Over two years ago, I had an episode of extreme back/buttock pain including numbness in my calf and toe that sent me to the emergency room. At the time I was a runner and had a stressful job. I ended up at the best ortho guy in the area and he scratched his head. The MRI showed a bulged disc, but apparently that is common--and shouldn't cause that much pain. Out of desperation, I went to my neighbor--a chiropractor. INSTANT relief. He diagnosed tight hamstrings, a pelvis tilt, pelvis twist, and previous blow/injury to my lower back--probably in childhood. He recommended I pick a new sport for awhile--maybe swimming and ICE, ICE, ICE. It took several weeks and two bottle of pain killers to get back to "normal." After a second episode, I demanded the Doc recommend a physical therapist. She was wonderful--didn't teach me any stretches I didn't already know (I showed up with a book, so she simply folded down corners for me) but taught me I would need to stretch twice a day, every day, for the rest of my life. She concurred that I had a twisted/tilted pelvis with a bulged vertebrae with tight hamstrings and hips.
I still stretch twice a day (there are great "back" yoga videos out there), see the chiropractor monthly, and switched to cycling. I know cycling tightens the quads which in turn stretches the hamstrings (I stretch after riding and the hammies are loosest then). However, I think I also "exhaust" my hips on long rides which is a positive. I hesitated to switch to a road bike because I didn't think I could take it, but it's actually helped my flexibility.
Thank goodness, I'm a slow runner and a terrible swimmer
"Well-behaved women seldom make history." --Laurel Thatcher Ulrich
'09 Trek WSD 2.1 with a Brooks B-68 saddle
'11 Trek WSD Madone 5.2 with Brooks B-17