This mechanical exoskeleton makes walking more efficient - Device is super light weight

Unlike most muscles, the calf muscle doesn’t "turn on" by shortening itself and contracting. Instead, is provides a rigid link upon which the Achilles tendon can stretch and recoil. This is what the exoskeleton is replicating thanks to a system of springs and clutches. When the heel strikes the ground — a time when the Achilles tendon would normally hold onto the calf muscle with a high force — the clutch holds on to the spring of the exoskeleton. "From that point on, the forward momentum of your body is exchanged with the stretch of the spring; the spring kind of catches your forward movements," Sawicki says. This means that when the spring stretches some of the energy of the human body is transferred into it.

Collins, et al (2015)

The device is also super light weight. That means that the there’s no significant mass penalty that needs to be factored into the energy gains you get from wearing the exoskeleton on both legs. "The device weighs between 300 and 500 grams, which is a little heavier than your really lightweight running shoes," Sawicki says. "It’s about the weight of a normal dress loafer."

"The reported savings are impressive," says Heike Vallery, a biomechanical engineer at the Delft University of Technology in the Netherlands who didn't take part in the study. Art Kuo, a University of Michigan biomechanical engineer, also thinks that the findings are sound, but cautions that this is only a first step — medical applications are still far away, he says.

Others wonder how the device will fair with everyday use. "It isn't clear how the device would respond to non-rhythmical cyclic tasks," says Daniel Ferris, a biomedical engineer, also at the University of Michigan. Energy savings might not occur during tasks like standing, turning maneuvers, sit-to-stand and stand-to-sit motions. Still, Ferris thinks that the exoskeleton could prove useful for people who have reduced ankle strength — people with incomplete spinal cord injuries, the elderly, and people who suffer from multiple sclerosis, for instance.

Using the boot isn’t very hard, Sawicki says. "After 20 minutes or so, most people aren’t conscious of it; it gets integrated into their being." The only time users notice it is when they take it off. "There’s this heavy leg feeling after, that lasts for up to five minutes for some people," he says. "You feel like your leg is collapsing under you."

When you take it off, "you feel like your leg is collapsing under you."