Hey Kefu, I also noticed that on my affected side my deep abdominals didn’t seem to be firing as hard as my unaffected side.  Same thing for my glute med on the affected side.  My PT said that once I got the back issue under control the muscels should start firing again.  So far I’ve been pain free since starting the Mckenzie exercises, some tightness does comes back if I stay in flexion for too long, or slouch while standing during the day.  As soon as I notice it coming back I do some standing back extensions and it goes away in the next couple minutes.  The decreases in tightness seems to last longer each day as I continue to do the Mckenzie exercises and remind myself to stand with good posture at work.  Sitting is still tough for me and I have to overcompensate with a larger lumbar curve than natural.  I’m hoping this decreases as time goes on.  Not saying you definitely have the same issue, but since we seem to have similar symptoms I wouldn’t rule out the back.  Good luck and keep us updated.