A recent U. of Missouri study found that men who primarily cycle have lower bone density in their lower body and back than men who primarily run.
“In general, cyclists had lower bone mass throughout the body and 63 percent had osteopenia in the spine or hip, the researchers report in their study, published in the journal Metabolism. Osteopenia refers to abnormally low bone mass that could progress to the brittle-bone disease osteoporosis.”
It should be noted that high impact activities, such as running, stress the body and bones such that bones are forced to strengthen themselves. [Reuters Health]
This certainly has more severe implications for older men (and women) in terms of what types of exercises they should incorporate into their training programs.