  Optimal motion planning along prescribed paths can be solved with several
techniques, but most of them do not take into account the wrenches exerted by
the end-effector when in contact with the environment. When a dynamic model of
the environment is not available, no consolidated methodology exists to
consider the effect of the interaction. Regardless of the specific performance
index to optimize, this article proposes a strategy to include external
wrenches in the optimal planning algorithm, considering the task
specifications. This procedure is instantiated for minimum-time trajectories
and validated on a real robot performing an interaction task under admittance
control. The results prove that the inclusion of end-effector wrenches affect
the planned trajectory, in fact modifying the manipulator's dynamic capability.
