Who stays for the after party? Examining predictors of exercise engagement during and after an 8‐week gym‐based body composition challenge

Gym-based programming may be a useful strategy to help people re-establish consistency in their exercise routines and support long-term exercise engagement. However, the effectiveness of gym-based programs for behavior change is understudied. Using a prospective observational design, this study examines changes to participants' workout class attendance during and after an 8-week body composition challenge at three group fitness studios, as well as individual factors that may moderate behavior change. Ninety-one individuals (82.4% female) who were enrolled in the challenge completed an online survey assessing key predictors of exercise behavior identified by prior physical activity research, including prior exercise engagement, instrumental beliefs, enjoyment motives, and integrated regulation. Class attendance data were provided by the studios for the 8 weeks before, during, and after the challenge. This study found that class attendance generally increased for all participants during the challenge, and especially for those who previously attended fewer classes per week. These increases generally were not sustained after the challenge, returning to the same or less than pre-challenge attendance levels. However, declines in class attendance were attenuated by higher enjoyment motives. Findings provide initial insight into the effectiveness of a gym-based body composition challenge for behavior change, suggesting that while such programs might temporarily increase exercise engagement, additional strategies may be needed to sustain behavior change after program completion. Future research using experimental designs is needed to support these findings and better understand who may benefit most from gym-based body composition challenges and gym-based programming more broadly.