In this paper, we have reviewed various kinds of assistive
strategies employed in powered lower-limb exoskeletons for the
selected literature, including both multi-joint and single-joint devices
and focusing on the systems with user-in-the-loop validations.
Generally, an assistive strategy has to deal with two main
issues regarding the user-exoskeleton mutual interactions: a physical
interaction, i.e. the mechanical power transfer, and a cognitive