Strength training effects on bone mineral content and density in premenopausal women.

PURPOSE: Mechanical loading, such as that seen with physical activity, is thought to be the primary factor influencing bone strength. Previous randomized studies that assessed the effect of strength training on bone in premenopausal women report inconsistent results. The analysis herein examines the effect of a strength training program following published guidelines (US Department of Health and Human Services) on bone mineral content (BMC) and areal bone mineral content (aBMD) in the proximal femur and lumbar spine in premenopausal women. METHODS: One hundred and forty-eight overweight, sedentary, premenopausal women aged 25-44 were randomized to progressive strength training (ST, n = 72) or standard care (CO, n = 76) for 2 yr. Measurements occurred at baseline, 1 yr, and 2 yr. Proximal femur and lumbar spine BMC and aBMD were measured by dual energy x-ray absorptiometry. Intention-to-treat analyses were completed, and repeated-measures ANCOVA adjusted for baseline height and weight was used to assess the effect of strength training on bone. RESULTS: aBMD showed little change and did not differ between groups at any site. Femoral neck BMC showed a significant difference in the slopes between ST and CO (P = 0.04) with no change in the ST group and a 1.5% decrease in the CO. There were no significant between-group differences at any other measurement site. CONCLUSION: Strength training had no effect on aBMD after 2 yr of strength training. Femoral neck BMC decreased in CO and had no change in ST. Because there was no change in aBMD, strength training may have influenced bone size. Research to better understand changes in bone dimensions and geometry with strength training in premenopausal women is warranted.

Alterations in proximal femur geometry in children treated with glucocorticoids for Crohn disease or nephrotic syndrome: impact of the underlying disease.

UNLABELLED: Proximal femur geometry was assessed in children and young adults treated with chronic GCs for CD or SSNS. Subperiosteal width and section modulus were significantly lower in CD and greater in SSNS compared with controls, highlighting the importance of the underlying disease, persistent inflammation, and alterations in lean mass. INTRODUCTION: The impact of glucocorticoid (GC) therapy on bone structure during growth is unknown. Our objective was to characterize proximal femur geometry in children and young adults with Crohn disease (CD) or steroid-sensitive nephrotic syndrome (SSNS) compared with controls and to evaluate the influence of lean mass and GC therapy on bone parameters. MATERIALS AND METHODS: DXA scans of the hip and whole body were obtained in 88 subjects with CD, 65 subjects with SSNS, and 128 controls (4-26 years of age). Hip structural analysis parameters (subperiosteal width, cross-sectional area [CSA], and section modulus in the narrow neck [NN], intertrochanteric region [IT], and femoral shaft [FS]), areal BMD, and whole body lean mass were expressed as Z scores compared with controls. Multivariable linear regression was used to adjust outcomes for group differences in age, sex, race, and height. RESULTS: Mean lean mass Z scores were lower in CD (-0.63, p < 0.001) and greater in SSNS (0.36, p = 0.03) compared with controls. Hip areal BMD Z scores were lower in CD (-0.73, p < 0.001) but not SSNS (-0.02, p > 0.2) compared with controls. In CD, Z scores for subperiosteal width (NN: -1.66, p < 0.001; FS: -0.86, p < 0.001) and section modulus (NN: -0.60, p = 0.003; FS: -0.36, p = 0.03) were significantly lower than controls. In contrast, in SSNS, Z scores were greater for IT subperiosteal width (0.39, p = 0.02), FS CSA (0.47, p = 0.005), and FS section modulus (0.49, p = 0.004). Alterations in section modulus in CD and SSNS were eliminated after adjustment for lean mass. Cumulative GC dose was inversely associated with FS subperiosteal width and section modulus only in CD. CONCLUSIONS: These data show that the effects of GC on proximal femur geometry during growth are influenced by the underlying disease, persistent inflammation, and alterations in lean mass. These data also provide insight into the structural basis of hip fragility in CD.

Bone strength estimates relative to vertical ground reaction force discriminates women runners with stress fracture history.

