Cross-Calibrated Dual-Energy X-Ray Absorptiometry Scanners Demonstrate Systematic Bias in Pediatric and Young Adult Females.

Consistency of dual-energy X-ray absorptiometry (DXA) scan results is critical for data integrity. For pediatric subjects, the extent to which cross-calibration of DXA scanners alleviates model-to-model scanner differences is unclear. In the current study, DXA bone outcomes were compared for same-day measurements performed using different scanners, cross-calibrated to alleviate discrepancies (Hologic; Discovery A [DISCO] and QDR 4500W [QDR]). Interscanner differences were evaluated in approximately 130 females aged 8-24 yr. Scans were performed in a single session on both QDR and DISCO scanners to compare projected area, bone mineral content, and areal bone mineral density (BMD) outputs for the whole body (total, subhead, head, arm, and leg), forearm (1/3 and ultradistal radius), lumbar spine (vertebra L3 and L1-L4), and proximal femur (femoral neck). Paired t tests evaluated interscanner differences; concordance correlation coefficients (CCCs) evaluated interscanner correlations. Root mean square error coefficients of variation were compared to same-day duplicate DISCO scan root mean square error coefficients of variation for approximately 30 adult females. Deming regression equations were generated for conversion of QDR to DISCO results and vice versa. Interscanner correlations were very high (95% confidence interval for CCC > 0.90), for all outcomes except for femoral neck area and subhead area (95% confidence interval for CCC = 0.83-0.94, 0.57-073). However, QDR values were systematically lower than Discovery values (p < 0.05), except for head area, head bone mineral content, head BMD, ultradistal BMD (QDR > Discovery, p ≤ 0.05) and L1-L4 area, L3 area, and femoral neck BMD (no differences). Most Bland-Altman and Deming regression plots indicated good interscanner agreement, with little systematic variation based on bone or body size. In pediatric and young adult females, subtle but systematic differences were noted between scans obtained on DISCO and QDR scanners, despite cross-calibration, such that most outcomes are systematically higher for DISCO than for QDR. The use of conversion equations is warranted.

The Influence of Organized Physical Activity (Including Gymnastics) on Young Adult Skeletal Traits: Is Maturity Phase Important?

We prospectively evaluated adolescent organized physical activity (PA) as a factor in adult female bone traits. Annual DXA scans accompanied semiannual records of anthropometry, maturity, and PA for 42 participants in this preliminary analysis (criteria: appropriately timed DXA scans at ~1 year premenarche [predictor] and ~5 years postmenarche [dependent variable]). Regression analysis evaluated total adolescent interscan PA and PA over 3 maturity subphases as predictors of young adult bone outcomes: 1) bone mineral content (BMC), geometry, and strength indices at nondominant distal radius and femoral neck; 2) subhead BMC; 3) lumbar spine BMC. Analyses accounted for baseline gynecological age (years pre- or postmenarche), baseline bone status, adult body size and interscan body size change. Gymnastics training was evaluated as a potentially independent predictor, but did not improve models for any outcomes (p > .07). Premenarcheal bone traits were strong predictors of most adult outcomes (semipartial r2 = .21-0.59, p ≤ .001). Adult 1/3 radius and subhead BMC were predicted by both total PA and PA 1-3 years postmenarche (p < .03). PA 3-5 years postmenarche predicted femoral narrow neck width, endosteal diameter, and buckling ratio (p < .05). Thus, participation in organized physical activity programs throughout middle and high school may reduce lifetime fracture risk in females.

Distal radius strength: a comparison of DXA-derived vs pQCT-measured parameters in adolescent females.

