How is it going with your back problem?? Any updates? It's always difficult diagnosing a problem without actually physically being able to assess a person. You could have jarred your Wikipedia reference-linksacroiliac joint when you stamped your foot down on the ground while cycling. This can sometimes result in your ilium (part of your sacroiliac joint) being "stuck" for want of a better word in a forward or backward position. Some manual therapy techniques by your physiotherapist and some stretches by yourself can remedy this. However - the McKenzie exercises targetted at your lower back can also be beneficial for sacroiliac joint problems. Let us know how you are getting on.