Bone mineral density, muscle strength and physical activity. A population-based study of 332 subjects aged 15-42 years

Influence of a School-based Physical Activity Intervention on Cortical Bone Mass Distribution: A 7-year Intervention Study

Cortical bone mass and density varies across a bones length and cross section, and may be influenced by physical activity. This study evaluated the long-term effects of a pediatric school-based physical activity intervention on tibial cortical bone mass distribution. A total of 170 children (72 girls and 98 boys) from one school were provided with 200 min of physical education per week. Three other schools (44 girls and 47 boys) continued with the standard 60 min per week. Tibial total and cortical area, cortical density, polar stress-strain index (SSI), and the mass and density distribution around the center of mass (polar distribution, mg) and through the bones cortex (radial distribution subdivided into endo-, mid-, and pericortical volumetric BMD: mg/cm³) at three sites (14, 38, and 66 %) were assessed using peripheral quantitative computed tomography after 7 years. Girls in the intervention group had 2.5 % greater cortical thickness and 6.9 % greater SSI at the 66 % tibia, which was accompanied by significantly greater pericortical volumetric BMD compared to controls (all P < 0.05). Region-specific differences in cortical mass were also detected in the anterior, medial, and lateral sectors at the 38 and 66 % tibial sites. There were no group differences at the 14 % tibia site in girls, and no group differences in any of the bone parameters in boys. Additional school-based physical education over seven years was associated with greater tibial structure, strength, and region-specific adaptations in cortical bone mass and density distribution in girls, but not in boys.

A seven-year physical activity intervention for children increased gains in bone mass and muscle strength

AIM

This study evaluated the musculoskeletal effects of increased physical activity on children, starting at six to nine years of age.

METHODS

In one school we increased the physical education of 72 girls and 100 boys to 200 minutes per week over seven years. In three other schools, 45 girls and 47 boys continued to receive 60 minutes per week. We measured areal bone mineral density (aBMD) with dual energy X-ray absorptiometry and muscle strength with computerised dynamometer at baseline and after seven years and tibial cortical thickness with peripheral quantitative computed tomography after seven years.

RESULTS

Girls in the intervention group gained 0.04 g/cm(2) (0.01-0.08) more total spine aBMD (p < 0.05) and 6.2Nm (1.6, 10.7) more knee flexion strength (p < 0.01) than control group girls and had a 0.1 mm (0.0, 0.3) higher tibial cortical thickness at follow-up (p < 0.05). Boys in the intervention group gained 7.3Nm (0.4, 14.2) more knee extension strength (p < 0.05) and 7.4Nm (2.3, 12.4) more knee flexion strength (p < 0.01) than the control group boys, but their aBMD was no higher than the control group.

CONCLUSION

A seven-year, population-based moderately intense exercise intervention enhanced gains in spine bone mass in girls and knee muscle strength in both genders.

Is calcaneal stiffness more sensitive to physical activity than forearm bone mineral density? A population-based study of persons aged 20 - 79 years

Aims: The aim of this study was to investigate the associations between forearm bone mineral density (BMD), calcaneal stiffness, and physical activity levels in a normal population using different non-invasive methods. Methods: The participants were invited to undergo bone measurements using single photon absorptiometry of the forearm and quantitative ultrasound (QUS) of the calcaneal bone, and also to complete a questionnaire. Physical activity levels were designated low, moderate, and high in the question on leisure-time activity. Results: There were 956 participants included in the present study. Forearm BMD in the eighth age decade was 0.40 g/cm2 (95% CI 0.33 - 0.46 g/cm2) lower than in the third decade among women and 0.28 g/cm2 (95% CI 0.18 - 0.37 g/cm2) lower among men. The differences in calcaneal stiffness between the same age decades were 22.4 (95% CI 17.5 - 27.4) among women and 15.8 (95% CI 8.0 - 23.5) among men. The correlation between forearm BMD and calcaneal stiffness was 0.58 (95% CI 0.52 - 0.64) in women and 0.34 (95% CI 0.25 - 0.42) in men. Reported moderate and high leisure-time activity levels in both genders were associated with higher calcaneal stiffness but not with forearm BMD. Conclusions: The QUS may be used to measure the effect of present physical activity levels on calcaneal bone at the population level. Further longitudinal studies are warranted in order to determine the most appropriate non-invasive method in population-based studies.

Relationship of body composition, knee extensor strength, and standing balance to lumbar bone mineral density in postmenopausal females

[Purpose] This study aimed to investigate correlations between lumbar bone mineral density (BMD) and general characteristics of postmenopausal females, including body composition, knee extensor strength, standing balance, and femur BMD. [Subjects and Methods] A total of 40 postmenopausal females (55.6 ± 4.6 years) who were caregivers or guardians of patients in the K hospital were included in the study. The weight, height, body composition, left and right knee extensor strength, standing balance, femur BMD, and lumbar BMD measurements of the subjects were obtained. [Results] The effect of measurement variables on lumbar BMD was examined. Increases in age and menopausal duration were observed to significantly increase lumbar BMD, whereas an increase in height was found to significantly decrease lumbar BMD. An increase in soft lean mass, skeletal muscle mass, fat-free mass, and femur BMD was also associated with significantly decreased lumbar BMD. [Conclusion] Age, menopausal duration, soft lean mass, skeletal muscle mass, and fat-free mass were factors that decreased lumbar BMD in menopausal females. This study is expected to provide basic knowledge for osteoporosis prevention and treatment programs for postmenopausal females.

Greater association of peak neuromuscular performance with cortical bone geometry, bone mass and bone strength than bone density: A study in 417 older women

BACKGROUND

We evaluated which aspects of neuromuscular performance are associated with bone mass, density, strength and geometry.

METHODS

417 women aged 60-94years were examined. Countermovement jump, sit-to-stand test, grip strength, forearm and calf muscle cross-sectional area, areal bone mineral content and density (aBMC and aBMD) at the hip and lumbar spine via dual X-ray absorptiometry, and measures of volumetric vBMC and vBMD, bone geometry and section modulus at 4% and 66% of radius length and 4%, 38% and 66% of tibia length via peripheral quantitative computed tomography were performed. The first principal component of the neuromuscular variables was calculated to generate a summary neuromuscular variable. Percentage of total variance in bone parameters explained by the neuromuscular parameters was calculated. Step-wise regression was also performed.

RESULTS

At all pQCT bone sites (radius, ulna, tibia, fibula), a greater percentage of total variance in measures of bone mass, cortical geometry and/or bone strength was explained by peak neuromuscular performance than for vBMD. Sit-to-stand performance did not relate strongly to bone parameters. No obvious differential in the explanatory power of neuromuscular performance was seen for DXA aBMC versus aBMD. In step-wise regression, bone mass, cortical morphology, and/or strength remained significant in relation to the first principal component of the neuromuscular variables. In no case was vBMD positively related to neuromuscular performance in the final step-wise regression models.

