Between walking and running, human gaits can cover a wide range of speeds; for example, at low speeds, the metabolic rate of walking is lower than that of running in a slow jog. The opposite also is true: at high speeds, the metabolic cost of running is lower than that of speed-walking.
A portable exosuit was developed that assists with gait-specific hip extension during both walking and running. The lightweight exosuit is made of textile components worn at the waist and thighs, and a mobile actuation system attached to the lower back and controlled by an algorithm that can robustly detect the transition from walking to running and vice versa.
When worn by users in treadmill-based indoor tests, the exosuit, on average, reduced their metabolic costs of walking by 9.3% and of running by 4% compared to when they were walking and running without the device. The device also performed well during uphill walking, at different running speeds, and during overground testing outside
The hip exosuit assists the wearer via a cable actuation system. The actuation cables apply a tensile force between the waist belt and thigh wraps to generate an external extension torque at the hip joint that works in concert with the gluteal muscles. The device weighs 5 kg in total with more than 90% of its weight located close to the body’s center of mass. This approach to concentrating the weight, combined with the flexible apparel interface, minimizes the energetic burden and movement restriction to the wearer.
A major challenge the team had to solve was that the exosuit needed to be able to distinguish between walking and running gaits and change its actuation profiles accordingly with the right amount of assistance provided at the right time of the gait cycle. To explain the different kinetics during the gait cycles, biomechanists often compare walking to the motions of an inverted pendulum and running to the motions of a spring-mass system. During walking, the body’s center of mass moves upward after heel-strike, then reaches maximum height at the middle of the stance phase to descend towards the end of the stance phase. In running, the movement of the center of mass is opposite. It descends towards a minimum height at the middle of the stance phase and then moves upward towards push-off.
A biologically inspired gait classification algorithm was developed that can robustly and reliably detect a transition from one gait to the other by monitoring the acceleration of an individual’s center of mass with sensors attached to the body. Once a gait transition is detected, the exosuit automatically adjusts the timing of its actuation profile to assist the other gait, as demonstrated by its ability to reduce metabolic oxygen consumption in wearers.
The exosuit can be used in a range of applications including assisting those with gait impairments, industry workers at risk of injury performing physically strenuous tasks, or those engaged in recreational activities.