Effects of weight-bearing activities on bone mineral content and density in children and adolescents: a meta-analysis

Musculoskeletal health in children and adolescents

The purpose of this narrative review was to investigate the key determinants of musculoskeletal health in childhood and adolescence, with particular attention to the role of physical activity. First, we examined the importance of bone modeling and remodeling in maintaining the bone health and the integrity and mechanical characteristic of the skeleton. In addition, we reported the evidence on an appropriate calcium and vitamin D intake, as well as local load variation in achieving proper peak bone mass. Proteomic and transcriptomic studies identified the skeletal muscle "secretoma", consisting of several myokines involved in endocrine and paracrine functions. Among these, we explored the role of irisin, a myokine involved in the muscle-bone crosstalk, and in the regulation of metabolic pathways. It is known that physical activity during growing positively impacts on skeleton and can protect by bone loss in adulthood. However, there are still concerns about the optimal interval duration and exercise intensity, particularly at the pubertal growth spurt which represents a window of opportunity to increase skeletal strength. We reported data from clinical trials performed in the last 5 years analyzing the impact of the type and timing of physical activity during childhood on skeletal development. Finally, we reported recent data on the significance of physical activity in some rare diseases.

Interaction between Selected Adipokines and Musculoskeletal and Cardiovascular Systems: A Review of Current Knowledge

Adipokines are substances secreted by adipose tissue that are receiving increasing attention. The approach to adipose tissue has changed in recent years, and it is no longer looked at as just a storage organ but its secretion and how it influences systems in the human body are also looked at. The role of adipokine seems crucial in developing future therapies for pathologies of selected systems. In this study, we look at selected adipokines, leptin, adiponectin, chemerin, resistin, omentin-1, nesfatin, irisin-1, visfatin, apelin, vaspin, heparin-binding EGF-like growth factor (HB-EGF), and TGF-β2, and how they affect systems in the human body related to physical activity such as the musculoskeletal and cardiovascular systems.

Maximizing plyometric training for adolescents: a meta-analysis of ground contact frequency and overall intervention time on jumping ability: a systematic review and meta-analysis

Plyometric training boosts adolescents' jumping ability, crucial for athletic success and health. However, the best total ground contact frequency (TGCF) and overall intervention time (OIT) for these exercises remain unclear. This meta-analysis aims to identify optimal TGCF and OIT in plyometric training for adolescents, focusing on countermovement jump (CMJ) and squat jump (SJ) outcomes. This systematic review encompassed five databases and included 38 studies with 50 randomized controlled experiments and 3347 participants. We used the Cochrane risk assessment tool for study quality and Review Manager 5.4 for data analysis. The current meta-analysis incorporated a total of 38 studies, comprising 50 sets of randomized controlled trials, to investigate the influence of different TGCFs and OITs on plyometric training. The Cochrane risk assessment tool indicated that all the included studies were classified as low risk. Various TGCFs in plyometric training positively affected CMJ and SJ heights in adolescents. The TGCF of less than 900 was ideal for enhancing CMJ, whereas more than 1400 was effective for SJ. The optimal OIT was 400-600 min, specifically, 500-600 min for CMJ and 400-500 min for SJ. Plyometric training improves jumping ability in adolescents. Lower ground contact frequency (< 900 contacts) enhances CMJ, while higher ground contact frequency (> 1400 contacts) is more effective for SJ. Optimal intervention time ranges from 400 to 600 min, with 500 to 600 min benefiting CMJ and 400 to 500 min improving SJ.

The influence of diet and physical activity on bone density of children aged 5-7 years: The Belfast HAPO family study

OBJECTIVE

Osteoporosis is a global health issue, and modifiable behavioural factors need to be identified in childhood to reduce the risk of osteoporosis in later life. The aim of this study was to investigate the influence of diet and physical activity on bone density of children aged 5-7 years participating in the Belfast Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Family study.

DESIGN AND METHODS

Pregnant women were recruited to the Belfast centre of the HAPO study at 24-32 weeks gestation. Offspring were followed up at 5-7 years as part of the Belfast HAPO Family Study. Heel bone mineral density (BMD) and bone mineral apparent density (BMAD) were measured and calculated, respectively. Physical activity in the offspring was measured by accelerometery and dietary intakes were measured using a 4-day food diary.

RESULTS

Results from 793 offspring were analysed. Mean age of the offspring ± standard deviation was 6.4 ± 0.5 years. A mean of 48.3 ± 22.4 min each day was spent in moderate to vigorous physical activity (MVPA). Median (interquartile range) dietary calcium and vitamin D intakes were 844 (662-1073) mg/day and 1.7 (1.1-2.5) μg/day, respectively. Neither dietary vitamin D nor calcium intakes were significantly associated with offspring heel BMD or BMAD in multiple regression. However, controlling for confounders, a 30-min greater MVPA was associated with significantly larger heel BMD (0.018 g/cm² in boys and 0.010 g/cm² in girls) and BMAD (0.005 g/cm³ in boys and 0.003 g/cm³ in girls).

CONCLUSION

Physical activity was associated with better BMD and BMAD in 5-7-year-old children. Dietary calcium and vitamin D were not predictive of BMD and BMAD.

Time Trends in Trajectories of Forearm Mineral Content and Bone Size during Childhood-Results from Cross-Sectional Measurements with the Same Apparatus Four Decades Apart

Evidence suggests that single photon absorptiometry (SPA)-measured forearm bone mineral density (BMD) is lower in contemporary children in Malmö than it was four decades ago, but the fracture incidence in the at-risk population (all Malmö children) has been stable during the same period. The aim of this study was to evaluate if improvements in skeletal structure over time may explain this observation. In 2017-2018 we measured distal forearm bone mineral content (BMC; mg/cm) and periosteal diameter (mm) in 238 boys and 204 girls aged 7-15 using SPA. Based on the SPA measurements, we calculated forearm BMD (mg/cm²), bone mineral apparent density (BMAD, mg/cm³), section modulus, and strength index (BMAD × section modulus). The results were compared with those derived from measurements of 55 boys and 61 girls of the same ages using the same scanner in 1979-1981. We used log-linear regression with age, sex, and cohort as predictors to investigate differences in trait trajectories (trait versus age slopes [mean percent difference in beta values (95% confidence interval)]). SPA-measured forearm BMC was lower at each age in 2017-2018 compared to 1979-1981 (a mean age and sex adjusted relative difference of 9.1%), the forearm BMC trajectory was similar in 2017-2018 to that in 1979-1981 (reference) [0.0%/year (-1.0%, 1.0%)], while the 2017-2018 forearm periosteal diameter trajectory was steeper [1.1%/year (0.3%, 2.0%)]. Since bone size influences both BMD (BMC divided by scanned area) and mechanical characteristics, the forearm BMD trajectory was flatter in 2017-2018 [-1.1%/year (-2.0%, -0.2%)] and the forearm section modulus trajectory steeper [3.9%/year (1.4%, 6.4%)]. Forearm strength index trajectory was similar [1.8%/year (-0.5%, 4.1%)]. The lower SPA-measured forearm BMD trajectory in contemporary children compared to four decades ago may be offset by changes in forearm bone structure, resulting in similar overall bone strength. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Regulatory Mechanisms of Muscle Mass: The Critical Role of Resistance Training in Children and Adolescent

Muscle mass and strength are subjected to several regulations. We found endocrine signals such as growth hormone, insulin-like growth factor 1, testosterone, thyroid hormones, and glucocorticoids among them. Neural inputs also influence muscle development, modulating mass and strength. Among the external stimuli that modulate these muscular features is physical training such as resistance and endurance training. Specifically, resistance training can mediate an increase in muscle mass by hypertrophy in adults, but the effects in children and adolescents are full of myths for most of the population. However, the evidence shows that the impact of resistance training on children and adolescents is clear and provides a wide range of benefits. However, qualified professionals must be available since exercise prescription and subsequent supervision must follow this population's abilities, needs, and interests.

The Benefits to Bone Health in Children and Pre-School Children with Additional Exercise Interventions: A Systematic Review and Meta-Analysis

OBJECTIVE

Determine if exercise interventions, beyond what is already provided to children and preschool children, improve bone health and reduce fracture incidence.

DESIGN

Systematic review and meta-analysis reported using the PRISMA guidelines. Certainty of evidence was assessed using GRADE recommendations.

