Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid‐organ transplants and describe peak exercise performance following recovery from transplantation. Across all of the common transplants, evaluated significant reduction in
o
2
peak
is seen (typically renal and liver 65%‐80% with heart and/or lung 50%‐60% of predicted). Those with the lowest
o
2
peak
pretransplant have the lowest
o
2
peak
posttransplant. Overall very few patients have a
o
2
peak
in the normal range. Investigation of the cause of the reduction of
o
2
peak
has identified many factors pre‐ and posttransplant that may contribute. These include organ‐specific factors in the otherwise well‐functioning allograft (e.g., chronotropic incompetence in heart transplantation) as well as allograft dysfunction itself (e.g., chronic lung allograft dysfunction). However, looking across all transplants, a pattern emerges. A low muscle mass with qualitative change in large exercising skeletal muscle groups is seen pretransplant. Many factor posttransplant aggravate these changes or prevent them recovering, especially calcineurin antagonist drugs which are key immunosuppressing agents. This results in the reduction of
o
2
peak
despite restoration of near normal function of the initially failing organ system. As such organ transplantation has provided an experiment of nature that has focused our attention on an important confounder of chronic organ failure‐skeletal muscle dysfunction. © 2012 American Physiological Society.
Compr Physiol
2:1937‐1979, 2012.