Preventing the Risk of Osteoporotic Fracture in Premenopausal Women by a Spa Residential Physical Activity Program

Osteoporosis is an increasing public health problem. Involution of bone mass in women is due to a reduction in sensitivity of the bone to the mechanical stress due to the slow-down of the bone turnover after 35 years old. Osteoporosis is a silent disease combining a decrease in bone mass (quantity) and an impaired bone microarchitecture (quality) leading to an increased risk of fracture. Bone microarchitecture is an important element to be taken into account in assessing the bone properties, as demonstrated by numerous ex vivo studies. Bone densitometry only identifies 50% of osteoporotic fractures. The other half of the fractures appears in osteopenic women. The measurement of bone mineral density is too limited to assess risk of fracture. Bone microarchitecture can be assessed through a peripheral quantitative computed tomography scan (computed tomography peripherical - pQCT). The microarchitecture data allow the calculation of bone strength index (BSI) and stress strength index (SSI) highly predictive of fracture risk. These qualitative determinants of bone fragility are the most relevant to evaluate effect of physical activity over a short period compared with bone mineral content and density, which requires several months of constraints. Biochemical markers of bone turnover, specifically those of bone resorption, are predictive of the risk of osteoporotic fracture. Physical activity can reduce the risk of fracture up to 20-35% via direct effects on bone strength, at any age. However, response of bone varies with modalities of exercise. Repeated exercise produces greater bone adaptations than a single bout. Moreover, it has been well demonstrated since 1970 that bone responds to a dynamic stimulation, but not a static stimulation, with a dose response relationship. It has been confirmed in premenopausal women. The effect of physical activity on microarchitectural bone parameters (porosity and density of cortical and trabecular) has not been investigated in pr