Generally speaking, the glute med is one of the weakest muscles I test on a regular basis, even in monster athletes. When the glute med is weak, it can’t do much to stabilize your knee so the TFL kicks in. Now your TFL isn’t quite as big or powerful as the glute med so it can’t dynamically stabilize your knee nearly as well. It is, however, attached to this big thick piece of tissue (your IT band) that it can tighten up to help stabilize the knee statically. The problem with this is that you’re now statically using a structure to achieve dynamic stabilization. That’s kind of like responding to the shocks on your car being too loose by tightening them up so much that they can’t move.