Effects of 8-Week HIIT short interval training with extensive intensity and change of direction (COD) on aerobic and anaerobic capacity of youth soccer players

Abstract

The purpose of this study was to examine the effects of a high-intensity interval training (HIIT) program involving 30-second running intervals at intensities of 105%, 110%, 115%, and 120% of vVO₂max, interspersed with 30-second active recovery periods at 50% of vVO₂max. The program incorporated changes of direction (COD) at 45° and 90°. Eighteen 16-year-old soccer players from a football school participated in a single test group. The test group trained for 8 weeks on a running circuit of 115–130 meters, including COD at 45°–90°. Each running interval lasted 30 seconds, with 3-minute recovery periods between series. Aerobic capacity was measured using the Åstrand 6-minute cycle ergometer test (Monark 839), and anaerobic capacity was assessed with the Running-based Anaerobic Sprint Test (RAST, 6 × 35 m).The 12-minute Cooper test results showed a pvalue (<0.0001) well below 0.05, with a t-statistic (11.36) exceeding the critical value (1.771). Participants improved their average distance by 215 meters (95% CI: [175, 255]), representing a 7.9% increase. All 14 participants demonstrated improvements, with gains ranging from 80 m to 350 m. The effect size (Cohen’s d ≈ 3.04) indicates an extremely large effect (>0.8 is considered large). The Åstrand 6-minute test results were statistically significant, with a t-statistic (14.82) far exceeding the critical value (1.771) and a p-value (<0.001). Participants improved their VO₂max by an average of 8.96 units (95% CI: [7.59, 10.33]), a 18.89% increase, with all 14 participants showing significant gains. The RAST (6 × 35 m) results indicated statistical significance, with a t-statistic (-3.59) exceeding the critical value (±2.160) in magnitude and a p-value (<0.01). Participants improved their Fatigue Index (FI) by an average of 1.63 units (95% CI: [-2.58, -0.68]). Twelve of 14 participants improved, with two exceptions: Participant 9’s FI value increased by 0.66 (pre: 2.70; post: 3.36), and Participant 11’s FI value increased by 1.20 (pre: 1.53; post: 2.73). The effect size (Cohen’s d ≈ 0.96) indicates a large effect. Conclusion: High-intensity interval training with 30-second intervals at 105%, 110%, 115%, and 120% of vVO₂max, interspersed with 30-second active recovery at 50% of vVO₂max and combined with COD at 45° and 90°, significantly improves the aerobic and anaerobic capacities of 16-year-old soccer players.