Peak fat oxidation is positively associated with vastus lateralis CD36 content, fed-state exercise fat oxidation, and endurance performance in trained males

Purpose Whole-body fat oxidation during exercise can be measured non-invasively during athlete profiling. Gaps in understanding exist in the relationships between fat oxidation during incremental fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during prolonged fed-state exercise. Methods Seventeen endurance-trained males underwent a (i) fasted, incremental cycling test to assess peak whole-body fat oxidation (PFO), (ii) resting vastus lateralis microbiopsy, and (iii) 30-min maximal-effort cycling time-trial preceded by 2-h of fed-state moderate-intensity cycling to assess endurance performance and fed-state metabolism on separate occasions within one week. Results PFO (0.58 +/- 0.28 g(.)min(-1)) was associated with vastus lateralis citrate synthase activity (69.2 +/- 26.0 mu mol.min(-1).g(-1) muscle protein, r = 0.84, 95% CI 0.58, 0.95, P < 0.001), CD36 abundance (16.8 +/- 12.6 mu g.g(-1) muscle protein, r(s) = 0.68, 95% CI 0.31, 1.10, P = 0.01), pre-loaded 30-min time-trial performance (251 +/- 51 W, r = 0.76, 95% CI 0.40, 0.91, P = 0.001; 3.2 +/- 0.6 W.kg(-1), r = 0.62, 95% CI 0.16, 0.86, P = 0.01), and fat oxidation during prolonged fed-state cycling (r = 0.83, 95% CI 0.57, 0.94, P < 0.001). Addition of PFO to a traditional model of endurance (peak oxygen uptake, power at 4 mmol(.)L(-1) blood lactate concentration, and gross efficiency) explained an additional similar to 2.6% of variation in 30-min time-trial performance (adjusted R-2 = 0.903 vs. 0.877). Conclusion These associations suggest non-invasive measures of whole-body fat oxidation during exercise may be useful in the physiological profiling of endurance athletes.

Automated summary

The study found strong correlations between whole-body fat oxidation rate during fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during fed-state exercise, suggesting that non-invasive measures of fat oxidation may be useful in profiling endurance athletes.