Biological maturation determines the beneficial effects of high-intensity functional training on cardiorespiratory fitness in male adolescents

Abstract

Background: During adolescence, between 15-18 years of age, biological maturation is associated with changes in body composition, blood pressure (BP), and cardiorespiratory fitness (CRF). Also, environmental factors may influence the trajectory of these changes. The rising prevalence of physical inactivity calls for the identification of effective exercise modalities to mitigate adverse health outcomes in youth. Although high-intensity training regimens are increasingly recognized for their benefits in school settings, the specific role of biological maturation in determining adolescent responses to such intervention in health outcomes remains insufficiently understood.

Aim: This quasi-experimental study investigated the effects of chronological age (CA) and maturity offset (MO), defined as the time before/after peak height velocity, on changes in body fat (BF), BP, and CRF induced by high-intensity functional training (HIFT) and assessed the contribution of MO on these outcomes.

Methods: The sample consisted of 116 males, grouped by CA years (y) (15y [n = 30], 16y [n = 29], 17y [n = 30], 18y [n = 27]). The biological maturation effects were studied after separating the participants by quartiles of MO into four classes: late, middle late, middle early, and early matured. Participants were randomly allocated to experimental (EG) and control groups (CG). The EG performed HIFT for 8 weeks (6-14 min/twice a week). Changes in BF, BP, and CRF before and after the intervention were calculated. The MO role in the HIFT intervention was tested by MANCOVA and ANCOVA with post hoc detailed comparisons.

Results: MO contributed to the studied model more than CA (Wilk's Λ = 0.49, η_p ² = 0.24, p < 0.001; Wilk's Λ = 0.83, η_p ² = 0.07, p < 0.063, respectively). When controlling for age, MO was the main determinant (in comparison to CA) of the delta in CRF (F = 8.76, p < 0.001). Those who matured earliest (MO > 3.59 years after APHV) benefited more from HIFT intervention than biologically younger, independent of CA (improvement by 194.7 ± 151.5 m in the CRF test). Maturity offset was the primary contributor to the variance in ΔCRF (β = 0.71, r²sp = 9.3%, p = 0.014). When MO was combined with CA, both independent variables together explained 15% of the variance (p = 0.004).

Conclusion: Biological maturation plays a more important role than CA in determining HIFT-induced improvements in CRF among male adolescents: those who matured earliest exhibited the greatest gains, whereas changes in BP and BF were not significantly related to either factor. Tailoring HIFT-based interventions can be achieved by adjusting intensity, progression, and load according to each one maturity level, ensuring more developmentally appropriate exercise programs. Future research should investigate the feasibility of these maturity-focused strategies in broader adolescent populations, thereby informing larger-scale interventions and maximizing long-term health benefits.

Keywords: Body weight training; Circuit training; Functional training; Physical education; School; Youth.

Figure 1. The bubble plot presents the numbers of individuals from the chronological age groups in maturity offset class categories.

The wheel size represents the number of individuals. LM, late matured (biologically youngest, maturity offset <2.23 years after APHV); MLM, middle late matured (maturity offset <3.15 years after APHV); MEM, middle early matured (maturity offset <3.59 years after APHV); and EM, early matured (biologically oldest, maturity offset >3.59 year after APHV).