic exercise group or outdoor aerobic exercise group using sex-stratified block randomisation to ensure balanced allocation between male and female participants. Both groups will participate in an 8-week moderate-intensity aerobic exercise programme (2-3 sessions per week, 40 min per session), with heart rate monitoring employed to ensure consistency of exercise intensity across conditions. Depressive symptoms, anxiety and sleep quality will be assessed at baseline (week 0), mid-intervention (week 4) and post-intervention (week 8). Data analysis will be conducted according to the intention-to-treat principle.

Ethical approval has been obtained from the Ethics Committee of Capital University of Physical Education and Sports (Approval No. 2025A139). The findings of this study will be disseminated through peer-reviewed publications and academic conferences.

ChiCTR2500112215.