||PURPOSE: To estimate the contribution of the three energy systems to simulated judo matches. METHODS: Twelve judo athletes (18 +/- 1 years-old, 175.1 +/- 5.3 cm, 74.3 +/- 10.5 kg, 11.7 +/- 1.5 % body fat, and 8 +/- 2 years of practice) performed five combats with different durations (1, 2, 3, 4 and 5-min), against the same opponent, on different days and blinded to the duration. The estimated energy contribution for the oxidative, glycolytic and ATP-PCr systems were calculated based on VO2 during activity, delta of lactate and the fast phase of excess VO2, respectively. Analysis of mixed models for repeated measures were used to compare the contribution of the three energy systems and different durations of judo matches, followed by a post hoc Bonferroni. RESULTS: The oxidative system contribution (70%) was higher than the glycolytic (8%; p < 0.001) and ATP-PCr (21%; p < 0.001) energy systems (in all durations), and the ATP-PCr contribution was higher than the glycolytic energy system (up to 3-min). Additionally, during the match there was an increase in the oxidative (from 50% to 81%; p < 0.001), a decrease in the ATP-PCr (from 40% to 12%; p < 0.001) and maintenance of the glycolytic contributions (between 6% and 10%). CONCLUSIONS: There is a predominance of the oxidative system to supply the energy cost of judo matches from the first minute of combat up to the end, when compared to the anaerobic systems.