PURPOSE: To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture. METHODS: We recruited 32 competitive distance runners aged 18-35, with (SFX, n=16) or without (NSFX, n=16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm3), total (ToA) and cortical (CtA) bone areas (mm2), and estimated compressive bone strength (bone strength index; BSI, mg/mm4) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm3 and strength strain index; SSIp, mm3) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm2/N∗kg-1) at all cortical sites. RESULTS: SSIp and Zp were 9-11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11-17% lower bone strength relative to mean pkZ GRFs (p<0.05). CONCLUSION: These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.

Proximal femur bone geometry is appropriately adapted to lean mass in overweight children and adolescents.

It is unclear if the bones of overweight children are appropriately adapted to increased loads. The objective of this study was to compare bone geometry in 40 overweight (body mass index [BMI] > 85th percentile) and 94 healthy weight (BMI < or = 85th percentile) subjects, ages 4-20 years. Dual energy X-ray absorptiometry (Hologic QDR 2000) scans were analyzed at the femoral shaft (FS) and narrow neck (NN) by the Hip Structure Analysis program. Subperiosteal width, cortical thickness and indices of bone axial and bending strength (bone cross-sectional area [CSA] and section modulus [Z]) were measured from bone mass profiles. Multivariate regression models were used to compare overweight and healthy weight subjects. Z was 11 (95% CI 5, 19) and 13 (7, 20) percent higher at the FS and NN, respectively, in overweight subjects (P < 0.001), adjusted for height, maturation and gender. At the NN, higher Z was due to greater subperiosteal width [4% (2, 7)] and bone CSA [10% (5, 16]) and at the FS, to higher bone CSA [10% (5, 16)] and thicker cortices [9% (3, 15)]. When lean mass was added to the models, bone variables did not differ between overweight and healthy weight subjects (P > 0.22), with the exception of NN subperiosteal width [3% (0, 6), P = 0.04]. Fat mass did not contribute significantly to any model. In summary, proximal femur bone geometric strength in overweight children was appropriately adapted to lean mass and height but greater weight in the form of fat mass did not have an independent effect on bone bending strength. These geometric adaptations are consistent with the mechanostat hypothesis that bone strength adapts primarily to muscle forces, not to static loads represented by body weight.

Maturity- and sex-related changes in tibial bone geometry, strength and bone-muscle strength indices during growth: a 20-month pQCT study.

During growth, bone strength is conferred through subtle adaptations in bone mass and geometry in response to muscle forces. Few studies have examined the changes in bone geometry, strength and the bone-muscle strength relationship across maturity in boys and girls. Our aims were to describe (i) 20-month changes in bone geometry and strength at the tibial midshaft across three maturity groups of boys and girls, (ii) differences in these adaptations between sexes at the same approximate level of maturity and (iii) the bone-muscle strength relationship across maturity groups of boys and girls and between sexes. We used peripheral quantitative computed tomography (pQCT, Stratec XCT-2000) to measure change in total bone cross-sectional area (ToA, mm(2)), cortical area (CoA, mm(2)), average cortical thickness (C.Th., mm), section modulus (mm(3)) and muscle cross-sectional area (mm(2)) at the tibial midshaft (50% site) in 128 EARLY-, PERI- and POST-pubertal girls (n = 69, 11.9 +/- 0.6 years) and boys (n = 59, 12.0 +/- 0.6 years) across 20 months. We also calculated two bone-muscle strength indices (BMSI) for compression (CoA/MCSA) and bending [strength index/MCSA; where strength index = Z / (tibial length / 2)]. EARLY boys and girls had smaller ToA at baseline than same sex PERI or POST participants. There were no sex differences in ToA or CoA at baseline; however, boys increased both parameters significantly more than girls in every maturity group (8.5-11.1%, P < 0.01). These changes in bone geometry conferred greater gains in bone strength for boys compared with girls in each maturity group (13.8-15.6%, P < 0.01). Baseline BMSIs did not differ between sexes for EARLY and PERI groups, whereas BMSIs were significantly higher for POST boys compared with POST girls (P < 0.05). BMSIs decreased for EARLY and PERI girls (-7.4-(-1.1%)) whereas the ratios remained stable for EARLY and PERI boys (-0.6-2.5%). This sex difference in BMSI change was due to a relatively greater increase in CoA among EARLY and PERI boys compared with same-maturity girls. BMSIs remained stable in POST girls and decreased in POST boys due to relatively greater gains in MCSA. This study provides novel longitudinal descriptions of the maturity- and sex-specific changes in bone geometry, strength and bone-muscle strength indices.

