Symmorphosis and skeletal muscle : in vivo and in vitro measures reveal differing constraints in the exercise‐trained and untrained human

The concept of symmorphosis predicts that the capacity of each step of the oxygen cascade is attuned to the task demanded of it during aerobic exercise at maximal rates of oxygen consumption ( ) such that no single process is limiting or in excess at . The present study challenges the applicability of this concept to humans by revealing clear, albeit very different, limitations and excesses in oxygen supply and consumption among untrained and endurance‐trained humans. Among untrained individuals, is limited by the capacity of the mitochondria to consume oxygen, despite an excess of oxygen supply, whereas, among trained individuals, is limited by the supply of oxygen to the mitochondria, despite an excess of mitochondrial respiratory capacity.