Actuator- and Control-Less Ankle Exoskeleton for Push-Off Assistance During Treadmill Walking: a Proof-Of-Concept Study

We have previously proposed a novel tethered ankle exoskeleton AN-EXTRA-Push. It operated by exploiting the posterior movement of the leg on the treadmill to stretch an elastic tendon. The exoskeleton was controlled using an electromechanical brake. The objective of this case study with one healthy and one hemiparetic subjects was to test the feasibility of AN-EXTRAPUSH, modified in such a way that one end of the elastic tendon is permanently attached to a fixed point, eliminating any control. Subjects walked on a split-belt treadmill under 4 experimental conditions: one unassisted and at three different assistance levels. The healthy subject repeated the experimental procedure at three different walking speeds. The hemiparetic subject walked at a constant self-selected speed. In healthy subject, AN-EXTRA-PUSH assistance caused a decrease in peak biological torque accompanied with an increase in exoskeleton torque in the ankle joint. Biological power remained similar across conditions with the additional exoskeleton power contributing to increased total power generation. Exoskeleton torque and power increased with higher walking speeds. In hemiparetic subject, AN-EXTRA-PUSH did not affect biological torque and power, however, it added torque and power to reach higher totals. These preliminary results show that the proposed actuatorand control-less version of AN-EXTRA-Push is feasible and warrants further research.