Bone strength is preserved following bariatric surgery.

BACKGROUND: There is an increasing concern that bariatric surgery results in excessive bone loss as demonstrated by studies that use areal bone mineral density (aBMD) outcomes by dual energy X-ray absorptiometry (DXA). Thus, we explored the effect of bariatric surgery on bone mechanical strength. METHODS: Bone strength and body composition outcomes were measured in 21 adults (age 45.3 years; BMI 45.7 kg/m(2)) at baseline (pre-surgery) and 3, 6, and 12 months post-surgery. Bone geometry, density and strength were assessed by peripheral quantitative computed tomography (pQCT) at the distal (4 %) sites of the radius and tibia and at the midshaft sites of the tibia (66 %) and radius (50 %). Participants were divided into tertiles (high, medium, and low) of percentage weight loss at 6 months post-surgery. RESULTS: Participants in all three tertiles lost significant body weight by 6 months post-surgery (mean loss -5 to -30 %, all p < 0.05). At 6 months, all tertiles lost significant fat mass (-9 to -51 %, all p < 0.05), but only the high tertile lost significant fat-free mass (-8 %, p < 0.05). Despite a slight increase in tibia bone strength (SSIp) at 3 months (+1.1 %, p < 0.05), estimates of bone strength at the radius and tibia sites did not change at later post-surgical time points regardless of weight loss. CONCLUSIONS: Contrary to DXA-based aBMD outcomes in the current literature, these results suggest that bone strength was preserved up to 12 months following bariatric surgery. Future longer-term studies exploring bone strength and geometry are needed to confirm these findings.

Bone mass and structure are enhanced following a 2-year randomized controlled trial of exercise in prepubertal boys.

Exercise during growth has a positive influence on bone mineral accrual, yet little is known about how bone geometry and strength adapt to loading during growth. Our primary objective was to compare changes in proximal femur bone geometry and strength between 31 prepubertal (Tanner Stage 1) boys who participated in a school-based, high-impact circuit intervention (12 min, three times a week) for 20 months and 33 maturity-matched controls. Our secondary objective was to compare changes in total body (TB), proximal femur (PF), and lumbar spine (LS) bone mineral content (BMC) and bone area (BA) in these groups. We assessed geometric variables and bone strength at the narrow neck (NN), intertrochanteric (TR) region, and femoral shaft regions by applying the Hip Structure Analysis program to proximal femur dual energy X-ray absorptiometry scans (DXA, Hologic QDR 4500). Further, we assessed total body, lumbar spine, and proximal femur BMC and BA by DXA and derived total body lean mass and fat mass from total body scans. Intervention (10.2 +/- 0.5 years) and control boys (10.1 +/- 0.5 years) had similar baseline height (140.8 vs. 141.3 cm) and weight (36.9 vs. 35.4 kg), and average 20-month physical activity scores (Physical Activity Questionnaire for Children, PAQ-C) and calcium intakes (861 vs. 852 mg/day, food frequency questionnaire). Twenty-month height and weight changes were not significantly different between groups; lean mass changed more (P < 0.05) in intervention boys (22.8%) than control boys (18.6%). At the NN region, intervention boys had greater bone expansion on both the periosteal (+2.6%, P = 0.1) and endosteal (+2.7%, P = 0.2) surfaces, resulting in significantly greater changes in section modulus (bone bending strength) (+7.5%, P = 0.02, ANCOVA, adjusting for height change, final Tanner Stage, and baseline bone values). Changes at the intertrochanteric and femoral shaft regions were not significantly different between groups. Femoral neck (FN) BMC changes were significantly greater in intervention boys (+4.3%, P < 0.01); changes in BA and BMC for other regions were not significantly different between groups. In summary, a school-based, high-impact exercise intervention implemented three times a week for 12 min is an effective strategy for site-specific gains in bone strength at the narrow neck region of the proximal femur.

