1. Chapter 9 Skeletal health

2. Chapter overview Introduction Biology of bone Osteoporosis: definition, prevalence and consequences Physical activity and bone strength Physical activity and fracture risk Physical activity in prevention and management of osteoporosis Physical activity and osteoarthritis Summary

3. Structure of a long bone an average adult has 10–12 kg of bone; bone offers ‘strength with lightness’; cortical bone – dense, ivory-like; trabecular bone – lattice of thin, calcified struts membrane, the periosteum, covers surface of cortical bone.

4. Remodelling in trabecular bone Osteoclasts resorb (digest) old bone; osteoblasts fill this cavity with new bone; new bone undergoes remineralization.

5. Measuring the structural properties of bone Dual energy X-ray absorptiometry (DXA) – measures bone mineral content and bone mineral density (BMD). Quantitative ultrasound – measurements reflect bone architecture as well as bone mineral. Quantitative computed tomography – measures bone mineral content, BMD and axial cross- sectional area.

6. Changes in bone mineral density over the life-span

7. Adaptation to load bearing Bone is deposited according to the load it must bear; strains produced during loading stimulate an adaptive, osteogenic response; response is determined by the magnitude, rate and distribution of strains, as well as the number of repetitions (strain cycles); immobilization and space flight both lead to net bone loss.

8. Osteoporosis A skeletal disorder characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in fragility and susceptibility to fracture.

9. Osteoporotic changes in lumbar vertebrae Normal, good weight-bearingOsteoporotic, loss of weight- bearing competence

10. What determines likelihood of osteoporosis or osteopenia? Peak bone mass as a young adult –childhood and adolescence therefore a ‘window of opportunity’; rate of bone loss experienced with ageing –dietary factors –physical activity level; genetic variability.

11. Side-to-side differences in humerus of female tennis and squash players

12. Effect of 18 months of high-impact training in women aged 35–45

13. RCT of high-impact training in postmenopausal women

14. Clinical endpoint, hip fracture – Nurses’ Health Study (2002) 55% lower risk in postmenopausal women reporting > 24 MET-h per week, compared with < 3 MET-h per week; risk was 6% less for each increase in activity of 3 MET-h per week; in women who did no other exercise, walking for at least four hours per week was associated with a 41% lower risk than among those who walked for less than one hour per week.

15. Summary I Functional loading is the most important influence on bone remodelling. Strain rate and an unusual strain distribution largely determine its osteogenic effects. Bone mass increases during growth and reaches a peak towards the end of the second decade. Age­related loss of bone can lead to osteopenia and osteoporosis, compromising strength and increasing the risk of fracture.

16. Summary II In premenopausal women, the effect of exercise is mainly conservation of bone. In older women it is to reduce the rate of loss. Physically active women have a lower risk of osteoporotic fracture of the hip and maybe of the spine. Regular exercise may decrease the risk of fall-related fractures. Moderate amounts and intensities of exercise have a favourable effect on pain and function in osteoarthritis of the knee, but sports involving high-intensity impacts or torsional types of stress increase risk.