Email: coughlin@pop1.science.widener.edu
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The red and pink aerobic muscle fibers are used to power steady swimming in fishes.  We examined red and pink muscle recruitment and function during swimming in scup, Stenotomus chrysops, through electromyography and high-speed ciné.  Computer analysis of EMGs allowed determination of initial speed of muscle recruitment and duty cycle and phase of muscle EMG activity for both fiber types.  This analysis was carried out for three longitudinal positions over a range of swimming speeds.  Fiber type and longitudinal position both affected swimming speed of initial recruitment.  Posterior muscle is recruited at the lowest swimming speed, while more anterior muscle is not initially recruited until higher speeds.  At more anterior positions, the initial recruitment of pink muscle occurs at a higher swimming speed than red muscle. The duty cycle of pink muscle EMG activity is significantly shorter than red muscle, reflecting a difference in the onset time of activation during each length change cycle: pink muscle onset time follows that of red. The different patterns of usage of red and pink muscle reflect differences in their contraction kinetics.  Since pink muscle generates force more rapidly than red muscle, it can be activated later in each tailbeat cycle.  Pink muscle is used to augment red muscle power production at higher swimming speeds, allowing a higher aerobically-based steady swimming speed than that possible by red muscle alone.