Although quantitative computed tomography (QCT) is considered the gold standard for in vivo densitometry, dual-energy X-ray absorptiometry (DXA) scans assess larger bone regions and are more appropriate for pediatric longitudinal studies. Unfortunately, DXA does not yield specific bone architectural output. To address this issue in healthy, postmenarcheal girls, Sievänen's distal radius formulae [1996] were applied to derive indices of bone geometry, volumetric bone mineral density (vBMD), and strength from DXA data; results were compared to peripheral quantitative computed tomography (pQCT) output. Contemporaneous scans were performed on the left, distal radii of 35 gymnasts, ex-gymnasts, and nongymnasts (aged 13.3-20.4 yr, mean 16.6 yr). For 4% and 33% regions, pQCT measured cross-sectional areas (CSAs) and vBMD; comparable DXA indices were generated at ultradistal and 1/3 regions. Index of structural strength in axial compression was calculated from 4% pQCT and DXA output for comparison; 33% pQCT strength-strain index was compared to 1/3 DXA section modulus. Sievänen DXA indices were significantly, positively correlated with pQCT output (R=+0.61 to +0.98; p<0.0001). At the distal radius, in healthy postmenarcheal girls, Sievänen's method yielded potentially useful DXA indices of diaphyseal cortical CSA and bone strength at both the diaphysis (section modulus) and the metaphysis (index of structural strength in axial compression).

Correcting fan-beam magnification in clinical densitometry scans of growing subjects.

As children grow, body and limb girths increase. For serial densitometric measurements, growth increases the distance between the bone region of interest and X-ray source over time, thereby increasing fan-beam magnification. To isolate bone accrual from magnification error in growing subjects, we developed a correction method based on waist girth, a common anthropometric measure. This correction was applied to dual-energy X-ray absorptiometry output obtained in a cohort of premenarcheal gymnasts and nongymnasts. After correcting for magnification, results for projected area and bone mineral content (BMC) increased by 0.4-1.1% at the lumbar spine and 8-16% at the femoral neck, decreasing areal bone mineral density (aBMD) by 0.4-2.3% at both sites. The effects of magnification correction were similar in magnitude to BMC and aBMD gains previously reported in longitudinal studies of normoactive children. Because of body size differences, the effect of correction for BMC and aBMD was 10-20% greater in nongymnasts than in gymnasts, which increased the observed aBMD differential between gymnasts and nongymnasts. Fan-beam magnification distorts true changes in bone mineral measures in growing premenarcheal girls and, therefore, may obscure additional activity-related changes during growth. Our correction technique may enhance detection of skeletal adaptation, particularly in pediatric populations.

A 2-yr, School-Based Resistance Exercise Pilot Program Increases Bone Accrual in Adolescent Girls.

PURPOSE: The current analysis evaluates cumulative benefits after year two (Y2) of a school-based resistance training intervention. METHODS: Adolescent girls were enrolled and measured at the beginning of 6th grade (baseline, BL) and again at 1st follow-up (FU1: Y1 end) and 2nd follow-up (FU2: Y2 end). School gym classes met alternate school days. Site 1 had standard gym classes (CON). Site 2 gym classes included 8-12 minutes of resistance training (INT); INT girls were categorized based on observed participation effort and time (LO, HI). Measurements included: 1) height and weight; 2) questionnaires to assess extracurricular exercise and diet (calcium, vitamin D); 3) dual-energy X-ray absorptiometry (DXA, Lunar Prodigy). Whole body less head (SUB) scans yielded bone mineral content (BMC) and body composition. Lumbar spine (L1-L4) and femoral neck (FN) scans yielded BMC and areal bone mineral density (BMD); radius scans yielded ultradistal and 1/3 BMD. ANCOVA compared group means for percent gains from BL to FU2, accounting for biological maturity, BL height, height change, inter-scan interval, organized activity, calcium and vitamin D. RESULTS: In 62 girls (21 CON, 41 INT), intention to treat analyses detected INT vs. CON advantages for L1-L4 BMC and BMD (4.1%, 5.6%: p<0.05). HI effort participants (n=19) demonstrated advantages for BMC and BMD at L1-L4 and FN (5.7% to 8.2%, p<0.01) vs. CON. CONCLUSIONS: Over two school years, this resistance intervention yielded lumbar spine advantages; enthusiastic participation (HI) yielded lumbar spine and femoral neck advantages. Further work is warranted to evaluate benefit persistence after intervention cessation.

Circum-menarcheal bone acquisition is stress-driven: A longitudinal study in adolescent female gymnasts and non-gymnasts.