Femoral bone structural geometry adapts to mechanical loading and is influenced by sex steroids: the Penn State Young Women's Health Study.

We used 10 years of longitudinal data from Penn State Young Women's Health Study to explore predictors of adult bone structural geometry and strength. One hundred twelve participants were enrolled in the study at age 12. We report findings on the 76 participants who remained in the study for 10 years. Measurements were recorded biannually for the first 4 years and annually thereafter. Proximal femur DXA scans (Hologic QDR 2000) were taken from 17-22 years and analyzed using a hip structure analysis program to assess areal bone mineral density (BMD, g/cm2), subperiosteal width, cortical thickness, bone cross-sectional area (CSA), and section modulus (Z) at the narrow neck and femoral shaft. Total body lean mass (g) was measured with DXA total body scans. Nutrition, anthropometry, and sex steroids [testosterone (T) and estradiol (E2)] were measured from ages 12-22 years. Multiple regression models were used to assess predictors of change in bone variables (17-22 years) and absolute bone values (average of age 21 and 22 years, n = 79). Neck Z (+3.1%) and width (+1.3%), but not BMD (-0.8%), increased significantly from age 17 to 22 years. At the shaft, all variables increased (+1.0-4.0%, P < 0.01). After controlling for baseline (age 17) height, weight and bone measurement, weight change (neck) or lean mass (shaft), and age of menarche were the primary predictors of change in bone strength. After controlling for height and weight, only lean mass predicted absolute young adult Z at both the neck (r2 = 0.48, P < 0.01) and the shaft (r2 = 0.67, P < 0.01). When lean mass was removed from the model, sports exercise score replaced lean mass as a predictor of Z at both neck (r2 = 0.40, P < 0.01) and shaft (r2 = 0.60, P < 0.01) sites. For neck and shaft cortical thickness and BMD, both estradiol and sports score/lean mass were positive predictors (r2 = 0.15-0.40, P < 0.01). For neck bone width, testosterone levels (negative) and lean mass (positive) were significant (r2 = 0.48). Results were similar for each geometric variable at the shaft site. These data suggest that bone adapts its bending strength primarily to mechanical loading (represented by lean mass and sports exercise score) and that sex steroids are associated with bone geometric structure.

Application of magnetic resonance imaging to evaluation of femoral neck structure in growing girls.

Conventional density measures by dual-energy X-ray absorptiometry (DXA) are confounded by increases in bone size and do not assess bone geometry. We assessed precision of magnetic resonance imaging (MRI) and used MRI, DXA, and hip structure analysis (HSA) to assess 7-mo changes in bone structure at the femoral neck in 18 prepubertal girls. At baseline, girls were 10.4 (0.5) yr, 144.0 (8.2) cm, and 35.2 (7.0) kg, on average. Total bone and cortical cross-sectional area (ToA and CoA) were calculated from high-resolution T1-weighted MRI oblique axial images of the femoral neck. We used proximal femur DXA scans (Hologic QDR-4500) and the HSA program to estimate bone cross-sectional area (CSA), and calculate section modulus. MRI precision was determined by scanning 10 volunteers (13-46 yr old) three times with and without repositioning. Precision (CVrms) was 2% for ToA and 7% for CoA. Significant correlations were observed between FN area and MRI-derived ToA (r = 0.57, p = 0.013) and CoA (r = 0.47, p = 0.050). There were significant positive changes over 7 mo by both methods. In conclusion, MRI provides useful information on femoral neck bone area in children. The reproducibility of cortical dimensions at the femoral neck needs improvement through technical modifications and appropriate analysis software.

