Fractures (particularly osteoporotic fractures) among the aging population constitute a substantial public health burden. They are a major cause of disability, morbidity, reduction in health-related quality of life, mortality and are associated with increased costs to healthcare systems. The role of regular physical activity in the prevention of vascular disease, other chronic diseases and mortality is very well established. Epidemiological data also suggests that physical activity is associated with reduced fracture risk. Cardiorespiratory fitness (CRF) measured by maximal oxygen uptake (VO2max), is the gold standard for assessing aerobic capacity and is an indicator of habitual physical activity. Like physical activity, a wealth of epidemiologic evidence consistently shows CRF to be independently and inversely associated with adverse vascular outcomes, other chronic diseases and mortality. One of the pathways by which physical activity reduces fracture risk is by increasing or maintaining bone mineral density (BMD). A limited number of studies have reported increased levels of CRF to be associated with reduced risk for low BMD; however, whether this translates to a reduced risk of fractures is uncertain. The association between objectively measured CRF and future risk of fractures is unknown. In this context, we sought to investigate the prospective association between objectively measured CRF and fracture risk in a general population of middle-aged Caucasian men.