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.

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.

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.

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.

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.

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.

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.

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.

Greater adipose tissue infiltration in skeletal muscle among older men of African ancestry.

CONTEXT: There is substantial variability across ethnic groups in the predisposition to obesity and associated metabolic abnormalities. Skeletal muscle fat has been identified as an important depot that increases with aging and may contribute to the development of diabetes. OBJECTIVE: We tested whether men of African ancestry have greater calf intermuscular adipose tissue (IMAT), compared to Caucasian men, and whether IMAT is associated with type 2 diabetes (T2D). DESIGN: We measured fasting serum glucose, body mass index, total body fat by dual-energy x-ray absorptiometry, and calf skeletal muscle composition by quantitative computed tomography in 1105 Caucasian and 518 Afro-Caribbean men aged 65+. RESULTS: Compared to Caucasian men, we found greater IMAT and lower sc adipose tissue in Afro-Caribbean men at all levels of total adiposity (P < 0.0001), including the subset of men matched on age and dual-energy x-ray absorptiometry total body fat percentage (P < 0.001). In addition, IMAT was 29 and 23% greater, whereas sc adipose tissue was 6 and 8% lower among Caucasian and Afro-Caribbean men with T2D, respectively, compared to men without T2D (P < 0.01). Observed differences in intermuscular and sc fat, both ethnic and between men with and without T2D, were independent of age, height, calf skeletal muscle and total adipose tissue, and lifestyle factors. CONCLUSIONS: Our analyses suggest that despite lower total adiposity, skeletal muscle fat infiltration is greater among African than among Caucasian ancestry men and is associated with T2D in both ethnic groups. Additional studies are needed to determine the mechanisms contributing to ethnic differences in skeletal muscle adiposity and to define the metabolic and health implications of this fat depot.

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)).

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.

Bone structure and volumetric BMD in overweight children: a longitudinal study.

The effect of excess body fat on bone strength accrual is not well understood. Therefore, we assessed bone measures in healthy weight (HW) and overweight (OW) children. Children (9-11 yr) were classified as HW (n = 302) or OW (n = 143) based on body mass index. We assessed total (ToD) and cortical (CoD) volumetric BMD and bone area, estimates of bone strength (bone strength index [BSI]; stress-strain index [SSIp]), and muscle cross-sectional area (CSA) at the distal (8%), midshaft (50%), and proximal (66%) tibia by pQCT. We used analysis of covariance to compare bone outcomes at baseline and change over 16 mo. At baseline, all bone measures were significantly greater in OW compared with HW children (+4-15%; p

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.

Proximal femur mechanical adaptation to weight gain in late adolescence: a six-year longitudinal study.

UNLABELLED: The effect of weight gain in late adolescence on bone is not clear. Young women who consistently gained weight (n = 23) from 17 to 22 yr of age had increased BMD but a lack of subperiosteal expansion compared with stable weight peers (n = 48). Bone strength increased appropriately for lean mass in both groups but decreased relative to body weight in weight gainers, suggesting increased bone fragility in weight gainers. INTRODUCTION: Weight gain leading to obesity often starts in adolescence, yet little is known about its effects on bone. We used longitudinal data to examine the effects of weight gain in late adolescence (from 17 to 22 yr of age) on proximal femur BMD, geometry, and estimates of bending strength. MATERIALS AND METHODS: Participants were classified as either weight gainers (WG, n = 23) or stable weight (SW, n = 48) using a random coefficients model. Weight gainers had positive increases in weight (p < 0.05) at each clinic visit from age 17 onward. Proximal femur DXA scans (Hologic QDR 2000) taken annually from 17 to 22 yr of age were analyzed for areal BMD (g/cm(2)), subperiosteal width (cm), and bone cross-sectional area (CSA) at the proximal femoral shaft. Cortical thickness was measured, and section modulus (Z, cm(3)) was calculated as a measure of bone bending strength. Total body lean (g) and fat (g) mass were measured from DXA total body scans. RESULTS: Over ages 17-22, height remained stable in both groups. Weight remained static in the SW group but increased 14% on average in the WG group (p < 0.05). After controlling for age 17 baseline values, WG had higher BMD (+2.6%), thicker cortices (+3.6%), and greater bone CSA (+2.3%). Increased BMD did not translate to greater increases in bone bending strength (Z). The SW group achieved similar gains in Z by greater subperiosteal expansion. Bone strength index (SI = Z/height) normalized for body weight remained constant in the SW group but decreased significantly in the WG group. In contrast, SI normalized to lean mass did not change over time in either group. Other variables including physical activity, nutrition, and hormone levels (estradiol, testosterone, cortisol) did not differ significantly between groups. CONCLUSIONS: These data suggest that weight gain in late adolescence may inhibit the periosteal expansion known to normally occur throughout life in long bones, resulting in decreased bone strength relative to body weight.

Lessons learned from school-based skeletal loading intervention trials: putting research into practice.

In recent years, there have been a number of school-based physical activity intervention trials aimed at optimizing bone development. Various approaches have been taken including interventions ranging from 3 to 50 min in length performed 2-5 times per week incorporated within the school day (typically in physical education) or as an after-school program. Overall, these studies showed that school-based skeletal loading interventions are efficacious, safe, and feasible. Furthermore, studies to date have shown that interventions are most effective when initiated during prepuberty and early puberty, and consist of dynamic activities that are high in magnitude (i.e. jumping, skipping, hopping) and include multidirectional movements. Recent work also suggests that adding rest intervals and performing short bouts of activity a few times per day may enhance the effectiveness of loading on bone health. In this chapter, we discuss important training principles and lessons learned from these intervention trials and provide practical guidelines, tips and sample programs that can be used by health care professionals interested in optimizing bone health of children and adolescents.

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.

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.