  Numerous natural processes are contingent on microorganisms' ability to swim
through fluids with non-Newtonian rheology. Here, we use the model organism
Caenorhabditis elegans and tracking methods to experimentally investigate the
dynamics of undulatory swimming in shear-thinning fluids. Theory and simulation
have proposed that the cost of swimming, or mechanical power, should be lower
in a shear-thinning fluid compared to a Newtonian fluid of the same zero-shear
viscosity. We aim to provide an experimental investigation into the cost of
swimming in a shear-thinning fluid from (i) an estimate of the mechanical power
of the swimmer and (ii) the viscous dissipation rate of the flow field, which
should yield equivalent results for a self-propelled low Reynolds number
swimmer. We find the cost of swimming in shear-thinning fluids is less than or
equal to the cost of swimming in Newtonian fluids of the same zero-shear
viscosity; furthermore, the cost of swimming in shear-thinning fluids scales
with a fluid's effective viscosity and can be predicted using fluid rheology
and simple swimming kinematics. Our results agree reasonably well with previous
theoretical predictions and provide a framework for understanding the cost of
swimming in generalized Newtonian fluids.
