Undulatory swimming with and without waves of contraction

IT HAS been accepted generally that the waves of bending observed in swimming vertebrates are produced by contraction on the concave side of each bend of the body at any point within the cycle of movement1–3. “Waves of contraction” are imagined to pass down the serial mytomes with the velocity of the propagated bends. Another concept, designed primarily to explain snake locomotion4, differs by a 90° shift in the timing of contraction on the bending wave, accounting for propulsion but resulting in illogical analysis of fish movement5. The former interpretation gives no explanation of the source of locomotory thrust, assuming falsely that the muscular activity required for a given body position is similar whether the position is held or passed through in locomotion. The dominant responsibility of locomotory activity is the propagation rather than the formation of bends, but how is propagation achieved against external resistance? Relevant electromyography of spinal dogfish6,7 has not been related to this mechanical problem. I present here a preliminary report of electromyographic studies of developmental stages of the palmate newt, Triturus helveticus (Razoumowsky), and adult tench, Tinca tinca L., which show that undulatory propulsion in some animals does not involve waves of contraction and that the “waves” recorded in others function in reducing lateral oscillation anteriorly and adapting tail flexibility to different swimming speeds.