What Happened in ‘The HERizon Project’?—Process Evaluation of a Multi-Arm Remote Physical Activity Intervention for Adolescent Girls

This mixed-methods process evaluation examines the reach, recruitment, fidelity, adherence, acceptability, mechanisms of impact, and context of remote 12-week physical activity (PA) interventions for adolescent girls named The HERizon Project. The study was comprised of four arms—a PA programme group, a behaviour change support group, a combined group, and a comparison group. Data sources included intervention deliverer and participant logbooks (100 and 71% respective response rates, respectively), exit surveys (72% response rate), and semi-structured focus groups/interviews conducted with a random subsample of participants from each of the intervention arms (n = 34). All intervention deliverers received standardised training and successfully completed pre-intervention competency tasks. Based on self-report logs, 99% of mentors adhered to the call guide, and 100% of calls and live workouts were offered. Participant adherence and intervention receipt were also high for all intervention arms. Participants were generally satisfied with the intervention components; however, improvements were recommended for the online social media community within the PA programme and combined intervention arms. Autonomy, sense of accomplishment, accountability, and routine were identified as factors facilitating participant willingness to adhere to the intervention across all intervention arms. Future remote interventions should consider structured group facilitation to encourage a genuine sense of community among participants.