Modern life stopped asking anything of your body.

In about three generations we built a life you can get all the way through without ever doing anything physically hard. The food arrives at the door. The stairs are a lift. The mile is a car. The day ends in a chair, and over the years your body takes the shape of it.

That is not a failure on your part, and it is not something to be nostalgic about. It is good engineering. But it removed the one thing that used to keep people in working order, which was simply that the day demanded it.

What came instead is a set of problems far too common to be normal: obesity, type 2 diabetes, heart disease, and backs that hurt without anyone being able to say why. Underneath those there is something quieter. Sit down on the floor in a deep squat and see how long you can stay there comfortably — for most adults the answer is not very long. Decades in chairs close the hips and shorten the hamstrings, and you meet the result somewhere you were not expecting it, in a stride that cannot fully extend or a swimming stroke with no room in it.

It does not have to go this way, and we know that because some people still live the other way. There are populations today who move for most of the day because their day requires it, and heart disease and diabetes are rare among them. They are small groups and nobody has run the experiment, so treat it as a signal rather than proof. It is a hard signal to ignore. Their bodies are the same as yours. What gets asked of those bodies is not.