AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 481-R488, Copyright © 1994 by American Physiological Society
Modeling red muscle power output during steady and unsteady swimming in largemouth bass
T. P. Johnson, D. A. Syme, B. C. Jayne, G. V. Lauder and A. F. Bennett
Department of Ecology and Evolutionary Biology, University of California, Irvine 92717.
We recorded electromyograms of slow-twitch (red) muscle fibers and
videotaped swimming in the largemouth bass (Micropterus salmoides) during
cruise, burst-and-glide, and C-start maneuvers. By use of in vivo patterns
of stimulation and estimates of strain, in vitro power output was measured
at 20 degrees C with the oscillatory work loop technique on slow-twitch
fiber bundles from the midbody area near the soft dorsal fin. Power output
increased slightly with cycle frequency to a plateau of approximately 10
W/kg at 3-5 Hz, encompassing the normal range of tail-beat frequencies for
steady swimming (approximately 2-4 Hz). Power output declined at cycle
frequencies simulating unsteady swimming (burst-and-glide, 10 Hz; C-start,
15 Hz). However, activating the muscle at 10 Hz did significantly increase
the net work done compared with the work produced by the inactive muscle
(work done by the viscous and elastic components). Thus this study provides
further insight into the apparently paradoxical observation that red muscle
can contribute little or no power and yet continues to show some
recruitment during unsteady swimming. Comparison with published values of
power requirements from oxygen consumption measurements indicates a limit
to steady swimming speed imposed by the maximum power available from red
muscle.
