I just started riding a road bike this past December. As my ride time increased, I started having pretty bad lower back pain at about the 3 hour mark. The pain was on both sides of my spine at the bottom of my back. I could tell it was a muscle pain & not a nerve/joint pain. I couldn't do anything to fix it until I went to a get a sports massage & told the massage therapist of the pain. He said it most likely as the piraformis (spelling???) muscle. He did some specific stretches and treatment on my hip area. Since then I've been able to increase my ride time to 5 hours with minimal lower back pain. Also, I had a professional bike fit when I started getting more serious from the guys at Specialized, so I don't think my issue was due to fit. I think mine was just lack of stretching that muscle & the rapid increase of time in the saddle.