Anatomically speaking, all this walking, running and jumping humans do is no easy trick. The body is a complicated system, and the ankle – a critical joint for shock absorption and propulsion – is among its more distinctive structures.
“It’s not anything like a simple joint,” says Neville Hogan, the Sun Jae Professor of Mechanical Engineering at MIT. “If you think, for example, of your elbow, it’s fairly well-described as a simple hinge. Your shoulder is more-or-less like a ball-and-socket joint. The ankle is nothing like that. It’s basically a collection of bones all moving relative to each other.”
One more vivid description Hogan uses? A “collection of pebbles wrapped inside elastic bands.”
Still, despite its importance in locomotion, Hogan says the world was lacking measurements of “dynamic behavior” in the ankle – the stiffness and strength of the joint as the toes go up or down, or the foot rolls in and out. To help fill that void in understanding, Hogan and his colleagues at MIT’s Newman Laboratory for Biomechanics and Human Rehabilitation developed the Anklebot.
A robot mounted to a specially-designed knee brace that’s attached to a custom shoe, the Anklebot moves the foot in different directions according to a preset pattern. Electrodes measure the stiffness of the joint, allowing researchers to see points of strength and weakness in the ankle, and measure progress over time. Importantly, Hogan notes, the Anklebot is “highly backdriveable,” meaning it only helps the foot move when needed, and gets out of the way when not.
Anklebot was developed as a rehabilitation tool for stroke victims and other patients forced to relearn the mechanics of walking, but it has shown value as a research tool because it provides a greater understanding of the ankle’s mechanics. The bot has led to unexpected discoveries, like the fact that the ankle’s side-by-side movements are entirely independent of its up-and-down movement. It has also formally measured what most people already assume, like the fact that the ankle is weakest when the foot rolls inward and the body’s weight is on the outside – that’s a sprained ankle, in normal person-speak.
While Anklebot wasn’t developed with sports in mind and hasn’t been tested or applied specifically for athletes, Hogan believes both the machine and the information it has revealed could have real impact in athletics. First, he believes, it provides doctors, trainers, and physical therapists more information about the behavior of the ankle. Second, should injury occur, Anklebot’s success as a physical therapy device indicates it could also be helpful as a tool for athletes recovering from soft tissue injuries.
“That’s essentially what the Anklebot lets you do. It lets you provide a gentle interaction between the human and the machine, structured in a manner that will help with recovery,” he says.
Hogan’s peers are beginning to acknowledge his work, too. Eric Perreault, a professor of biomechanical engineering and physical medicine and rehabilitation at Northwestern wasn’t a part of the study, but his intellectual eyebrows are raised by what the team at MIT has revealed about the ankle’s mechanics and the role of muscle activation, as well as the device’s value post-injury.
“An intriguing extension of this work is that it may be possible to train individuals to activate their ankle musculature in a way that helps reduce the chance of injury,” Perreault says. “A more immediate benefit of the study is that it presents a method for quantifying the impact of existing rehabilitation therapies on the mechanical properties of the ankle.”
Once more, in normal person-speak? Anklebot just might help athletes recover from, and even prevent, those pesky sprained ankles.
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