Background: The incidence of osteoporotic fractures is increasing and has become one of the major health problems in developed countries. Physical exercise has been found to be effective in the prevention of osteoporosis. However, the optimal amount of exercise is not known. The aim of this study was to examine the association between the intensity of physical activity and bone mineral density at the proximal femur, using long-term quantification of daily physical activity.
Methods: The study subjects were 64 women (age 35-40 years), who carried an accelerometer-based body movement recorder for 12 months for individual quantification of their daily physical activity. The average distribution of daily accelerations was defined using 33 acceleration levels.
Findings: A significant relationship between physical activity data and proximal femur bone mineral density was found. Physical activity that induced acceleration levels exceeding 3.6g correlated positively with the bone mineral density change at the proximal femur, the association being strongest at the femoral neck at 5.7 g (r = 0.416, P = 0.001).
Interpretation: The association between physical activity and changes in proximal femur bone mineral density was dependent on the acceleration level of exercise. The quantity and quality of exercise can be monitored with the accelerometer-based physical activity monitor, and the method might be used for optimizing exercise for prevention of osteoporosis.