Effects of two forms of school-based high-intensity interval training on body fat, blood pressure, and cardiorespiratory fitness in adolescents: randomized control trial with eight-week follow-up-the PEER-HEART study.

Abstract

Introduction: This study examined the effects of 8-week interventions based on two variants of typical exercises, namely, high-intensity interval training (HIIT) and high-intensity plyometric training (HIPT), on body fat (BF%), blood pressure, and cardiorespiratory fitness (CRF). In addition, the sustainability of the effects after another 8 weeks was assessed.

Methods: The project was designed as a randomized controlled trial with eight groups of participants (two variants, two sexes, and two groups (experimental and control)) and was conducted in a school physical education (PE) program. The outcomes analyzed were the BF%, systolic (SBP), diastolic blood pressure (DBP), and CRF expressed in terms of maximum oxygen uptake (VO_2max). A total of 307 healthy adolescents participated in this study and were randomly assigned into the two groups. During the 8 weeks, the participants completed two exercise sessions each week with progressively increasing volumes. For the first 2 weeks, the sessions involved four rounds of 20 s of intense effort followed by 10 s of rest; this increased to six rounds during weeks 3-4 and eight rounds during weeks 5-8. The HIPT program was based on plyometric exercises, whereas the HIIT was based on bodyweight resistance exercises.

Results: Multidimensional analysis of variance (ANOVA) indicated a statistically significant second-order interaction (time × variant × group: Ʌ = 0.943, F = 2.20, p < 0.027, η² _pG = 0.057, d = 0.25), confirming the changes in the BF%, SBP, DBP, and VO_2max dependent on the type of intervention and group assignment. The ANOVA results revealed significant main and interaction effects for BF%, SBP, and DBP, with time and the HIIT variant as the main contributors (BF%: F = 3.911, p = 0.023, η² _pG = 0.001, d = 0.04 vs. F = 9.900, p < 0.001, η² _pG = 0.001, d = 0.03; SBP: F = 31.801, p < 0.001, η² _pG = 0.012, d = 0.16 vs. F = 8.939, p = 0.003, η ² _pG = 0.026, d = 0.16; DBP: F = 3.470, p = 0.033, η² _pG = 0.002, d = 0.06 vs. F = 4.982, p = 0.026, η² _pG = 0.014, d = 0.12). The second-order interaction for VO_2max (time × sex × group: F = 6.960, p = 0.001, η² _pG = 0.003, d = 0.05) indicated that the improvements over time were not related to the training variant. Although these effects were small (low eta values), post hoc tests (all comparisons in post-intervention, p > 0.05) showed that both the HIIT and HIPT groups exhibited beneficial changes compared to controls; however, no statistically significant differences were observed between the experimental and control groups. Furthermore, the observed improvements were maintained through the 8-week follow-up period, as demonstrated by no significant changes between the post-intervention and follow-up measurements (p > 0.05). Discriminant analysis showed that BF% and SBP were the key variables for the two exercise variants in men, with HIPT yielding greater reductions in SBP and HIIT resulting in more pronounced decreases in BF%.

Discussion: In conclusion, both HIIT and HIPT interventions effectively improved health-related parameters, providing valuable enrichment to the PE lessons in schools. These benefits were also sustained for at least 8 weeks post-intervention.