In a single-molecule assay, the motion of a molecular motor is often inferred by measuring the stochastic trajectory of a large probe particle attached to it. We discuss a simple model for this generic setup taking into account explicitly the elastic coupling between the probe and the motor. The combined dynamics consists of discrete steps of the motor and the continuous Brownian motion of the probe. Motivated by recent experiments on the F1-ATPase, we investigated three types of efficiencies both in simulations and in a Gaussian approximation. Overall, we obtained good quantitative agreement with the experimental data. In particular, we clarify the conditions under which one of these efficiencies becomes larger than 1.
