  We propose a theoretical model which relies on the generalized Langevin
equation and may account for various dynamical features of the thermal motion
of organelles, vesicles or macromolecules in viscoelastic media such as polymer
networks. In particular, we consider inertial and hydrodynamic effects at short
times, subdiffusive scaling at intermediate times, and eventually optical
trapping at long times. Simple analytical formulas for the mean square
displacement and velocity auto-correlation function are derived. The developed
theory is applied to the analysis of fifty-second long trajectories of
micron-sized spherical tracers in actin gels that were acquired at one
microsecond temporal resolution by using optical tweezers single-particle
tracking. For the first time, both the subdiffusive scaling and hydrodynamic
effects are observed within a single experiment and accurately described by a
minimal phenomenological model.
