If you talk to a physical therapist or orthopedic surgeon over a certain age, they are bound to tell you that the key to avoiding knee pain is strong quads. More specifically it is the vastus medialis – the part of the quad is the innermost muscle – that stabilizes the knee. Yet if you talk to a younger PT or knee doc they are more likely to point to a growing body of research that suggests that knee pain is related to weak glutes, not quads.
The weak glute theory goes like this: When your foot strikes the ground at the start of your run stride it is the job of the glutes to stabilize your hips and keep them level. When your glutes are weak, the hip opposite the leg that is posting drops down. When the hip drops down, the instability moves through the kinetic chain and causes your knee to go valgus (i.e. collapse inward). When your knee collapses toward your midline, bad things happen.
A recent study from the U.K. furthers this theory into common thinking and indirectly makes a case for glute-focused strength training for runners. The study looked at athletes who suffered from patellafemoral pain syndrom (PFPS) – pain at the back of their knee. They hooked up an EMG to see what muscles fired and to what extent in these people relative to the rest of us who don’t suffer from PFPS. They found that “gluteus medius activity is delayed and of a shorter duration during running” for the PFPS group. In english, this means that people with knee pain have weak butt muscles and/or lack the mind-body ability to use the muscles they do have. Specifically, they are weaker (or lack firing capability) in the part of the glute that sits underneath and toward the outside of the glute maximus (with the glute max being the big muscley part of the butt you can slap).
So what do we do to strengthen glute med and avoid this problem? Sprinkle in exercises that either work the hip in abduction, like 45 Degree Leg Raises, or add an element of instability to traditional glute max exercises, like doing your Dead Lifts on one leg like a weighted Floor Reach with strict emphasis on keeping your hips level.
Source: Barton, et al. Gluteal muscle activity and patellofemoral pain syndrom: a systematic review. British Journal of Sports Medicine. 2013 Mar.