Osteoporosis is a common disease in Norway, and is a skeletal disorder characterized by low bone mass and micro-architectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. Physical activity is essential for bone remodeling and prevention of osteoporosis. Studies report that mechanical loading of the skeleton is especially important for achieving higher BMD among children before entering puberty. The peak bone mass plays an important role for further BMD during life, which indicates that prevention should start early. The objectives of this literature study were to review present knowledge of physical activity’s influence as prevention and reduction of osteoporosis among humans according to women, men and children. I also included animal and cell studies which investigated the impact of mechanical strain. Studies among adults report that exercise rather prevents bone loss, inhibiting the endocortical bone resorption rather than new periosteal bone formation. There are no common training recommendations for prevention of osteoporosis, but there is a general consensus that weight-bearing activity combined with resistance training is optimal. Although no clear optimal duration and intensity has been delineated, there is general consensus that the activity should be of high impact, done 3-5 times weekly, if possible daily, and last for 10-45 minutes per time. The activity should be of a magnitude 3-9 times corresponding to the body weight. There exist few RCT today which are performed among men and children. Before final conclusions can be made; it’s necessary with several long term trials and further studies which involve men, premenopausal women and children.
Key words: Bone remodeling-Bone mineral density (BMD) - Exercise-Mechanical loading-Osteoporosis