What is an exoskeleton?

An exoskeleton is a robot you wear. It's a frame fitted outside the body, around the legs, hips, back or arms, that supports or adds to the work of your own joints and muscles. Some help people who can't walk stand up and take steps; others help warehouse and construction workers lift and reach with less strain.

How they work

There are two basic kinds:

• Powered (active) exoskeletons use motors, pneumatics or hydraulics. Medical walking suits have motors at the hips and knees and sensors that detect how the wearer is moving.
• Passive exoskeletons have no power source. Springs and counterweights store and release the wearer's own movement. These dominate the workplace market today.

Work models usually target one area: the back for lifting, the shoulders and arms for overhead jobs, a support arm for heavy tools, or the knees for kneeling.

Where they're used

• Medicine and rehab. In 2014 the US FDA cleared ReWalk as the first powered exoskeleton in a new device category, for some people with spinal cord injuries walking under supervision. A 2016 review found most patients could walk without physical help after training.
• Industry and construction. In studies NIOSH cites, back devices cut back muscle activity by 3 to 11%, and knee devices cut knee muscle activation by up to 39%.
• Military research. DARPA's now-finished Warrior Web program worked on a lightweight suit to reduce injuries for soldiers carrying heavy gear.

The open questions

• Evidence. NIOSH, the US workplace-safety research agency, says most studies are small, lab-based and use young, healthy people, so injury-prevention claims aren't proven on real job sites.
• Fit. A poorly fitted suit can shift strain to other joints, irritate skin or affect balance, and many one-size designs fit women poorly.
• Cost. Personal medical exoskeletons have cost around $70,000 to $100,000.

Like humanoid robots, exoskeletons are one way robotics is moving out of labs and closer to people.