CONCLUSION

Peak neuromuscular performance has a stronger relationship with leg and forearm bone mass and cortical geometry as well as proximal forearm section modulus than with vBMD.

The health benefits of muscular fitness for children and adolescents: a systematic review and meta-analysis

BACKGROUND

Physical fitness during childhood and adolescence has been identified as an important determinant of current and future health status. While research has traditionally focused on the association between cardio-respiratory fitness and health outcomes, the association between muscular fitness (MF) and health status has recently received increased attention.

OBJECTIVE

The aim of this systematic review and meta-analysis was to evaluate the potential physiological and psychological benefits associated with MF among children and adolescents.

METHODS

A systematic search of six electronic databases (PubMed, SPORTDiscus, Scopus, EMBASE, PsycINFO and OVID MEDLINE) was performed on the 20th May, 2013. Cross-sectional, longitudinal and experimental studies that quantitatively examined the association between MF and potential health benefits among children and adolescents were included. The search yielded 110 eligible studies, encompassing six health outcomes (i.e., adiposity, bone health, cardiovascular disease [CVD] and metabolic risk factors, musculoskeletal pain, psychological health and cognitive ability). The percentage of studies reporting statistically significant associations between MF and the outcome of interest was used to determine the strength of the evidence for an association and additional coding was conducted to account for risk of bias. Meta-analyses were also performed to determine the pooled effect size if there were at least three studies providing standardised coefficients.

RESULTS

Strong evidence was found for an inverse association between MF and total and central adiposity, and CVD and metabolic risk factors. The pooled effect size for the relationship between MF and adiposity was r = -0.25 (95% CI -0.41 to -0.08). Strong evidence was also found for a positive association between MF and bone health and self-esteem. The pooled effect size for the relationship between MF and perceived sports competence was r = 0.39 (95% CI 0.34-0.45). The evidence for an association between MF and musculoskeletal pain and cognitive ability was inconsistent/uncertain. Where evidence of an association was found, the associations were generally low to moderate.

CONCLUSION

The findings of this review highlight the importance of developing MF in youth for a number of health-related benefits.

Femoral neck bone strength estimated by hip structural analysis (HSA) in Swedish Caucasians aged 6-90 years

Dual-energy X-ray absorptiometry hip scans of 1,760 population-based Caucasians, 599 girls and 642 boys aged 6-19 years and 270 women and 249 men aged 20-90 years, were analyzed with the hip structural analysis (HSA) software to present age- and sex-specific normative HSA data of the femoral neck (FN). Measured traits included bone mineral density (BMD), cross-sectional area (CSA), section modulus (Z), periosteal diameter (PD), endosteal diameter (ED), cortical thickness (CT), and cross-sectional moment of inertia (CSMI). When plotting the measured traits versus age, the curves increased with higher ages until statistically significant break points were reached, for all traits at age 17 in girls and age 19 in boys. After the break points, PD and ED increased with higher ages but, as ED increased more than PD, BMD and CT decreased significantly with higher ages. The decline in BMD was counteracted by the increase in bone size so that there was only a nonstatistically significant decrease in bone strength, estimated as Z and CSMI, from break point to age 90. The partial preservation of bone strength was more obvious in men than in women as the decline in BMD was higher in women than in men, while the expansion in PD was larger in men than in women. The sex difference in the normative FN bone strength data seems to be related to sex discrepancies in the development of both bone mass and geometrical parameters during both growth and adulthood.

CORRELATIONS BETWEEN ISOMETRIC QUADRICEPS MUSCLE STRENGTH AND BONE MINERAL DENSITY

The purpose of this study was to evaluate the relationship between isometric quadriceps muscle strength and measurements of bone density (BMD), mass (BMC) and ultrasound properties. A total of 113 individuals were included, 53 men and 60 women aged 22-85 years. Isometric quadriceps muscle strength correlated significantly to BMD of the total body for both men (r=0.63, p=0.02) and women r=0.77, p=0.04) after adjustments for age, weight and height. In women, there was also an association between isometric quadriceps muscle strength and BMD of the lumbar spine (r=0.67, p=0.04). These correlations were evident in premenopausal women for BMD at the lumbar spine, femoral neck and total body whereas no significant relationships were seen in postmenopausal women or any age group of men. For isometric quadriceps muscle strength and the ultrasound measurements of the heel, a positive correlation was seen in men and women aged 41-60 years. The findings point to a role of endogenous sex steroids, primarily estrogens, in the correlation between BMD and isometric quadriceps muscle strength.

What happens to femoral neck bone mineral density after hip resurfacing surgery?

The major advantage of hip resurfacing is the decreased amount of bone resection compared with a standard total hip replacement. Fracture of the femoral neck is the most common early complication and poor bone quality is a major risk factor. We undertook a prospective consecutive case control study examining the effect of bone mineral density changes in patients undergoing hip resurfacing surgery. A total of 423 patients were recruited with a mean age of 54 years (24 to 87). Recruitment for this study was dependent on pre-operative bilateral femoral bone mineral density results not being osteoporotic. The operated and non-operated hips were assessed. Bone mineral density studies were repeated over a two-year period. The results showed no significant deterioration in the bone mineral density in the superolateral region in the femoral neck, during that period.

These findings were in the presence of a markedly increased level of physical activity, as measured by the short-form 36 health survey physical function score.

Normative dual energy X-ray absorptiometry data in Swedish children and adolescents

AIM

To present normative dual energy X-ray absorptiometry data in healthy young Swedes.

METHODS

Included were 710 girls and 759 boys aged 6-30 years from southern Sweden. Bone mineral content, bone mineral density, bone size, lean body and fat mass were measured by dual energy X-ray absorptiometry in total body, lumbar spine, hip, arms and legs.

RESULTS

Swedish children had similar bone mass to children in the Netherlands but higher than children in Canada and Korea. Height, weight, bone mass, bone size and lean mass increased at a constant rate from age 6 until the rapid increase in all traits at puberty. The pubertal growth spurt started earlier in girls than in boys, while the spurt in boys was larger in magnitude and occurred for a longer period. Around one-quarter of the adult total body and lumbar spine peak bone mineral content was gained during the 2 years with the fastest gain in both genders.

CONCLUSION

This study presents normative bone mass data in Swedish children, data that are similar to that in Dutch children but higher than in Canadian and Korean children. The gain in Swedish children seems to mimic the gain seen in children in other settings.

