Tamara A. Scerpella

Sustained skeletal benefit from childhood mechanical loading

SummaryPreliminary prospective, longitudinal results suggest that pre-menarcheal exposure to artistic gymnastics is associated with greater radius BMC, aBMD, and projected area throughout growth and into early adulthood, more than 4xa0years after activity cessation. Any loss of benefit associated with de-training appears to be temporary.IntroductionMechanical loading may enhance bone accrual during growth, but prospective evidence of benefit retention is limited. This prospective, longitudinal cohort study tests whether gymnastics is linked to distal radius advantages during growth and four or more years post-training cessation.MethodsSemi-annually, female ex/gymnasts and non-gymnasts underwent height and weight measurements; questionnaires assessed calcium intake, physical activity, and maturation. Annual dual energy X-ray absorptiometry scans (Hologic QDR 4500W) measured total body fat-free mass, skull areal density (aBMD), and bone mineral content (BMC); forearm scans measured ultradistal and 1/3 radius area, BMC, and aBMD. Analysis inclusion criteria were: (1) achievement of gynecological age >4xa0years and (2) for gymnasts, >2xa0years of pre-menarcheal training (>6xa0h/week), ceasing between 0.5xa0year pre-menarche and 1xa0year post-menarche. Hierarchical linear modeling (HLM v6.0) evaluated outcomes for ex/gymnasts versus non-gymnasts; a slope/intercept discontinuity evaluated de-training effects.ResultsData from 14 non-gymnasts and six ex/gymnasts represented outcomes from 4xa0years pre-menarche to 9xa0years post-menarche. All adjusted distal radius parameters were higher in ex/gymnasts than non-gymnasts (pu2009<u20090.02). Ultradistal BMC, ultradistal aBMD, and 1/3 aBMD temporarily decreased with gymnastic cessation (pu2009<u20090.04); ultradistal area, 1/3 area, and 1/3 BMC did not change significantly. Skull outcomes did not differ between groups or change with activity cessation.ConclusionGymnastic exposure during childhood and early puberty is associated with greater radius bone mass, size, and aBMD. Despite brief de-training losses in density and mass, significant skeletal benefits are manifested throughout growth and at least 4xa0years beyond activity cessation into early adulthood.

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

PURPOSEnWe 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).nnnMETHODSnSubjects 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.nnnRESULTSnAt 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).nnnCONCLUSIONSnMaturity-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.

Agreement between pQCT- and DXA-derived indices of bone geometry, density, and theoretical strength in females of varying age, maturity, and physical activity.

Measurement of bone mass, geometry, density, and strength are critical in bone research and clinical studies. For peripheral quantitative computed tomography (pQCT), single and repeated measurements are particularly adversely affected by movement and positional variation. Dual‐energy X‐ray absorptiometry (DXA)–derived indices may alleviate these problems and provide useful alternative assessments. To evaluate this hypothesis, distal radius DXA and pQCT indices were compared in 101 healthy females aged 8.0 to 22.8 years (prepuberty to adulthood), reflecting a broad range of body sizes, physical maturity, and activity exposures. At the diaphysis, correlations were ρu2009=u2009+0.74 to +0.98, with strong intermethod agreement for most indices. At the metaphysis, correlations were ρu2009=u2009+0.64 to +0.97; intermethod agreement improved with modifications to the simplified geometric formulas more closely reflecting metaphyseal bone geometry. Further improvements may be possible because skeletal size and maturity‐related biases in agreement were detected. Overall, DXA‐derived indices may provide a useful assessment of bone geometry, density, and theoretical strength contingent on appropriate consideration of their limitations.

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.

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

SummaryTrabecular 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.IntroductionTrabecular 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 (≥xa01.35) is reached in the first year post-menarche and (2) the role of maturational timing (menarcheal age) and status (gynecological age) in TBS variation.MethodsFor 44 healthy girls aged 11 to 13xa0years, whole body and LS DXA scans were obtained within 1xa0year 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.ResultsLowest observed TBS exceeded 1.35 (rawTBSxa0=xa01.362; corrTBSxa0=xa01.352). Menarcheal age correlated negatively with rawTBS (rxa0=xa0−xa00.34, pxa0=xa00.02), with a similar trend for corrTBS (rxa0=xa0−xa00.29, pxa0<xa00.06). Gynecological age did not correlate with TBS but was positively correlated with LSBMD (rxa0=xa0+xa00.37, pxa0=xa00.01). Correlations with body composition variables differed between rawTBS and corrTBS.ConclusionsIn this healthy cohort, “normal” adult TBS is present by 1xa0year post-menarche, 2xa0years 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.

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.

A school-based resistance intervention improves skeletal growth in adolescent females

SummaryTwenty-two sixth-grade girls who participated in a 7-month school-based resistance-training program were compared to 22 controls. In a subanalysis of Tanner breast II (T2) and III (T3) subjects (nu2009=u200921 controls subjects (CON), nu2009=u200917 subjects in the high-intervention (INT)-dose group (HI)), T2 HI had greater narrow neck (NN) width gains than T2 CON (pu2009<u20090.05) and T3 HI had greater L3 bone mineral density (BMD) gains than T3 CON (pu2009<u20090.05).IntroductionPhysical activity modulates bone growth during adolescence, but an effective activity has not been identified for general use. The purpose of this study was to examine the effect of a school-based resistance-training program on skeletal growth in pre-menarcheal females.MethodsSixth-grade girls participated in a 7-month, resistance-training program (INT) embedded in physical education (PE) classes. Age- and maturity-matched CON from a neighboring school participated in the standard PE classes. INT dose defined high (HI) and low (LO) groups. At baseline (BL) and follow-up (FU), non-INT organized physical activity (PA, hours per week) and maturity status were recorded; DXA scans assessed total body, distal radius, proximal femur, and lumbar spine. Regression models analyzed growth in bone outcomes for HI versus CON, accounting for age, Tanner stage, height, and PA.ResultsForty-four girls (22 HI, 22 CON) were 11.7u2009±u20090.3xa0years of age at BL; all were ≤6xa0months postmenarche and did not differ in bone growth over the course of the intervention (pu2009>u20090.05). However, in a subanalysis limited to subjects who were T2 or T3 at BL (nu2009=u200921 CON, nu2009=u200917 HI), T2 HI had greater gains in NN width (pu2009=u20090.01) compared to T2 CON, while T3 HI had greater gains in L3 BMD (pu2009=u20090.03) compared to T3 CON.ConclusionsIn a group of T2 and T3 sixth-grade girls, a school-based resistance-training intervention produced maturity-specific differential gains for HI versus CON at the hip and spine.

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

Mini-abstractIn 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.PurposeChildhood 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.MethodsThis 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.ResultsAfter 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 (pxa0<xa00.05). 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”xa0palatIBS, and palatFRI benefits (pxa0<xa00.05).ConclusionsPhysical 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.

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 4u202fyears 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.

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 8-24u2009yr. 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 CCCu2009>u20090.90), for all outcomes except for femoral neck area and subhead area (95% confidence interval for CCCu2009=u20090.83-0.94, 0.57-073). However, QDR values were systematically lower than Discovery values (pu2009<u20090.05), except for head area, head bone mineral content, head BMD, ultradistal BMD (QDRu2009>u2009Discovery, pu2009≤u20090.05) 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.