I was doing a golf lesson at my local golf club with instructor.
After hitting about 150 balls or something and driving back home in my car. I just had this terrible pain in my middle back / lower back.
My muscles are not like "super-weak" or whatever. I'm pretty fit average or better (percentile of age group 24 yrs) according to my personal trainer and recent fitness test.
The only muscle possibility seems to be imbalance. weaker back and abs muscles, in relation to my stronger legs and stronger arms and chest. Possibly...
I don't have much deformities that I know of!
Culprit could also be something in the golf swing.
I remember that the golf pro noted to me, that I raise my left heel at the backswing. It seems that many pro golfers do this also.
Could it be affecting the back pain issue though? Like a tilted hip turn causing pain of vertebrae? http://www.golfdigest.com/golf-instruction/2010-03/save-your-back-foley