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

Abstract

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 to maximize consistency across subdisciplines. We summarize nine key parameters used to characterize walking behaviors in mammals, birds, reptiles, amphibians, and fishes. After identifying consistent patterns across groups, we propose a comprehensive definition for a walking gait. A walk is a form of locomotion where the majority 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 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 quadrupedal movements are still poorly understood and much work remains to be done to understand the movements of small, exothermic tetrapods.

Different Purkinje cell pathologies cause specific patterns of progressive ataxia in mice

“…The new analysis methods introduced in this study allow us to retrieve the placement of all four limbs, a feature that was not readily available previously for the ErasmusLadder (Vinueza Veloz et al, 2015). This enabled us to construct Hildebrand plots, pioneered for the study of horse gaiting and later applied to several other species (Hildebrand, 1965; Cartmill et al, 2020; Struble and Gibb, 2022). Possibly related to the relatively short gangway of the ErasmusLadder, Hildebrand plots from individual mice turned out to be too noisy for further analysis, so that we had to group all steps per session and genotype.…”

A functional framework for interpreting phalangeal form

“…Shortening the proximal phalanx, as shown by our biomechanical and robotic models, serves a clear purpose: namely increasing forces at proximal digital joints by reducing the out-lever length to the PIP joint and thus increasing mechanical advantage [38,40]. Biologically, we observe that several avian orders appear to have converged upon this morphotype: including raptorial birds, vertically climbing woodpeckers and parrots [25,26,29,30].…”

“…More recently, a general trend towards increasing penultimate phalanx length in grasping arboreal species has been observed [13,25,27,37], leading to use of this trait as a diagnostic tool for arboreality in the fossil record. Similarly, theoretical biomechanical models of the avian foot suggest that shortening the proximal phalanx and elongating its distal counterparts may function to increase the pressure exerted by the proximal interdigital pads, but not the talons-an observation that would apparently support the elongated distal, and shortened proximal, phalanges seen in many perching birds [38]. This notion aligns well with biomechanical modelling presented by Backus et al [39] suggesting that proximally inserting flexor muscles play a greater role during perching behaviours than during carrying tasks (which can be performed well using only distally inserting muscles).…”

A deep learning-based approach for unbiased kinematic analysis in CNS injury

“…This stringent exclusion criterion is set to allow for the most accurate representation of the walking oscillation pattern of the mouse. This oscillation pattern is obtained by graphing the x coordinates of the 4 limbs over the span of the recording, which in a healthy mouse shows synchronous phasing of inter- paired appendages (Struble and Gibb, 2022).…”

“…Synchronicity "Synchronicity" describes a quadrupedal gait where the inter-paired appendages exhibit synchronous phasing, meaning that the timing of movements between forelimbs and hindlimbs is coordinated (Struble and Gibb, 2022). In this phased gait, the limbs within the same girdle (forelimbs or hindlimbs) are out of phase with each other, ensuring that there is always at least one limb serving as a support during locomotion.…”