@article {69624, title = {Leg compliance is required to explain the ground reaction force patterns and speed ranges in different gaits}, journal = {Royal Society of Open Science}, year = {2025}, month = {2025 October 15}, abstract = {

Two simple models{\textemdash}vaulting over stiff legs and rebounding over compliant legs{\textemdash}are employed to describe the mechanics of legged locomotion. It is agreed that compliant legs are necessary for describing running, and that leg compliance is also present during walking. Stiff legs continue to be employed to model walking under the assumption that the compliance of the leg during walking is low enough to be considered stiff. Here we study gait choice and walk-to-run transition in a biped with compliance and show that the principles underlying gait choice and transition are completely different from stiff legs. Two findings underpin our conclusions: First, at the same speed, step length and stance duration, multiple gaits that differ in the number of times the leg expands and contracts during a single stance are possible. Among them, humans and other animals choose the (normal) gait with M-shaped vertical ground reaction forces (vGRF) not just because of energy considerations but also constraints from forces. Second, the transition from walking to running occurs because of three factors: vGRF minimum at mid-stance characteristic of normal walking, synchronization of horizontal and vertical motions during single support, and velocity redirection during the double support. The insight above required an analytical approximation of the double spring-loaded pendulum (DSLIP) model describing the intricate oscillatory dynamics that relate single and double support phases. Additionally, we also examined DSLIP as a quantitative model for locomotion and conclude that DSLIP speed range is limited. However, insights gleaned from the analytical treatment of DSLIP are general and will inform the construction of more accurate models of walking.

bioRxiv preprint:\ https://doi.org/10.1101/2024.09.23.612940

}, doi = {10.1098/rsos.250527}, url = {https://doi.org/10.1098/rsos.250527}, author = {Safa, Ali Tehrani and Biswas, Tirthabir and Ramakrishnan, Arun and Bhandawat, Vikas} } @article {66027, title = {Drosophila uses a tripod gait across all walking speeds, and the geometry of the tripod is important for speed control.}, journal = {eLife}, volume = {10}, year = {2021}, month = {2021 Feb 03}, abstract = {

Changes in walking speed are characterized by changes in both the animal{\textquoteright}s gait and the mechanics of its interaction with the ground. Here we study these changes in walking . We measured the fly{\textquoteright}s center of mass (CoM) movement with high spatial resolution and the position of its footprints. Flies predominantly employ a modified tripod gait that only changes marginally with speed. The mechanics of a tripod gait can be approximated with a simple model - angular and radial spring-loaded inverted pendulum (ARSLIP) - which is characterized by two springs of an effective leg that become stiffer as the speed increases. Surprisingly, the change in the stiffness of the spring is mediated by the change in tripod shape rather than a change in stiffness of the individual leg. The effect of tripod shape on mechanics can also explain the large variation in kinematics among insects, and ARSLIP can model these variations.

}, issn = {2050-084X}, doi = {10.7554/eLife.65878}, author = {Chun, Chanwoo and Biswas, Tirthabir and Bhandawat, Vikas} }