Beyond locomotion: How specialized motor patterns enable a vertebrate to struggle free from capture.

Animals captured by predators can still survive the attack by struggling to release themselves. We investigated how Xenopus tadpoles use struggling movements to free themselves from head restraint. High-speed video tracking revealed a stereotyped sequence of body flexions with distinct kinematics during capture and release. We further recorded motoneuron activities along the body axis during fictive struggling to reconstruct biologically realistic spatio-temporal motoneuronal firing patterns, to drive the movement of a 3D biomechanically detailed tadpole model. Simulations showed that struggling-characterized by long-duration, low-frequency, and caudorostral muscle activation-was optimized to generate freeing forces. Notably, hydrodynamic thrust alone proved insufficient for release. However, direct mechanical interactions between the tadpole's body and the restraining object generated additional reactive forces that facilitated escape. These findings demonstrate how animals use coordinated motor outputs and body mechanics to interact with the gripping object to generate maximal freeing forces as the fundamental survival strategy.