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