Mechanical loading through youth exercise is highly modifiable and represents a strategy to maximize peak adult bone mass, with the potential for broad implementation across the population to lower fracture risk. For girls, circum-menarcheal growth is critical, with around 50% of adult bone acquired over a 4-year period. Here, we prospectively followed 10 gymnasts and 12 age-matched non-gymnasts across approximately 4 years circum-menarche. A combination of pQCT and subject-specific finite element models were used to measure differences in bone acquisition and structure between the groups, and to determine the degree to which specific mechanical factors predict change in bone structure. At baseline, gymnasts had stronger bone, including 26% higher BMC, 51% greater compressive strength, and 21% higher trabecular density. Over the study period, both groups more than doubled their bone strength. Pre-menarcheal principal stresses predicted change in pQCT variables for non-gymnasts, but not gymnasts. The bone of non-gymnasts became more asymmetrical than the bone of gymnasts. Our results suggest that exposure to the diverse, intense mechanical signals of gymnastic loading during adolescence imparts substantial benefits to bone geometry and mechanical function. Specifically, the bone of gymnasts is better able to resist loading from multiple directions, and operates with a higher factor of safety compared to non-gymnasts.

Bone geometry, density, and strength indices of the distal radius reflect loading via childhood gymnastic activity.

The distal radius bears unique forces during gymnastic activity. Its relatively simple anatomy, minimal soft tissue envelope, and varied composition make the distal radius ideal for evaluating the effects of loading on bone properties. For 56 premenarcheal gymnasts and nongymnasts, ultradistal and 1/3 distal radius DXA scans measured bone mineral content (BMC), areal bone mineral density, and projected area. Simplified geometric models were used to generate bone mineral apparent density (BMAD), geometric indices, strength indices, and fall strength ratios. Ratios of regional BMC vs total body fat-free mass (FFM) were calculated. Separate Tanner I and II analyses of covariance adjusted bone parameters for age and height. Ratios were compared using maturity-matched analyses of variance. At the 1/3 region, periosteal width, BMC, cortical cross-sectional area, and section modulus were greater in gymnasts than nongymnasts (p<0.05); 1/3 BMAD means were equivalent. Ultradistal BMAD, BMC, and index for structural strength in axial compression were higher in gymnasts than nongymnasts; ultradistal periosteal width was only larger in Tanner I gymnasts. Fall strength ratios and BMC/FFM ratios were greater in gymnasts (p<0.05). Geometric and volumetric responses to mechanical loading are site specific during late childhood and early adolescence.

A focused evaluation of lumbar spine trabecular bone score in the first year post-menarche.

Trabecular bone score, an index of lumbar spine trabecular texture, has not been explored fully in adolescent girls. Our cross-sectional analysis supported the hypothesis that "adult normal" trabecular bone score has been achieved by the end of the first year post-menarche, providing a potential screening tool, independent from bone density. INTRODUCTION: Trabecular bone score (TBS) evaluates lumbar spine (LS) trabecular texture from DXA images. Limited evidence suggests low TBS in pre-pubertal girls. TBS has not been assessed in the context of the key peri-menarcheal bone accrual phase. Thus, we evaluated (1) whether "normal" adult TBS (≥ 1.35) is reached in the first year post-menarche and (2) the role of maturational timing (menarcheal age) and status (gynecological age) in TBS variation. METHODS: For 44 healthy girls aged 11 to 13 years, whole body and LS DXA scans were obtained within 1 year post-menarche. As TBS is optimized for adults and can be affected by body thickness, custom software provided unadjusted "rawTBS" and adjusted for tissue thickness "corrTBS" (TBS iNsight, Medimaps, France). Correlations evaluated menarcheal age and gynecological age as factors in LS bone mineral content (BMC), areal bone mineral density (BMD), and TBS. RESULTS: Lowest observed TBS exceeded 1.35 (rawTBS = 1.362; corrTBS = 1.352). Menarcheal age correlated negatively with rawTBS (r = - 0.34, p = 0.02), with a similar trend for corrTBS (r = - 0.29, p < 0.06). Gynecological age did not correlate with TBS but was positively correlated with LSBMD (r = + 0.37, p = 0.01). Correlations with body composition variables differed between rawTBS and corrTBS. CONCLUSIONS: In this healthy cohort, "normal" adult TBS is present by 1 year post-menarche, 2 years before projected LS peak bone mass. Thus, TBS may be a useful bone architectural screen during the first post-menarcheal year, enabling intervention to improve structure prior to "peak bone mass". Longitudinal studies are needed to elucidate TBS development and intervention response.

