Here's the story and maybe it will help somebody else.
It started last July when I was doing squats with 345 and on my third rep as was coming out of the hole, I felt a sickening pull in my lower back. I managed to rack the weight and sit down, turning pale and getting nauseous from the experience.
A burning pain radiated throughout the lower back area and it immediately tightened up. For the next few days it was a struggle to get out of bed, sit, or simply move around. My family Doctor put me on muscle relaxers, pain meds, and told me to let it rest.
It gradually got better after a couple of weeks and by the third week I barely noticed it. Since then I've pulled it 3 more times doing squats and deadlifts and in January this year I'd had enough. I was talking to a workout partner about it and he said he has multiple disk bulges and recommended me to a D.C. who specializes in disk decompression.
I did a visit and the Xrays showed that my disks were in good shape (thank God) and he suggested alignment work. After he told me I needed to give up Squats and Deadlifts I left his office and never looked back.
Decided to do a search on Orthopaedic Sports Medicine specialists that had a history of working with football players. Felt that was my best shot at having a Dr. familiar with these types of injuries. After searching a bunch of websites I found a Orthopaedic Surgeon who in the past was an NFL team Doctor.
He did Xrays and confirmed the disks looked surprisingly good for someone "my age". He said degenerated disks are also called "The Gray Hair Disease" because nearly everybody experiences it as we age.
He said not to worry about the disks. He told me to keep squatting and doing deadlifts but first go through Physical Therapy with one of his references.
He never did tell me what the root cause of the injury was or why it happened.
The Physical Therapist is awesome. In our first session she examined my lower vertebra and at one point said, is this where you experience the pulling and pain? It was the exact spot. She said, "I can move L3 but all the other vertebra are fairly secure." She put me through about a dozen other tests of muscle isolation strength and flexibility then made the diagnosis.
I over-extend the Ligaments that connect the L1-L5 vertebra together. That is the pulling sensation I get during the injury. It is NOT tendon pull of the Erector Spinae or Iliopsoas like I assumed it was.
The pain and stiffness occurs because the Erector Spinae and other supporting muscles swell and tighten to protect the spinal ligaments from further stretching. It's our bodies defense mechanism against further stupidity that we would otherwise inflict on it.
The reason it happened to me is because:
a) I lack hip mobility which causes me to loose a straight/arched back at the bottom of the lift and
b) I lack enough core strength to maintain a straight/arched back at the bottom under heavy load.
After explaining all of this to me the PT has put me on some isolation exercises primarly for the TVA, mobility exercises for the hips, and stretching routines for the posterior chain.
Won't be long and I'll have some heavy weight on my shoulders again.