Effects of a 12-Week Combined Circuit Training Intervention in Physical Education on Motor Performance in Adolescents: A Cluster-Randomized Controlled Trial

Abstract

Introduction & Purpose

Physical education (PE) is an underused setting for resistance training (Cox et al., 2020). This cluster-randomized controlled trial evaluated a combined resistance and plyometric circuit integrated into PE over 12 weeks on motor performance in lower secondary students.

Methods

183 lower secondary students (11–13 years) were cluster-randomised by class to an intervention group (IG; 4 classes, n = 85) or a control group (CG; 4 classes, n = 98). The IG completed 24 circuit sessions over 12 training weeks spread across a longer period (2/week, 15–20 min; six stations: strength, plyometrics, bands; 40 s : 20 s); the CG received regular PE. Countermovement jump (CMJ), 30 m sprint, standing long jump (SLJ), sit-and-reach (SAR) and grip strength were assessed at T1 and T2. The primary intention-to-treat analysis used 2 × 2 repeated-measures ANOVA (η²_p; α = .05), complete-case per outcome (n = 160–167). As randomisation was at class level, group × time interactions were confirmed with a cluster-adequate mixed model (Kenward-Roger), a cluster-level test and an exact permutation test (Billot et al., 2024), with per-protocol and age-adjusted sensitivity analyses.

Results

Groups were comparable at baseline in sex and maturity (age difference 0.49 y, reflecting one younger CG class). Interactions robust across all analysis paths emerged for SAR (p = .001, η²_p = .065) and SLJ (p = .002, η²_p = .061; Figure 1). The SAR interaction reflected an IG gain (+1.39 cm, d_z = 0.40) with a stable CG, whereas the SLJ interaction was driven by a CG decline (−4.75 cm, d_z = 0.43) against a stable IG. CMJ improved only per-protocol and was a non-significant trend under intention-to-treat (p = .089). No effects emerged for sprint or grip strength. All between-group differences remained below the smallest detectable change.

Discussion

The flexibility gain in the IG is consistent with resistance training-induced range-of-motion improvements (Alizadeh et al., 2023). The SLJ interaction reflects a group difference in change, as the IG did not improve. Group-level effects (Cohen's d ≈ 0.5) were comparable to measurement variability, so individual relevance is uncertain. Null effects for sprint and grip strength are consistent with training specificity. Only four clusters per arm limit cluster-level power.

Conclusion

A brief, teacher-led combined circuit integrated into PE produced flexibility gains and a favourable between-group difference in horizontal jump, offering a scalable PE-integrated approach to youth muscular-fitness promotion.

References

Alizadeh, S., Daneshjoo, A., Zahiri, A., Hadjizadeh Anvar, S., Goudini, R., Hicks, J. P., Konrad, A., & Behm, D. G. (2023). Resistance training induces improvements in range of motion: A systematic review and meta-analysis. Sports Medicine, 53(3), 707–722. https://doi.org/10.1007/s40279-022-01804-x

Billot, L., Copas, A., Leyrat, C., Forbes, A., & Turner, E. L. (2024). How should a cluster randomized trial be analyzed? Journal of Epidemiology and Population Health, 72(1), Article 202196. https://doi.org/10.1016/j.jeph.2024.202196

Cox, A., Fairclough, S. J., Kosteli, M.-C., & Noonan, R. J. (2020). Efficacy of school-based interventions for improving muscular fitness outcomes in adolescent boys: A systematic review and meta-analysis. Sports Medicine, 50(3), 543–560. https://doi.org/10.1007/s40279-019-01215-5