This study evaluated the effects of high-intensity interval training (HIIT) incorporating Fartlek and change-of-direction (COD) components on aerobic and anaerobic capacities in young soccer players. Fifteen 18-year-old male soccer players from a football academy participated in an 8-week intervention as a single test group. The training consisted of two weekly sessions, each involving two series of seven 200-m circuits (total distance: 2800 m per session), with varying running speeds and COD angles (45–90°). Each circuit was completed in 60 seconds, with segment distances and times as follows: 20 m in 2.6 s, 70 m in 20 s, 35 m in 7 s, and 75 m in 31.3 s. A 5-minute recovery period separated the two series (1400 m each). Aerobic capacity was assessed using the Astrand 6-minute cycle ergometer test (Monark 839), anaerobic capacity with the Running-based Anaerobic Sprint Test (RAST, 6 × 35 m), and endurance with the Cooper Test. Statistical analyses revealed significant improvements. The Cooper Test showed a pre-test mean distance of 228.59 m, with a very large effect size (Cohen’s d = 2.79). The Astrand Test indicated a pre-test mean VO2max of 50.86 mL/kg/min and a post-test mean of 59.74 mL/kg/min, yielding a mean improvement of 8.88 mL/kg/min (17.46% increase), a 95% confidence interval of 7.63, 10.13, and a very large effect size (Cohen’s d = 4.19). The RAST Test demonstrated a pre-test mean fatigue index of 4.33 and a post-test mean of 2.52, with a mean improvement of -1.81, a 95% confidence interval of -2.65, -0.97, and a large effect size (Cohen’s d = -1.16). In conclusion, HIIT with Fartlek and COD significantly enhances VO2max and anaerobic capacity in 18-year-old soccer players, offering a practical training strategy for improving performance in youth soccer.
Bici et al. (Sat,) studied this question.