DATA SOURCES

Five electronic databases were searched for records: PUBMED; CINAHL; CENTRAL; SPORTDiscus; Web of Science.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Randomised, quasi-randomised and non-randomised controlled trials (including cluster-randomised) assessing the impact of additional exercise interventions (e.g., increased physical education classes or specific jumping programs) on bone health in children (6-12 years) and pre-school children (2-5 years) without dietary intervention.

RESULTS

Thirty-one records representing 16 distinct clinical trials were included. Dual-energy X-ray Absorptiometry (DXA) and/or peripheral Quantitative Computed Tomography (pQCT) were used to quantify bone health. Increased femoral neck bone mineral content in children with additional exercise interventions (n = 790, SMD = 0.55, 95% CI = 0.01 to 1.09) was reported, however this was not significant following sensitivity analysis. Other DXA and pQCT measures, as well as fracture incidence, did not appear to significantly differ over time between intervention and control groups. No studies reported adverse events. Studies failed to report all domains within the TIDieR checklist. All studies were at high risk of bias using the Cochrane RoB Tool 2.0. The certainty of the evidence was very low.

CONCLUSIONS

The addition of exercise interventions, beyond what is provided to children, does not appear to improve DXA and pQCT measures of bone health. The effect of additional exercise interventions on bone health in pre-school children is largely unknown. Future trials should ensure adherence is clearly reported and controlled for within analysis as well as including reports of adverse events (e.g., apophysitis) that occur due to increased exercise interventions.

Global trends and hotspots in research on osteoporosis rehabilitation: A bibliometric study and visualization analysis

Background

The field of rehabilitation medicine plays an essential role in the comprehensive management of osteoporosis and its consequences. The benefits of therapeutic exercise are increasingly being recognized in this area, which receives an increasing number of publications. this study was designed to comprehensively identify collaborative networks, parse and track research trends, spotlight present hotspots, and accurately predict frontiers and focus on the health topics related to osteoporosis rehabilitation.

Methods

This research adopted computer retrieval of osteoporosis rehabilitation-related research published in the Web of Science Core Collection (WoSCC) from inception to June 14, 2022. The bibliometric visualization and comparative analysis involving countries, institutions, journals, authors, references, and keywords were performed using the CiteSpace and VOSviewer software.

Results

A total of 3,268 articles were included, and the number of articles published each year has demonstrated a steady increase. The United States and the University of Melbourne were the highest productive country and institution, with 1,325 and 87 articles, respectively. The journal of osteoporosis international has published the greatest number of articles, with 221 publications, and the journal of bone and mineral research ranked first in the co-citation counts (cited by 11,792 times). The most productive and highly-cited authors were Heinonen A and Cummings S, with 35 publications and 680 citations.

Conclusions

At present, "physical activity," "weight bearing exercise," "muscle strength," "whole body vibration," "postmenopausal women," "older women," children, men are the noteworthy research hot topics. Future research that focus on the major modes and parameters of physical activity/exercise for osteoporosis (including whole body vibration, weight bearing exercises, resistance training), targeted multicomponent training regimens, rehabilitation therapy for postmenopausal women, older women, children and men, osteoporosis related-sarcopenia and fractures, and mesenchymal stem cells are becoming frontiers and focus on the health topics related to osteoporosis rehabilitation in the upcoming years, which are worthy of further exploration.

Adolescent Bone Advantages 3 Years After Resistance Training Trial

PURPOSE

We assessed maintenance of skeletal advantages 3 years after completion of a 2-year, school-based, controlled exercise trial in adolescent girls.

METHOD

Middle-school girls participated in a resistance training program embedded in physical education classes. Effort groups (low-effort group [LO] and high-effort group [HI]) were identified; the control group (CON) participated in standard physical education at a separate school. Baseline and follow-up (FU) assessments at 6, 18, and 54 (FU3) months included densitometry, anthropometry, and questionnaires assessing physical maturity and nonintervention organized physical activity. Linear mixed effects models were fit to evaluate bone outcomes across all FU time points for CON versus LO/HI.

RESULTS

Sixty-eight girls (23 CON/25 HI/20 LO) were 11.6 (0.3) years at baseline. Bone parameters did not differ at baseline, except femoral neck bone mineral density (LO < HI/CON, P < .05). Forty-seven participants provided FU3 assessment: 17 CON/16 HI/14 LO. After adjusting for height, gynecologic age, baseline bone, and organized physical activity, bone gains across all time points were greater for HI versus CON for legs bone mineral content, femoral neck bone mineral content/bone mineral density, and third lumbar vertebra bone mineral content/bone mineral density (P ≤ .05). At FU3, bone values were greater for HI versus CON at subhead, legs, femoral neck, and third lumbar vertebra (P < .03).

CONCLUSION

Adolescent girls who exerted high effort in a school-based resistance training program demonstrated significant skeletal benefits 3 years after program completion.

Evaluating and optimizing bone health in children with chronic health conditions

Paediatric health care providers (HCPs) play an important role in optimizing bone health. Early intervention is essential to maximize the accrual of peak bone mass in adolescence and young adulthood and to reduce osteoporosis and fracture risk later in life. Children and adolescents with chronic health conditions may have several risk factors for poor bone health, including underlying inflammatory conditions, reduced weight-bearing activity, delayed puberty, and inadequate intake of calcium and vitamin D. Some medications-particularly glucocorticoids-can compromise bone mass and place a child at risk for fragility fractures. This practice point describes a targeted approach to identifying bone health risk factors in children and youth with chronic health conditions, highlights office initiatives aimed at optimizing bone mass accrual, and links HCPs to useful web-based tools and medical references. Indications for referral to a bone health specialist and bone-specific pharmacotherapeutic interventions are also reviewed.

L'évaluation et l'optimisation de la santé osseuse chez les enfants ayant des affections chroniques

Les professionnels de la santé des enfants jouent un rôle important dans l'optimisation de la santé osseuse. Il est essentiel d'intervenir rapidement pour maximiser le pic de masse osseuse à l'adolescence et au début de l'âge adulte et d'ainsi réduire le risque d'ostéoporose et de fractures plus tard dans la vie. Les enfants et les adolescents ayant une affection chronique peuvent présenter plusieurs facteurs de risque de mauvaise santé osseuse, notamment des maladies inflammatoires sous-jacentes, des activités avec mise en charge limitées, un retard pubertaire et un apport insuffisant de calcium et de vitamine D. Certains médicaments, et particulièrement les glucocorticoïdes, peuvent compromettre la masse osseuse et exposer l'enfant à un risque de fractures de fragilisation. Le présent point de pratique décrit une approche ciblée pour déterminer les facteurs de risque liés à la santé osseuse chez les enfants et les adolescents ayant une affection chronique, expose les mesures à prendre en cabinet pour optimiser l'acquisition de la masse osseuse et propose des outils en ligne utiles et des références médicales à l'intention des professionnels de la santé des enfants. Les indications pour diriger les patients vers un spécialiste de la santé osseuse et pour procéder à des interventions pharmacologiques visant les os sont également abordées.

A comparison of the associations between bone health and three different intensities of accelerometer-derived habitual physical activity in children and adolescents: a systematic review

Positive associations have been identified between bone outcomes and accelerometer-derived moderate (MPA) and vigorous (VPA) physical activity (PA) in youth; however, it remains unclear which intensity is most beneficial. This systematic review aimed to summarise accelerometer-derived methods used to estimate habitual PA in children and adolescents and determine whether the magnitude of association was consistently stronger for a particular intensity (MPA/MVPA/VPA). Observational studies assessing associations between accelerometer-derived MPA and/or MVPA and VPA with bone outcomes in children and adolescents (≤ 18 years) were identified in MEDLINE, EMBASE, Web of Science, SPORTDiscus and the Cochrane Central Register of Controlled Trials. Thirty articles were included (total n = 20,613 (10,077 males), 4-18 years). Chi-square tests determined whether the proportion of significant associations and strongest within-study associations differed significantly between intensities. Results demonstrated that accelerometer methods were highly variable between studies. Of the 570 associations analysed, 186 were significant (p < 0.05). The proportion of within-study strongest associations differed by PA intensity (3 × 2 χ2 = 86.6, p < 0.001) and was significantly higher for VPA (39%) compared to MVPA (5%; 2 × 2 χ2 = 55.3, p < 0.001) and MPA (9%, 2 × 2 χ2 = 49.1, p < 0.001). Results indicated a greater benefit of VPA over MPA/MVPA; however, variability in accelerometer-derived methods used prevents the precise bone-benefitting amount of VPA from being identified. Long epochs and numerous intensity cut-point definitions mean that bone-relevant PA has likely been missed or misclassified in this population. Future research should explore the use of shorter epochs (1 s) and identify bone-specific activity intensities, rather than using pre-defined activity classifications more relevant to cardiovascular health.

