Elite male football players have high peak fat oxidation (PFO), and recently PFO was reported to increase following preseason (PS) training in semi-professional male players. Whether PFO increases from PS to competitive season (CS) in elite male football players remains unknown. This study investigated if PFO increases from PS to CS in elite male football players, and secondarily, it explored the interplay between PFO and running performance. Twenty-two elite male outfield football players reported to the laboratory during PS and CS. Testing included a resting blood sample, a dual-energy X-ray absorptiometry scan, and a graded treadmill running test. The players' load during training and matches was monitored between the test days. PFO, the intensity eliciting PFO (Fatmax) and peak oxygen consumption (VO2peak) did not change from PS to CS (mean difference with 95% confidence intervals: -1.0 mg·kg FFM-1·min-1 (95% CI: -2.4 to 0.3 mg·kg FFM-1·min-1), 1% VO2peak (95% CI: -4% to 6% VO2peak) and 0.2 mL·kg-1·min-1 (95% CI: -1.0 to 1.4 mL·kg-1·min-1), respectively). Intra-individual changes in PFO, Fatmax and VO2peak from PS to CS were not positively correlated with weekly distance covered during football training, or with changes in distance covered during matches, neither in total nor within intensity domains. Whole body fat-free mass increased by 1.2 kg (95% CI: 0.4 to 1.9 kg) and fat percentage decreased by 0.4% points (95% CI: 0.1% to 0.8% points) from PS to CS. In conclusion, PFO, Fatmax and VO2peak did not change from PS to CS, and PFO was not associated with training or match running performance of elite male football players.
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