Examining the link between bariatric surgery, bone loss, and osteoporosis: a review of bone density studies.

As the popularity of bariatric surgery to treat morbid obesity has risen, so has a concern of increased skeletal fragility secondary to accelerated bone loss following bariatric procedures. We reviewed cross-sectional and prospective literature reporting bone density outcomes following bariatric surgical treatment for morbid obesity. Prospective research provides evidence of hip and lumbar spine areal bone mineral density (aBMD) reductions primarily in women despite calcium and vitamin D supplementation. Femoral neck aBMD declines of 9-11% and lumbar spine aBMD reductions up to 8% were observed at the first post-operative year following malabsorptive procedures. Mean T- and Z-scores up to 25 years following surgery remained within normal and healthy ranges. Of those studies reporting development of osteoporosis following gastric bypass, one woman became osteoporotic after 1 year. Despite observed bone loss in the hip region post-surgery, data do not conclusively support increased incidence of osteoporosis or increased fracture risk in post-bariatric patients. However, given the limitations of dual energy X-ray absorptiometry technology in this population and the relative lack of long-term prospective studies that include control populations, further research is needed to provide conclusive evidence regarding fracture outcomes in this population.

Confounders in the association between exercise and femur bone in postmenopausal women.

INTRODUCTION: Abundant animal and human evidence demonstrates that loading stimuli generate positive adaptive changes in bone, but effects of activity on bone mineral density (BMD) are often modest and frequently equivocal. HYPOTHESIS: Physical activity effects on the femur would be better reflected in measurements of geometry than BMD. STUDY DESIGN: Cross-sectional cohort study. METHODS: We used data from 6032 women of mixed ethnicity aged 50-79 yr who had dual-energy x-ray absorptiometry (DXA) scans of the total body and hip from the Women's Health Initiative observational study. Subjects were distributed in three ways: self-report categories included 1) tertiles of MET and 2) reported minutes per week walking for exercise. A third, more objective, category was based on tertile of lean body mass fraction (LMF) from DXA scans. Femur outcomes included conventional femoral neck and total hip BMD, bone mineral content and region area, and geometry measurements using the Hip Structure Analysis software. Outcomes were compared between activity groups using models adjusted for common confounders. RESULTS: Adjusted bone measurements showed similar activity effects with all three grouping variables, but these were greater and more significant when evaluated by LMF tertile. Women in the highest LMF tertile had the widest femurs. Differences in section modulus between highest and lowest tertile of LMF were 50%-80% greater than the association with bone mineral content and two to three times that on BMD. CONCLUSIONS: More active women in the Women's Health Initiative observational study had geometrically stronger femurs, although effects are underestimated, not apparent, or sometimes negative when using BMD as an outcome. CLINICAL RELEVANCE: Exercise improves the strength of the femur largely by adding bone to the outer cortical surface; this improves resistance to bending, but because of the way DXA measurements are made, this may paradoxically reduce BMD.

Bone strength measured by peripheral quantitative computed tomography and the risk of nonvertebral fractures: the osteoporotic fractures in men (MrOS) study.

Many fractures occur in individuals without osteoporosis defined by areal bone mineral density (aBMD). Inclusion of other aspects of skeletal strength may be useful in identifying at-risk subjects. We used surrogate measures of bone strength at the radius and tibia measured by peripheral quantitative computed tomography (pQCT) to evaluate their relationships with nonvertebral fracture risk. Femoral neck (FN) aBMD, measured by dual-energy X-ray absorptiometry (DXA), also was included. The study population consisted of 1143 white men aged 69+ years with pQCT measures at the radius and tibia from the Minneapolis and Pittsburgh centers of the Osteoporotic Fractures in Men (MrOS) study. Principal-components analysis and Cox proportional-hazards modeling were used to identify 21 of 58 pQCT variables with a major contribution to nonvertebral incident fractures. After a mean 2.9 years of follow-up, 39 fractures occurred. Men without incident fractures had significantly greater bone mineral content, cross-sectional area, and indices of bone strength than those with fractures by pQCT. Every SD decrease in the 18 of 21 pQCT parameters was significantly associated with increased fracture risk (hazard ration ranged from 1.4 to 2.2) independent of age, study site, body mass index (BMI), and FN aBMD. Using area under the receiver operation characteristics curve (AUC), the combination of FN aBMD and three radius strength parameters individually increased fracture prediction over FN aBMD alone (AUC increased from 0.73 to 0.80). Peripheral bone strength measures are associated with fracture risk and may improve our ability to identify older men at high risk of fracture.