A school-based exercise intervention program increases muscle strength in prepubertal boys

This prospective controlled intervention study over 12 months evaluated the effect of exercise on muscular function, physical ability, and body composition in pre-pubertal boys. Sixty-eight boys aged 6-8 years, involved in a general school-based exercise program of 40 min per school day (200 min/week), were compared with 46 age-matched boys who participated in the general Swedish physical education curriculum of mean 60 min/week. Baseline and annual changes of body composition were measured by dual energy X-ray absorptiometry (DXA), stature, and body mass by standard equipments, isokinetic peak torque (PT) of the knee extensors, and flexors at 60 and 180 deg/sec by computerized dynamometer (Biodex) and vertical jump height (VJH) by a computerized electronic mat. The annual gain in stature and body mass was similar between the groups whereas the increase in total body and regional lean mass (P < .001) and fat mass (P < .001) was greater in the exercise group. The one-year gain in body mass-adjusted knee extensor and flexor PT at 180 deg/sec was significantly greater in the intervention group compared with the control group (P < .01, adjusted for age at baseline and P < .001, adjusted for age and muscle strength at baseline, resp.). There was no group difference in VJH. In conclusion, the increase in school-based physical education from 60 to 200 minutes per week enhances the development of lean body mass and muscle strength in pre-pubertal boys.

Effect of a comprehensive lifestyle modification program on the bone density of male heavy drinkers

BACKGROUND

Heavy alcohol drinking is implicated in osteoporosis. Although abstinence is rapidly followed by a restoration of osteoblastic activity, little is known about the contributions of alcohol-related factors or the effectiveness of a lifestyle modification program (LMP) on bone density.

METHODS

We conducted a study of 138 male alcoholic patients to investigate whether drinking history and concurrent factors were associated with the bone density of the calcaneus. A 2.5-months LMP in an institutionalized setting was completed by 20 of them, and its effect on bone density, serum parathyroid hormone (PTH), and 1.25-(OH)(2) vitamin D levels were assessed.

RESULTS

The patients had a high prevalence of daytime drinking (93.5%), continuous drinking (84.1%), and current smoking (82.0%) with mean duration of alcohol abuse of 30.0 +/- 12.8 years. The patients had lower bone density than a reference control group (Z-scores: -0.45 +/- 1.02). Multiple stepwise regression analysis identified age, poor activities of daily living (ADL), continuous drinking, absence of liver cirrhosis, depression, and dementia as determinants of low bone density. The bone density of the 20 participants in the LMP improved 2.3% (p = 0.0003) with a more ameliorating effect on bone density than a conventional abstinence therapy (p = 0.014 for interventional effect). The upper normal range of PTH levels at baseline were significantly decreased, and 1.25-(OH)(2) vitamin D levels also had a trend toward decrease during the abstinence.

CONCLUSIONS

Alcoholic patients may have many complications such as poor ADL and dementia, which are independently associated with decreased bone density. The results of this study support the idea that comprehensive approach to lifestyle factors to minimize risk of osteoporosis is the best way to improve bone density.

Muscle strength and bone mineral density in mine victims with transtibial amputation

The aims of this study were to: (i) Determine if there were significant bone mineral density and muscle strength differences between intact and amputated limbs, and (ii) investigate the possible relationship between local bone loss and muscle strength in transtibial amputees. Fifteen male veterans with traumatic unilateral transtibial amputations who ranged in age from 18-45 years were included in this prospective study. Lower limb muscle strength was measured with an isokinetic dynamometer. Dual energy X-ray absorptiometry was used to determine bone mineral density of the femur and tibia. The bone mineral density values of the femur and tibia were found significantly decreased on the amputated side. Significant decreases (p < 0.001) in strength of the quadriceps and hamstrings were observed in the amputated limb. There was a weak correlation between quadriceps strength and total femur bone mineral density (p = 0.048, r = 0.518) on the amputated limb. Transtibial amputees are prone to bone mineral loss and muscle strength decrease on the amputated side. Our results also indicate that muscle strength itself might not be of decisive importance for bone mass in transtibial amputees.

Muscle mass is more strongly related to hip bone mineral density than is quadriceps strength or lower activity level in adults over age 50 year

This cross-sectional study examined whether reduced hip bone mineral density (BMD) is better explained by isokinetic knee extensor strength (KES), lower limb lean body mass (L-LBM), or Physical Activity Scale for the Elderly (PASE). Through population-based recruitment, 1543 adults without knee osteoarthritis were recruited. For men and women respectively, means+/-SD were age 60.8+/-8.0 and 61.1+/-7.9 yr; body mass index 29.6+/-4.6 and 29.1+/-5.4 kg/m(2); hip BMD 1.025+/-0.138 and 0.895+/-0.128 g/cm(2); KES 124.9+/-41 and 72.7+/-22.9 N.m; L-LBM 10.3+/-1.5 and 7.0+/-1.2 kg; and PASE 206.4+/-99.7 and 163.8+/-77.0. The relationship between BMD and KES in men (r(2)=0.21, p> or =0.002) and women (r=0.23, p<0.001) was significant before adjustment. However, this association was no longer significant after controlling for L-LBM. Even after controlling for age, race, and sex, the association between BMD and KES was better explained by L-LBM (partial R(2)=0.14, p<0.001) than by PASE (partial R(2)=0.00). Allometric scaling of KES to body size attenuated the association of BMD with KES (Std Beta=0.03). The significant association between BMD and L-LBM (Std Beta=0.36) remained stronger than that between BMD and weight (Std Beta=0.21). Therefore, muscle mass accounted for a greater proportion of the variance in hip BMD than KES or activity level and explained a significant proportion of the association between weight and BMD.

A one-year exercise intervention program in pre-pubertal girls does not influence hip structure

Background

We have previously reported that a one-year school-based exercise intervention program influences the accrual of bone mineral in pre-pubertal girls. This report aims to evaluate if also hip structure is affected, as geometry independent of bone mineral influences fracture risk.

Methods

Fifty-three girls aged 7 – 9 years were included in a curriculum-based exercise intervention program comprising 40 minutes of general physical activity per school day (200 minutes/week). Fifty healthy age-matched girls who participated in the general Swedish physical education curriculum (60 minutes/week) served as controls. The hip was scanned by dual X-ray absorptiometry (DXA) and the hip structural analysis (HSA) software was applied to evaluate bone mineral content (BMC), areal bone mineral density (aBMD), periosteal and endosteal diameter, cortical thickness, cross-sectional moment of inertia (CSMI), section modulus (Z) and cross-sectional area (CSA) of the femoral neck (FN). Annual changes were compared. Group comparisons were done by independent student's t-test between means and analyses of covariance (ANCOVA). Pearson's correlation test was used to evaluate associations between activity level and annual changes in FN. All children remained at Tanner stage 1 throughout the study.

Results

No between-group differences were found during the 12 months study period for changes in the FN variables. The total duration of exercise during the year was not correlated with the changes in the FN traits.

