Activity of trunk muscles during aquatic and terrestrial locomotion in Ambystoma maculatum.

The activity of seven trunk muscles was recorded at two sites along the trunk in adult spotted salamander, Ambystoma maculatum, during swimming and during trotting in water and on land. Several muscles showed patterns of activation that are consistent with the muscles producing a traveling wave of lateral bending during swimming and a standing wave of bending during aquatic and terrestrial trotting: the dorsalis trunci, subvertebralis lateralis and medialis, rectus lateralis and obliquus internus. The interspinalis showed a divergent pattern and was active out of phase with the other muscles suggesting that it functions in vertebral stabilization rather than lateral bending. The obliquus internus and rectus abdominis showed bilateral activity indicating that they counteract sagittal extension of the trunk that is produced when the large dorsal muscles are active to produce lateral bending. Of the muscles examined, only the obliquus internus showed a clear shift in function from lateral bending during swimming to resistance of long-axis torsion during trotting. During terrestrial trotting, muscle recruitment was greater in several muscles than during aquatic trotting, despite similar temporal patterns of muscle activation, suggesting that the trunk is stiffened during terrestrial locomotion against greater gravitational forces whereas the basic functions of the trunk muscles in trotting are conserved across environments.