I was thinking of starting a new thread, but I will hijack this one (with apologies).
I am currently 30. When I was 19, I herniated and slipped a disc in my back. Physical pain means nothing in the gym after that experience. (I also had a spinal tap at seven which comes pretty close to the pain threshold.)
I hobbled my way to the University Hospital after being told I was a "pussy" by my lifting partner. Thanks, Adam.
I rehabed, was told I have degenerative disc disease (I will get fusion in the inevitible future). I was told to swim and not lift weights.
As I read the posts here, I know there are a variety of reasons we all lift. But I must say, the main reason for me is mental health. When I don't lift heavy, I lose myself in my life. I lose my way. I've had three month stretches where I could not lift (or barely walk) because of my back. At first I am full of rage (wolf hour happens often), and then it appears I lose all my will (depression) after a long enough absence from the iron.
Injury happens, you rehab, you come back. But my warning to anyone reading is to not ignore true injury. At 23, I reinjured my disc while doing squats. I rested and came back, but there were reprecussions for not seeing a medical professional.
I pinched a nerve that caused atrophy in the inside of my left calf. My left calf is now all but tendon and skin. I cannot even get on the ball of my left foot when I attempt to do so. It was a gradual atrpophy, but I remember the day I reinjured my disc, I didn't see a physician. My main point here is that the muscle is never going to return and I will always walk with a limp.
I will have the unavoidable surgery in the future (the disc disease and rupture are two different problems).
I still lift heavy, but listen to my body. Hammer machines have helped a great deal (I am sure many will rip me a new one for that comment, but they allow me to safely increase weight.)
Be careful of that back! If you ever injure it, many people will come tell you their sob stories (like me), but most just suffer and do nothing about it. The best rehab for me is having loose hamstrings and strong abs (I am 6'3", 270 lbs and can touch my palms to the gound when I bend over and do 4 sets of twelve on hanging leg raises). This has helped more than anything.
The spine is a funny thing, please protect it so you don't go through what I went through.