Meeting Abstract

62.6  Thursday, Jan. 6  Sandfish model predicts muscle activation pattern during subsurface sand diving STEINMETZ, S.M.*; DING, Y.; GOLDMAN, D.I.; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology ssteinmetz3@gatech.edu

Desert dwelling animals like the sandfish lizard (Scincus scincus) dive into and move within surrounding sand to escape heat and predators. The sandfish uses a traveling wave undulation to swim into sand at an average angle of 28° ±5°. As the sandfish moves deeper into the medium, grain pressure increases but the animal maintains a similar waveform regardless of depth. To predict how internal forces change during dives, we utilize a multi-segment numerical simulation of a sandfish coupled to an experimentally validated Molecular Dynamics model of a 3 mm diameter granular medium. In the model the relative angles versus time between segments are specified to generate a traveling wave like that observed in the animal; the COM position and inter-segment torques are unconstrained. The model reproduces kinematic features of the locomotion (e.g. wave efficiency). When constrained to dive at 28°, activation torque in the model increases with increased depth as expected due to increased pressure in the medium. We test the simulation prediction by using electromyographic (EMG) recordings in epaxial musculature and synchronized x-ray video of the sandfish moving in 0.3 mm diameter glass beads, close in size to the natural substrate. In accord with simulation, EMG burst intensity increases significantly (P<0.05) as the sandfish moves deeper into the medium. The activation timing patterns in both simulation and experiment are independent of depth and take the form of similarly phased rostrocaudal traveling waves that travel faster than the wave of axial flexion. The similarities between simulation and experiment imply that the observed activation pattern is a result of interaction with granular media.