Passive Exotendon Spring Elements can replace Muscle Torque during Gait

Nowadays, exoskeletons are widely used as assistive tools during gait rehabilitation, implementing strategies such as gravity compensation and metabolic cost reduction. However, these devices often require the use of motors and controllers. Our research is driven by the need for a simple, inexpensive and customizable device, a passive exotendon able to provide a desired torque profile to multiple joints. In a simulation model study, we asked whether it was possible to use diagonal tension elements, which act mathematically as basis functions, in order to reproduce the torque field generated by a healthy person during walking. This would allow us to create a wearable exotendon system made of passive elastic elements able to deliver this torque field to the lower extremity of the patient during gait rehabilitation. Our results showed that it is indeed possible to create a passive torque field from elastic elements that approximates the muscular torque demand for the walking cycle. This represents a starting point for the design of a passive exotendon capable of providing assistive torques to patients with motor deficits, thus reducing the metabolic cost of walking.