A recent study published in the Proceedings of the National Academy of Sciences suggests your bones may be weaker than those of your forebears because of the sedentary life brought about by civilization. By analyzing fossil bones of early Homo sapiens, as well as earlier hominids and chimpanzees, researchers have come to the conclusion that as we came more to depend on technology for our food, the less active life this led to fostered a loss of bone density. PNAS has an abstract and the original article, here: http://www.pnas.org/content/early/2014/12/17/1411696112.abstract?sid=1eb53c48-09a5-4e9f-a554-68e4620d4eff

The Oregonian has a less technical take on the ramifications, here: http://www.oregonlive.com/health/index.ssf/2014/12/obesity_paradox_protects_heart.html#incart_river

Of course, it has been known for some time that exercise helps prevent the loss of bone density, particularly that associated with ageing. This just puts that into a larger context. Also, it is unclear whether the researchers studied folks such as these, before coming to their conclusions: http://www.bbc.com/news/magazine-30500591