Conclusion

Evaluated by the DXA technique and the HSA software, a general one-year school-based exercise program for 7–9-year-old pre-pubertal girls seems not to influence the structure of the hip.

Exercise, bone mass and bone size in prepubertal boys: one-year data from the pediatric osteoporosis prevention study

This non-randomized prospective controlled study evaluates a daily school-based exercise intervention program of 40 min/school day for 1 year in a population-based cohort of 81 boys aged 7-9 years. Controls were 57 age-matched boys assigned to the general school curriculum of 60 min/week. Bone mineral content (BMC; g) and areal bone mineral density (aBMD; g/cm(2)) were measured with dual X-ray absorptiometry (DXA) of the total body, the third lumbar vertebra (L3) and the femoral neck (FN). Bone width for L3 and FN was calculated from the lumbar spine and hip scan. No differences between the groups were found at baseline in age, anthropometrics or bone parameters. The mean annual gain in L3 BMC was 5.9 percentage points higher (P<0.001), L3 aBMD a mean 2.1 percentage points higher (P=0.01) and L3 width a mean 2.3 percentage points higher (P=0.001) in the cases than in the controls. When all individuals were included in one cohort, the total duration of exercise including both school-based and spare-time training correlated with L3 BMC (r=0.26, P=0.003), L3 aBMD (r=0.18, P=0.04) and L3 width (r=0.24, P=0.006). The study suggests that exercise in pre-pubertal boys influences the accrual of bone mineral and bone width and that a 1-year school-based exercise program confers skeletal benefits, at least in the lumbar spine.

A school curriculum-based exercise program increases bone mineral accrual and bone size in prepubertal girls: two-year data from the pediatric osteoporosis prevention (POP) study

This 2-year prospective controlled exercise intervention trial in 99 girls at Tanner stage 1, evaluating a school curriculum-based training program on a population-based level, showed that the annual gain in BMC, aBMD, and bone size was greater in the intervention group than in the controls.

INTRODUCTION

Most exercise intervention studies in children, evaluating the accrual of BMD, include volunteers and use specifically designed osteogenic exercise programs. The aim of this study was to evaluate a 2-year general school-based exercise intervention program in a population-based cohort of girls at Tanner stage 1.

MATERIALS AND METHODS

Forty-nine girls 7-9 years of age in grades 1 and 2 in one school were included in a school curriculum-based exercise intervention program of general physical activity for 40 minutes per school day (200 minutes/week). Fifty healthy age-matched girls in three neighboring schools, assigned to the general Swedish school curriculum of physical activity (60 minutes/week), served as controls. All girls were premenarchal, remaining in Tanner stage 1 during the study. BMC (g) and areal BMD (aBMD; g/cm2) were measured with DXA of the total body (TB), the lumbar spine (L2-L4 vertebrae), the third lumbar vertebra (L3), the femoral neck (FN), and the leg. Volumetric BMD (vBMD; g/cm3) and bone size were calculated at L3 and FN. Total lean body mass and total fat mass were estimated from the total body scan. Height and weight were also registered. Baseline measurements were performed before the intervention was initiated. Follow-up was done after 2 years.

RESULTS

No differences between the groups were found at baseline in age, anthropometrics, or bone parameters. The annual gain in BMC was greater in the intervention group than in the controls: L2-L4, mean 3.8 percentage points (p = 0.007); L3 vertebra, mean 7.2 percentage points (p < 0.001); legs, mean 3.0 percentage points (p = 0.07). The intervention group had a greater annual gain in aBMD: total body, mean 0.6 percentage points (p = 0.006), L2-L4, mean 1.2 percentage points (p = 0.02), L3 vertebra, mean 1.6 percentage points (p = 0.006); legs, mean 1.2 percentage points (p = 0.007). There was also a greater mean annual gain in bone size in the L3 vertebra (mean 1.8 percentage points; p < 0.001) and in the FN (mean 0.3 percentage points; p = 0.02).

CONCLUSIONS

A general school-based exercise program for 2 years for 7- to 9-year-old girls (baseline) enhances the accrual of BMC and BMD and increases bone size.

Alcohol-induced bone loss and deficient bone repair

BACKGROUND

Chronic consumption of excessive alcohol eventually results in an osteopenic skeleton and increased risk for osteoporosis. Alcoholics experience not only increased incidence of fractures from falls, but also delays in fracture healing compared with non-alcoholics. In this review the term "alcohol-induced bone disease" is used to refer to these skeletal abnormalities. Alcohol-induced osteopenia is distinct from osteoporoses such as postmenopausal osteoporosis and disuse osteoporosis. Gonadal insufficiency increases the rate of bone remodeling, whereas alcohol decreases this rate. Thus, histomorphometric studies show different characteristics for the bone loss that occurs in these two disease states. In particular, alcohol-induced osteopenia results mainly from decreased bone formation rather than increased bone resorption. Human, animal and cell culture studies of the effects of alcohol on bone strongly suggest alcohol has a dose-dependent toxic effect on osteoblast activity. The capacity of bone marrow stromal cells to differentiate into osteoblasts has a critical role in the cellular processes involved in the maintenance of the adult human skeleton by bone remodeling. Chronic alcohol consumption suppresses osteoblastic differentiation of bone marrow cells and promotes adipogenesis. In fracture healing, the effect of alcohol is to suppress synthesis of an ossifiable matrix, possibly due to inhibition of cell proliferation and maldifferentiation of mesenchymal cells in the repair tissue. This results in the deficient bone repair observed in animal studies, characterized by repair tissue of lower stiffness, strength and mineral content. Current knowledge of cellular effects and molecular mechanisms involved in alcohol-induced bone disease is insufficient to develop interventional strategies for its prevention and treatment.

OBJECTIVES

The objectives of this review are 1) to identify the characteristics of alcohol-induced bone loss and deficient bone repair as revealed in human and animal studies, 2) to determine the current understanding of the cellular effects underlying both skeletal abnormalities, and 3) to suggest directions for future studies to resolve current ambiguities regarding the cellular basis of alcohol-induced bone disease.

Daily physical education in the school curriculum in prepubertal girls during 1 year is followed by an increase in bone mineral accrual and bone width--data from the prospective controlled Malmö pediatric osteoporosis prevention study

The aim of this study was to evaluate a general school-based 1-year exercise intervention program in a population-based cohort of girls at Tanner stage I. Fifty-three girls aged 7-9 years were included. The school curriculum-based exercise intervention program included 40 minutes/school day. Fifty healthy age-matched girls assigned to the general school curriculum of 60 minutes physical activity/week served as controls. Bone mineral content (BMC, g) and areal bone mineral density (aBMD, g/cm(2)) were measured with dual X-ray absorptiometry (DXA) of the total body (TB), lumbar spine (L2-L4 vertebrae), third lumbar vertebra (L3), femoral neck (FN), and leg. Volumetric bone mineral density (g/cm(3)) and bone width were calculated at L3 and FN. Total lean body mass and total fat mass were estimated from the TB scan. No differences at baseline were found in age, anthropometrics, or bone parameters when the groups were compared. The annual gain in BMC was 4.7 percentage points higher in the lumbar spine and 9.5 percentage points higher in L3 in cases than in controls (both P < 0.001). The annual gain in aBMD was 2.8 percentage points higher in the lumbar spine and 3.1 percentage points higher in L3 in cases than in controls (both P < 0.001). The annual gain in bone width was 2.9 percentage points higher in L3 in cases than in controls (P < 0.001). A general school-based exercise program in girls aged 7-9 years enhances the accrual of BMC and aBMD and increases bone width.

