  Experiments on particles' motion in living cells show that it is often
subdiffusive. This subdiffusion may be due to trapping, percolation-like
structures, or viscoelatic behavior of the medium. While the models based on
trapping (leading to continuous-time random walks) can easily be distinguished
from the rest by testing their non-ergodicity, the latter two cases are harder
to distinguish. We propose a statistical test for distinguishing between these
two based on the space-filling properties of trajectories, and prove its
feasibility and specificity using synthetic data. We moreover present a
flow-chart for making a decision on a type of subdiffusion for a broader class
of models.
