Muscle activity in steady swimming scup, Stenotomus chrysops, varies
with fiber type and body position.  Coughlin DJ, Rome LC.  Source

Science Division, Widener University, Chester, Pennsylvania 19013,
USA. coughlin@pop 1.science.widener.edu Abstract

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 electromyograms (EMGs) allowed
determination of initial speed of muscle recruitment and duty cycle and
phase of muscle electromyographic 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, whereas 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 the
recruitment of red muscle. The duty cycle of pink muscle EMG activity is
significantly shorter than that of red muscle, reflecting a difference
in the onset time of activation during each cycle of length change:
pink muscle onset time follows that of red. The different patterns of
usage of red and pink muscle reflect differences in their contraction
kinetics. Because 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.

PMID:
    10226354 [PubMed - indexed for MEDLINE]

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