Bulking Up By Riding Fixed

I heard that this happens, but didn't expect to notice it on myself. I've found new muscles in my arms, legs, and back since starting to ride a fixed gear. That's the only change I've made in my exercise regime. I'm not swimming more or lifting or climbing more or anything. I think all the growth is attributable to the fixie. I've paid special attention to the muscles I use on a steep climb and they match up with the ones that have grown since I got the Uno. I wonder if I can get even more buff by increasing my ratio.