Bone mass and strength in older men with type 2 diabetes: the Osteoporotic Fractures in Men Study.

The effects of type 2 diabetes mellitus (T2DM) on bone volumetric density, bone geometry, and estimates of bone strength are not well established. We used peripheral quantitative computed tomography (pQCT) to compare tibial and radial bone volumetric density (vBMD, mg/cm(3)), total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area and estimates of bone compressive and bending strength in a subset (n = 1171) of men (> or =65 years of age) who participated in the multisite Osteoporotic Fractures in Men (MrOS) study. Analysis of covariance-adjusted bone data for clinic site, age, and limb length (model 1) and further adjusted for body weight (model 2) were used to compare data between participants with (n = 190) and without (n = 981) T2DM. At both the distal tibia and radius, patients with T2DM had greater bone vBMD (+2% to +4%, model 1, p < .05) and a smaller bone area (ToA -1% to -4%, model 2, p < .05). The higher vBMD compensated for lower bone area, resulting in no differences in estimated compressive bone strength at the distal trabecular bone regions. At the mostly cortical bone midshaft sites of the radius and tibia, men with T2DM had lower ToA (-1% to -3%, p < .05), resulting in lower bone bending strength at both sites after adjusting for body weight (-2% to -5%, p < .05) despite the lack of difference in cortical vBMD at these sites. These data demonstrate that older men with T2DM have bone strength that is low relative to body weight at the cortical-rich midshaft of the radius despite no difference in cortical vBMD.

Muscle power and physical activity are associated with bone strength in older men: The osteoporotic fractures in men study.

The purpose of these analyses was to explore whether physical activity score, leg power or grip strength were associated with tibia and radius estimates of bone strength, cortical density, or total bone area. Peripheral quantitative computed tomography (pQCT) was used to compare tibial and radial bone volumetric density (vBMD, mg/cm(3)), total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area, and estimates of bone compressive strength (bone strength index, BSI) and bending strength (polar strength strain index, SSIp) in a subset (n=1171) of men (> or = 65 years) who participated in the multi-site Osteoporotic Fractures in Men (MrOS) study. Physical activity was assessed by questionnaire (PASE), leg power by Nottingham Power Rig, and grip strength by a hand-held Dynamometer. Participants were categorized into quartiles of PASE, grip strength or leg power. The model was adjusted for age, race, clinic, weight, and limb length. In the tibia, BSI (+7%) and SSIp (+4%) were highest in the most active physically quartile compared to the least active (p<0.05). At the 4% site of the tibia, men with the greatest leg power had both greater ToA (+5%, p<0.001) and BSI (+5.3%, p=0.086) compared to men with the least leg power. At the 66% site of the tibia, the men with the highest leg power, compared to the men with the lowest leg power, had greater ToA (+3%, p=0.045) SSIp (+5%, p=0.008). Similar results were found at both the distal and midshaft of the radius. The findings of this study suggest the importance of maintaining levels of physical activity and muscle strength in older men to prevent bone fragility.

Correlates of trabecular and cortical volumetric bone mineral density of the radius and tibia in older men: the Osteoporotic Fractures in Men Study.

