Do We All Walk the Walk? A Comparison of Walking Behaviors across Tetrapods

A "walking"gait has been identified in a range of vertebrate species with different body plans, habitats, and life histories. With increased application of this broad umbrella term, it has become necessary to assess the physical characteristics, analytical approaches, definitions, and diction used to describe walks. To do this, we reviewed studies of slow-speed locomotion across a range of vertebrates to refine the parameters used to define walking, evaluate analytical techniques, and propose approaches tomaximize consistency across subdisciplines of zoology. We summarize nine key parameters used to characterize walking behaviors inmammals, birds, reptiles, amphibians, and fish. After identifying consistent patterns across groups, we propose a comprehensive definition for a walking gait. Awalk is a formof locomotion where themajority of the forward propulsion of the animal comes from forces generated by the appendages interacting with the ground. During a walk, an appendage must be out of phase with the opposing limb in the same girdle and there is always at least one limb acting as ground-support (no suspension phase). Additionally, walking occurs at dimensionless speeds <1 v. and the average duty factor of the limbs is always >0.5. Relative to other gaits used by the same species, the stance duration of a walk is long, the cycle frequency is low, and the cycle distance is small. Unfortunately, some of these biomechanical parameters, while effectively describing walks, may also characterize other, non-walking gaits. Inconsistent methodology likely contributes to difficulties in comparing data across many groups of animals; consistent application of data collection and analytical techniques in research methodology can improve these comparisons. Finally, we note that the kinetics of quadrupedalmovements are still poorly understood andmuch work remains to be done to understand the movements of small, ecothermic tetrapods.