If humans walked like robots, engineers already would have perfected zero-effort, mechanically-assisted walking. But what about people who bounce on their toes, power walkers, those who sashay? Habits, diseases, and disabilities can affect someone’s gait in unique ways. An idealized exoskeleton needs to be both easily accessible and personalized.

The Chipotle of exoskeletons doesn’t quite exist yet. Computers still struggle to anticipate how people will move—they're literally a moving target. From a data standpoint, humans are noisy, says Katherine Poggensee, a biomechatronics researcher at Carnegie Mellon. Plus, “they have brains, so they adapt over time.” And although humans generally find the easiest way to do any motion, very few people have the physical and spatial awareness to explain why one stride feels easier than another. That's why researchers are turning to algorithms to make exoskeletons more efficient.

So far, automatically tuning an exoskeleton’s force, and the timing of that oomf, is faster and better than hand-tuning. Thursday, in a paper published in Science, Poggensee and her fellow researchers outline an algorithm that calibrates an exoskeleton to best assist its user. To do that, they use a type of optimization that’s also helped govern how animated characters interact with their environments in CGI.

Instead of supplying users with standardized assistance, these control algorithms set themselves up like an eye doctor who flips through lenses while asking “better, or worse?” But instead of actually asking users, the algorithms rely on sensor feedback. To minimize the energy required to walk, for example, they track respiration to calculate metabolic rate, then optimize to minimize the calorie burn.

This algorithmic tuning can only happen in a lab, on a treadmill, where there are machines to perform and analyze these extra measurements. The idea is that eventually, you could get fitted for your exoskeleton or robotic prosthetic limb in a clinic, then transfer your personalized profile to the outside world. And in this study as well as others, automatically tuned exoskeletons do successfully lower the energy it takes to walk.

This is an improvement over previous versions of exoskeletal tuning, which were slower, and in some cases, demanded more effort than normal non-assisted walking. For simpler approaches that relied on a brute-force sweep through many different options, “the numbers get really hard to deal with,” says Daniel Ferris, who has developed similar algorithms to calibrate exoskeletons. There are different mathematical approaches to automating this tuning, but the most effective ones all start by guessing how a human will respond, then monitoring their actual response while offering up different calibrations.