Purpose:
The aim of the study was to verify the effect of mental fatigue on tactical actions quality and the intensity of covered distance in soccer players.

Methods:
Six U-15 male soccer players participated in this study (14.7 ± 0.59 years of age). For data collection, the FUTSAT and GPSports® (SPI-HPU) systems were applied. To induce mental fatigue, the Stroop task was used for 20 minutes. The individuals were evaluated in 2 conditions: mental fatigue and control (with and without the Stroop task). Statistical analysis was performed with the Kolmogorov-Smirnov test, t-test, and Wilcoxon test.

Results:
The results displayed significant differences in actions related to principles of balance (p = 0.02), defensive unity (p < 0.01), and total defensive actions (p = 0.02), as well as in the covered distance in intensity related to zones 3 (p = 0.03) and 6 (p < 0.01). In mental fatigue, the players revealed a decrease in tactical action quality referring to movements that aimed at numerical stability in relations of opposition and at defending in unity and in block, and covered greater distances in zones 3 and 6.

Conclusions:
Mental fatigue modified the players’ movement dynamics on the pitch with reference to the quality of tactical actions and covered distance intensity.