Impact of recreational physical activity on bone mineral density in middle-aged men

Physical activity is known to exert beneficial effects on general health status of young, adult and elderly populations. Exercise (aside from genetic, hormonal, nutritional and pathological factors) also influences bone mineral density (BMD). Unfortunately, the association between physical exercise and BMD in adult population is controversial. Our aim was to assess relations between recreational physical activity and BMD in middle-aged men. We performed densitometry and hormonal measurements (total testosterone, free testosterone, dehydroepiandrosterone sulfate, estradiol) in a homogenous group of 38 subjects. Among them, we distinguished 22 who had not engaged in any physical activity, and 16 who had recreationally exercised for about 10 years. Both groups did not differ in regard to hormonal status. Similarly, densitometry did not reveal any statistically significant differences in BMD between both groups of men. Upon our observation, we can hypothesize that recreational physical activity does not affect bone mineral density in middle-aged men.

The association between physical activity and forearm bone mineral density in healthy premenopausal women

PURPOSE

To analyze the association between recreational and occupational physical activity and forearm bone mineral density (BMD) in healthy premenopausal women.

METHODS

During 1984-1986, a population-based health survey (HUNT 1) was conducted among women and men aged >19 years in Nord-Trøndelag county in Norway. The second, follow-up survey (HUNT 2) was conducted during 1995-1997. The subjects in this study consist of healthy premenopausal women (n = 1396) < 45 years old in the year of participation of HUNT 2 who had undergone distal and ultradistal radius densitometry in 1995-1997, performed with single-energy x-ray absorptiometry.

RESULTS

Women with the highest scores of estimated combined recreational and occupational physical activity (PA) in 1984 and 1995 had significantly higher BMD in the distal radius (mean BMD 0.487 compared with mean BMD 0.480 among those with a low combined PA score) (p for trend = 0.04). At the ultradistal site of the radius, women with a high combined PA score had mean a BMD = 0.403 compared with women with low PA scores (mean BMD = 0.384) (p for trend = 0.017). After adjusting for age, marital status, smoking, amenorrhea, body mass index (BMI), and daily milk consumption, the associations remained the same or got even stronger.

CONCLUSIONS

The small group of women in the highest category of PA had a significantly higher forearm BMD and the smallest risk of low BMD. Important unanswered questions remain about the optimal relationship between intensity, amount and type of PA, and BMD and later risk of osteoporosis. Further research on BMD as a surrogate measure of structural and architectural bone quality and the sensitivity of different measuring sites for estimation of the effect of PA on bone is warranted.

Relationships between muscle strength and bone mineral density of three body regions in sedentary postmenopausal women

This cross-sectional study was designed to investigate correlations between muscle strength and regional bone mineral density (BMD) in sedentary postmenopausal women. Sixty-two women who ranged in age from 41 to 76 years were investigated. Hip and trunk muscle strength was measured by isokinetic dynamometry. Grip strength of the nondominant hand was measured using a hand-held dynamometer. Bone mineral density of the lumbar spine, femur, and distal radius was measured by dual-energy X-ray absorptiometry. Only the correlation between hip abductor strength and femoral BMD was significant (P = 0.009, r = 0.327). There was no correlation between trunk muscle strength and lumbar vertebral BMD or between grip strength and distal radius BMD. Subjects with osteoporosis (T score < -2.5) or osteopenia T (-2.5 to -1) and normal subjects (T > -1) exhibited similar isokinetic hip and trunk muscle strength. Women with osteoporotic distal radii had significantly lower grip strength than subjects who were osteopenic or normal at this site, but the osteoporotic group was also significantly older. In conclusion, our results indicate that the isokinetic strength of hip abductors weakly correlates with femoral BMD in postmenopausal women with and without osteoporosis. Trunk muscle strength did not correlate with lumbar vertebral BMD in either of these groups. The weaker handgrip we observed in the women with osteoporotic radii may be attributed to older age.

Associations between physical activity and bone mass in black and white South African children at age 9 yr

We investigated differences in physical activity (PA) levels between black and white South African 9-yr-old children and their association with bone mineral content (BMC) and density (BMD) by using dual-energy X-ray absorptiometry. PA was analyzed in terms of a metabolic (METPA; weighted metabolic score of intensity, frequency, and duration) and a mechanical (MECHPA; sum of all ground reaction forces multiplied by duration) component. There were significant ethnic differences in patterns of activity. White children expended a significantly greater energy score (METPA of 21.7 +/- 2.9) than black children (METPA of 9.5 +/- 0.5) (P < 0.001). When children were divided into quartiles according to the amount and intensity of sport played, the most active white children (using METPA scores) had significantly higher whole body BMD and higher hip and spine BMC and BMD than less active children. White children in the highest MECHPA quartile also showed significantly higher whole body, hip, and spine BMC and BMD than those children in the lowest quartile. No association between exercise and bone mass of black children was found. In this population, PA has an osteogenic association with white children, but not black children, which may be explained by the lower levels of PA in the black children. Despite this, black children had significantly greater bone mass at the hip and spine (girls only) (P < 0.001) even after adjustment for body size. The role of exercise in increasing bone mass may become increasingly critical as a protective mechanism against osteoporosis in both ethnic groups, especially because the genetic benefit exhibited by black children to higher bone mass may be weakened with time, as environmental influences become stronger.

