Comparative effects of high intensity interval and functional training on performance outcomes in adolescent female volleyball players.

BACKGROUND: Volleyball requires repeated explosive actions, agility, and technical precision, demanding contributions from both aerobic and anaerobic energy systems. Time-efficient training methods such as resistance-based high intensity interval training (HIIT) and high intensity functional training (HIFT) have been proposed to enhance multidimensional performance in young athletes. However, direct comparisons of their effects in adolescent female volleyball players are limited. METHODS: Thirty-two licensed female volleyball players (aged 15-18 years) were randomly assigned to a resistance-based HIIT group (n = 10), a HIFT group (n = 11), or a control group (n = 11). The training interventions lasted 12 weeks with two supervised sessions per week, in addition to regular volleyball practice. The HIIT program consisted of progressive resistance-based high intensity intervals performed at 85-95% HRmax, while the HIFT program comprised multimodal circuit-style functional exercises performed at comparable intensities (~ 85-95% HRmax). Performance assessments were conducted pre- and post-intervention and included the countermovement jump (CMJ), standing long jump (SLJ), medicine ball throw (MBT), pro-agility test, 20 m sprint, repeated sprint fatigue index (RSI), volleyball skill test, Yo-Yo IR1 distance, VO₂max, blood lactate concentration, and maximal heart rate (MaxHR). Data were analyzed using a 3 × 2 mixed-model ANOVA with Tukey post hoc tests, and effect sizes were reported as Cohen's d and partial eta squared (ηp²). RESULTS: Significant Group × Time interactions were observed for CMJ (F(2,29) = 9.14, p < 0.001, ηp²=0.39), SLJ (F(2,29) = 12.08, p < 0.001, ηp²=0.45), VO₂max (F(2,29) = 11.53, p < 0.001, ηp²=0.44), MaxHR (F(2,29) = 3.56, p = 0.041, ηp²=0.20), and volleyball skill test (F(2,29) = 7.44, p = 0.002, ηp²=0.34). HIFT produced the greatest improvements in explosive power (CMJ Δ=+5.15 cm; SLJ Δ=+12.82 cm), RSI (Δ=-1.56), and volleyball skill performance (Δ=+13.18 points), with large effect sizes (d = 1.3-3.2). HIIT showed relatively greater improvements in aerobic capacity (VO₂max Δ=+0.90 ml·kg⁻¹·min⁻¹) and endurance (d = 0.7-2.0). No significant between-group differences were observed for lactate. CONCLUSIONS: Both resistance-based HIIT and HIFT proved effective in improving several physical and volleyball-specific performance components in adolescent female players. HIIT produced slightly greater gains in aerobic capacity, while HIFT showed larger numerical improvements in explosive strength, agility, and technical skill performance; however, these between-intervention differences were not statistically significant. Overall, the findings suggest that each modality offers complementary benefits, and integrating both HIIT and HIFT may provide a balanced conditioning approach for the holistic development of youth volleyball athletes. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT07181031. Registered on September 04, 2025.