Between walking at a relaxed pace and running for one’s life, human gaits can manage a broad range of speeds. Usually, a person chooses the gait wherein the least amount of energy is consumed at a particular speed. For instance, at low speeds, the metabolic rate of walking is less than slowly jogging; vice versa at high speeds, the metabolic cost of running is lesser than that of speed walking.
Scientists in academic and industry labs have built robotic devices for rehabilitation and other areas of life that can either support running or walking, but no untethered portable device could efficiently handle both.
Assisting running and walking with a single device is not simple given that the primary biomechanics of the two gaits are different. However, both gaits have in common an extension of the hip joint, which begins around the time when the foot makes contact with the ground and requires substantial energy for pushing the body forward.
As described recently in Science, a team of scientists at Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS), and the University of Nebraska Omaha currently have designed a portable exosuit that assists with gait-specific hip extension during walking as well as running.
This lightweight exosuit is composed of textile components worn at the thighs and waist, and a mobile actuation system attached to the lower back which is regulated by an algorithm that can strongly detect the change from walking to running and vice versa.
The researchers first demonstrated that the exosuit worn by users in treadmill-based indoor tests, on average, lowered their metabolic costs of walking by 9.3% and of running by 4% compared to when they were running and walking without the device.
“We were excited to see that the device also performed well during uphill walking, at different running speeds and during overground testing outside, which showed the versatility of the system,” said Conor Walsh, Ph.D., who led the study. Walsh is a Core Faculty member of the Wyss Institute, the Gordon McKay Professor of Engineering and Applied Sciences at SEAS, and Founder of the Harvard Biodesign Lab.
While the metabolic reductions we found are modest, our study demonstrates that it is possible to have a portable wearable robot assist more than just a single activity, helping to pave the way for these systems to become ubiquitous in our lives.
Conor Walsh, Ph.D., Study Led and Core Faculty Member, Wyss Institute, Harvard University
The hip exosuit was created as part of the Defense Advanced Research Projects Agency (DARPA)’s former Warrior Web program and is the culmination of years of study and improvisation of the soft exosuit technology by the team. An earlier multi-joint exosuit built by the team could support both the ankle and hip during walking, and a medical version of the exosuit aimed at enhancing gait rehabilitation for stroke survivors is presently commercially available in the US and Europe, via a partnership with ReWalk Robotics.
The team’s latest hip-assisting exosuit is engineered to be simpler and lighter weight than their earlier multi-joint exosuit. It assists the wearer via a cable actuation system. The actuation cables transmit a tensile force between the waist belt and thigh wraps to produce an external extension torque at the hip joint that functions in concert with the gluteal muscles. The device weighs 5 kg in total with over 90% of its weight situated 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,” said co-first-author Jinsoo Kim, a SEAS graduate student in Walsh’s group. “This is important for walking, but even more so for running as the limbs move back and forth much faster.”
Kim shared the first-authorship with Giuk Lee, Ph.D., a former postdoctoral fellow on Walsh’s team and now Assistant Professor at Chung-Ang University in Seoul, South Korea.
A huge challenge the team had to crack was that the exosuit had to be able to differentiate between walking and running gaits and alter its actuation profiles accordingly with the appropriate amount of assistance provided at the right time of the gait cycle.
To describe the different kinetics during the gait cycles, biomechanists frequently compare running to the motions of a spring-mass system and walking to the motions of an inverted pendulum. While walking, the body’s center of mass travels upward after heel-strike, then reaches maximum height at the middle of the stance phase to descend towards the end of the stance phase. While running, the movement of the center of mass is contrary. It descends towards a minimum height at the middle of the stance phase and then travels upward towards push-off.
We took advantage of these biomechanical insights to develop our biologically inspired gait classification algorithm 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 that are attached to the body.
Philippe Malcolm, Ph.D., Study Co-Corresponding Author and Assistant Professor, University of Nebraska Omaha
“Once a gait transition is detected, the exosuit automatically adjusts the timing of its actuation profile to assist the other gait, as we demonstrated by its ability to reduce metabolic oxygen consumption in wearers.”
Going forward, the team will be concentrating on enhancing all aspects of the technology, including additional reduction of weight, individualizing assistance, and refining ease of use.
“It is very satisfying to see how far our approach has come,” said Walsh, “and we are excited to continue to apply it to a range of applications, including assisting those with gait impairments, industry workers at risk of injury performing physically strenuous tasks, or recreational weekend warriors.”
This breakthrough study coming out of the Wyss Institute’s Bioinspired Soft Robotics platform gives us a glimpse into a future where wearable robotic devices can improve the lives of the healthy, as well as serve those with injuries or in need of rehabilitation.
Donald Ingber, M.D., Ph.D., Founding Director, Wyss Institute, Harvard University
Donald Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School, the Vascular Biology Program at Boston Children’s Hospital, and Professor of Bioengineering at SEAS.
Other authors on the study are past and present members of Walsh’s team, including data analyst Roman Heimgartner; Research Fellow Dheepak Arumukhom Revi; Control Engineer Nikos Karavas, Ph.D.; Functional Apparel Designer Danielle Nathanson; Robotics Engineer Ignacio Galiana, Ph.D.; Robotics Engineer Asa Eckert-Erdheim; Electromechanical Engineer Patrick Murphy; Engineer David Perry; Software Engineer Nicolas Menard, and graduate student Dabin Kim Choe. The study was funded by the Defense Advanced Research Projects Agency’s Warrior Web Program, the National Science Foundation, and Harvard’s Wyss Institute for Biologically Inspired Engineering.
This video shows demonstrates the use of the hip-assisting exosuit in different natural environments, and shows how the robotic device senses changes in the gait-specific vertical movements of the center of mass during walking and running to rapidly adjust its actuation. (Credit: Wyss Institute at Harvard University)