Smith, NicolasBarclay, ChristopherLoiselle, Denis2011-09-062005Prog Biophys Mol Biol 88(1):1-58 May 20050079-6107https://hdl.handle.net/2292/7827When a muscle contracts and shortens against a load, it performs work. The performance of work is fuelled by the expenditure of metabolic energy, more properly quantified as enthalpy (i.e., heat plus work). The ratio of work performed to enthalpy produced provides one measure of efficiency. However, if the primary interest is in the efficiency of the actomyosin cross-bridges, then the metabolic overheads associated with basal metabolism and excitation–contraction coupling, together with those of subsequent metabolic recovery process, must be subtracted from the total heat and work observed. By comparing the cross-bridge work component of the remainder to the Gibbs free energy of hydrolysis of ATP, a measure of thermodynamic efficiency is achieved. We describe and quantify this partitioning process, providing estimates of the efficiencies of selected steps, while discussing the errors that can arise in the process of quantification. The dependence of efficiency on animal species, fibre-type, temperature, and contractile velocity is considered. The effect of contractile velocity on energetics is further examined using a two-state, Huxley-style, mathematical model of cross-bridge cycling that incorporates filament compliance. Simulations suggest only a modest effect of filament compliance on peak efficiency, but progressively larger gains (vis-a-vis the rigid filament case) as contractile velocity approaches " Vmax: This effect is attributed primarily to a reduction in the component of energy loss arising from detachment of cross-bridge heads at non-zero strain.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from http://www.sherpa.ac.uk/romeo/issn/0079-6107/https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmenergyenthalpyefficiencycross-bridgesfibre-typespecies-differencesDOGFISH SCYLIORHINUS-CANICULACROSS-BRIDGE MODELDISTRIBUTION-MOMENT MODELFROG SKELETAL-MUSCLESLOW-TWITCH MUSCLESX-RAY-DIFFRACTIONCREATINE-KINASE EQUILIBRIUMNUCLEAR MAGNETIC-RESONANCEMYOSIN ISOFORM COMPOSITIONATP HYDROLYSIS EQUILIBRIAJournal Article10.1016/j.pbiomolbio.2003.11.014Copyright: 2003 Elsevier Ltd.15561300http://purl.org/eprint/accessRights/RestrictedAccess