Powered prosthetic legs are a bit like supercars – they're brilliant pieces of engineering, but they need regular expert care to keep them at peak performance. That can be an expensive and time-consuming necessity, so biomedical engineer s at North Carolina (NC) State University and the University of North Carolina at Chapel Hill are developing an algorithm that automatically tunes artificial limbs while walking.

A powered artificial limb can't simply be slipped on. It needs to be fitted like a custom shoe to the stump of the remaining limb and then it needs to be "tuned" to match the physical characteristics, such as size and strength, and the behavior of the patient. Normally, this requires the services of a prosthetics expert to make the necessary adjustments. It's a slow, expensive process that often needs to be repeated because the patient's condition changes due to becoming accustomed to the limb or weight changes.

The NC State team's solution was a software algorithm that does the job of the prosthetist automatically and at lower cost. It's capable of being installed in any powered prosthesis and tunes the power supplied to the motors that operate the joints, so the patient can walk comfortably even when carrying out tasks like carrying heavy luggage through an airport lobby.

Prosthetic legs work by mimicking how a living leg works. They're engineered so the angle of the prosthetic joints is programmed to match normal movements for tasks, such as walking. The algorithm records the angles of the joints in real time, compares them against the proper angles, calculates any adjustments needed, and carries them out automatically.

According to the team, tests of the algorithm show that it's able to make adjustments better than a human prosthetist, but more work is needed.

"Prosthetists rely on years of experience to not only adjust the joint angle, but to adjust a prosthesis to help patients maintain a comfortable posture while walking," says Helen Huang, associate professor in the biomedical engineering program at NC State and UNC-Chapel Hill. "We’re not yet able to replicate the prosthetist’s success in achieving those comfortable 'trunk motions,' but it’s something we’re working on."

The team's findings were published in the Annals of Biomedical Engineering.

The video below shows the system in action.