A stress fracture develops from a substantial load on the bone exceeding its normal healing capacity, leading to microfractures that do not heal due to insufficient rest, especially with concurrent increases in running frequency, distance, and speed.

“a stress fracture is something that occurs slowly so a stress fracture at Baseline potentially normal bone with a substantial load to that bone that is in excess of what the normal healing capacity is of that bone that is bone constantly remodels every time we put stress on it the microarchitecture is changing there's small tiny micr fractures that occur from normal weight bearing the body is very capable of adjusting to that load and making new bone when you start exercising or working out or running the bone will get stronger based on the stresses that that bone sees so for runners for for example um if you are training properly there's no reason to expect that that bone can can't adjust to the increased load that it's seeing but often times due to overtraining where you're not giving that bone enough of a chance to heal you develop these tiny little micr fractures that aren't given enough time to then heal and then it gets compounded when you go run the next day and the next day and you're increasing not only the number of times that you run but you're increasing the distance and the speed all at the same time”