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Dual energy X-ray absorptiometry (DXA)
DXA scanners have been available since 1987. According to the WHO, DXA is considered as the gold standard to assess bone density (Garg and Kharb, 2013). It is the most commonly used method to determine BMD and therefore to diagnose osteoporosis. Before introducing DXA, many devices were mainly used for osteoporosis diagnostics (for example: Dual and single photon Absorptiometry) (Pisani et al., 2013). DXA has many advantages compared to its antecedents, including a decrease in radiation exposure, an energy source that is more stabilised, a faster pace and a more precise data acquisition. The investment in a DXA device is small compared to 3D imaging devices. In addition, DXA tests are mainly inexpensive. DXA measurements are validated in adults, adolescents and children (Weaver et al., 2016).
A DXA machine involves an examination table for the patient, a mobile part below the patient that produces X-ray (X-ray source) and a system above the examination table that detects the produced radiation. The X-ray source and the X-ray detector move together and are located precisely in an opposite way (figure 2)
Dual energy X-ray absorptiometry as its name shows, uses X-ray that is composed of dual photon energy (high and low; constant and pulsed energy) (Pisani et al., 2013). It is a technology that measures the attenuation of X-rays (of high-energy and low-energy) passing through tissues of varying densities. In addition to bone mineral content, DXA can calculate many bone variables (table 2).
Age gender and peak bone mass
The development of bone mass begins in foetal life, continues throughout childhood and ends in the end of the third decade of life (Weaver et al., 2016). Age and sex affect bone growth evolution. Slow gain in bone mass is found in childhood. This gain significantly accelerates with puberty and then decelerates after it. (figure 12). The period of puberty (fast and strong bone growth) is very important and vital to reach PBM.
Figure 12: Bone mineral content gain in relation to age and sex (Bailey et al., 1999). Difference in bone mass observed in adults in both sexes is first observed at puberty (Bonjour et al, 1994). Before puberty, both sexes do not differ in bone mass. Theintz et al. (1992) showed in their longitudinal study, a significantly noticeable increase in L2-L4 BMD and BMC and FN BMD from 11 to 14 years (3-year period) and an intense decrease after the age of 16 in adolescent females. After menarche, gain in bone mass dropped rapidly and became not significant (2 years later). In contrast, an increase in BMD and BMC was significantly high for both L2-L4 and mid-femoral from the age of 13 to 17 (4-year period) in adolescent males then decreased but remained significant until the age of 20 (3 years) at the lumbar level and at the level of the femoral shaft but not at the level femoral neck (Theintz et al., 1992). Moreover, an increase in bone mass was only shown in men who were growing less than 1 cm per year and who reached pubertal age P5 (Weaver et al., 2016). A higher increase in bone mass development in males compared to females was shown during the pubertal phase leading to an important difference between men and women. This is not due to a higher maximal gain in bone bass but to a longer pubertal maturation period (Weaver et al., 2016).
Muscle Contraction Forces
It is recognised that bone adapts to the mechanical stress that is applied to it. Muscle contraction applies mechanical stress to the bone. This is found by corresponding changes in both muscle strength and bone size (Robling, 2009; Daly et al., 2004). Daly et al. (2004) compared the BMD of the dominant arm of a tennis player to the non-dominant arm. They found that the dominant arm has higher muscle and bone mass com-pared to the other arm. This suggests that muscle contraction is associated to an increase in bone and muscle mass.
Rector et al. (2009) found that muscle mass of athletes who perform resistance training exercises for all major muscle groups (lower and upper body) was positively correlated to arm BMD, leg BMD, hip BMD and lumbar spine BMD. This proposes that there is a positive correlation between muscle mass and BMD of the arm (a non-weight bearing site) which highlights how muscle contraction without gravitational forces contributes to an increase in muscle mass that is correlated to an increase in BMD. In addition, Carter (2012) found that a 12-month period of resistance training showed an improvement in the BMD of the arm. This change in arm BMD is positively related to the change in arm muscle mass. Thus, muscle contraction forces are beneficial for increasing bone mass and strength. Resistance training programs also influence bone health by increasing the levels of several anabolic hormones (GH, testosterone and IGF-1) which positively influence bone mass. Resistance training also decreases fat mass percentage and thus the level of inflammatory cytokines which are harmful for bone health.
