Meeting Abstract

3.6  Monday, Jan. 4  Muscle activation during surface and subsurface locomotion in sandfish (Scincus scincus) STEINMETZ, Sarah M*; MALADEN, Ryan D; DING, Yang; GOLDMAN, Daniel I; Bioengineering Program, Georgia Tech; Bioengineering Program, Georgia Tech; School of Physics, Georgia Tech; School of Physics, Georgia Tech ssteinmetz3@gatech.edu

A recent study (Maladen et. al, Science, 2009) found that sandfish swim in sand using a traveling wave body undulation without limb use and that kinematics are independent of volume fraction (φ) due to identical scaling of thrust and drag forces, which double between loose (low φ) and close (high φ) sand packings. Additionally, our numerical model of the sandfish indicates that a traveling wave muscle activation pattern is required to achieve the observed kinematics. Consequently, we hypothesize that animal muscle activation varies with varying φ . We test our hypothesis by combining high speed x-ray and visible light imaging with synchronized electromyography (EMG) of sandfish back (epaxial) muscle during surface and subsurface motion. While running on the surface, body oscillation was not observed and simultaneous EMG recordings revealed only a low intensity activation level. During burial, the animal executes a stereotypical entry, gradually ceasing limb use while increasing body undulation amplitude, and the EMG signal increases from zero to a fixed intensity level for periods of activation. During sand swimming the EMG signal reveals a uniphasic rostrocaudal traveling wave of muscle activation similar to our numerical model. However, in contradiction to our hypothesis both the activation duration and intensity are independent of φ (P> 0.05). Potential explanations of this surprising result include (1) muscle activation onset changes relative to the phase of the kinematic wave, and (2) the sand immediately surrounding the animal and in which it swims evolves to the same critical packing state independent of the initial preparation.