Quantitative computed tomography (QCT) can estimate volumetric bone mineral density (vBMD) and distinguish trabecular from cortical bone. Few comprehensive studies have examined correlates of vBMD in older men. This study evaluated the impact of demographic, anthropometric, lifestyle, and medical factors on vBMD in 1172 men aged 69 to 97 years and enrolled in the Osteoporotic Fractures in Men Study (MrOS). Peripheral quantitative computed tomography (pQCT) was used to measure vBMD of the radius and tibia. The multivariable linear regression models explained up to 10% of the variance in trabecular vBMD and up to 9% of the variance in cortical vBMD. Age was not correlated with radial trabecular vBMD. Correlates associated with both cortical and trabecular vBMD were age (-), caffeine intake (-), total calcium intake (+), nontrauma fracture (-), and hypertension (+). Higher body weight was related to greater trabecular vBMD and lower cortical vBMD. Height (-), education (+), diabetes with thiazolidinedione (TZD) use (+), rheumatoid arthritis (+), using arms to stand from a chair (-), and antiandrogen use (-) were associated only with trabecular vBMD. Factors associated only with cortical vBMD included clinic site (-), androgen use (+), grip strength (+), past smoker (-), and time to complete five chair stands (-). Certain correlates of trabecular and cortical vBMD differed among older men. An ascertainment of potential risk factors associated with trabecular and cortical vBMD may lead to better understanding and preventive efforts for osteoporosis in men.

Effect of resistance exercise on bone mineral density in premenopausal women.

OBJECTIVE: To assess the effect of 9 months of strength training on total body and regional bone mineral density (BMD, g/cm(2)) in 58 premenopausal women aged 30-50 years. METHODS: Participants were randomized to either twice weekly supervised strength training for 15 weeks followed by 24 weeks of unsupervised training (treatment group) or control group. Height, weight, maximal muscular strength, nutrient intake and physical activity were assessed. Total body dual energy X-ray absorptiometry (DXA, Lunar Prodigy) scans were taken and analyzed for body composition (lean and fat mass), and BMD for total body and its sub-regions (spine, hip, arms and legs). All measurements were performed at baseline, 15 and 39 weeks. Analysis of covariance was used to assess group differences in BMD change adjusted for baseline BMD, weight, energy and calcium intake. RESULTS: At baseline, the two groups had similar BMD and body size characteristics ( P<0.05 for all), except that the treatment group had lower body weight (-7.1 kg), and higher energy (+259 kJ/d) and calcium (+232 mg/d) intake at baseline. Adjusted % change in BMD over 15 weeks (0.5% vs. 0.4%) or 39 weeks (0.9% vs. 1.2%) did not differ significantly between the exercise and control groups, respectively. The exercise group increased BMD at the spine and legs (1-2.2%), while there was no change in the controls, but differences between groups were not significant. CONCLUSION: Strength training over 9 months did not lead to significantly greater change in total body or regional BMD in premenopausal women.

Does obesity really make the femur stronger? BMD, geometry, and fracture incidence in the women's health initiative-observational study.

Heavier individuals have higher hip BMD and more robust femur geometry, but it is unclear whether values vary in proportion with body weight in obesity. We studied the variation of hip BMD and geometry across categories of body mass index (BMI) in a subset of postmenopausal non-Hispanic whites (NHWs) from the Women's Health Initiative Observational Cohort (WHI-OS). The implications on fracture incidence were studied among NHWs in the entire WHI-OS. Baseline DXA scans of hip and total body from 4642 NHW women were divided into BMI (kg/m(2)) categories: underweight (<18.5), healthy weight (18.5-24.9), overweight (25-29.9), and mild (30-34.9), moderate (35-39.9), and extreme obesity (>40). Femur BMD and indices of bone axial (cross-sectional area [CSA]) and bending strength (section modulus [SM]) were extracted from DXA scans using the hip structure analysis (HSA) method and compared among BMI categories after adjustment for height, age, hormone use, diabetes, activity level, femur neck-shaft angle, and neck length. The association between BMI and incident fracture was studied in 78,013 NHWs from the entire WHI-OS over 8.5 +/- 2.6 (SD) yr of follow-up. Fracture incidence (cases/1000 person-years) was compared among BMI categories for hip alone, central body (hip, pelvis, spine, ribs, and shoulder girdle), upper extremity (humerus and distal), and lower extremity (femur shaft and distal but not hip). Femur BMD, CSA, and SM were larger in women with higher BMI, but values scaled in proportion to lean and not to fat or total body mass. Women with highest BMI reported more falls in the 12 mo before enrollment, more prevalent fractures, and had lower measures of physical activity and function. Incidence of hip fractures and all central body fractures declined with BMI. Lower extremity fractures distal to the hip trended upward, and upper extremity incidence was independent of BMI. BMD, CSA, and SM vary in proportion to total body lean mass, supporting the view that bones adapt to prevalent muscle loads. Because lean mass is a progressively smaller fraction of total mass in obesity, femur BMD, CSA, and SM decline relative to body weight in higher BMI categories. Traumatic forces increase with body weight, but fracture rates at the hip and central body were less frequent with increasing BMI, possibly because of greater soft tissue padding. There was no evident protective effect in fracture rates at less padded distal extremity sites. Upper extremity fractures showed no variation with BMI, and lower extremity fracture rates were higher only in the overweight (BMI = 25-29.9 kg/m(2)).

