I'm in a similar boat. I was mountain biking 3x+ a week (6+ mi. climb at avg 6% grade) - I was getting fitter and losing weight. But my back would hurt on the d

I'm in a similar boat. I was mountain biking 3x+ a week (6+ mi. climb at avg 6% grade) - I was getting fitter and losing weight. But my back would hurt on the down hill. Every jostle was teeth gritting. I started weight training and stretching and my regular back pain is a thing of the past. My backs squat went from around body weight to 2x body weight. When ever a pain shows up anywhere for me (knee, shoulder, wrist, back, etc), it is because of a muscle pulling on it out of balance. I stretch the muscle, the opposing muscle, and related muscles. Generally if my back is sore these days it is because I need to stretch my hips. A few minutes of stretching and I'm good to go.