Gait is not just a way to get from point A to point B. Each step, arm swing, and torso tilt is like a signature the body leaves in space. Doctors have long noticed that disease alters gait, but they considered it merely a symptom of a specific problem: if you limp, your leg hurts. Now it turns out that gait is a whole book about health, and you can read it with an ordinary camera.

In the new study, 3414 adults performed five simple tasks in front of a camera: normal walking, turns, and getting up from a chair. A computer program turned their movements into a three-dimensional skeleton, like in movies where actors wear motion-capture suits, but without the suits. From this skeleton, the program learned to predict age to within a few years and even the amount of visceral fat, which is invisible from the outside and accumulates around organs. Visceral fat is more dangerous than subcutaneous fat, and it is usually measured with complex equipment, but here, a simple walk suffices.

The most interesting part is how gait is structured. It turns out that the legs reveal the most about metabolism — how the body processes energy. Meanwhile, the torso and shoulders betray habits: how much a person sleeps, how active they are during the day. In other words, gait is not a single signal but an entire orchestra, where each body part plays its own part. And from this score, you can read far more than previously thought.

In the future, such models could run on ordinary smartphone cameras. Then gait would become an unobtrusive but constant health indicator: every day, without doctors or devices, just from a video in the hallway or on a walk. This is not a replacement for a doctor, but rather a smart assistant that notices changes before symptoms appear.