Lower back pain is a common complaint in cyclists. If a weak core is not to blame then it is most likely being caused by one or both of the following:
A handlebar that is too close to the saddle or too high
Research conducted in Belgium and at the Sport Science Institute of South Africa both indicate that lower back pain may be alleviated by increasing the reach (distance between the handlebar and saddle). When the handlebar is placed in an overly shortened or upright position, the shoulder is under-extended and unstable. Over time, the rider will extend the shoulder, but at the same time this results in slumping of the lower back. Slumping causes the muscles on each side of the lower back to relax, in turn causing the discs and ligaments that support the spine to be overloaded, causing pain and muscle spasm on either side of the lower back.
Excessively high saddle with or without tight hamstrings
With the saddle set too high, the pelvis will rock excessively in an attempt to reach the pedal when it passes through the bottom dead centre on each side of the bike. As a result, the little facet joints on the sides of each vertebra will flex and extend excessively during each pedal stroke. This causes joint injury and inflammation, felt as a sharp pain on either side of the lower back.
If you have pain that gets worse with riding, but settles as soon as you get off, then it is most likely the former. If the pain persists and results in stiffness later in the day or the following day, then it is most likely the latter. Importantly: If you have any pain that radiates down the leg or numbness in any area of the leg, a more extensive medical evaluation is necessary and you should see a specialist.
Jeroen Swart is a sports physician and exercise physiologist at the Sports Science Institute of South Africa.