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Runner on a treadmill wearing an exosuit

Robotic exosuit could improve athletic performance

Image credit: The Wyss Institute at Harvard University

Harvard University scientists have designed a simple exosuit which acts as a second pair of hip extensor muscles and reduces the metabolic cost of running by more than five per cent. Their work could lead to new wearable technologies for athletes and consumers.

Running is a highly energy-intensive activity. While humans have become effective long-distance runners, researchers at the Harvard Biodesign Lab believed that our performance could be improved with the assistance of technology.

Exosuits and exoskeletons are wearable machines which allow the user to move with superhuman endurance and strength. They are used in rehabilitation to help seriously injured patients walk again and to help emergency workers move safely in dangerous environments. Military exoskeletons could help soldiers march further and faster while carrying heavy loads.

The new Harvard exosuit is a lightweight, tethered, textiles-based design which moves with the body. Flexible wires tethered to an external actuation unit are attached to the back of the thighs and the waist belt.

As the wearer begins to run, the actuation unit pulls on these wires, which apply force to the legs with each stride, essentially acting as a second pair of hip extensor muscles.

The researchers tested two patterns of wire-pulling, or “assistance profiles” to see which would support the wearer more effectively. The first pattern was based on human biology, applying a force at the point of maximum hip extension, while the other was based on simulations of exoskeleton-assisted running, and applied a force later in the stride.

They found that the simulation-inspired profile was much more effective. This assistance profile outperformed the biology-inspired assistance profile in reducing the metabolic cost by a factor of two, to 5.4 per cent.

This is the equivalent of making a standard 26.2 mile marathon feel like a 24.9 miles marathon.

“Our finding supports a paradigm shift towards the concept that mimicking our current understanding of biology is not necessarily always optimal,” they report in Science Robotics.

By observing the wearer’s other joints while running with the exosuit, the researchers found that the effective simulation-based profile affected knee extension and the forces between foot and ground, while the biology-based profile did not.

“The biological profile only takes into account the amount of torque in the hip joint, but the human body is not a series of independently acting parts,” said Dr Giuk Lee, who led the study. “Applying force to the hip affects the whole body system, and we need to consider that in order to give the best assistance.”

The team hope to continue to reduce metabolic cost further by testing new actuation profiles and to make a portable battery-powered system with a high power-to-weight ratio, so that the benefit of using the suit offsets the energy cost of wearing it.

“We believe this technology could augment the performance of recreational athletes and/or help with recovery after injury,” Dr Lee said.

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