Hypothesized whole muscle activity patterns of the intrinsic caudal muscle inteleost fishes. Axial swimming with increasing speed (solid line) is characterized byred muscle activity at slower speeds (1–2); at higher speeds, white muscle activityincreases to power swimming (4) and red muscle activity is reduced (3). Becausered and white muscle fibers may be non-regionalized in a single intrinsic caudalmuscle, electromyographic studies suggest a linear increase in whole muscle activityis possible with increasing speed (dashed line).Adapted from