Bone mineral density and body composition in normal weight, overweight and obese children

BACKGROUND

There is a possibility that excess body fat affects bone mass gain and may compromise skeletal health in obese children. The purpose of the study was to identify the relationship between bone mineral density (BMD) and body composition in normal weight, overweight and obese children.

METHODS

This was a cross-sectional study of 6- to 11-year-old children who attended the hospital's outpatient clinic. They were apparently healthy and had no history of prematurity, low birth weight, or chronic diseases. Body mass index (BMI) was used to identify subjects as normal weight, overweight or obese. BMD and body composition were assessed by dual energy X-ray absorptiometry. The BMD values (total and lumbar spine) were compared between normal weight, overweight and obese children. Correlation coefficients were calculated, and multivariate models were performed.

RESULTS

Forty-nine children were included: 16 with normal weight, 15 that were overweight and 18 with obesity; the mean age was 8.4 ± 1.7 years. All the participants had a normal BMD (> - 2 SD). BMD was higher in obese children and had a positive correlation with total and trunk lean mass in the three study groups (p < 0.001). In obese children, an inverse correlation of lumbar spine BMD (Z score) with total and trunk fat mass (p < 0.05) was identified. In the multivariate models (with the whole group), the total lean mass was the only significant variable that explained BMD variability.

CONCLUSIONS

BMD in obese children was higher than that in normal weight children, which is explained by their greater lean mass and not by excess body fat. In obese children, a higher fat mass was related to a lower lumbar spine BMD. Lean mass had a direct correlation with BMD in the three study groups and was the most important predictor of BMD, reflecting the importance of strengthening the muscular system through performing physical activity and practicing a healthy lifestyle.

Drug Treatment of Low Bone Mass and Other Bone Conditions in Pediatric Patients

Osteoporosis may affect young individuals, albeit infrequently. In childhood, bone mass increases, reaching its peak between the second and third decades; then, after a period of stability, it gradually declines. Several conditions, including genetic disorders, chronic diseases, and some medications, can have an impact on bone homeostasis. Diagnosis in young patients is based on the criteria defined by the International Society for Clinical Densitometry (ISCD), published in 2013. High risk factors should be identified and monitored. Often simple interventions aimed to eliminate the underlying cause, to minimize the negative bone effects linked to drugs, or to increase calcium and vitamin D intake can protect bone mass. However, in selected cases, pharmacological treatment should be considered. Bisphosphonates remain the main therapeutic agent for children with significant skeletal fragility and are also useful in a large number of other bone conditions. Denosumab, an anti-RANKL antibody, could become a potential alternative treatment. Clinical trials to evaluate the long-term effects and safety of denosumab in children are ongoing.

Single bout of exercise triggers the increase of vitamin D blood concentration in adolescent trained boys: a pilot study

Vitamin D is necessary for musculoskeletal health, however, the supplementation of vitamin D above the sufficiency level does not bring additional bone mass density (BMD), unlike physical exercise which enhances the bone formatting process. Regular physical activity has been shown to upregulate VDR expression in muscles and to increase circulating vitamin D. Here we investigate whether a single bout of exercise might change 25(OH)D₃ blood concentration and how it affects metabolic response to exercise. Twenty-six boys, 13.8 years old (SD ± 0.7) soccer players, participated in the study. The participants performed one of two types of exercise: the first group performed the VO₂max test until exhaustion, and the second performed three times the repeated 30 s Wingate Anaerobic Test (WAnT). Blood was collected before, 15 min and one hour after the exercise. The concentration of 25(OH)D₃, parathyroid hormone (PTH), interleukin-6 (IL-6), lactate, non-esterified fatty acids (NEFA) and glycerol were determined. 25(OH)D₃ concentration significantly increased after the exercise in all boys. The most prominent changes in 25(OH)D₃, observed after WAnT, were associated with the rise of PTH. The dimensions of response to the exercises observed through the changes in the concentration of 25(OH)D₃, PTH, NEFA and glycerol were associated with the significant increases of IL-6 level. A single bout of exercise may increase the serum’s 25(OH)D₃ concentration in young trained boys. The intensive interval exercise brings a more potent stimulus to vitamin D fluctuations in young organisms. Our results support the hypothesis that muscles may both store and release 25(OH)D₃.

Regular Exercise and Weight-Control Behavior Are Protective Factors against Osteoporosis for General Population: A Propensity Score-Matched Analysis from Taiwan Biobank Participants

The rising prevalence of osteoporosis, which can lead to osteoporotic fractures, increases morbidity, mortality, and socioeconomic burden. Multiple factors influencing bone mass have already been identified. The aim of this study was to investigate whether exercise habits and weight-control behaviors can lower the incidence of osteoporosis in the general population. This retrospective study recruited all participants aged 35–70 years who underwent dual-energy X-ray absorptiometry (DXA) from Taiwan Biobank (TWB). The final analysis consisted of 3320 eligible participants divided into two groups; demographic characteristics, prevalence of clinical symptoms, comorbidities, and daily behavior were collected using a self-reported questionnaire. After propensity score matching with a 1:1 ratio, 1107 out of 2214 individuals were classified into the osteoporosis group. Age, body fat rate, body shape, diabetes mellitus, and social status were found to affect the incidence of osteoporosis. Subjects with a habit of regular exercise and weight-control behavior showed decreased odds of osteoporosis. (odds ratio: 0.709 and 0.753, 95% confidence interval: 0.599–0.839 and 0.636–0.890). In the general population, regular exercise or weight-control behavior lowers the incidence of osteoporosis.

Adolescent female handball players present greater bone mass content than soccer players: A cross-sectional study

BACKGROUND

Osteoporosis is a systemic disease affecting half of women over the age of 50 years. Considering that almost 90% of peak of bone mass is achieved until the second decade of life, ensuring a maximal bone mineral content acquisition may compensate for age-associated bone loss. Among several other factors, physical activity has been recommended to improve bone mass acquisition. However, it is unknown whether athletes involved with sports with different impact loading characteristics differ in regards to bone mass measurements.

AIM

To compare the bone mass content, bone mass density and lean mass of young female soccer players (odd-impact loading exercise), handball players (high-impact loading exercises) and non-athletes.

METHODS

A total of 115 female handball players (15.5 ± 1.3 years, 165.2 ± 5.6 cm and 61.9 ± 9.3 kg) and 142 soccer players (15.5 ± 1.5 years, 163.7 ± 6.6 cm and 56.5 ± 7.7 kg) were evaluated for body composition using a dual-emission X-ray absorptiometry system, and 136 female non-athletes (data from NHANES) (15.1 ± 1.32 years, 163.5 ± 5.8 cm and 67.2 ± 19.4 kg) were considered as the control.

RESULTS

Handball players presented higher bone mass content values than soccer players for upper limbs (294.8 ± 40.2 g and 270.7 ± 45.7 g, p < 0.001), lower limbs (1011.6 ± 145.5 g and 967.7 ± 144.3 g, p = 0.035), trunk (911.1 ± 182.5 g and 841.6 ± 163.7 g, p = 0.001), ribs (312.4 ± 69.9 g and 272.9 ± 58.0 g, p < 0.001), spine (245.1 ± 46.8 g and 222.0 ± 45.1 g, p < 0.001) and total bone mass (2708.7 ± 384.1 g and 2534.8 ± 386.0 g, p < 0.001). Moreover, non-athletes presented lower bone mass content for lower limbs (740.6 ± 132.3 g, p < 0.001), trunk (539.7 ± 98.6 g, p < 0.001), ribs (138.2 ± 29.9 g, p < 0.001), pelvis (238.9 ± 54.6 g, p < 0.001), spine (152.8 ± 26.4 g, p < 0.001) and total bone mass (1987.5 ± 311.3 g, p < 0.001) than both handball and soccer players. Handball players also presented higher bone mass density values than soccer players for trunk, ribs and spine (p < 0.05) and handball and soccer players presented higher bone mass density than non-athletes for all measurements (p < 0.005). Finally, the non-athletes' lower limb lean mass was lower than soccer and handball players values (p < 0.05).

