  In this work we consider the following question: given a mechanical
microswimming mechanism, does increased deformability of the swimmer body
hinder or promote the motility of the swimmer? To answer this we study a
microswimmer model composed of deformable beads connected with springs. We
determine the velocity of the swimmer analytically, starting from the forces
driving the motion and assuming that the oscillations in the effective radii of
the beads are known and are much smaller than the radii themselves. We find
that to the lowest order, only the driving frequency mode of the surface
oscillations contributes to the swimming velocity, and that this velocity may
both rise and fall with the deformability of the beads depending on the spring
constant. To test these results, we run immersed boundary lattice Boltzmann
simulations of the swimmer, and show that they reproduce both the
velocity-promoting and velocity-hindering effects of bead deformability
correctly in the predicted parameter ranges. Our results mean that for a
general swimmer, its elasticity determines whether passive deformations of the
swimmer body, induced by the fluid flow, aid or oppose the motion.
