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

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 thr…