In a study published in the Journal of Bone and Mineral Research, Nordstrm et al. evaluated the association of being physically fit as a young man with the incidence of fracturing later in life. What they found is that exercise DOES pay off! Being aerobically fit and strong as a young adult helps prevent fractures decades later.
Results of this Swedish study showed that young men with poor aerobic capacity would have twice the risk of fracturing and the highest risk of breaking a hip later on in life. On the other hand, men with higher aerobic capacity and muscle strength had a substantial reduction in fracture risk. This demonstrates that regular exercise as a young adult "has potential to reduce fracture risk later in life at least by one-third, or that a fracture is postponed by several years."
"Our data provide the first evidence that objective measures of physical fitness in young adulthood convey an important risk factor for fracture more than 30 years later."
Nordstrom, P, et al. 2013. High physical fitness in young adulthood reduces the risk of fractures later in life in men: A nationwide cohort study. JBMR 28(5):1061-1067.