AbstractAcute aerobic exercise increases the number and proportions of circulating peripheral blood mononuclear cells (PMBC) and can alter PBMC mitochondrial bioenergetics. In this study, we aimed to examine the impact of a maximal exercise bout on immune cell metabolism in collegiate swimmers. Eleven (7 M/4F) collegiate swimmers completed a maximal exercise test to measure anaerobic power and capacity. Pre‐ and postexercise PBMCs were isolated to measure the immune cell phenotypes and mitochondrial bioenergetics using flow cytometry and high‐resolution respirometry. The maximal exercise bout increased circulating levels of PBMCs, particularly in central memory (KLRG1+/CD57−) and senescent (KLRG1+/CD57+) CD8+ T cells, whether measured as a % of PMBCs or as absolute concentrations (allp< 0.05). At thecellularlevel, the routine oxygen flow (IO2[pmol·s−1·106PBMCs−1]) increased following maximal exercise (p= 0.042); however, there were no effects of exercise on theIO2measured under the LEAK, oxidative phosphorylation (OXPHOS), or electron transfer (ET) capacities. There were exercise‐induced increases in thetissue‐leveloxygen flow (IO2‐tissue[pmol·s−1·mL blood−1]) for all respiratory states (allp< 0.01), except for the LEAK state, after accounting for the mobilization of PBMCs. Future subtype‐specific studies are needed to characterize further maximal exercise's true impact on immune cell bioenergetics.