Relationships among diet, physical activity, and dual plane dual-energy X-ray absorptiometry bone outcomes in pre-pubertalgirls.

In pre-pubertal girls, nutrient intakes and non-aquatic organized activity were evaluated as factors in vertebral body bone mass, structure, and strength. Activity, vitamin B12, and dietary fiber predicted bone outcomes most consistently. Exercise and vitamin B12 appear beneficial, whereas high fiber intake appears to be adverse for vertebral body development. PURPOSE: Childhood development sets the baseline for adult fracture risk. Most studies evaluate development using postero-anterior (PA) dual-energy X-ray absorptiometry (DXA) areal bone mineral density, bone mineral content, and bone mineral apparent density. In a prior analysis, we demonstrated that PA DXA reflects posterior element properties, rather than vertebral body fracture sites, such that loading is associated with subtle differences in vertebral body geometry, not 3D density. The current analysis is restricted to pre-pubertal girls, for a focused exploration of key nutrient intakes and physical activity as factors in dual plane indices of vertebral body geometry, density, and strength. METHODS: This cross-sectional analysis used paired PA and supine lateral (LAT) lumbar spine DXA scans to assess "3D" vertebral body bone mineral apparent density (PALATBMAD), "3D" index of structural strength in axial compression (PALATIBS), and fracture risk index (PALATFRI). Diet data were collected using the Youth/Adolescent Questionnaire (YAQ, 1995); organized physical activity was recorded via calendar-based form. Pearson correlations and backward stepwise multiple linear regression analyzed associations among key nutrients, physical activity, and bone outcomes. RESULTS: After accounting for activity and key covariates, fiber, unsupplemented vitamin B12, zinc, carbohydrate, vitamin C, unsupplemented magnesium, and unsupplemented calcium intake explained significant variance for one or more bone outcomes (p < 0.05). After adjustment for influential key nutrients and covariates, activity exposure was associated with postero-anterior (PA) areal bone mineral density, PA bone mineral content, PA width, lateral (LAT) BMC, "3D" bone cross-sectional area (coronal plane), "3D" PALATIBS, and PALATFRI benefits (p < 0.05). CONCLUSIONS: Physical activity, fiber intake, and unsupplemented B12 intake appear to influence vertebral body bone mass, density, geometry, and strength in well-nourished pre-pubertal girls; high fiber intakes may adversely affect childhood vertebral body growth.

Maturity and activity-related differences in bone mineral density: Tanner I vs. II and gymnasts vs. non-gymnasts.

This study tests the hypotheses that (1) Tanner I and Tanner II girls comprise distinct maturational cohorts, exhibiting BMD differences that are not explained by age and body size alone; and (2) within these distinct maturational cohorts, BMD is higher in gymnasts than non-gymnasts, independent of age and body size. Premenarcheal artistic gymnasts (n=28) and non-gymnasts (n=28) were evaluated. Fan-beam DXA measured areal BMD (aBMD) at the forearm, femoral neck, and lumbar spine; fat free mass (FFM) was derived from whole-body scans. Height, weight, physical activity and calcium intake were assessed. Group means were compared using ANOVA; ANCOVA was used to adjust for age, height and FFM. For all 3 sites and both maturity levels, gymnasts had higher aBMD than non-gymnasts, independent of age and body size (7.2-20.8%, p<0.04). After adjustment for age, height and FFM, Tanner II gymnasts demonstrated lower aBMD than Tanner I gymnasts at the femoral neck (7.6%, p<0.05); no other maturity group comparisons yielded statistically significant differences independent of age and body size. In conclusion, for both Tanner groups, the osteogenic role of impact activity is evident at all three sites. Trends in Tanner group differences in aBMD were specific to gymnast and non-gymnast activity groups and therefore were not generalizable to all subjects. Overall, aBMD correlations and ANCOVA results differ by activity group, maturity level and site. These results highlight the need to consider both maturity and activity status in studies assessing bone accrual.

Site-specific, adult bone benefits attributed to loading during youth: A preliminary longitudinal analysis.

