Osteoporosis is an increasing problem in the Western World, now affecting 1 in 3 women and 1 in 12 men. It is characterised by a fall in bone mass causing the bones to become porous and fragile, and in the UK alone, this condition results in about 200,000 fractures a year. Such fractures cause great pain and can lead to permanent disability. Exercise and a diet rich in calcium can help strengthen bones. These researchers will study several groups of children to see whether combining calcium and exercise is even more beneficial to growing bone. They hope to show that if children have a healthy diet and take plenty of exercise, they will have a much lower risk of developing osteoporosis in later life.