The Effects of Incline Level on Optimized Lower-Limb Exoskeleton Assistance: A Case Series

For exoskeletons to be successful in real-world settings, they will need to be effective across a variety of terrains, including on inclines. While some single-joint exoskeletons have assisted incline walking, recent successes in level-ground assistance suggest that greater improvements may be possible by optimizing assistance of the whole leg. To understand how exoskeleton assistance should change with incline, we used human-in-the-loop optimization to find whole-leg exoskeleton assistance torques that minimized metabolic cost on a range of grades. We optimized assistance for three non-disabled, expert participants on 5 degree, 10 degree, and 15 degree inclines using a hip-knee-ankle exoskeleton emulator. For all assisted conditions, the cost of transport was reduced by at least 50% relative to walking in the device with no assistance, which is a large improvement to walking comparable to the benefits of whole-leg assistance on level-ground (N = 3). Optimized extension torque magnitudes and exoskeleton power increased with incline. Hip extension, knee extension and ankle plantarflexion often grew as large as allowed by comfort-based limits. Applied powers on steep inclines were double the powers applied during level-ground walking, indicating that greater exoskeleton power may be optimal in scenarios where biological powers and costs are higher. Future exoskeleton devices could deliver large improvements in walking performance across a range of inclines if they have sufficient torque and power capabilities.

Automated summary

In order for exoskeletons to be effective in real-world situations, they need to be able to function across various terrains, including inclines. Recent research suggests that by optimizing the assistance provided by the entire leg, greater improvements can be achieved compared to single-joint exoskeletons. Using a human-in-the-loop optimization approach, this study determined the optimal torque assistance provided by a hip-knee-ankle exoskeleton emulator on inclines of different degrees. The results showed that the assistance significantly reduced the cost of transport and that the torque and power applied by the exoskeleton increased with incline.