I did 6km this morning... or rather walked half of the way. My lower back spine or muscles were shooting the hell out of me halfway thru the run.
I don't think its a spinal problem - more likely tight muscles - my hamstrings and lower back muscles are tight. I've seen chiros and physios in the past - but neither of them have discovered anything serious like a slipped disc.
The pain does go away after the run. So its quite likely just tight muscles.
This site has got good tips for that problem.
Maybe I'll go for a swim tomorrow or do a shorter run.