We examined site-specific bone development in relation to childhood and adolescent artistic gymnastics exposure, comparing up to 10years of prospectively acquired longitudinal data in 44 subjects, including 31 non-gymnasts (NON) and 13 gymnasts (GYM) who participated in gymnastics from pre-menarche to ≥1.9years post-menarche. Subjects underwent annual regional and whole-body DXA scans; indices of bone geometry and strength were calculated. Anthropometrics, physical activity, and maturity were assessed annually, coincident with DXA scans. Non-linear mixed effect models centered growth in bone outcomes at menarche and adjusted for menarcheal age, height, and non-bone fat-free mass to evaluate GYM-NON differences. A POST-QUIT variable assessed the withdrawal effect of quitting gymnastics. Curves for bone area, mass (BMC), and strength indices were higher in GYM than NON at both distal radius metaphysis and diaphysis (p<0.0001). At the femoral neck, greater GYM BMC (p<0.01), narrower GYM endosteal diameter (p<0.02), and similar periosteal width (p=0.09) yielded GYM advantages in narrow neck cortical thickness and buckling ratio (both p<0.001; lower BR indicates lower fracture risk). Lumbar spine and sub-head BMC were greater in GYM than NON (p<0.036). Following gymnastics cessation, GYM slopes increased for distal radius diaphysis parameters (p≤0.01) and for narrow neck BR (p=0.02). At the distal radius metaphysis, GYM BMC and compressive strength slopes decreased, as did slopes for lumbar spine BMC, femoral neck BMC, and narrow neck cortical thickness (p<0.02). In conclusion, advantages in bone mass, geometry, and strength at multiple skeletal sites were noted across growth and into young adulthood in girls who participated in gymnastics loading to at least 1.9years post-menarche. Following gymnastics cessation, advantages at cortical bone sites improved or stabilized, while advantages at corticocancellous sites stabilized or diminished. Additional longitudinal observation is necessary to determine whether residual loading benefits enhance lifelong skeletal strength.

Subclinical atherosclerotic risk in endurance-trained premenopausal amenorrheic women.

PURPOSE: In premenopausal women, amenorrhea contributes to endothelial dysfunction. It is unknown whether this vascular functional change is associated with vascular structural change. METHODS: This study examined regional and systemic vascular structure and function to gain insight into subclinical atherosclerotic risk in 10 amenorrheic athletes, 18 eumenorrheic athletes, and 15 recreationally active controls. Brachial flow-mediated dilation (FMD) and low flow mediated constriction (L-FMC) were used to measure global endothelial function. Carotid-femoral pulse wave velocity (PWV) was used to measure aortic stiffness. Doppler-ultrasound of the superficial femoral artery (SFA) was used to assess intima-media thickness (IMT) and vessel diameter as indicators of vascular remodeling. RESULTS: Amenorrheic athletes had significantly lower brachial FMD adjusted for shear stimulus (6.9 ± 1.3%) compared with eumenorrheic athletes (11.0 ± 1.0%) and controls (11.0 ± 1.1%, p = 0.05). Brachial L-FMC (-1.8 ± 4.3%) and aortic PWV (5.0 ± 1.0 m/s) of amenorrheic athletes were similar to those of eumenorrheic athletes (L-FMC, -1.6 ± 4.6%; PWV, 4.6 ± 0.5 m/s) and controls (L-FMC, -1.5 ± 2.8%, p = 0.98; PWV, 5.4 ± 0.7 m/s, p = 0.15). SFA diameters were similar in amenorrheic athletes (5.7 ± 0.7 mm) and eumenorrheic athletes (5.7 ± 0.7 mm), but amenorrheic athletes had larger SFA diameters compared with controls (5.1 ± 0.6 mm, p = 0.04). In amenorrheic athletes, SFA IMT (0.31 ± 0.03 mm) was similar to that of eumenorrheic athletes (0.35 ± 0.07 mm) but significantly thinner compared to that of controls (0.38 ± 0.06, p = 0.01). CONCLUSION: Vascular dysfunction in female amenorrheic athletes is not systemic. Parenthetically, amenorrhea may not prevent favorable peripheral vascular structural adaptations to habitual exercise training.

Muscle function, dynamic loading, and femoral neck structure in pediatric females.

