Physical activity and the young female skeleton

The aim of this thesis was to identify the influence of calcium, physical activity and detraining on bone mass and bone size in girls and young women. We hypothesised that calcium intake above a specific level does not enhance the accrual of bone mineral, that exercise predominantly influences the skeleton in the early pubertal period and that reduced training is followed by a loss of exercise-induced skeletal benefits. To scrutinise our hypothesis we followed 103 girls aged 7-9 in a 1-year prospective controlled exercise intervention study, 78 girls aged 13-15 in a 5-year and 130 females aged 13-54 in a 8-year prospective observational study. It seems that an exercise intervention programme during the first school year increases the accrual of bone mass and the gain in bone size. Continued physical activity in the peri- and post-pubertal period seems to be associated with maintenance of a high bone mass. It appears that the bone mass could be enhanced by increasing the intake of calcium in adolescent girls consuming less than 800 to 1000 mg per day. It seems as if exercise-induced benefits in bone mass could be achieved also in post-pubertal women but that the benefits are at least partially reduced with detraining. The thesis supports the view that physical activity could be recommended to increase peak bone mass but it must be further validated whether exercise during growth could be recommended to remain at a high bone mass level decades after an exercise career