I was recently evaluated at the Egoscue clinic in San Diego and the therapists were able to determine that my left hip was not functioning properly. The therapists explained that my hip was shutting down and it was forcing other muscles in the leg to take over. This could explain why I have felt symptoms in my calf, quad and hamstring at different times.
One interesting thing they discovered was when I lie flat on my back and bring one knee towards my chest, the right leg tracks properly but my left leg moves out to the side when it goes past 90 degrees. They were also able to see the difference between the two hips by watching me walk and trying to balance on one foot.
They gave me a long exercise routine but made it clear that by far and away the most important thing that I should do to correct this is an exercise called supine progressive groin stretch. This one exercise takes about 50 minutes per day but they said it was worth it.
I'm still skeptical, but we'll see....