REILLY, S.M.*; WHITE, T.D.: Abdominal motor dynamics in mammal locomotion I: Asymmetrical modulation of “cross-couplet” body support in trotting opossums

Electromyographical patterns of abdominal muscles and muscles associated with the epipubic bones were studied in the Virginia (Didelphis virginiana) and Pygmy (Monodelphis domestica) Opossums during treadmill locomotion at different speeds. Both species exhibited a striking pattern of asymetrical activation of a specific set of abdominal wall and epipubic muscles summing to produce a linear pattern of contraction spanning diagonal fore- and hind limb pairs during the time they are supporting the body during trotting gaits. In effect, a series of muscles contract diagonally to stiffen and bend the body during the time that a given diagonal couplet is on the ground. The epipubic bones move little and appear to act as a mid-abdominal strut serving to align and anchor the diagonal muscle array. The pectineus exhibits a peculiar pattern of isometric tetanus during locomotion.