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The efficiency of muscle contraction
Nicholas P Smith1, Christopher J Barclay, Denis S Loiselle
1Bioengineering Institute, University of Auckland, Auckland, New Zealand.
Progress in Biophysics and Molecular Biology
|November 25, 2004
Summary
Muscle contraction efficiency is determined by partitioning energy expenditure. Actomyosin cross-bridge efficiency is optimized by accounting for metabolic costs and filament compliance, especially at maximal velocities.
Area of Science:
- Muscle physiology
- Bioenergetics
- Biophysics
Background:
- Muscle contraction performs work fueled by metabolic energy (enthalpy).
- Quantifying muscle efficiency requires separating actomyosin cross-bridge energy use from metabolic overheads.
- Thermodynamic efficiency of muscle can be assessed by comparing cross-bridge work to ATP hydrolysis free energy.
Purpose of the Study:
- To describe and quantify the partitioning of metabolic energy in muscle contraction.
- To estimate the thermodynamic efficiency of actomyosin cross-bridges.
- To examine the influence of factors like species, fiber type, temperature, and velocity on muscle efficiency.
Main Methods:
- Partitioning observed heat and work to isolate cross-bridge energy expenditure.
- Comparing cross-bridge work to the Gibbs free energy of ATP hydrolysis.
- Utilizing a two-state Huxley-style mathematical model with filament compliance to simulate cross-bridge cycling.
Main Results:
- Estimates of efficiency for specific steps in muscle energetics were provided.
- Factors influencing efficiency, including animal species, fiber type, temperature, and contractile velocity, were considered.
- Simulations indicated filament compliance has a modest effect on peak efficiency but increases gains at velocities approaching Vmax.
Conclusions:
- Accurate quantification of muscle efficiency requires careful partitioning of energy expenditure.
- Filament compliance plays a role in optimizing muscle efficiency at high contractile velocities by reducing energy loss during cross-bridge detachment.
- Understanding these energetic principles is crucial for comprehending muscle function across various conditions.