Human walking now becomes more efficient

Human walking now becomes more efficient

Humans have evolved to be incredibly efficient at walking. In fact, simulations of human locomotion show that walking on level ground and at a steady speed should theoretically require no power input at all. But anyone who works on their feet or has taken an arduous hike knows otherwise. In fact, people expend more energy during walking than any other activity in daily life, and for the elderly and those with mobility issues, that energy can be precious.

Walking around campus with the exoskeleton on one leg. The unpowered clutch (upper left) engages a spring (left) in parallel with the Achilles tendon when the foot is on the ground, offloading the calf muscles and making walking easier. Credit: Carnegie Mellon University College of Engineering

For decades, engineers have envisioned systems that could make walking easier. In fact, so many researchers have tried to build unpowered exoskeletons and failed that it was hotly debated in the field whether it was even possible to improve the efficiency of walking without adding an external energy source. In news reported today in Nature, researchers from Carnegie Mellon University and North Carolina State University have demonstrated an unpowered ankle exoskeleton that reduces the metabolic cost of walking by approximately 7 percent. The results are roughly the equivalent of taking off a 10-pound backpack, and are equivalent to savings from exoskeletons that use electrically-powered devices. The research was based upon work supported by the National Science Foundation.

An unpowered clutch engages a spring in parallel with the Achilles tendon when the foot is on the ground, offloading the calf muscles and making walking easier. Credit: Steve Collins

"It's a real exciting milestone for the field of assistive devices," said Thomas Roberts, a professor of ecology and evolutionary biology at Brown University and an expert in the biomechanics of locomotion, who was not involved in the research. "They've taken an assistive device and lowered the cost of human walking. That's kind of a big deal because walking is already really cheap, and they did it with a very simple, but clever device." The device is the result of eight years of patient and incremental work, mapped out on a whiteboard by Steve Collins and Greg Sawicki when they were graduate students together at the University of Michigan in 2007.

"Walking is more complicated than you might think," said Collins, an assistant professor of mechanical engineering at Carnegie Mellon. "Everyone knows how to walk, but you don't actually know how you walk." "You can imagine these lightweight efficient devices being worn on the affected limb to help people with the permanent aftereffects of stroke," Collins said. "We're hopeful that designs that use similar techniques can help people who have had a stroke walk more easily. We're still a little ways away from doing that, but we certainly plan to try."

In the future, the team intends to test the current device with individuals who have a variety of mobility issues to determine what designs might work best for different populations. They are also interested in developing exoskeleton components for the knee and the hip, where they believe they may be able to garner even larger benefits. "As we understand human biomechanics better, we've begun to see wearable robotic devices that can restore or enhance human motor performance," said Collins. "This bodes well for a future with devices that are lightweight, energy-efficient, and relatively inexpensive, yet enhance human mobility." (Source:


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