Bone geometry, strength, and muscle size in runners with a history of stress fracture.

PURPOSE: Our primary aim was to explore differences in estimates of tibial bone strength, in female runners with and without a history of stress fractures. Our secondary aim was to explore differences in bone geometry, volumetric density, and muscle size that may explain bone strength outcomes. METHODS: A total of 39 competitive distance runners aged 18-35 yr, with (SFX, n = 19) or without (NSFX, n = 20) a history of stress fracture were recruited for this cross-sectional study. Peripheral quantitative computed tomography (XCT 3000; Orthometrix, White Plains, NY) was used to assess volumetric bone mineral density (vBMD, mg x mm(-3)), bone area (ToA, mm(2)), and estimated compressive bone strength (bone strength index (BSI) = ToA x total volumetric density (ToD(2))) at the distal tibia (4%). Total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area, cortical vBMD, and estimated bending strength (strength-strain index (SSIp), mm(3)) were measured at the 15%, 25%, 33%, 45%, 50%, and 66% sites. Muscle cross-sectional area (MCSA) was measured at the 50% and 66% sites. RESULTS: Participants in the SFX group had significantly smaller (7%-8%) CoA at the 45%, 50%, and 66% sites (P

Bone volumetric density, geometry, and strength in female and male collegiate runners.

PURPOSE: To explore differences in tibial bone geometry, volumetric density, and estimates of bone strength in runners and healthy controls. METHODS: Male (n = 21) and female (n = 38) runners (49.1 +/- 13.2 miles x wk(-1)) and inactive healthy controls (17 males and 32 females; mean age = 22 +/- 3.3 yr) were recruited to participate. Peripheral quantitative computed tomography was used to assess total volumetric bone mineral density (vBMD, mg x mm(-3)), total bone area (ToA, mm2), and an estimate of compressive bone strength (bone strength index (BSI) = ToA x total bone volumetric density (ToD2)) at the distal (4%) site of the tibia. ToA (mm2) and cortical bone area (CoA, mm2), cortical vBMD (CoD, mg x mm(-3)), cortical thickness (CoTh, mm), and an estimate of bone bending strength (polar strength strain index (SSIp), mm3) were measured at 50% and 66% sites. RESULTS: ToA and BSI were significantly greater (+11%-19%, P < 0.05) in female runners than controls at the 4% site. At the proximal sites, female runners had significantly greater ToA, CoA, CoTh, and SSIp (+9%-19%, all P < 0.001) compared with female controls. vBMD was similar at all tibia sites. Compared with controls, male runners had significantly greater CoTh at the 50% and 66% sites (+8% and 14%, respectively, P < 0.05) as well as greater CoA (+11%, P < 0.009) at the 66% site. There were no differences in bone strength or density at any site in the male runners. CONCLUSIONS: Greater bone strength in female runners was attributable to greater bone area rather than density. Although male runners did not show greater bone strength, they did exhibit favorable bone geometric properties. These data further document that running has osteogenic potential.