I sort of have this mathematical picture of why physical therapy is useful even though it sometimes seems counterintitive due to it exercising the very body parts that you damaged through use. Damage to the body, let's say muscle for now, stimulates repair mechanisms. But there's a nonlinearity in the repair. For example, in ordinary every day use you are always doing minor damage to muscles and that damage is always being repaired so you end up in a steady state. But if you start working some muscles harder, you'll do more damage, and the response will actually be more than is needed for simple repair. As a consequence you build up muscle mass. But the nonlinearity applies at the lower end too. If you repeatedly use the same finger to press the mouse button you're doing damage. But the nonlinearity means the repair mechanism is less than needed to achieve steady state. The repair message from many small stimulations is much less than a small number of large ones. And that's why you can end up with repetitive strain injuries despite the fact that the muscle use is minuscule compared to what you might do at the gym. That explains things like the Alfredson protocol for repairing the Achilles' tendon that apparently came from Alfredson trying to damage his own Achilles. (Which is perfectly rational because American health plans have their own nonlinearities!)