Fatigue index (FI) and anaerobic capacity (AC) are critical indicators of soccer performance, particularly for athletes who rely on short bursts of high-intensity activity. This study aims to analyze the relationship between FI and AC in competitive soccer players, focusing on how these parameters fluctuate at different times of the day (6 a.m., 11 a.m., 3 p.m., and 8 p.m.). Given the influence of circadian rhythms on athletic performance, understanding these variations can help optimize training schedules and match performance. The research involves a systematic evaluation of anaerobic power using the Wingate Anaerobic Test (WAnT) and sprint-based fatigue assessment at different times of the day.

The results indicated significant variations in FI and AC throughout the day. Peak anaerobic performance was observed at 3 p.m., with the highest peak power output (PPO) and mean power output (MPO), as well as the lowest fatigue index, suggesting optimal physiological conditions for high-intensity performance.