Exercise interventions during childhood, adolescence, adulthood and older age
Meyer et al. (2013) showed in their longitudinal study that children who participated in school-based interventions presented a greater bone mineral content in their FN and TH and WB (8.1%, 7.7% and 6.2% respectively) compared to non-active controls. Moreover, BMC benefits remained after 3 years of the end of the intervention with a continuous BMC increase of 7 to 8% in FN and TH (Meyer et al., 2013). Among the choices of exercises, walking had a minimal positive effect on BMD because of its low impact nature and the minimal mechanical load that it exerts on the bones. This is supported by a recent systematic review by MacKelvie et al. (2002) that presented the effect of weight-bearing exercises on bone strength in children before and at puberty. On the other hand, strength training and high impact activities had additional effects on the prevention of bone loss (Gómez-Cabello et al., 2012). In addition to the effect of exercise on children, systematic reviews by Hamilton et al. (2010) and Bolam et al. (2015) showed that bone loading exercises have a beneficial effect on bone creation in middle-aged persons but in a smaller degree compared to children and adolescents (Hind and Burrows, 2007; Nogueira et al., 2014). According to Heinonen et al. (1996), practicing a high impact sport for a duration of 18 months performed by 35 to 45-year pre-menopausal women produced gradual increase in femoral neck BMD. Inactive controls did not show any BMD changes. In addition, a meta-analysis showed that different exercise regimes lasting for a period of 24 weeks increase FN and lumbar spine BMD (Kelley et al., 2013). Studies investigating the effect of exercise on bone health in older people (>50 years) were less compared to children and adolescents. Weight bearing activities are effective in preserving bone mass in older individuals. Maddalozzo and Snow (2000) showed that high intensity training or moderate strength training for a 6-month period in men and women (50 years) increased spine BMD by 1.9 % in men, while women did not show any increase. In addition, a longer training duration of 12 months resulted in an increase in the geometry, BMD and BMC of the FN in elderly men aged between 65 to 80 years (Allison et al. 2013).
Principles of the American College of Sports Medicine
In order to achieve significant bone gains and induce osteogenic effect, the following principles should be taken into consideration while planning physical training programs (Kohrt et al., 2004):
Specificity: Only the bone sites associated to mechanical stresses undergo a positive bone adaptation.
Overload: An osteogenic response only takes place when the load exerted on the bone exceeds the habitual load that is imposed on it. A gradual increase in load or an overload is required to achieve this response.
Reversibility: If sports practice is interrupted or stopped, its positive effects on BMD do not persist. The volume and intensity of practice that maintains BMD remains to be determined.
Start-up capital: In general, the higher the baseline BMD of a subject is, the lower the benefits associated with physical training will be low. The lower a subject’s baseline BMD is, the higher the benefits associated with physical training will be high.
Trainability: The maximum achievable BMD is affected by genetic factors and varies widely among individuals. This “ceiling” value determines the potential progress of each individual.
Table of contents :
ABBREVIATIONS
LIST OF FIGURES
LIST OF TABLES
INTRODUCTION
FIRST PART: LITERATURE REVIEW
1. Osteoporosis
1.1 Definition of osteoporosis 13 1.1.1 Diagnostics of osteoporosis: T-score and Z-score
1.1.2 Reference data
1.4.1 Worldwide
1.4.2 Europe 25 1.4.3 Middle east and Lebanon
1.4.4 Economic impact
2. Bone strength and fracture risk
2.1 Peak bone mass
2.1.1 Definition of peak bone mass and prevention of osteoporosis
2.1.2 Age gender and peak bone mass
2.3 Determinants of peak bone mass
2.3.1 Genetic factors
2.3.2 Hormonal factors
2.3.3 Nutritional factors
2.3.4 Physical activity
2.3.5 Body weight
3. Bone adaptation to exercise
3.1 Gravitational loads
3.2 Muscle Contraction Forces
3.3 Exercise interventions during childhood, adolescence, adulthood and older age
3.4 Principles of the American College of Sports Medicine
4. Soccer and bone
4.1 Effects of soccer training on different bone parameters in males aged between 8 to 16 years
4.2 Effects of soccer training on several bone parameters in males aged between 20 and 54 years
4.3 Effects of soccer practice on bone parameters in male aged 60 years and above
4.4 Effects of soccer on bone parameters in females aged between 30 and 61 years
4.5 Cross sectional studies related to female soccer players and inactive controls aged between 15 and 27 years
4.6 Cross-sectional studies related to male soccer players and inactive controls aged between 18 and 30 years
4.7 Cross sectional studies related to male soccer players and inactive controls aged between 10 to 17 years
4.8 Cross sectional studies related to female soccer players and inactive controls aged between 10 to 18 years
4.9 Cross-sectional studies related to male soccer players and inactive controls aged between 50 years and older
SECOND PART: PERSONAL CONTRIBUTION
GENERAL METHODOLOGY
Study 1: Muscular power and maximum oxygen consumption predict bone density in a group of middle-aged men
Study 2: Composite Indices of Femoral Neck Strength in Middle-Aged Inactive Subjects Vs Former Football Players
GENERAL DISCUSSION
CONCLUSIONS AND PERSPECTIVES
SUMMARY OF THE THESIS IN FRENCH
BIBLIOGRAPHY
