Mechanical and energy characteristics during shortening in isolated type-1 muscle fibres from Xenopus laevis studied at maximal and submaximal activation |
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Authors: | H P J Buschman M Linari G Elzinga R C Woledge |
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Institution: | (1) Institute of Human Performance, Royal National Orthopaedic Hospital Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK, GB;(2) Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, I-50134 Firenze, Italy, IT;(3) Laboratory for Physiology, Institute for Cardiovascular Research, Vrije Universiteit, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands, NL |
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Abstract: | The mechanical and energy characteristics of isolated fast-twitch muscle fibres (type 1) of Xenopus laevis in isometric- and isovelocity contractions were measured at 20°C. The fibres were stimulated at either 60 Hz or 20 Hz to
produce contractions at different levels of activation. The high stimulation frequency gave fused contractions, while at the
low stimulation frequency tension fluctuated. When maximum isometric force had been reached, the fibres were shortened by
10% of the fibre length at different velocities. At 60 Hz stimulation during shortening the rate of heat production increased
above the isometric rate of heat production. At 20 Hz stimulation during shortening, however, the rate of heat production
was not different from the isometric rate of heat production. Mechanical efficiency was the same at the high and low level
of activation. The actomyosin efficiency (i.e. the mechanical efficiency corrected for ”activation heat”) was highest at the
low level of activation. We conclude that in fast-twitch muscle fibres from X. laevis, actomyosin efficiency is highest for partially activated muscle. From a comparison of the present results with those obtained
from a study of slow-twitch muscle fibres presented earlier, it is concluded that fast-twitch muscle fibres are less efficient
than slow-twitch muscle fibres.
Received after revision: 13 May 1997 / Accepted: 1 July 1997 |
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Keywords: | Skeletal muscle Force production Heat production Fast-twitch muscle Muscle energetics Fenn effect Efficiency |
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