REILLY, Stephen M.; BIKNEVICIUS, Audrone R.; Ohio University; Ohio University: Integrating mechanics and kinematic gaits in tetrapod locomotion: congruence and variation in “walking” and “running”

Two descriptive paradigms have emerged from studies of terrestrial vertebrate locomotion: kinematic patterns of footfalls are used to describe the gaits used by animals and kinetic patterns are used to describe external mechanical energy fluctuations during the step. Symmetrical gaits (footfall patterns) are described on the basis of duty factor and the phase relationships of the hind and fore-feet on one side of the body (the Hildebrand model). Mechanical energy patterns appear to fall into two energy-saving modes based on the phase relationships of the kinetic and potential energy profiles (the Cavagna model). Each model has definitions of walking and running which appear to be widely observed in tetrapods. Yet, surprisingly little effort has been made to integrate these two models and much confusion arises by not considering them both when describing tetrapod locomotion. For example, what do you think a “trot” is? With data from lizards, birds, dogs, opossums, and alligators we compare kinematic gaits to mechanical energy patterns. What emerges from this comparison are patterns of expected congruence in some taxa and unexpected patterns in other taxa. The kinematic and kinetic models appears to integrate well but not perfectly in some species, and tails, bellies and postures clearly negate the notion that all terrestrial animals will customarily use energy savings mechanisms when they walk and run.