I'm no doctor but...When a stress fracture heals, a calcium deposit is made on the spot that is fractured. When you get an MRI, it will show the deposit. From that day forward, the wound is healing. As it heals, you have to put a little bit of stress on the area in order for it to grow stronger. So, in the first stages you put no pressure (ie using crutches). After the deposit is formed, you can put a little pressure (ie walking). Then, as time goes by, you can actually run on the area, even if it is not completely healed. That added bit of pressure helps it to heal. My understanding is that once the calcium deposit is there, the wound is healing, and will not regress unless you put an extreme amount of pressure on it too fast, or your bones are insanely weak.