Comparative Contributions of Oxygen Uptake Efficiency and Maximal Oxygen Uptake to Fat Oxidation Metrics in Healthy Male Adults.

Background: Maximal fat oxidation (MFO) and its intensity (FAT_max) are important for metabolic health, but current models explain only partially their variability. Research suggests that factors like oxygen uptake efficiency (i.e., OUES and OUEP) may better predict MFO and FAT_max than maximal oxygen uptake (VO_2max) and the first ventilatory threshold (VT1). This study investigates whether OUES and OUEP can explain more of the variation in fat oxidation during exercise.

Methods: Fifty-five healthy male participants underwent a series of tests, including body composition measurements, resting metabolic rate, and a treadmill exercise trial to assess cardiovascular fitness (CRF) and fat oxidation. The incremental exercise test measured gas exchange and heart rate, and blood samples were collected for glucose and lactate analysis. Statistical analyses, including multivariate regression, were used to explore relationships between CRF biomarkers, OUES, OUEP, and fat oxidation, with significance set at p < 0.05.

Results: Participants with excellent cardiovascular fitness (CRF) showed lower body fat, higher fat-free mass, and higher VO_2max, MFO, and FAT_max compared to those with poor or regular CRF. When oxygen uptake efficiency and VT1 were included in the models, VT1 and OUEP emerged as stronger predictors of MFO and FATmax than VO_2max. The OUES did not significantly relate to MFO or FAT_max but was a key moderator of VO_2max, explaining 71% of its variance.

Conclusions: VT1 and OUEP are stronger predictors of MFO and FAT_max than VO_2max, while OUES significantly moderates VO_2max, highlighting the importance of submaximal biomarkers in fat oxidation capacity.