CONCLUSION

Adolescent females engaged in handball training for at least one year present higher bone mass contents than those who are engaged in soccer training, which, in turn, present higher bone mass contents than non-athletes. These results might be used by physicians and healthcare providers to justify the choice of a particular sport to enhance bone mass gain in female adolescents.

Description of Bone Health Changes in a Cohort of Children With Acute Flaccid Myelitis (AFM)

OBJECTIVES

To qualitatively describe bone health changes in children with acute flaccid myelitis (AFM) and assess relationships with muscle mass and strength and functional performance.

METHODS

Retrospective analysis of a cohort of 79 children with AFM seen consecutively in one specialized academic center between January 1, 2007, and December 31, 2019.

RESULTS

Of the 79 participants who were aged 4 months to 21 years old, 41 (52%) had bone density measured by dual energy absorptiometry (DXA) and 32 of them (78%) were diagnosed with low bone mass (LBM). We recorded 25 fractures that occurred after onset of neurologic deficit in 14 of the children in the cohort (18%). Lean muscle mass correlated with bone mass and functional performance as assessed by Physical Abilities and Mobility Scale (PAMS) but not with muscle strength as assessed by manual muscle testing (MMT). Bone density in the lower limbs was associated with ambulatory status.

CONCLUSION

Children with AFM have a high likelihood of muscle and bone loss and frequently sustain pathologic fractures. Bone health in children with AFM should be carefully monitored, and efforts should be made to preserve bone mass and maximize muscle mass.

Low bone mass in Noonan syndrome children correlates with decreased muscle mass and low IGF-1 levels

Although musculoskeletal abnormalities have long been described in patients with Noonan syndrome (NS), only a few studies have investigated the bone status of these patients. The aim of this retrospective observational study was to describe the bone health of children with NS. Thirty-five patients with a genetically confirmed diagnosis of NS were enrolled. We analyzed the axial skeleton (lumbar spine) using dual energy X-ray absorptiometry and the appendicular skeleton (hand) with the BoneXpert system. Bone metabolism markers, including mineral homeostasis parameters, serum 25-hydroxy vitamin D (25-OHD) levels and markers of bone formation and resorption were also reported. Compared to the general population, axial and appendicular bone mass was significantly decreased in children with NS (p < 0.0001). Serum 25-OHD levels were low in about half of the patients and were negatively correlated with age (r = -0.52; p < 0.0001). Patients with NS exhibited reduced bone formation marker levels and increased bone resorption marker levels (p < 0.0001). No gender difference or genotype-phenotype correlations were found for the different bone parameters. Muscle mass and, to a lesser extent, serum insulin-like growth factor 1 (IGF-1) levels were independent predictors of whole-body bone mineral content (p < 0.0001 for both parameters; adjusted R² = 0.97). In conclusion, bone mass is reduced in children with NS and correlates with decreased muscle mass and low serum IGF-1 levels. These data justify addressing all potential threats to bone health including sufficient calcium and vitamin D intake, regular physical exercise, and hormone replacement therapy.

Physical Activity at Growth Induces Bone Mass Benefits Into Adulthood – A Fifteen‐Year Prospective Controlled Study

Daily school physical activity (PA) improves musculoskeletal traits. Whether or not benefits remain in adulthood is debated. We included in this study 131 children that took part in an intervention with 40 minutes of PA per school day (200 minutes per week) from age 6 to 9 years (grade one) to age 14 to 16 years (grade nine), whereas 78 children continued with national recommended school physical education of 60 minutes per week. Measurements were done with dual‐energy X‐ray absorptiometry (bone mineral content [BMC], bone mineral density [BMD], and bone area), and a computerized knee dynamometer (peak torque muscle strength) at study start, at the end of the intervention, and 7 years after the intervention. Group differences from study start and end of the intervention to 7 years thereafter were estimated by analyses of covariance (adjusted for sex and follow‐up time). Musculoskeletal gains from study start to 7 years after termination of the intervention were higher in the intervention group (total body less head BMC +182.5 g [95% confidence interval {CI}, 55.1–309.9] and BMD +0.03 g/cm² [95% CI, 0.003–0.05], femoral neck area + 0.2 cm² [95% CI, 0.1–0.4], and knee flexion peak torque muscle strength at 60 degrees per second +9.2 Nm [95% CI, 2.9–15.5]). There was no attenuation during the 7 years that followed termination of the intervention (all group comparisons p > 0.05). Benefits in musculoskeletal gains remain 7 years after termination of a daily school‐based PA program, without attenuation after termination of the program. Daily school PA may counteract low bone mass and inferior muscle strength in adulthood. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Downturn in Childhood Bone Mass: A Cross‐Sectional Study Over Four Decades

Screen time and physical inactivity have increased among children. As physical activity is a determinant of bone mass, there is a concern that children today have lower bone mass than earlier. If this is true, fractures may become more common in the future. In 2017–2018, we used single‐photon absorptiometry (SPA) to measure distal forearm bone mineral density (BMD; mg/cm²) in a normative cohort of 238 boys and 204 girls aged 7 to 15 years. We compared these results to BMD in a normative cohort collected in 1979–1981 (55 boys and 61 girls aged 7 to 15 years) measured by the same scanner. To investigate difference between the two cohorts, we used multiple linear regression with age, sex, and cohort as predictors. Predicted bone density at age 16 years was estimated through the slope values. The bone density‐age slope was flatter in the cohort measured in 2017–2018 than in the cohort measured 1979–1981 (−5.6 mg/cm²/yr [95% confidence interval −9.6 to −1.5]). Predicted bone density was at age 16 years in 2017–2018 in boys was 10% lower (−0.9 SD) and in girls 11% lower (−1.1 SD) than in their counterparts measured in 1979–1981. We found indications that children nowadays develop lower bone mass than four decades ago, giving concern that they may have a higher risk of osteoporosis and fragility fractures as they grow old. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Longitudinal trends and predictors of muscle-strengthening activity guideline adherence among Canadian youths

OBJECTIVES

Muscle-strengthening activity (MSE e.g. push-ups, sit-ups, use of weight machines) is linked to multiple health benefits for youth, and is part of the global physical activity guidelines for children and adolescents (5-17 years). However, MSE is rarely assessed in youth health surveillance. This study describes the longitudinal trends and predictors of MSE among a cohort of Canadian youths.

DESIGN

Longitudinal.

METHODS

Data were drawn from a cohort of 3366 youths who participated in three waves of COMPASS, a longitudinal study of secondary school students across Canada [Wave 1 (T1) 2015/16, Wave 2 (T2) 2016/17, Wave 3 (T3) 2018/19]. The prevalence of the sample meeting the MSE guideline (≥3 days/week) was calculated for each wave. A multivariable logistic regression assessed the odds of meeting the MSE guideline for each wave (T1 and T2 and T3) across sociodemographic/lifestyle characteristics (e.g. sex, race, regionally, Body Mass Index, and aerobic physical activity).

RESULTS

For the total sample, MSE guideline adherence significantly declined across each study wave (T1 = 57.0%; T2 = 52.0%; T3 = 48.5%; p < 0.001 for linear trend). Population sub-groups less likely to meet the guideline at each wave included females, youth who were underweight or obese, those reporting insufficient aerobic physical activity, those from large urban settings, and youth who identify as Asian.

CONCLUSIONS

Among a large sample of Canadian youths, approximately half met the MSE guideline, with this prevalence declining over time. Large-scale MSE interventions are needed to address the low and decreasing adherence to this key modifiable health-related behavior among Canadian youths.

Modeling the musculoskeletal loading in bone remodeling at the hip of a child

BACKGROUND AND OBJECTIVES

The mechanical load associated with physical activity affects the bone adaptation process. The bone adaptationeffect varies with age, being more effective during childhood and adolescence, particularly during pre-pubertal years. Bone-strengthening physical activity is recommended for children and adolescents. The number of time periods (bouts) per day of vigorous physical activity seems to be more important than the total cumulative time for optimal bone strength. So, the aim of this study was to evaluate the effects of weight-bearing physical activity on bone mineral density (BMD) of the proximal femur through computational simulation considering the intensity, exposure time (bouts) and regionalization of the results.

