Muscular fitness profiles in relation to the response in body fat during school-based high-intensity intervention.

BACKGROUND: We aimed to assess the equivalence of the muscular fitness (MF) between body fat percentage (BFP) responders (Rs<inf>BFP</inf>) and non-responders (NRs<inf>BFP</inf>) to school-based high-intensity interval training (HIIT). Adolescents aged 16 (N.=73, 42.5% of males) were identified as Rs<inf>BFP</inf> (N.=45) or NRs<inf>BFP</inf> (N.=28). MF was assessed based on hand strength (HS), abdominal muscle strength (ABS), and leg power (VJ).

METHODS: Profile analysis showed distinct patterns of MF changes in both response categories. Despite the presence of parallelism (Wilks' Λ=0.979, Pillai's V=0.212, P=0.473), a gradient of increasing changes (HS-ABS-VJ) was found in the Rs<inf>BFP</inf>, while a gradient of decreasing changes was shown in the NRs<inf>BFP</inf>, and a significant level of inequality (F<inf>(1,71)</inf>=7.823, P=0.047, partial eta-squared [η2 <inf>p</inf>] 0.041).

RESULTS: One-way analysis showed a significant and moderate effect on VJ (F<inf>(1,71)</inf>=7.080, P=0.010, η2 <inf>P</inf>=0.091), a close to significant effect on ABS (F<inf>(1,71)</inf>=3.300, P=0.074, η2 <inf>P</inf>=0.044) and lack of an effect on HS (F<inf>(1,71)</inf>=0.699, P=0.406, η2 <inf>P</inf>=0.010). The test of equal means across the condition categories (separately for Rs<inf>BFP</inf> and NRs<inf>BFP</inf>) indicated that there was no multivariate statistically significant within-group effect (F<inf>(2, 70)</inf>=0.517, P=0.599).

CONCLUSIONS: The findings may help teachers assess the potential and indirect changes in muscle performance after employing a body weight intervention (based on the HIIT program). A more targeted approach to treating adolescents with excessive BF, in parallel with improving MF, can be individually tailored.