I just read an article in the New York Times about cycling and bone loss. Recent studies on bone density in elite cyclists show that they have weaker bones than normal. My three-point common sense survey of all the research: * Cycling is a very low impact activity that does not stress bones * When bones are stressed they get stronger * When bones are not stressed (but the rest of your body is stressed) your body can redirect the effort it would take to maintain or increase bone strength and put it somewhere else. (That's my hypothesis based on reading the article.) Some additional points: * The studies covered elite cyclists that apparently don't much outside of cycling, but they do it at high intensity for long periods of time * They are likely to be weight-weenies concerned with keeping their body mass as low as functionally possible * Triathlon has cross training built in. ;) http://well.blogs.nytimes.com/2009/07/01/is-bicycling-bad-for-your-bones...