title: Energy demand and supply in human skeletal muscle.
abstract: The energy required for muscle contraction is provided by the breakdown of ATP but the amount of ATP in muscles cells is sufficient to power only a short duration of contraction. Buffering of ATP by phosphocreatine, a reaction catalysed by creatine kinase, extends the duration of activity possible but sustained activity depends on continual regeneration of PCr. This is achieved using ATP generated by oxidative processes and, during intense activity, by anaerobic glycolysis. The rate of ATP breakdown ranges from 70 to 140 mM min-1during isometric contractions of various intensity to as much as 400 mM min-1during intense, dynamic activity. The maximum rate of oxidative energy supply in untrained people is ~50 mM min-1which, if the contraction duty cycle is 0.5 as is often the case in cyclic activity, is sufficient to match an ATP breakdown rate during contraction of 100 mM min-1. During brief, intense activity the rate of ATP turnover can exceed the rates of PCr regeneration by combined oxidative and glycolytic energy supply, resulting in a net decrease in PCr concentration. Glycolysis has the capacity to produce between 30 and 50 mM of ATP so that, for example, anaerobic glycolysis could provide ATP at an average of 100 mM min-1over 30 s of exhausting activity. The creatine kinase reaction plays an important role not only in buffering ATP but also in communicating energy demand from sites of ATP breakdown to the mitochondria. In that role, creatine kinases acts to slow and attenuate the response of mitochondria to changes in energy demand.
authors.affiliation: School of Allied Health Sciences, Griffith University, Gold Coast, QLD, 4222, Australia. cj.barclay.muscle.energetics@gmail.com.
authors.forename: C J
authors.identifier: 0000-0002-0903-3111
authors.initials: CJ
authors.lastname: Barclay
mesh_terms: D004734:Energy Metabolism; D006801:Humans; D018482:Muscle, Skeletal / Q000378:metabolism*
keywords: ATP turnover; Energy supply; Muscle; Muscle energetics; Skeletal muscle