Sorry I really couldnt resist this..... I was browsing re benefits of swimming for cyclists and there it was! ... he said beating a hasty retreat.. " the longest stint of cycling i've done was around 8 hours per day for 3 months, when i was 23. i put ON about 4 kilos. a lot of it was muscle, mainly of my lower back, butt and thighs. if anything my calf muscles became smaller (in normal life i walk a lot) but ignoring the increase in muscle-mass, i also developed a bit of a tummy. I put that down to the fact that I was eating about 3 times as much per day as in my normal life, and sitting on an upright bike doesn't work your abdominal muscles too well. the really funny thing was though, if you looked at the group of us cycling, all us girls got bigger and developed little tummies, and all the boys wasted away until they were wiry scraps of their former selves - nothing but lean muscle and bone. "