Grade-Specific Effects of Recess HIIT and MICT on Classroom Attention-Related Behavior in Primary School Children

This randomized controlled trial evaluated whether structured exercise during school recess could improve observable classroom attention-related behavior in primary school children and whether the effects differed between grade levels. A total of 144 third- and fifth-grade students were randomly assigned to one of three groups: high-intensity interval training (HIIT), moderate-intensity continuous training (MICT), or routine recess activity. The intervention lasted 6 weeks and was conducted three times per week during scheduled school recess. Each structured exercise session lasted 15 minutes, including warm-up, a 9-minute main exercise component, and cool-down. Observable classroom attention-related behavior was assessed before and after the intervention using an automated video-based behavioral analysis system. The system evaluated observable indicators including head posture, eye gaze, eye opening or closing, and facial detection persistence. The study compared changes among the three groups and examined whether the effects of HIIT and MICT differed between third- and fifth-grade students.

Inclusion Criteria: * Students enrolled in the third or fifth grade at the participating primary school. * Aged 8 to 12 years. * Able to participate in routine physical education classes and school recess activities. * Free from musculoskeletal injury or any medical condition that contraindicated participation in physical exercise. * Written informed consent provided by a parent or legal guardian. * Verbal assent provided by the participating child. * Willing and able to complete the baseline assessment, exercise intervention, and post-intervention assessment. Exclusion Criteria: * Musculoskeletal injury, cardiovascular disease, respiratory disease, neurological disorder, or other medical condition that made participation in moderate- or high-intensity exercise unsafe. * A diagnosed attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety disorder, depressive disorder, intellectual disability, or other psychological or developmental condition that could substantially affect participation or assessment of classroom attention-related behavior. * Color blindness or another visual impairment that could interfere with the study assessments. * Participation in a structured high-intensity exercise training program during the 3 months before enrollment. * Regular participation in systematic extracurricular exercise training that could substantially affect the intervention response. * Inability to complete the intervention or study assessments. * Absence from three or more intervention sessions. * Withdrawal of parental or guardian consent or withdrawal of the child's assent.