PURPOSE: Muscle forces influence the development of bone mass and structure, but dynamic loading via impact exercise is considered particularly osteogenic. We hypothesized that indices of local muscle function and physical activity exposure would predict femoral neck (FN) structure in premenarcheal females. METHODS: We tested this hypothesis in 76 healthy, premenarcheal girls (46 gymnasts and 30 nongymnasts). Height, weight, Tanner breast stage, and prior year nonaquatic, organized physical activity level (PAL) were recorded semiannually. Hologic dual-energy x-ray absorptiometry scans (whole body, left FN) yielded total body nonbone lean mass and bone outcomes, including narrow neck (NN) hip structural analysis data. Dynamometers assessed nondominant hand grip and left hip flexion/extension indices. Parsimonious regression models tested the following as predictors of bone outcomes: local muscle function, PAL, gymnast status, and lean mass, accounting for Tanner breast stage and height, as appropriate. RESULTS: Hip flexion indices were significantly correlated with indices of FN mass, density, structure, and strength (P < 0.05). However, the entry of PAL, gymnast status, and lean mass into regression models supplanted local muscle function explanatory value. In contrast, for many variables, the significant association of gymnast status persisted after accounting for physical maturity, body size/lean mass, and PAL. For all skeletal indices except FNArea, NNwidth, NN endosteal diameter, and NN buckling ratio, gymnast status was more strongly associated with bone outcomes than PAL. CONCLUSIONS: Greater activity doses and exposure to extreme dynamic loading provide independent benefits to FN structure during growth. Furthermore, weight-bearing activity and high-impact exercise exposure appear superior to local muscle force measures for prediction of FN structure.

Improved body composition assessment using biceps skinfold and physical activity score in premenarcheal girls: a DXA-based validation study.

OBJECTIVE: Age-specific body mass index (BMI) is commonly employed as an index of adiposity for pediatric clinical and research purposes. However, BMI fails to discriminate between fat and lean mass, making it an imperfect monitor for obesity. We hypothesized that simple anthropometry and organized non-aquatic physical activity assessment (PA) would provide superior explanatory value for pediatric body composition outcomes. RESEARCH METHODS AND PROCEDURES: In a cross-sectional analysis, whole body DXA assessed body composition in 120 pre-menarcheal girls. Questionnaires were used to record and generate annual means for PA. Age, Tanner breast self-stage, height, weight, BMI, skinfold thicknesses, girths and PA were examined as potential predictors of body composition outcomes, using backward stepwise multiple linear regression. A parsimonious regression model was developed in 75% and cross-validated in 25% of the total sample; models were rerun with the total sample. RESULTS: Subject means were as follows: age = 10.4±1.2 y; lean soft tissue (LST) = 24.4±4.2 kg; fat mass (FM) = 8.1±4.1 kg; BMI = 17.6±2.5 kg/m2; PA = 6.8±5.0 h/wk; Tanner breast self-stage ranged from 1 to 3. BMI for age Z scores ranged from -2 to 2.1. Age and BMI alone yielded adjusted model r2=0.44 to 0.78. The final model, including age, height, weight, biceps skinfold and PA, yielded adjusted r2=0.61 to 0.92, P <0.001. Prediction of LST and FM increased from r2=0.64 and 0.76 to r2=0.92 and 0.91, respectively. DISCUSSION: Compared to BMI and age alone, models including biceps skinfold, PA, height, weight and age had superior explanatory value for clinically-relevant body composition outcomes, and are feasible for clinical use.

Site-specific advantages in skeletal geometry and strength at the proximal femur and forearm in young female gymnasts.

