Supplementary file 2_School-based high-intensity interval training for children: a focused systematic review of implementation and school-relevant outcomes.docx

Analysed sample sizes ranged from 18 to 67 participants. Interventions ranged from 6-minute classroom micro-sessions to 20-minute PE-based programmes delivered for 4–12 weeks. Some studies reported between-group or group-by-time findings favouring HIIT for selected functional-strength, aerobic-fitness, arterial-stiffness, and heart-rate-variability outcomes; other findings were limited to within-group change, and effects were not consistent across protocols.

One study assessed inhibitory control and reported improvements after both HIIT and moderate-intensity continuous training, providing no evidence of a HIIT-specific cognitive advantage. No included study directly assessed mental health, academic attainment, attendance, or classroom engagement. Three studies were judged to have a high overall risk of bias and three raised some concerns.</p>Conclusions<p>School-based HIIT may be a brief adjunct to, rather than a replacement for, comprehensive PE.

Preliminary findings suggest possible benefits for selected fitness and cardiovascular outcomes, while evidence for cognitive, mental-health, and academic benefits remains limited or absent. Given the small evidence base and risk-of-bias concerns, these findings should be interpreted cautiously. The current findings apply to the primary-school-aged samples represented and should not be extrapolated to adolescents.

Larger, adequately powered school trials with stronger implementation and outcome reporting are required.</p>