Lower-limb single-joint exoskeletons are easily divided into
hip, knee or ankle systems. The role of these joints is fundamentally
different [74]: in level walking, knee is mostly a free-damping joint
in the swing phase, while almost locked during the stance phase;
hip and ankle are mostly related to the swing dynamic handling
and the stance-phase ground propulsion respectively, but more
recent researches have also showed their mutual dependence. In
all of the following cases, the addressed DOF is always the sagittal
plane joint, thus the f/e (or the analogous d/p, for the ankle) one.
Some examples of the single-joint exoskeletons presented in this
section are shown in Fig. 4.