METHODS

For this purpose, a finite element model of a 7 year-old child femur was developed based on computed tomography images. Musculoskeletal loads were obtained from experimental kinematic data of weight-bearing physical activity performed by children of the same age (standing, walking, running, jumping). The effects of physical activity on BMD of several regions of interest of the femur were analyzed using a bone remodeling model. A daily accumulation of 400 min of physical activity (200 min walking and 200 min standing) was considered as reference, against with which the effects of additional 10 min loading bouts were compared: 10 min bouts of vigorous intensity physical activity vs. 10 min bouts of light to moderate intensity physical activity.

RESULTS

The simulations revealed greater increases in BMD associated with higher intensity and longer duration of physical activity. The largest BMD increases occurs during the first 10 min bout compared to longer durations and in less mineralized central regions compared to regions far from the neutral axis of the bone.

CONCLUSION

Weight bearing physical activity is more effective in bone remodeling when the musculoskeletal loading is more intense and of short duration and, under these conditions, less mineralized regions are more positively impacted.

Musculoskeletal Benefits from a Physical Activity Program in Primary School are Retained 4 Years after the Program is Terminated

Daily school physical activity (PA) improves musculoskeletal traits. This study evaluates whether the benefits remain 4 years after the intervention. We followed 45 boys and 36 girls who had had 40 min PA/school day during the nine compulsory school years and 21 boys and 22 girls who had had 60 min PA/school week (reference), with measurements at baseline and 4 years after the program terminated. Bone mineral content (BMC; g) and bone mineral density (BMD; g/cm²) were measured by dual-energy X-ray absorptiometry and knee flexion peak torque relative to total body weight (PT_flexTBW) at a speed of 180 degrees/second with a computerized dynamometer. Group differences are presented as mean differences (adjusted for sex and duration of follow-up period) with 95% confidence intervals. The total gain bone mass [mean difference in spine BMC +32.0 g (14.6, 49.4) and in arms BMD of +0.06 g/cm² (0.02, 0.09)] and gain in muscle strength [mean difference in PT_flex180TBW +12.1 (2.0, 22.2)] were greater in the intervention than in the control group. There are still 4 years after the intervention indications of benefits in both bone mass and muscle strength gain. Daily school PA may counteract low bone mass and inferior muscle strength in adult life. ClinicalTrials.gov.NCT000633828 retrospectively registered 2008-11-03.

Bone mineral density and its influencing factors in Chinese children with spinal muscular atrophy types 2 and 3

Background

Patients with spinal muscular atrophy (SMA) are at risk of decreased bone mineral density (BMD). The bone health status of Chinese patients with SMA has been poorly studied. We aimed to evaluate the BMD of children with SMA types 2 and 3 in mainland China and investigate its influencing factors.

Methods

Forty patients with a mean age of 5.5 years affected by SMA types 2 and 3 (n = 22 and n = 18, respectively) were enrolled between September 2017 and May 2019. Total body less head (TBLH) BMD, lumbar spine (LS) BMD, and body composition were measured using dual-energy X-ray absorptiometry (DXA). Serum bone metabolism markers and complete spinal radiographs were assessed. We utilized a linear regression model to explore the correlations between BMD and its related factors.

Results

A total of 67.5% (27/40) of patients were diagnosed with low BMD and 2.5% (1/40) were diagnosed with osteoporosis. The TBLH BMD and LS BMD Z-scores in children with SMA type 2 were significantly lower than those with SMA type 3. Both TBLH and LS BMD Z-scores tended to increase with the change of SMA subtypes from 2a-3b. Vitamin D insufficiency and deficiency were found in 37.5% (15/40) of the patients. Serum Ca, phosphorus (P), alkaline phosphatase (ALP) and parathormone (PTH) levels were normal. There were no significant differences among the four subtypes in terms of all the serum bone metabolism markers. Phenotype was significantly associated with TBLH BMD and LS BMD Z-scores, and serum PTH levels were significantly associated with TBLH BMD Z-scores.

Conclusions

Low BMD and osteoporosis were highly prevalent in mainland Chinese children with SMA types 2 and 3. Phenotype and serum PTH level might be the influencing factors of BMD. Regular monitoring of BMD by DXA scan and taking active interventions aim to SMA children with different types are important.

The epidemiology of muscle-strengthening activity among adolescents from 28 European countries

AIMS

This study aimed to describe the prevalence and socio-demographic and lifestyle-related correlates of muscle-strengthening activity (MSA; strength/resistance training, sit-ups/push-ups, etc.) among a large sample of European adolescents.

METHODS

Data were drawn from the European Health Interview Survey Wave 2 (2013-2014), including 8818 adolescents (15-17 years) from 28 European countries. Self-reported MSA was assessed using a previously validated survey item. Population-weighted prevalence ratios were calculated for (a) 'none' (0 days/week), (b) 'insufficient MSA' (1-2 days/week) or (c) 'sufficient MSA' (⩾3 days/week). Generalised linear models using Poisson regression with robust error variance were used to calculate the prevalence ratios for adolescents reporting sufficient MSA by socio-demographic/lifestyle characteristics and by European region.

RESULTS

Overall, 19.4% (95% confidence interval (CI) 18.3-20.7) reported sufficient (⩾3 days/week) MSA and 57.9% (95% CI 56.4-59.6) reported none. Females, adolescents from Southern and Eastern European regions, those not meeting the aerobic guideline and adolescents classified as overweight were significantly associated with a lower likelihood of reporting sufficient MSA, independent of other characteristics.

CONCLUSIONS

The majority of European adolescents do not meet the MSA guidelines. Future large-scale MSA public-health interventions should target female and currently inactive adolescents, as well as those from Southern and Eastern European regions.

Home-Based Telehealth Exercise Intervention in Early-On Survivors of Childhood Acute Lymphoblastic Leukemia: Feasibility Study

Background

Acute lymphoblastic leukemia is the most common type of pediatric cancer. Acute lymphoblastic leukemia causes an altered bone mineral homeostasis state, which can contribute to osteopenia, and bone fractures, most commonly vertebral fractures. With the increasing number of childhood cancer survivors, late adverse effects such as musculoskeletal comorbidities are often reported and are further influenced by inactive lifestyle habits. Physical activity has been shown to increase the mechanical workload of the bone, mitigating bone impairment in other cancer-specific populations.

Objective

This interventional pilot study aims to investigate the use of telehealth to deliver a home-based exercise intervention for early-on survivors of bone marrow–related hematological malignancies and to assess its impact on survivors’ musculoskeletal and functional health.

Methods

We aimed to recruit a group of 12 early-on survivors of acute lymphoblastic leukemia, within 6 months to 5 years of treatment, to participate in and complete the proposed telehealth intervention with a parent. The 16-week intervention included 40 potential home-based physical activity interventions supervised by a kinesiologist through a telehealth internet platform, with monthly progression. Patients were recruited to the cohort if they were able to participate in the intervention during the first month (minimum 12 weeks of intervention). Evaluation before and after the intervention protocol highlighted differences in functional capacities and musculoskeletal health of patients using mechanography, peripheral quantitative computed tomography, 6-minute walk test, and grip force test.

Results

The recruitment rate for the intervention was low (12/57, 21% of contacted patients). Of 12 patients, 3 were excluded (1=relapse, 1=failure to meet technical requirements, and 1=abandoned). The 9 patients who completed the intervention (6 girls; mean age 10.93, SD 2.83 years; mean BMI 21.58, SD 6.55 kg/m²; mean time since treatment completion 36.67, SD 16.37 months) had a mean adherence of 89% and a completion rate of 75%. In addition, these patients showed functional improvements in lower limb muscle force and power as well as in the 6-minute walk test distance. Participants also showed improved bone health after the intervention on the following parameters: bone mineral content, stress-strain index, total and cortical cross-sectional area at the 14% site (P=.03, P=.01, P=.01, and P=.001, respectively) and 38% site of the tibia (P=.003, P=.04, P=.001, and P=.003, respectively).

Conclusions

High adherence and participation rates suggest that telehealth is a feasible method to deliver exercise interventions to young early-on survivors of acute lymphoblastic leukemia. The proposed intervention seems promising in providing benefits to patients’ functional performance and bone health, but a large-scale study is needed to confirm this assumption.

Patient and Parent Experiences with Group Telerehabilitation for Child Survivors of Acute Lymphoblastic Leukemia

BACKGROUND

Acute Lymphoblastic Leukemia (ALL) is the most common pediatric cancer. ALL and its treatment cause altered bone-mineral homeostasis, which can contribute to musculoskeletal late adverse effects (LAEs). With the increasing number of childhood cancer survivors, LAEs are reported often, and are aggravated by inactive lifestyles. A telerehabilitation program is proposed to strengthen the muscle-bone complex and prevent future impairment.