Noninvasive estimation of bone mass in ancient vertebrae

Histomorphometry is useful in the assessment of trabecular bone mass (TBM), and thus, in the estimation of the prevalence and intensity of osteopenia in ancient population groups. However, it is a destructive method. It is therefore necessary to explore the accuracy of nondestructive approaches, such as radiography, bone mineral density (BMD) assessed by double-energy X-ray absorptiometry (DEXA), bone density (BD), or optical density (OD) in the diagnosis of osteopenia. We selected 51 vertebrae out of a total sample composed of 333 T12, L1, and L2 vertebrae belonging to adult pre-Hispanic inhabitants from El Hierro. These vertebrae underwent histomorphometrical analysis, a fine-grained film radiography with assessment of trabecular pattern following standard methods, OD, DEXA-assessed BMD, and BD. The presence of biconcave vertebrae and wedge-shaped vertebrae was also assessed by measuring anterior height (a), posterior height (p), and height at the middle point of the vertebral body (m), and further calculating the indices 2m/(a + p) ("spine score") and a/p. Significant correlations were observed between TBM and BMD (r=0.43), TBM and BD (r=0.49), TBM and OD (r=0.52), BMD and OD (r=0.51), and BMD and BD (r=0.36), but not between TBM and the indices 2m/(a + p) and a/p. In the stepwise multiple correlation analysis between TBM and BMD, BD, and OD, OD entered into first place and BD into second place, whereas BMD became displaced; the multiple correlation coefficient was 0.63, with a standard error of 3.78. A BMD greater than 0.60 g/cm2, or a bone density greater than 0.60 g/cm3, excluded osteopenia (TBM <15%) with a specificity greater than 90%, whereas a BMD value less than 0.35 g/cm2, a BD less than 0.35 g/cm3, or optical density >1.6 excluded a normal bone mass (TBM >20%) with a specificity greater than 90%. Based on radiographic criteria on the total sample, we also conclude that the overall prevalence of vertebral fractures in the adult pre-Hispanic population of El Hierro of any age is 7.5%.

Avaliação do estado nutricional de atletas de ginástica olímpica do Rio de Janeiro e São Paulo

Com o objetivo de avaliar o estado nutricional de atletas de ginástica olímpica, do sexo feminino, foram estudadas 46 ginastas, de 11 a 14 anos, pertencentes a clubes e academias das cidades do Rio de Janeiro e São Paulo. O estudo antropométrico envolveu medidas de massa corporal, estatura, dobras cutâneas e perímetros. Observou-se diferença significativa para as dobras cutâneas tricipital, suprailíaca, da coxa e da panturrilha e para o percentual de gordura (p<0,05). Para o estudo dietético foram utilizados recordatório de 24 horas e registro alimentar de três dias. As ginastas apresentaram baixo consumo energético. A percentagem de carboidratos, 50% a 58%, e a ingestão protéica de 1,5 a 1,7 g/kg de peso mostraram-se baixa e adequada, respectivamente, frente ao proposto para atletas. O conteúdo de vitaminas foi satisfatório, com exceção do ácido fólico para as adolescentes cariocas. Os minerais julgados inadequados foram cálcio, magnésio, ferro e zinco. O estado nutricional de ferro não apresentou alterações.

Double-energy X-ray absorptiometry in the diagnosis of osteopenia in ancient skeletal remains

Bone mineral density (BMD) assessed by double-energy X-ray absorptiometry (DEXA) accurately estimates the bone mass in living individuals, and is thus the method usually employed in the diagnosis and follow-up of osteopenia. It is preferred, in clinical settings, to the more invasive and destructive histomorphometrical assessment of trabecular bone mass in undecalcified bone samples. This study was performed in order to examine the value of DEXA-assessed BMD at the proximal end of the right tibia, either alone or in combination with the cortico-medullary index at the midshaft point of the right tibia (CMI), in the diagnosis of osteopenia in a prehistoric sample composed of 95 pre-Hispanic individuals from Gran Canaria. Age at death could be estimated in 34 cases. Diagnosis of osteopenia was performed by histomorphometrical assessment of trabecular bone mass (TBM) in an undecalcified bone section of a small portion of the proximal epiphysis of the right tibia. A high prevalence of osteopenia was found among the population of Gran Canaria. Both TBM and BMD were significantly lower in the older individuals than in younger ones, and BMD was also significantly lower in female individuals. BMD was moderately correlated with TBM (r = +0.51); the correlation was higher if CMI was included (multiple r = +0.615). BMD values lower than 0.7 g/cm2 showed a high specificity (>93%) at excluding normal TBM values. These methods were prospectively applied in a further sample of 21 right tibiae from Gran Canaria, Tenerife, and El Hierro. The results were similar to those obtained in the larger sample. Thus, DEXA-assessed BMD combined with CMI (noninvasive procedures) may be useful in detecting osteopenia in ancient populations.

Intensive exercise may preserve bone mass of the upper limbs in spinal cord injured males but does not retard demineralisation of the lower body

STUDY DESIGN

Cross-sectional study comparing a group of active spinal cord injured (SCI) males carefully matched for age, height, and weight with active able-bodied male controls.

OBJECTIVES

To compare bone mass of the total body, upper and lower limbs, hip, and spine regions in active SCI and able-bodied individuals.

SETTING

Outpatient study undertaken in two centres in New Zealand.

METHODS

Dual energy X-ray absorptiometry (DEXA) scanning was used to determine bone mass. Questionnaires were used to ascertain total time spent in weekly physical activity for each individual. The criterion for entry into the study was regular participation in physical activity of more than 60 min per week, over and above that required for rehabilitation.

RESULTS

Seventeen SCI and their able-bodied controls met our required activity criterion. Bone mineral density (BMD) values of the total body and hip regions were significantly lower in the SCI group than in their controls (P=0.0001). Leg BMD and bone mineral content (BMC) were also significantly lower in the SCI group (P=0.0001). By contrast, lumbar spine BMD and arm BMD and BMC did not differ between the SCI and control groups. Arm BMD and BMC were greater (not significant) than the reference norms (LUNAR database) for both groups.

CONCLUSION

Intensive exercise regimens may contribute to preservation of arm bone mass in SCI males, but does not prevent demineralisation in the lower body.

Muscle cross-sectional area is associated with specific site of bone in prepubertal girls: a quantitative magnetic resonance imaging study

It is well established that forces applied to bone are the result of muscle contraction. However, data regarding the contribution of muscle cross-sectional area (because muscle area is proportional to muscle strength) to cortical bone area before puberty are controversial. We tested the hypothesis that muscle cross-sectional area is associated with total cortical bone area, and whether there is a region-specific relationship between these parameters in prepubertal and early pubertal girls. Seventeen healthy (9-11 years, Tanner stages I-II) white girls participated in the study. We measured bone loading characteristics (maximal ground reaction forces; GRFs) for a drop jump (50 cm) and side-to-side jump (over a 20-cm-high fence) on a multicomponent force platform. Muscle cross-sectional area and bone cortical area (square centimeters) of the proximal third of the left and right lower leg was measured with a 1.5 T magnetic resonance system using a quadrature head coil. The sequence was T(1) weighted, with spin-echo in transverse (tibial) planes and 3 mm sections with no gap (ten slices). The tibial cross-sectional areas were subdivided into three anatomical sectors (SI-SIII), with the tibial centroid as origin. SI extended from the medial tibial border to the most anterior edge, SII extended from the anterior edge laterally to the interosseous border, and SIII extended posteromedially from the interosseous border to the medial tibial border. The nonparametric bone and muscle volume correlations demonstrated that the total muscle cross-sectional area correlated significantly with the total cortical area in both legs (left leg: r(s) = 0.59, p = 0.020; right leg: r(s) = 0.57, p = 0.016). Significant correlations were also found between left and right muscle area and cortical area in SII (r(s) = 0.68, p = 0.003, 0.67, and 0.003, respectively). There was no significant association between the muscle area and cortical area in SI or SIII. In addition, there was a significant correlation between GRFs of the side-to-side jump and total cortical area (left leg: r = 0.75, p < 0.01; right leg: r = 0.78, p < 0.01). Thus, we found that muscle area was most highly associated with bone cortical area in SII, the anterolateral sector of the tibia, which emphasizes the specific interplay of muscles and bone in the lower limb. This relationship was present in a regional, site-specific fashion.

