Abstract
Some frog species, such as Kassina maculata (red-legged running frog), use an asynchronous walking/running gait as their primary locomotor mode. Prior comparative anatomy work has suggested that lateral rotation of the pelvis improves walking performance by increasing hindlimb stride length; however, this hypothesis has never been tested. Using non-invasive methods, experimental high-speed video data collected from eight animals were used to create two three-dimensional kinematic models. These models, each fixed to alternative local anatomical reference frames, were used to investigate the hypothesis that lateral rotation of the mobile ilio-sacral joint in the anuran pelvis plays a propulsive role in walking locomotion by increasing hindlimb stride length. All frogs used a walking gait (duty factor greater than 0.5) despite travelling over a range of speeds (0.04–0.23 m s−1). The hindlimb joint motions throughout a single stride were temporally synchronized with lateral rotation of the pelvis. The pelvis itself, on average, underwent an angular excursion of 12.71° (±4.39°) with respect to the body midline during lateral rotation. However, comparison between our two kinematic models demonstrated that lateral rotation of the pelvis only increases the cranio-caudal excursion of the hindlimb modestly. Thus, we propose that pelvic lateral rotation is not a stride length augmenting mechanism in K. maculata.
Highlights
Anurans are recognized for their jumping and swimming abilities; walking is thought to be a key behaviour present since the origin of the group [1]
Building on prior work which established that frogs use well-developed musculature to actively rotate the pelvis [6], we further show that pelvic oscillations are consistent and spatio-temporally coordinated with the leg in a manner favourable for augmenting stride length
Lateral rotation has been shown to augment walking/running stride length in other tetrapods
Summary
Anurans are recognized for their jumping and swimming abilities; walking is thought to be a key behaviour present since the origin of the group [1]. Biomechanists have investigated walking/running frogs to expand our fundamental understanding of quadrupedal vertebrate locomotion [3,4] as well as to link behavioural traits to morphology [5], muscular function [6] and energetics [7,8]. Frogs employ a quadrupedal limb contact cycle where the forelimb (on the leading side) makes contact first, followed by the leading hindlimb the trailing hindlimb and, the trailing forelimb [5]. This contact sequence, known as the lateral sequence [27] is common among many quadrupedal taxa [28], including walking salamanders (but not trotting [29])
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