CARRIER, David/R; University of Utah: Function of the Axial Muscles during Running.

The axial muscles of tetrapods perform two functions during walking and running: generation of work and postural support. Work is produced when active flexion and extension of the trunk contribute to displacement of the body. In lizards, for example, the muscles of the lateral body wall produce work through lateral bending of the trunk during running. Independent of work production, the axial muscles must provide postural support against forces and torques that tend to deform the trunk. These include forces required to overcome inertia, torques imposed on the trunk by the extrinsic limb muscles, and gravity. In tetrapods with sprawling limb posture, resistance against torques inducing long-axis torsion of the trunk appears to be provided by the oblique hypaxial muscles. In mammals with a more parasagittal limb posture, limb protraction and retraction induce moments on the trunk about transverse axes through the limb girdles. These torques tend to shear the trunk in the sagittal plane and appear to also be resisted by the oblique hypaxial muscles. The locomotor functions of the axial muscles are complicated by the fact that some of these same muscles also produce lung ventilation. If locomotion is to be sustained, the locomotor work and postural support of the trunk must be 1) integrated with activity of the hypaxial muscles that produce lung ventilation and 2) accomplished in a manner that does not interfere with cardiovascular circulation.