Maximal Fat Oxidation Is Associated With Moderate- and High-Speed Running Performance During Competitive Matches in Youth National-Level Football Players: A Retrospective In-Season Study.

PURPOSE: This retrospective study investigated the relationships between maximal oxygen uptake (V˙O2max), maximal fat oxidation (MFO), maximal lower-limb power output (Pmax), and match running performance in youth national-level football players across a competitive season. METHODS: During the preseason period, 41 youth national-level football players from the academy of a French Ligue 1 club completed a series of laboratory and field-based assessments. Incremental and fasted submaximal graded treadmill tests were performed to determine V˙O2max and MFO via indirect calorimetry, whereas a horizontal force-velocity-power profile was used to assess Pmax. Match running performance was monitored throughout the season using 10-Hz GPS. A nonlinear, decision tree modeling approach was then applied to identify discriminative thresholds in physiological variables that characterize distinct player profiles. RESULTS: Among the 3 determinants of game performance examined, V˙O2max was the only variable linearly associated with total match distance (P < .01). In contrast, MFO was the sole predictor identified of distance covered at speed running >15 km·h-1 (P < .01), with a threshold of 0.73 g·min-1 distinguishing players covering greater moderate- to high-speed distances (P < .01). CONCLUSIONS: These results suggest that monitoring both V˙O2max and MFO are complementary for optimizing football players' match performance. While V˙O2max remains crucial for achieving a high total match distance in national-level players, MFO appears more strongly associated with the distance covered at moderate and high running speeds.