While bending over, exp sudden intense pulling/popping in lower back. severe pain. muscles tightening, posture distortion. hurts to move. advice?

Pinched Nerve/Muscle: Most times back pain that is sudden onset will resolve. He should use anti-inflammatory meds like ibuprofen, aleve around the clock and even tylenol (acetaminophen) to help. If this does not resolve he should see his doctor for a muscle relaxant as well. If it still does not resolve, i would recommend him to see a spine specialist for a full evaluation and testing. He may need to get an MRI to see inside.

Should see: Your doctor for a more thorough history and exam in order to give you any advice. Try moist heat, gentle stretching and Ibuprofen (if not allergic) for now. Good luck!

Disc: You most likely have an inter vertebral disc that is buldging and causing pressure on you nervse.

Back strain: Based on the information you are providing seems like a back strain. Rest for couple of days, ice and anti inflammatory meds help. If you experience numbness, loss of control of urine or bowel movement, or severe pain you should be evaluated immediately.