Effects of the Two Forms of School-Based High-Intensity Interval Training on Body Fat, Blood Pressure and Cardiorespiratory Fitness in adolescents: Randomized Control Trial with Eight Weeks Follow-Up -the PEER-HEART study

Jarosław Domaradzki Marek Popowczak Katarzyna Kochan-Jacheć Paweł Szkudlarek Eugenia Murawska-Cialowicz Dawid Koźlenia ^*

• Wroclaw University of Health and Sport Sciences, Wroclaw, Poland

This study examined the effects of eight-week intervention of two variants of the high-intensity interval training interventions, with typical forms of exercise (HIIT) and incorporating plyometric exercises(HIPT) on body fat(BF%), blood pressure(BP) and cardiorespiratory fitnes(CRF). In addition, sustainability of the effects after following eight weeks were assessed. The project design is a Randomized Controlled Trial with eight groups (two variants, two sex, experimental and control groups), conducted in a school physical education(PE). The analyzed outcomes were BF%, systolic(SBP) and diastolic blood pressure (DBP) and CRF(VO2max). 307 healthy adolescents participated in this study and were assigned into training and control groups. They completed two exercise sessions per week with progressively increasing volume. For the first two weeks, sessions involved four rounds of 20seconds of intense effort followed by 10seconds of rest; this increased to six rounds in weeks 3–4 and eight rounds in weeks 5–8. HIPT program was based on plyometric exercises, whereas HIIT was based bodyweight resistance exercises. Multidimensional analysis of variance indicated a statistically significant second-order interaction (time×variant×group: Ʌ=0.943, F=2.20, p<0.027, η2pG=0.057, d=0.25), confirming changes in BF%, SBP, DBP, and VO2max that depended on the type of intervention and group assignment. The set of ANOVA analyses 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=0.023,2pG=0.001,d=0.04,F=9.900,p<0.001,η2pG=0.001,d=0.03;SBP:F=31.801,p<0.001,η2pG=0.012,d=0.16,F=8.939,p=0.003,η2pG=0.026,d=0.16;DBP:F=3.470,p=0.033,η2pG=0.002,d=0.06,F=4.982,p=0.026,η2pG=0.014,d=0.12). A second-order interaction for VO2max (time×sex×group:F=6.960,p=0.001,η2pG=0.003,d=0.05) indicated that improvements over time were not related to the variant. These effects were small, post-hoc tests (all comparisons in post-intervention p>0.05) showed that both HIIT and HIPT groups exhibited beneficial changes compared to controls, yet no statistically significant differences were observed between experimental and control groups. rhese improvements were maintained through the eight-week follow-up, as demonstrated by no significant changes between post-intervention and follow-up measurements(p>0.05). Discriminant analysis highlighted BF% and SBP as key variables differentiating the two HIIT variants in males, with HIPT yielding greater reductions in SBP and HIIT resulting in more pronounced decreases in BF%. Both HIIT and HIPT interventions effectively improved health-related parameters providing avaluable enrichment to PE lessons in schools. These benefits were sustained for at least eight weeks post-intervention.