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

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.