Introduction:
Small-sided games (SSGs) and running-based high-intensity interval training (HIIT) are training methods that has been used in combination or isolation to improve performance of soccer players.

Aim of the study:
This study aimed to compare the effects of an eight-week training intervention using SSGs combined with running-based HIIT versus runningbased HIIT alone on the physical fitness of young male soccer players.

Material and methods:
Thirty-six young male soccer players (aged 14.0 ± 1.1 years) participated in the study. Both intervention groups completed an eight-week training protocol with two sessions per week. The SSGs + HIIT group used different SSGs formats (e.g., 5 vs 5) in combination with running-based HIIT. In contrast, the HIIT group performed running-based HIIT alone. Pre- and post-intervention 10 m and 30 m linear sprint (i.e., acceleration and maximal speed), aerobic capacity, body fat percentage (%BF), and change of direction (COD) were measured, using validated tests.

Results:
The HIIT and SSGs + HIIT interventions showed no significant differences in improving 10 m linear sprint (HIIT: 6.3% vs SSGs + HIIT: 7.4%), 30 m linear sprint (HIIT: 3.4% vs SSGs + HIIT: 4.2%), and %BF (HIIT: 11.6% vs SSGs + HIIT: 7.3%; p > 0.05). However, SSGs + HIIT induced significantly greater improvements in maximal oxygen consumption (HIIT: 6.7% vs SSGs + HIIT: 9.1%; p = 0.003) and COD (HIIT: 4% vs SSGs + HIIT: 1.9%; p = 0.002) compared to the HIIT group.

Conclusions:
The findings suggest that the SSGs + HIIT intervention was more effective in improving aerobic performance and COD among young soccer players. However, both training interventions were similarly effective in improving the 10 m and 30 m linear sprint times.