This week, the LA Times reported on a study that showed the higher incident of early onset of osteoporosis in cyclists due to its non-impact nature. Your bones get stronger and rebuild themselves in response to impact. Cyclists may be fit, but by removing this bone growth cycle plus possible calcium leeching from sweat, those using the bike as their only form of exercise increase their risk of bone fractures even at an early age.
The article says:
“You don’t achieve peak bone mass until your late 20s,” says Debra Bemben, co-author of the more recent study and an associate professor in the health and exercise science department at the University of Oklahoma. “If cyclists are in their early 20s and they’re not doing anything else for exercise that’s going to load their spine and help them achieve peak bone mass, it may put them at risk if they fall, since they’ll have a greater chance of fracture. This is a pretty important health issue.”
The non-impact nature of cycling is one of the best things about it. I can ride for hours but am pretty sore after about an hour of running. It appears this advantage has its draw backs when taken to an extreme.
So train to run a 5 or 10 K, hit the weight room occasionally, or do a triathlon. Your bones will be glad you did.