Preliminary Impacts of a 3-Month School-Based Exercise and Data Recording Intervention on Lifestyle Habits, Psychological Health, and Physical Health in Japanese Adolescents

Background/Objectives: This study evaluated the impact of short-duration physical exercise sessions and daily exercise recordings on the physical health and psychological health of junior high school students in Japan. Methods: A 3-month longitudinal school-based intervention initially enrolled 235 students, and the final analysis included 127 students who completed the program. The study was conducted using a single-arm pre–post design without a control group. The intervention included biweekly group exercise sessions and daily activity recordings. Students were separated into two groups based on their screen time (≥4 h per day or <4 h per day). Results: After the intervention, a significant decrease in screen time was observed in the group with baseline screen time of 4 h or more, whereas the group with baseline screen time of less than 4 h showed an increase in daily screen time. The results indicated a significant increase in body mass index and trunk muscle mass in both groups. For psychological measures, including the General Self-Efficacy Scale and Communicative and Critical Health Literacy scale, no significant changes over time or group × time interactions were observed, although post-intervention scores were significantly higher in the lower screen time group compared to the higher screen time group. However, significant changes in skeletal muscle index, eHealth literacy, and sleep duration were not observed. Conclusions: Due to the lack of a control group, these findings remain preliminary, and observed changes cannot be definitively attributed solely to the intervention. However, the program showed potential in reducing excessive screen time and increasing trunk muscle mass. Future randomized controlled trials are required to confirm the true efficacy of the intervention.