Lower back pain often results from improper positioning on the bike, so have your bike evaluated by a local pro who can fit you appropriately on your bike. Other common causes of back pain include fatigue and poor hip mobility. When either occurs, your body compensates by flexing your back or pulling harder on the handlebars, which puts stress on your lower back. To overcome this, work on improving your hip mobility and strength with a progression of Romanian deadlifts.
Step 1. Stand with your knees slightly bent, holding a dowel along your spine from the back of your head to your lower back. The dowel should touch the back of your head, your back, and your butt. Bend forward at the waist, keeping the dowel in contact with your head and back until you feel a stretch in your hamstrings. Contract your glutes (butt muscles) and hamstrings to return to a standing position. (Click here to watch an instructional video.)
Step 2. Once you’ve mastered this, try adding some weight to the movement. Instead of the dowel, hold a pair of dumbbells with an overhand grip (palms facing toward you). Lower the dumbbells to your shins as you bend at the waist, and then return to a standing position. (Click here to watch the video.)