MIT researchers have tested a way to track muscle movement using tiny magnets placed inside the body. In a study involving three people with below-knee amputations, the method showed promise for improving control of prosthetic, or artificial, limbs. The findings appeared in Nature Sensors.
The technique uses pairs of magnetic beads, each about 3 millimeters wide. As a muscle contracts or stretches, sensors worn over the skin measure changes in the distance between the beads. Researchers use these measurements to calculate muscle length and how quickly it changes.
All three participants had undergone surgery that reconnects opposing muscle groups in the remaining leg. This connection helps preserve their sense of limb position and movement. During the experiments, they used muscle movements to guide a cursor toward targets on a screen. They were not wearing prosthetic limbs during these tasks.
The team compared the magnetic method with electrodes, which detect electrical activity, both inside muscles and on the skin. The results suggest that magnets can offer more accurate and stable control. Skin electrodes can be affected by sweat or pick up signals from nearby muscles, while electrical activity does not directly measure muscle movement. A larger study is now evaluating how well the magnetic measurements help people control prosthetic limbs.