OBJECTIVE

This study aimed to explore and better understand patient and parent experience of a telerehabilitation program after completion of ALL treatment.

METHODS

ALL survivors (n = 12), 75% girls, 7.9 to 14.7 years old, within six months to five years of treatment, were recruited to participate in the proposed study, along with a parent. The 16-week group program included 40 potential home-based physical activities, with monthly progression, supervised by a kinesiologist, through an online telerehabilitation platform. Patients could be included in the study if they joined during the first month of intervention of their group (minimum 12 weeks of intervention). A semi-structured post-intervention interview was conducted with the patients and their parent during the final assessment, along with a review of the kinesiologist's clinical notes, to obtain a portrait of the participants' experience with the telerehabilitation program. Overarching themes were identified by one author and confirmed by two senior authors before extracting the various aspects of each theme.

RESULTS

Of the 12 patients recruited, three were excluded from the analysis because they did not complete the minimum 12 weeks of intervention (one = relapse, one = failure to meet technical requirements, and one = abandoned due to parent's disinterest). The nine patients who completed the program (six girls; 10.93 ± 2.83 years) had a mean adherence of 89%. The overarching themes identified were the program modalities (group approach with patient-parent paired training, supervised by a kinesiologist), the telerehabilitation system, the participants' perception of the benefits, and recommendations and suggestions from the families. Both patients and parents expressed very high satisfaction with the program and perceived benefits.

CONCLUSION

Participants appreciated the program and reported they would all recommend it to other families in similar situations. The telerehabilitation method of service delivery was perceived by some as decisive in choosing to participate, while the supervision and intra- and inter-family interactions were the motivating factors that were key to program adherence.

Narrative review of the influence of high-intensity interval training on adolescents' bone health: commentary and perspectives

Although several benefits have been associated to high-intensity interval training (HIIT), there is a lack of clarity on the HIIT effects in adolescents, especially on bone health outcomes. To address this gap, our research aimed to perform a systematic review, which focus on the influence of HIIT on adolescents' bone health. Our search strategy was conducted on three databases (PubMed, SCOPUS, and Embase). For our review, we included articles with the following characteristics: (I) sample consisting of adolescents (10-19 years old), (II) HIIT interventions; and (III) assessment of bone health outcomes. Longitudinal and clinical trials studies with no language and year of publications restrictions were eligible to be included. A total of 63 eligible studies were identified. After removing the duplicates and screening the titles and abstracts, six articles remained to be read in full text. However, none of the articles met our criteria. Studies in which no article meets the eligibility criteria are also essential and need to be shared with the academic community because it may stimulate appropriate future investigations in this field. This lack in the review results highlights the need for further epidemiological research focusing on this topic, including high quality, large scale, and longitudinal studies, as well as randomized controlled trials to confirm or refute efficacy.

2019 EULAR points to consider for non-physician health professionals to prevent and manage fragility fractures in adults 50 years or older

OBJECTIVE

To establish European League Against Rheumatism (EULAR) points to consider for non-physician health professionals to prevent and manage fragility fractures in adults 50 years or older.

METHODS

Points to consider were developed in accordance with EULAR standard operating procedures for EULAR-endorsed recommendations, led by an international multidisciplinary task force, including patient research partners and different health professionals from 10 European countries. Level of evidence and strength of recommendation were determined for each point to consider, and the mean level of agreement among the task force members was calculated.

RESULTS

Two overarching principles and seven points to consider were formulated based on scientific evidence and the expert opinion of the task force. The two overarching principles focus on shared decisions between patients and non-physician health professionals and involvement of different non-physician health professionals in prevention and management of fragility fractures. Four points to consider relate to prevention: identification of patients at risk of fracture, fall risk evaluation, multicomponent interventions to prevent primary fracture and discouragement of smoking and overuse of alcohol. The remaining three focus on management of fragility fractures: exercise and nutritional interventions, the organisation and coordination of multidisciplinary services for post-fracture models of care and adherence to anti-osteoporosis medicines. The mean level of agreement among the task force for the overarching principles and the points to consider ranged between 8.4 and 9.6.

CONCLUSION

These first EULAR points to consider for non-physician health professionals to prevent and manage fragility fractures in adults 50 years or older serve to guide healthcare practice and education.

Association of objectively measured physical activity and bone health in children and adolescents: a systematic review and narrative synthesis

The influence of day-to-day physical activity on bone in adolescence has not been well characterized. Forty articles were identified that assessed the relationship between accelerometry-derived physical activity and bone outcomes in adolescents. Physical activity was positively associated with bone strength in peri-pubertal males, with less consistent evidence in females. Physical activity (PA) is recommended to optimize bone development in childhood and adolescence; however, the influence of day-to-day PA on bone development is not well defined. The aim of this review was to describe the current evidence for objectively measured PA on bone outcomes in healthy children and adolescents. MEDLINE, Embase, Cochrane Library, Scopus, Web of Science, CINAHL, PsycInfo, and ClinicalTrials.gov were searched for relevant articles up to April 2020. Studies assessing the relationship between accelerometry-derived PA and bone outcomes in adolescents (6-18 years old) were included. Two reviewers independently screened studies for eligibility, extracted data, and rated study quality. Forty articles met inclusion criteria (25 cross-sectional, 15 longitudinal). There was significant heterogeneity in accelerometry methodology and bone outcomes measured. Studies in males indicated a significant, positive relationship between moderate to vigorous PA (MVPA) and bone outcomes at the hip and femur, particularly during the peri-pubertal years. The results for MVPA and bone outcomes in females were mixed. There was a paucity of longitudinal studies using pQCT and a lack of data regarding how light PA and/or impact activity influences bone outcomes. The current evidence suggests that objectively measured MVPA is positively associated with bone outcomes in children and adolescents, especially in males. However, inconsistencies in methodology make it difficult to determine the amount and type of PA that leads to favorable bone outcomes. Given that the majority of research has been conducted in Caucasian adolescents, further research is needed in minority populations.

Exercise and Peak Bone Mass

PURPOSE OF REVIEW

The main goal of this narrative review is to assess whether physical activity (PA) influences peak bone mass and fracture risk.

RECENT FINDINGS

Several randomized controlled trials (RCT) show that short-term PA intervention programs in childhood improve the accrual of bone mineral. There are now also long-term controlled PA intervention studies demonstrating that both boys and girls with daily school PA through puberty gain higher bone mineral content (BMC) and bone mineral density (BMD) and greater bone size than boys and girls with school PA 1-2 times/week. These benefits seem to be followed by a gradual reduction in expected fracture rates, so that in children with daily school PA, the incidence rate ratio (IRR) after 8 years is less than half that expected by age. Daily school PA from before to after puberty is associated with beneficial gains in bone traits and gradually lower relative fracture risk.

Cross-sectional and longitudinal associations between physical activity, sedentary behaviour and bone stiffness index across weight status in European children and adolescents

Background

The associations between physical activity (PA), sedentary behaviour (SB) and bone health may be differentially affected by weight status during growth. This study aims to assess the cross-sectional and longitudinal associations between PA, SB and bone stiffness index (SI) in European children and adolescents, taking the weight status into consideration.

Methods

Calcaneus SI was first measured by quantitative ultrasound among children aged 2–9 years old in 2007/08. It was measured again after 2 years in the IDEFICS study and after 6 years in the I. Family study. A sample of 2008 participants with time spent at sports clubs, watching TV and playing computer/games self-reported by questionnaire, and a subsample of 1037 participants with SB, light PA (LPA) and moderate-to-vigorous PA (MVPA) objectively measured using Actigraph accelerometers were included in the analyses. Weight status was defined as thin/normal and overweight/obese according to the extended International Obesity Task Force criteria. Linear mixed-effects models were used to estimate the cross-sectional and longitudinal associations between PA, SB and SI percentiles, stratified by weight status.

