Improving your pedaling power and reducing low back pain from riding both require more efficient lower body movement on the bike. And this requires both strong hips and hip flexors that sync up and work together when pedaling.
A major problem for a lot of riders is that they have tight, weak hip flexors and so they end up using their low back to assist with the top of the pedal stroke, placing extra stress on this sensitive area. This also takes away from the hip drive of the other leg, which reduces pedaling power.
In this video I show you my favorite exercise for helping riders, the Ramping Isometric Single Leg Knee Raise. Use it to help reset your pedal stroke and improve the strength and movement efficiency of your pedal stroke.