Low back pain is typically caused by bike fit. A stretched out or cramped up positioning set up on the bike puts an unnecessary strain on the lower back muscles by either trying to reach too far to the handlebars or having an arched back from being too cramped. Muscle imbalances and leg length discrepancies can also cause back pain by putting an increased strain on the muscles on one side or the other in the lower back.
Another cause of lower back pain is an uncomfortable saddle. An uncomfortable saddle leads to an uncomfortable sitting position, causing strain on the low back. Often times, cyclists will tuck their pelvis under, or roll back on their sit bones, to relieve pressure from soft tissue areas. Doing this can cause sit bone pain, but also can cause an outward arch in the low back and engaging the lower back muscles more than necessary. With a proper relief channel, or short nosed saddle that allows the rider to sit with the sensitive organs over the front of the saddle, the cyclist has the ability to roll the hips forward, keeping the back flat so to not strain lower back muscles.
Core strength is also key in combating lower back pain. A good test of core strength, and bike fit, is to check and see if you can lift your hands about an inch or two off the handlebars for 5 seconds. If not, it may be helpful to check the tilt on your saddle or re-evaluate your bike fit. A strong core will hold the body in a stable position, not stressing the lower back muscles. Flexibility is also a tool that can reduce back pain. Stretching a few minutes every day can improve the muscles function and reduce strain.