Effect of impact load and active load on bone metabolism and body composition of adolescent athletes

PURPOSE

It is unclear whether adolescents involved in nonweight-bearing activities experience a delay in bone growth acquisition and sexual maturation. The purpose of this study was to compare bone mineral density (BMD), body composition, hormonal profile, and bone biochemical markers of adolescent athletes active in sports involved in impact load sports with those participating in active load sports.

METHODS

Forty-five male Caucasian athletes aged 12--18 yr were divided into two groups according to type of skeleton loading, impact (N = 18), or active (N = 27). Twenty-four male Caucasian adolescents (12--18 yr) served as controls and only performed the activities included in their physical education classes. All subjects were assessed for bone mass, body composition, and bone age by dual x-ray absorptiometry (DXA). Serum calcium (Ca), phosphorus (P), bone-specific alkaline phosphatase (BAP), total testosterone, FSH, LH, urinary calcium to creatinine ratio (Ca/Cr), and urinary deoxypyridinoline crosslinks to creatinine ratio (DPD/Cr) were measured.

RESULTS

The impact load group presented the highest BMD among the three groups for all studied sites. Lean mass and absolute weight were correlated with all of the bone mass measurements. BAP levels were significantly higher and testosterone levels significantly lower in the active load group compared with the impact group.

CONCLUSION

High-impact load exercises have a beneficial effect on bone mass in male adolescents. There is also a positive correlation of weight and body composition with BMD. However, further longitudinal studies are necessary to determine whether there is a delay in bone growth acquisition among adolescents involved in a nonweight-bearing exercise regimen and its association with sex hormones.

Dose-response of physical activity and low back pain, osteoarthritis, and osteoporosis

PURPOSE

The purpose of this study was to examine the evidence for causal relationships between physical activity (PA) and low back pain (LBP), osteoarthritis (OA), and osteoporosis (OP), and for dose-response relations involved.

METHODS

Computer database searches and personal retrieval systems were used to locate relevant literature.

RESULTS

PA can be effective in preventing LBP (Category A) but prolonged, heavy loading can lead to LBP (Category C). Specific exercises have not been found effective in treatment of acute LBP (Category A), but PA can be effective in chronic LBP (Category B), especially for diminishing the effects of deconditioning. No evidence indicates that PA directly prevents OA. Large amounts of intensive PA involving high impacts or torsional loadings or causing injuries increases risk of OA (Category C). Light or moderate PA does not increase the risk of OA (Category C). PA can be effective in the treatment and rehabilitation of OA (Category B). High-intensity loading is osteogenic and possibly useful in prevention of OP (Category A) at the loaded site, but low to moderate loading is not osteogenic (Category D). Static efforts and slow movements are ineffective or less effective than fast application of force (Category B). The types of PA to attain the effects mentioned above are known except in the case of prevention of LBP, but dose-response relationships are poorly known; at best, semiquantitatively on the basis of just a few studies.

CONCLUSION

Given the shown primary and/or secondary preventative effectiveness of PA regarding LBP, OA, and OP, research to elucidate the inadequately known dose-response relations should be given high priority.

Distúrbios nutricionais em atletas femininas e suas inter-relações

Pesquisas indicam que é elevada a prevalência de distúrbios alimentares em atletas femininas jovens envolvidas em esportes que preconizam a magreza e o baixo peso corporal, tais como ginástica olímpica e corridas de longa distância. A fim de compreender a etiologia destes problemas, esta revisão apresenta os principais distúrbios nutricionais encontrados em atletas femininas, incluindo definições, critérios para diagnóstico, fatores de risco, presença de desordens inter-relacionadas - anemia, irregularidades menstruais e desmineralização óssea e suas conseqüências sobre a saúde e rendimento atlético. É fundamental ressaltar a importância da nutrição no desempenho físico. A presença de um baixo peso corporal e um consumo energético severamente restrito é o principal fator de risco para o desenvolvimento de tais distúrbios. Como as atletas e seus treinadores não apresentam adequados conhecimentos sobre nutrição, é necessária uma orientação nutricional individualizada, de forma a evitar o desenvolvimento destas alterações.

Effect of physical activity during teenage years, based on type of sport and duration of exercise, on bone mineral density of young, premenopausal Japanese women

In this cross-sectional study, 91 healthy premenopausal women aged 20-39 years were investigated to determine the effect of physical activities during their teenage years on their current bone mineral densities (BMD). We measured whole-body BMD (WBMD), lumbar BMD (LBMD), and radial BMD (RBMD) with dual energy X-ray absorptiometry (DXA). Using a questionnaire, we asked the women about their physical activities during junior and senior high school and at present. We also asked about their current nutritional status and past and current milk intake. After adjusting for age, body mass index (BMI), current total calorie and calcium (Ca) intake, and milk intake when they were teenagers and at present, we determined that subjects who exercised during extracurricular activities at each of the three periods (during junior and senior high school and at present) had significantly higher WBMD and LBMD (P <0.01, respectively) than did those who did not exercise at those times. Subjects who played high-impact sports at each period had significantly higher WBMD and LBMD than did subjects who played low-impact sports (P <0.05, respectively). Subjects who had exercised regularly from their teenage years to the present had significantly higher BMD at all sites than BMD in other subjects after adjusting for the potential confounders described above (P <0.05, respectively). Our data suggest that continuous exercise beginning in junior high school, especially high-impact sports, may be associated with greater current bone mass. It is important to incorporate adequate exercise beginning in the teenage years to lower one's future risk for osteoporosis.

