  We consider the dynamics of a microswimmer and show that they can be
approximated by active Brownian motion. The swimmer is modeled by coupled
overdamped Langevin equations with periodic driving. We compare the energy
dissipation of the real swimmer to that of the active Brownian motion model,
finding that the latter can massively underestimate the complete dissipation.
This discrepancy is related to the inability to infer the full dissipation from
partial observation of the complete system. We introduce an efficiency that
measures how much of the dissipated energy is spent on forward propulsion.
