Low-intensity exercise stimulates bioenergetics and increases fat oxidation in mitochondria of blood mononuclear cells from sedentary adults

Aim: Exercise training induces adaptations in muscle and other tissue mitochondrial metabolism, dynamics, and oxidative phosphorylation capacity. Mitochondrial fatty acid oxidation was shown to be pivotal for the anti-inflammatory status of immune cells. We hypothesize that exercise training can exert effects influence mitochondrial fatty acid metabolism in peripheral blood mononuclear cells (PBMCs). The aim was to investigate the effect of exercise on the fatty acid oxidation-dependent respiration in PBMCs. Design: Twelve fasted or fed volunteers first performed incremental-load exercise tests to exhaustion on a cycle ergometer to determine the optimal workload ensuring maximal health benefits in volunteers with a sedentary lifestyle. In addition, the same volunteers performed 60 min of low-intensity constant-load exercise. Results: In the incremental-load exercise, the maximal whole-body fat oxidation rate measured by indirect calorimetry was reached at the fasted state already at a 50 W workload. At the 75–175 W workloads, the contribution of fat oxidation significantly decreased to only 11%, the heart rate increased to 185 BPM, and the study participants reached exhaustion. These results show that low-intensity exercise (50W) is optimal for maximal whole-body fat utilization. After low-intensity exercise, the ROUTINE mitochondrial respiration, as well as fatty acid oxidation-dependent respiration in PBMCs at LEAK and OXPHOS states, were significantly increased by 31%, 65%, and 76%, respectively. In addition, during 60 min of low-intensity (50W) exercise, a 2-fold higher lipolysis rate was observed and 13.5 ± 0.9 g of fat was metabolized, which was 57% more than the amount of fat that was metabolized during the incremental-load exercise. Conclusions: In individuals with a sedentary lifestyle participating in a bicycle ergometry exercise program, maximal lipolysis and whole-body fat oxidation rate is reached in a fasted state during low-intensity exercise. For the first time, it was demonstrated that low-intensity exercise improves bioenergetics and increases fatty acid oxidation in PBMCs and may contribute to the anti-inflammatory phenotype.