High impact training is essential for building and maintaining strong bones throughout life. Adequate load will stimulate strength independently of age, sex and hormonal production, but the effect may be small (elderly) or pronounced (certain athletes, prepubertal children). Gained bone mass is partly preserved with age. Walking has no osteogenic effect except in very inactive persons. In postmenopausal women the effect of added training to estrogen-treatment is modest. Exercises to prevent falls are important in this group. Hormonal contraceptives may reduce the effect of training in premenopausal women.