Functional Analysis of Anuran Pelvic and Thigh Anatomy Using Musculoskeletal Modelling of Phlyctimantis maculatus

Abstract

Using their abundant musculature, frogs are able to exhibit outstanding behavioural versatility. However, understanding the dynamic motion of their 30 + hindlimb muscles, with multi-joint action, and curved pathways, is challenging. This is particularly true in walking, a relatively understudied, but complex frog gait. Building on prior musculoskeletal modelling work we construct and analyse a 3D musculoskeletal model of the spine, pelvis, and hindlimb of Phlyctimantis maculatus (previously known as Kassina maculata) to simulate the natural motion of muscle pathways as joints rotate during locomotion. Combining experimental kinematics and DICE-CT scan data we use several simulations conducted in MuJoCo to decouple femur and pelvic motions, generating new insights into the functional mechanics of walking in frogs. Outputs demonstrate pelvic lateral rotation about the iliosacral joint influences moment arm magnitude in the majority of hindlimb muscles. The extent of pelvic influence depends on femoral angle which changes muscle function in some instances. The workflow presented here can be used to help experimentalists predict which muscles to probe with in vivo techniques towards a better understanding of how anuran musculoskeletal mechanics enable multiple behaviours.

Modern three-dimensional digital methods for studying locomotor biomechanics in tetrapods

“…This combination can be achieved using empirical data as per above, or using robotics or fluid dynamics approaches. A variety of studies have combined empirical data with simulations to study 3D locomotor dynamics – including prediction of jumping performance in frogs ( Kargo et al, 2002 ; Porro et al, 2017 ; Richards et al, 2018 ; see also Collings et al, 2022 ), joint reaction forces and soft tissue strains as well as substrate dynamics in horse forelimbs (e.g. Swanstrom et al, 2005 ; Becker et al, 2019 , 2020 ; Harrison et al, 2010 ; Symons et al, 2016 , 2017 ), neuromuscular control in rats and mice (e.g.…”

“…These musculoskeletal models (see Glossary) normally are grounded in empirical data such as dissections or 3D imaging of soft tissue morphology (e.g. Brown et al, 2003 ; Nagano et al, 2005 ; Zarucco et al, 2006 ; Hutchinson et al, 2015 ; Charles et al, 2016 ; Regnault and Pierce, 2018 ; Sullivan et al, 2019 ; Bishop et al, 2021b ; Wiseman et al, 2021 ; Collings et al, 2022 ), or a 3D polygonal modelling approach ( Demuth et al, 2022a ; Herbst et al, 2022b ), and are sometimes placed within a phylogenetic context ( Brocklehurst et al, 2022 ; Löffler et al, 2022 ). Musculature must be reconstructed if the research question pertains to the moment arms (see Glossary), moment-generating capacity and/or activation of specific muscles/muscle groups.…”

“… Sample musculoskeletal model of the hindlimbs of a red-legged frog, Kassina . The model is shown in dorsal (A,B) and ventral (C) views (from Collings et al, 2022) . Limbs are in a straightened reference pose.…”