my SI joint has been painful, off and on, for 6 years. when the doc took a picture of it, he said I have some bridging, meaning the joint is starting to grow together. I recently did a few easy runs, 'cause my SI felt pretty good. after two weeks and six runs of 3 miles, the pain was unbearable. today, even though it hurt, I hopped on my cross bike, and rode an hour and a half as hard as I could. when I got back, the pain had decreased substantially. something about that time out of the saddle that somehow re-align the SI joint, I suppose. does anyone else find that riding actually helps a bad SI joint?