PURPOSE: We evaluated site-specific skeletal adaptation to loading during growth, comparing radius (RAD) and femoral neck (FN) DXA scans in young female gymnasts (GYM) and non-gymnasts (NON). METHODS: Subjects from an ongoing longitudinal study (8-26yr old) underwent annual DXA scans (proximal femur, forearm, total body) and anthropometry, completing maturity and physical activity questionnaires. This cross-sectional analysis used the most recent data meeting the following criteria: gynecological age ≤2.5yr post-menarche; and GYM annual mean gymnastic exposure ≥5.0h/wk in the prior year. Bone geometric and strength indices were derived from scans for 173 subjects (8-17yr old) via hip structural analysis (femoral narrow neck, NN) and similar radius formulae (1/3 and Ultradistal (UD)). Maturity was coded as M1 (Tanner I breast), M2 (pre-menarche, ≥Tanner II breast) or M3 (post-menarche). ANOVA and chi square compared descriptive data. Two factor ANCOVA adjusted for age, height, total body non-bone lean mass and percent body fat; significance was tested for main effects and interactions between gymnastic exposure and maturity. RESULTS: At the distal radius, GYM means were significantly greater than NON means for all variables (p<0.05). At the proximal femur, GYM exhibited narrower periosteal and endosteal dimensions, but greater indices of cortical thickness, BMC, aBMD and section modulus, with lower buckling ratio (p<0.05). However, significant interactions between maturity and loading were detected for the following: 1) FN bone mineral content (BMC) and NN buckling ratio (GYM BMC advantages only in M1 and M3; for BMC and buckling ratio, M1 advantages were greatest); 2) 1/3 radius BMC, width, endosteal diameter, cortical cross-sectional area, and section modulus (GYM advantages primarily post-menarche); and 3) UD radius BMC and axial compressive strength (GYM advantages were larger with greater maturity, greatest post-menarche). CONCLUSIONS: Maturity-specific comparisons suggested site-specific skeletal adaptation to loading during growth, with greater advantages at the radius versus the proximal femur. At the radius, GYM advantages included greater bone width, cortical cross-sectional area and cortical thickness; in contrast, at the femoral neck, GYM bone tissue cross-sectional area and cortical thickness were greater, but bone width was narrower than in NON. Future longitudinal analyses will evaluate putative maturity-specific differences.

Mechanical loading during growth is associated with plane-specific differences in vertebral geometry: A cross-sectional analysis comparing artistic gymnasts vs. non-gymnasts.

Lumbar spine geometry, density and indices of bone strength were assessed relative to menarche status, using artistic gymnastics exposure during growth as a model of mechanical loading. Paired posteroanterior (pa) and supine lateral (lat) DXA scans of L3 for 114 females (60 ex/gymnasts and 54 non-gymnasts) yielded output for comparison of paired (palat) versus standard pa and lat outcomes. BMC, areal BMD, vertebral body dimensions, bone mineral apparent density (BMAD), axial compressive strength (IBS) and a fracture risk index were evaluated, modeling vertebral body geometry as an ellipsoid cylinder. Two-factor ANCOVA tested statistical effects of gymnastic exposure, menarche status and their interaction, adjusting for age and height as appropriate. Compared to non-gymnasts, ex/gymnasts exhibited greater paBMD, paBMC, paWidth, pa Cross-sectional area (CSA), paVolume, latBMD, latBMAD, palatCSA and palatIBS (p<0.05). Non-gymnasts exhibited greater latDepth/paWidth, latBMC/paBMC, latVHeight, latArea and Fracture Risk Index. Using ellipsoid vertebral geometric models, no significant differences were detected for pa or palat BMAD. In contrast, cuboid model results (Carter et al., 1992) suggested erroneous ex/gymnast paBMAD advantages, resulting from invalid assumptions of proportional variation in linear skeletal dimensions. Gymnastic exposure was associated with shorter, wider vertebral bodies, yielding greater axial compressive strength and lower fracture risk, despite no BMAD advantage. Our results suggest the importance of plane-specific vertebral geometric adaptation to mechanical loading during growth. Paired scan output provides a more accurate assessment of this adaptation than pa or lat plane scans alone.

Skeletal benefits of pre-menarcheal gymnastics are retained after activity cessation.

Mechanical loading during childhood and adolescence may yield skeletal benefits that persist beyond activity cessation and menarche. At 1 year pre- and 2 years post-menarche, nondominant forearm areal bone mineral density (aBMD), bone mineral content (BMC) and projected area (area) were compared in gymnasts (n = 9), ex-gymnasts (n = 8) and nongymnasts (n = 13). At both observations, gymnasts and ex-gymnasts had higher forearm aBMD, BMC and area than nongymnasts. Gymnasts had higher postmenarcheal means than ex-gymnasts for all three parameters. Childhood mechanical loading yields skeletal advantages that persist at least 24 months after loading cessation and menarche. Continued postmenarcheal loading yields additional benefit.