title: An integrative view of limitations to muscular performance.
abstract: First we describe the changing site of limitation to maximal O2 transport with increasing fitness in mammals. The capacity for diffusion and airway/parenchymal flow rate and volume are markedly overbuilt in the sedentary subject's lung, but undergo little change with increased training/fitness; accordingly, as demand for O2 transport increases in the highly fit, the limits for maximal diffusion and ventilation are surpassed or met at maximal exercise. Secondly, low-frequency diaphragmatic fatigue occurred with by heavy endurance exercise. This fatigue resulted from increased diaphragmatic work together with the major contribution from the secondary effects of increased locomotor muscle activity; namely, metabolic acidosis and increased requirement for blood flow.
authors.affiliation: John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Department of Preventive Medicine, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Dempsey
authors.forename: M A
authors.initials: MA
authors.lastname: Babcock
mesh_terms: D015444:Exercise / Q000502:physiology*; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D009132:Muscles / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*
chemical_list: D010100:Oxygen