Osteopenia assessed by body composition analysis is related to malnutrition in alcoholic patients

Osteopenia is frequent among alcoholics. Its pathogenesis seems to be multifactorial, including ethanol intake, hormonal changes, liver cirrhosis, and malnutrition. Our objective is to determine the relative role of malnutrition on bone loss. One hundred and eighty-one male alcoholic patients, drinkers of more than 80 g ethanol/day, were included, recording data on the intensity of alcoholism, liver cirrhosis, nutritional assessment based on feeding habits, body mass index (BMI), midarm anthropometrics, subjective nutritional assessment, lean and fat mass by dual energy X-ray absorptiometry (DEXA), serum proteins and insulin growth factor Type I (IGF-I), calcitropic hormones, parathyroid hormone (PTH), osteocalcin 25OHD3, and bone mass assessed by DEXA, which was also performed in 43 healthy controls. Alcoholics showed decreased serum osteocalcin, PTH, 25OHD3, IGF-I, and bone mass. Alcoholics were frequently malnourished with decreased BMI, lean, and fat mass. The loss of bone mass was not related to the alteration of calcitropic hormones, to the intensity of alcoholism, or to the existence of liver cirrhosis, but to malnutrition. For a similar BMI, bone loss was more intense in alcoholics than in controls, especially in those with irregular feeding habits. Although cross-sectional ones, our data suggest that alcoholic osteopenia may be interpreted as a form of nutritional osteoporosis, notwithstanding the influence of other factors.

Body composition predicts bone mineral density and balance in premenopausal women

Low bone mineral density (BMD) and poor stability both contribute to increased risk of fractures associated with a fall. Our aim in this cross-sectional study was to determine the anthropometric and/or performance variables that best predicted BMD and stability in women. BMD, body composition, muscle strength, muscle power, and dynamic stability were evaluated in 61 women (age 40 +/- 4 years; % body fat 27% +/- 5%). In correlation analyses, BMD at all sites was significantly related to height, lean mass, strength, and leg power (r2 = 0.25-0.49). Significant inverse relationships were found between all independent variables and dynamic stability (r2 = 0.23-0.52). In stepwise regression, lean mass independently predicted BMD at the femoral neck (R2 = 0.20), total hip (R2 = 0.24), and whole body (R2 = 0.17), whereas hip abductor torque predicted 23% of the variance in trochanter BMD and added 6% to the variance in total hip BMD. Leg power was the only predictor of spine BMD (R2 = 0.14). Fat and lean mass both independently predicted poor performance on postural stability, with fat mass contributing 31% of the total variance (R2 = 0.38). In conclusion, we found lean mass to be a robust predictor of BMD in premenopausal women. Furthermore, both hip abductor torque and leg power independently predicted BMD at clinically relevant fracture sites (hip and spine). The finding that higher fat mass contributes to the majority of the variance in poor stability indicates that greater fat mass may compromise stability and, thus, increase fall risk in heavier individuals.

Physical activity, diet and skeletal health

Diet and physical exercise concur in the determination of skeletal mass at the end of adolescence and in the conservation of it during adult life. The functional demand imposed on bone is a major determinant of its structural characteristics. Stress applied to a skeletal segment affects the geometry of the bone, the microarchitecture and the composition of the matrix. The stimulatory effect occurs when the skeleton is subjected to strains exceeding habitual skeletal loads, and the intensity of load is more important than the duration of the stimulus. Physical activity leads to greater bone density in children and adolescents and, to a minor extent, in adults. Weight bearing activities, such as walking, have a greater effect than non weight bearing activities, such as cycling and swimming. Reduction of loads as in bed resting or in space flights leads to bone loss. Intense training may cause damage, promptly repaired, as in stress fractures observed in army recruits. Female athletes may experience oligo-amenorrhea, though they still have a positive bone balance. There is an important interaction between the mechanical demands and the availability of nutrients to manufacture bone tissue. The increase in bone density in post-menopausal women is positively related to calcium intake when calcium supplementation is accompanied by exercise. When mechanical demands are low, such as during immobilisation, the intestinal calcium absorption is reduced. Calcium intake should also be analysed in the light of other dietary factors affecting the balance between absorption and excretion, and in combination with a number of other minerals, trace elements and bioactive substances with an impact on bone metabolism.

Lifetime physical activity is associated with bone mineral density in premenopausal women

Osteoporosis causes premature disability among millions of elderly people in the United States, particularly women. Exercise helps to maintain bone mass, yet it remains unclear what type of physical activity during what age periods is most beneficial for bone mass and density. This cross-sectional study investigated the relationship between different measures of lifetime physical activity and bone mineral density (BMD) in 25 premenopausal women (mean age 41 years, range 28-50 years). BMD of the total, entire axial, and entire peripheral skeleton were measured by dual energy x-ray absorptiometry (DXA). Lifetime history of physical activity was obtained by a structured interview, and estimates of lifetime weight-bearing exercise, total exercise, total weight-bearing physical activity (including occupational and household activities), and perceived physical activity were computed. Adjustments were made for current body weight and height and lifetime milk consumption. Lifetime weight-bearing exercise was significantly correlated with total and peripheral BMD (total BMD: r = 0.54; peripheral BMD: r = 0.54, all p < 0.05). Total weight-bearing physical activity, including occupational and household activity, was associated with total BMD (r = 0.51, p < 0.05). Physical activity during early age periods was more strongly associated with BMD at all sites than was physical activity in the past 2 years. Our findings suggest that lifetime weight-bearing exercise is more strongly related to BMD of the total and peripheral skeleton than is nonweight-bearing exercise. The inclusion of nonweight-bearing activity resulted in a weakening of the association. Weight-bearing household and occupational activity appeared to be related to BMD. Our results support recommendations to increase physical activity throughout life, particularly during early ages, as a means of osteoporosis prevention.

Dual X-Ray absorptiometry in pediatric studies: changing scan modes alters bone and body composition measurements

The use of dual X-ray absorptiometry (DXA) for measurement of bone mineral and body composition in pediatric subjects faces a major technical issue: body size dictates choice of scan mode. However, different scan modes change results in the same subject, thus affecting the accuracy of bone/body composition measurements and especially the capacity to measure changes owing to either growth or intervention. To evaluate the effect of scan mode selections on measurements of bone mineral and body composition, 13 children with weights at the cutoff point between the pediatric large and adult medium scan modes of Lunar DPX or DPXL (Lunar, Madison, WI) with software 3.6 g (35.3 +/- 0.9 kg or 77.7 +/- 2.0 lb) were scanned by both modes. Adult medium mode gave significantly higher results than pediatric large mode for total body fat mass (11.1%), fat% (10.5%), bone mineral content (8.1%), and bone area (1.3%) (p < 0.02). The differences between pediatric large and adult medium modes in fat measurements increased with increasing body mass index ([BMI], kg/m(2)), body surface area ([BSA], m(2)), and trunk size (mm), whereas the differences in bone mineral measurement tended to be greater only with increasing BMI and BSA. None of the differences were correlated to body weight. This study suggests that scan mode selections based on trunk size, BMI, or BSA instead of body weight may improve continuity of bone and body composition measurements by the DXA technique in pediatric subjects.