Results

The cross-sectional association between weekly duration of watching TV and SI percentiles was negative in thin/normal weight group (β = − 0.35, p = 0.008). However, baseline weekly duration of watching TV (β = − 0.63, p = 0.021) and change after 2 years (β = − 0.63, p = 0.022) as well as the change in weekly duration of playing computer/games after 6 years (β = − 0.75, p = 0.019) were inversely associated with corresponding changes in SI percentiles in overweight/obese group. Change in time spent at sports clubs was positively associated with change in SI percentiles after 2 years (β = 1.28, p = 0.001), with comparable effect sizes across weight status. In the subsample with accelerometer data, we found a positive cross-sectional association between MVPA and SI percentiles in thin/normal weight group. Baseline MVPA predicted changes in SI percentiles after 2 and 6 years in all groups.

Conclusions

Our results suggested the beneficial effect of PA on SI. However, the increasing durations of screen-based SB might be risk factors for SI development, especially in overweight/obese children and adolescents.

Bone accrual over 18 months of participation in different loading sports during adolescence

This study investigated the impact and non-impact sports on bone mineral density accrual in adolescents over 18 months. The impact sports were beneficial for bone health (accrual of bone density). In contrast, swimmers had similar or lower bone mineral density compared with the control group depending on the skeletal site.

PURPOSE

To investigate the impact and non-impact sports on bone mineral density (BMD) accrual in adolescents over a period of 18 months METHODS: The sample was composed of 71 adolescents, avarage age of 12.7 (± 1.7) years old at baseline. Bone outcomes were compared according to the loading of the sports practiced (impact sports, n = 33 [basketball, karate, and judo], non-impact sport, n = 18 [swimming], and control group, n = 20). Areal bone mineral density (aBMD) was measured by dual-energy X-ray absorptiometry (DXA) and bone mineral apparent density (BMAD) estimated through equation. The results were compared between the groups using analysis of variance and analysis of covariance.

RESULTS

Adjusted aBMD at lower limbs, whole body less head (WBLH), and adjusted WBLH BMAD were significantly greater in the impact sport group than the non-impact sport group at all time points. Adjusted upper limbs aBMD was significantly higher at the impact sports group compared to the non-impact sport group at 9 months and 18 months, besides compared to the control group at baseline and 18 months. Non-impact sport group presented a significant lower adjusted aBMD compared with control group at lower limbs and WBLH at 9 months, and at 9 months and 18 months in WBLH BMAD. There was a significant interaction (time × sport group) at upper limbs (p = 0.042) and WBLH aBMD (p = 0.006), and WBLH BMAD (p < 0.001).

CONCLUSION

Impact sports were more beneficial on accumulating aBMD and BMAD over a period of 18 months, while non-impact group (swimmers) had similar and lower aBMD and BMAD compared with the control group.

Celiac Disease and Bone Health in Children and Adolescents: A Systematic Review and Meta-Analysis

CONTEXT

Celiac disease is characterized by deficits in bone mineral accrual and longitudinal growth.

OBJECTIVE

The purpose of this study was to determine the differences in bone health and stature among children and adolescents with celiac disease versus healthy controls.

DATA SOURCES

Articles published before February 27, 2018 were located using searches of the Physical Education Index (n = 186), PubMed (n = 180), Scopus (n = 3), SPORTDiscus (n = 3), and Web of Science (n = 4).

STUDY SELECTION

Bone mineral content (BMC) and areal bone mineral density (aBMD) were assessed via dual-energy X-ray absorptiometry, and height was measured using a stadiometer.

DATA EXTRACTION

Effect sizes (ES) were calculated as follows: the mean difference of the celiac disease group and healthy control group, divided by the pooled standard deviation. The inverse variance weight was used to calculate the overall mean ES. Random-effects models were used to aggregate a mean ES, 95% confidence intervals (CIs) and to identify potential moderators.

RESULTS

The results of 30 effects gathered from 12 studies published between 1996 and 2017 indicated BMC (ES = -0.54, 95% CI: -0.69 to -0.40; p < 0.0001) and aBMD (ES = 0.72, 95% CI: -0.96 to -0.47; p < 0.0001) were lower in youth with celiac disease.

LIMITATIONS

These results were limited to only cross-sectional and baseline data from longitudinal studies reporting BMC and BMD, however did not assess changes in bone health over time.

CONCLUSION

Children and adolescents with celiac disease have suboptimal bone health and shorter stature.

Daily School Physical Activity from Before to After Puberty Improves Bone Mass and a Musculoskeletal Composite Risk Score for Fracture

This 7.5-year prospective controlled exercise intervention study assessed if daily school physical activity (PA), from before to after puberty, improved musculoskeletal traits. There were 63 boys and 34 girls in the intervention group (40 min PA/day), and 26 boys and 17 girls in the control group (60 min PA/week). We measured musculoskeletal traits at the start and end of the study. The overall musculoskeletal effect of PA was also estimated by a composite score (mean Z-score of the lumbar spine bone mineral content (BMC), bone area (BA), total body lean mass (TBLM), calcaneal ultrasound (speed of sound (SOS)), and muscle strength (knee flexion peak torque)). We used analyses of covariance (ANCOVA) for group comparisons. Compared to the gender-matched control group, intervention boys reached higher gains in BMC, BA, muscle strength, as well as in the composite score, and intervention girls higher gains in BMC, BA, SOS, as well as in the composite score (all p < 0.05, respectively). Our small sample study indicates that a daily school-based PA intervention program from Tanner stage 1 to 5 in both sexes is associated with greater bone mineral accrual, greater gain in bone size, and a greater gain in a musculoskeletal composite score for fractures.

Expert panel consensus recommendations for diagnosis and treatment of secondary osteoporosis in children

BACKGROUND

Osteoporosis incidence in children is increasing due to the increased survival rate of patients suffering from chronic diseases and the increased use of drugs that can damage bones. Recent changes made to the definition of childhood osteoporosis, along with the lack of guidelines or national consensuses regarding its diagnosis and treatment, have resulted in a wide variability in the approaches used to treat this disease. For these reasons, the Osteogenesis Imperfecta and Childhood Osteoporosis Working Group of the Spanish Society of Pediatric Rheumatology has sounded the need for developing guidelines to standardize clinical practice with regard to this pathology.

METHODS

An expert panel comprised of 6 pediatricians and 5 rheumatologists carried out a qualitative literature review and provided recommendations based on evidence, when that was available, or on their own experience. The level of evidence was determined for each section using the Oxford Centre for Evidence-based Medicine (CEBM) system. A Delphi survey was conducted for those recommendations with an evidence level of IV or V. This survey was sent to all members of the SERPE. All recommendations that had a level of agreement higher or equal to 70% were included.

RESULTS

Fifty-one recommendations, categorized into eight sections, were obtained. Twenty-four of them presented an evidence level 4 or 5, and therefore a Delphi survey was conducted. This was submitted electronically and received a response rate of 40%. All recommendations submitted to the Delphi round obtained a level of agreement of 70% or higher and were therefore accepted.

CONCLUSION

In summary, we present herein guidelines for the prevention, diagnosis and treatment of secondary childhood osteoporosis based on the available evidence and expert clinical experience. We believe it can serve as a useful tool that will contribute to the standardization of clinical practice for this pathology. Prophylactic measures, early diagnosis and a proper therapeutic approach are essential to improving bone health, not only in children and adolescents, but also in the adults they will become in the future.

Beat osteoporosis - nourish and exercise skeletons (BONES): a group randomized controlled trial in children

BACKGROUND

Lifelong healthy habits developed during childhood may prevent chronic diseases in adulthood. Interventions to promote these habits must begin early. The BONES (Beat Osteoporosis - Nourish and Exercise Skeletons) project assessed whether early elementary school children participating in a multifaceted health behavior change, after-school based intervention would improve bone quality and muscular strength and engage in more bone-strengthening behaviors.

METHODS

The 2-year BONES (B) intervention included bone-strengthening physical activity (85 min/week), educational materials (2 days/week), and daily calcium-rich snacks (380 mg calcium/day) delivered by after-school program leaders. BONES plus Parent (B + P) included an additional parent education component. From 1999 to 2004, n = 83 after-school programs (N = 1434 children aged 6-9 years) in Massachusetts and Rhode Island participated in a group randomized trial with two intervention arms (B only, n = 25 programs; B + P, n = 33) and a control arm (C, n = 25). Outcome measures (primary: bone quality (stiffness index of the calcaneus) and muscular strength (grip strength and vertical jump); secondary: bone-strengthening behaviors (calcium-rich food knowledge, preference, and intake; and physical activity level (metabolic equivalent time (MET) score, and weight-bearing factor (WBF) score)) were recorded at baseline, and after years one and two. Analyses followed an intent-to-treat protocol, and focused on individual subjects' trajectories along the three time points adjusting for baseline age and race via a mixed-effects regression framework. Analyses were performed with and without sex stratification.

