Reducing the energy cost of walking with low assistance levels through optimized hip flexion assistance from a soft exosuit

Abstract

As we age, humans see natural decreases in muscle force and power which leads to a slower, less efficient gait. Improving mobility for both healthy individuals and those with muscle impairments/weakness has been a goal for exoskeleton designers for decades. In this work, we discover that significant reductions in the energy cost required for walking can be achieved with almost 50% less mechanical power compared to the state of the art. This was achieved by leveraging human-in-the-loop optimization to understand the importance of individualized assistance for hip flexion, a relatively unexplored joint motion. Specifically, we show that a tethered hip flexion exosuit can reduce the metabolic rate of walking by up to 15.2 ± 2.6%, compared to locomotion with assistance turned off (equivalent to 14.8% reduction compared to not wearing the exosuit). This large metabolic reduction was achieved with surprisingly low assistance magnitudes (average of 89 N, ~ 24% of normal hip flexion torque). Furthermore, the ratio of metabolic reduction to the positive exosuit power delivered was 1.8 times higher than ratios previously found for hip extension and ankle plantarflexion. These findings motivated the design of a lightweight (2.31 kg) and portable hip flexion assisting exosuit, that demonstrated a 7.2 ± 2.9% metabolic reduction compared to walking without the exosuit. The high ratio of metabolic reduction to exosuit power measured in this study supports previous simulation findings and provides compelling evidence that hip flexion may be an efficient joint motion to target when considering how to create practical and lightweight wearable robots to support improved mobility.

Springs vs. motors: Ideal assistance in the lower limbs during walking at different speeds

“…It is possible that this counterintuitive benefit from simulation studies might not translate experimentally; it has, to the best of our knowledge, not been tested experimentally. Furthermore, previous experimental studies reported a metabolic decrease of 8.8% with hip flexion assistance compared to unassisted conditions (38) and 6.1% compared with a powered-off exoskeleton (39), which agrees with our predictions (9% near preferred walking speed). With spring-based hip flexion assistance, only two experimental studies reported metabolic rate reduction (19,40).…”

A Critical Review on Factors Affecting the User Adoption of Wearable and Soft Robotics

“…( A ) Noronha et al [ 51 ] describe their work on a tethered soft exosuit that comprises an elbow wearable and a hand exoskeleton. ( B ) Kim et al [ 42 ] describe their work on a tethered hip flexion exosuit which can reduce the metabolic rate of walking by up to 15.2%. ( C ) Chen et al [ 63 ], on the other hand, show that their lower limb wearable can be controlled using a portable system.…”

“…For example, Walsh’s group at Harvard University has done extensive work on tendon-driven soft exosuits that assist lower limb mobility [ 38 , 42 , 46 , 102 , 103 , 105 , 106 ], primarily hip flexion and ankle plantarflexion. The evolution of the soft exosuit has seen modifications made to the wearable, from its basic form [ 106 ] to the latest iteration [ 46 ], which uses fewer anchoring straps and more elaborate control systems.…”

Gait Recognition and Assistance Parameter Prediction Determination Based on Kinematic Information Measured by Inertial Measurement Units

“…Eight participants walked on the treadmill at a speed of 1.25 m/s, and the iterative optimization process took an average of two hours per participant. The research results indicate that metabolism significantly decreases under moderate intensity and optimal time [ 34 ]. Ye et al proposed a Bayesian optimization algorithm that uses minimum metabolic cost as an indicator to conduct parameter optimization, minimizing the metabolic cost for humans walking on a 1.25 m/s treadmill [ 23 ].…”