Efficiency of Energy Conversion During Sinusoidal Movement of White Muscle Fibres from the Dogfish Scyliorhinus Canicula

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Abstract
Net work output and heat production of white myotomal muscle fibres from the dogfish were measured during complete cycles of sinusoidal movement at 12°C. The peak-to-peak movement was about 9% of the muscle fibre length; three stimuli at 32ms intervals were given in each mechanical cycle. The frequency of movement and the timing of the stimulation were varied for each preparation to find the optimal conditions for power output and those optimal for efficiency (the ratio of net work output to total energy output as heat+work). To achieve either maximum power or maximum efficiency, the tetanus must start while the muscle fibres are being stretched, before the beginning of the shortening part of the mechanical cycle. The highest power output, averaged over one cycle, was 0.23±0.014 Wg−1 drymass (±S.E.M., N=9, 46.9±2.8mWg−1 wetmass) and was produced during movement at 3.5Hz. The highest efficiency, 0.41±0.02 (±S.E.M., N=13), occurred during movements at 2.0–2.5Hz. This value is higher than the efficiency previously measured during isovelocity shortening of these fibres. The implications of the high efficiency for crossbridge models of muscle contraction are discussed.