Figure 1.

Potential mechanisms of impaired VO₂ Max in CKD that may be reversed by kidney transplantation. Cardiopulmonary exercise testing enables measurement of VO₂ Max, which is defined as total body oxygen consumption at maximum exercise. VO₂ Max is an integrated measure that encompasses the contributions of all systems involved in exercise. Diseases of the cardiovascular, respiratory, vascular, hematologic, and musculoskeletal systems can each reduce VO₂ Max. CKD causes multiple alterations to each system that can be mitigated or reversed by kidney transplantation. How FGF23 excess might contribute to reduced VO₂ Max in CKD requires further study. (Created with BioRender.com.)