RESULTS

Children in B + P increased bone stiffness compared to C (p = 0.05); No significant changes were observed in muscle strength, food knowledge, or vertical jump. Children in B + P showed significant improvement in their MET and WBF scores compared to C (p < 0.01) with a stronger effect in boys in both B and B + P (all p < 0.01).

CONCLUSION

After-school programs, coupled with parental engagement, serving early elementary school children are a potentially feasible platform to deliver bone-strengthening behaviors to prevent osteoporosis in adulthood, with some encouraging bone and physical activity outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00065247. Retrospectively registered. First posted July 22, 2003.

Consumption of Greek yogurt during 12 weeks of high-impact loading exercise increases bone formation in young, adult males – a secondary analysis from a randomized trial

Exercise combined with protein and calcium has been shown to benefit bone turnover and bone metabolism. Greek yogurt (GY) contains important nutrients that support bone but has yet to be studied with exercise for this purpose. Thirty untrained, university-aged, males were randomized to 2 groups (n = 15/group): GY (20 g protein, 208 mg calcium/dose) or placebo pudding (PP; 0 g protein, 0 g calcium/dose) consumed 3×/day on training days and 2×/day on nontraining days. Both groups underwent a resistance/plyometric training program for 12 weeks. Blood was obtained at weeks 0, 1, and 12 to measure procollagen-type-I-N-terminal-propeptide (P1NP) and C-terminal-telopeptide (CTX). After outlier treatment, P1NP increased more over time in GY versus PP (p = 0.002; interaction). Both groups decreased CTX over time (p = 0.046; time effect). Following 1 week of training, there was a trend towards a significant increase in CTX in PP with no change in GY (p = 0.062; interaction). P1NP changed more in GY than PP (baseline to week 12; p = 0.029) as did the P1NP/CTX ratio (p = 0.015) indicating a greater increase in formation with GY. Thus, GY added to a high-load, high-impact exercise program positively shifted bone turnover towards increased formation while attenuating resorption. GY could be a plausible postexercise food to support bone health in young adult males.

Novelty Greek yogurt, with exercise, increased bone formation in young adult males over 12 weeks. After 1 week of an osteogenic exercise program, Greek yogurt tended to blunt a rise in bone resorption seen with the placebo. Greek yogurt is a plausible postexercise food that supports bone.

The Bones of Children With Obesity

Excess adiposity in childhood may affect bone development, ultimately leading to bone frailty. Previous reports showing an increased rate of extremity fractures in children with obesity support this fear. On the other hand, there is also evidence suggesting that bone mineral content is higher in obese children than in normal weight peers. Both adipocytes and osteoblasts derive from multipotent mesenchymal stem cells (MSCs) and obesity drives the differentiation of MSCs toward adipocytes at the expense of osteoblast differentiation. Furthermore, adipocytes in bone marrow microenvironment release a number of pro-inflammatory and immunomodulatory molecules that up-regulate formation and activation of osteoclasts, thus favoring bone frailty. On the other hand, body adiposity represents a mechanical load, which is beneficial for bone accrual. In this frame, bone quality, and structure result from the balance of inflammatory and mechanical stimuli. Diet, physical activity and the hormonal milieu at puberty play a pivotal role on this balance. In this review, we will address the question whether the bone of obese children and adolescents is unhealthy in comparison with normal-weight peers and discuss mechanisms underlying the differences in bone quality and structure. We anticipate that many biases and confounders affect the clinical studies conducted so far and preclude us from achieving robust conclusions. Sample-size, lack of adequate controls, heterogeneity of study designs are the major drawbacks of the existing reports. Due to the increased body size of children with obesity, dual energy absorptiometry might overestimate bone mineral density in these individuals. Magnetic resonance imaging, peripheral quantitative CT (pQCT) scanning and high-resolution pQCT are promising techniques for the accurate estimate of bone mineral content in obese children. Moreover, no longitudinal study on the risk of incident osteoporosis in early adulthood of children and adolescents with obesity is available. Finally, we will address emerging dietary issues (i.e., the likely benefits for the bone health of polyunsaturated fatty acids and polyphenols) since an healthy diet (i.e., the Mediterranean diet) with balanced intake of certain nutrients associated with physical activity remain the cornerstones for achieving an adequate bone accrual in young individuals regardless of their adiposity degree.

Hemozoin produced by mammals confers heme tolerance

Free heme is cytotoxic as exemplified by hemolytic diseases and genetic deficiencies in heme recycling and detoxifying pathways. Thus, intracellular accumulation of heme has not been observed in mammalian cells to date. Here we show that mice deficient for the heme transporter SLC48A1 (also known as HRG1) accumulate over ten-fold excess heme in reticuloendothelial macrophage lysosomes that are 10 to 100 times larger than normal. Macrophages tolerate these high concentrations of heme by crystallizing them into hemozoin, which heretofore has only been found in blood-feeding organisms. SLC48A1 deficiency results in impaired erythroid maturation and an inability to systemically respond to iron deficiency. Complete heme tolerance requires a fully-operational heme degradation pathway as haplo insufficiency of HMOX1 combined with SLC48A1 inactivation causes perinatal lethality demonstrating synthetic lethal interactions between heme transport and degradation. Our studies establish the formation of hemozoin by mammals as a previously unsuspected heme tolerance pathway.

Skeletal loading score is associated with bone microarchitecture in young adults

Physical activity that involves high strain magnitudes and high rates of loading is reported to be most effective in eliciting an osteogenic bone response. Whether a history of participation in osteogenic activities during youth, as well as current participation in osteogenic activities, contributes to young adult bone microarchitecture and strength is unknown.

PURPOSE

We determined the association between a new skeletal loading (SkL) score reflecting physical activity from age 11 to adulthood, the bone specific physical activity questionnaire (BPAQ) and bone microarchitecture in young Black and White men and women.

METHODS

We conducted a cross-sectional study of young ([mean ± SD] 23.7 ± 3.3 years) Black (n = 51 women, n = 31 men) and White (n = 50 women, n = 49 men) adults. Microarchitecture and estimated bone strength (by micro-finite element analysis) were assessed at the ultradistal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT). Physical activity questionnaires were administered and a SkL score was derived based on ground reaction force, rate of loading, frequency, duration, and life period of participation per activity from age 11 onwards. BPAQ score was also calculated. We used multiple linear regression to determine associations between both SkL score and BPAQ score and bone outcomes, adjusting for age, height, weight, sex, and race.

RESULTS

We found that SkL score, which accounts for current and historical physical activity, was significantly associated with most cortical bone parameters at the tibia including area, area fraction, porosity, thickness, and tissue mineral density (R² = 0.27-0.55, all p < 0.01). Further, trabecular thickness, separation, number, and bone mineral density (R² = 0.22-0.32, all p < 0.01), as well as stiffness and failure load (R² = 0.63-0.65, all p < 0.01), were associated with the SkL score. The BPAQ was also significantly associated with most bone parameters, but to a lesser degree than SkL score.

CONCLUSION

These findings suggest that among young adults, greater amounts of osteogenic physical activity, as assessed by the SkL score and BPAQ are associated with improved bone microarchitecture and strength. With the potential to predict bone parameters in young adults, these scores may ultimately serve to identify those most vulnerable to fracture.

Physical activity levels are associated with regional bone mineral density in boys

Background: Youth is a crucial period for bone gain, and physical activity (PA) has shown to increase bone mineral density (BMD) in this period. However, whether PA affects regional BMD is unclear. Thus, the aim of this study was to analyze the relationship between PA levels and regional BMD in youths. Methods: The sample included 110 children and adolescents aged 6-14 years. Body mass, height, sitting trunk length, and leg length were obtained for body mass index and maturity offset calculation. The arms, pelvis, spine, trunk, and legs BMD were measured by double energy X-ray absorptiometry. The PA was evaluated by questionnaire, and youths were classified as low, moderately, or highly physically active. Results: The sample included 63.7% boys and 36.3% girls with mean age of sample 9.5 (±1.6) yrs. Age, body mass index, and maturity offset were similar between sexes (p > 0.05). Boys with low PA levels had lower BMD Z-score for arms (-0.20 ± 0.71 vs. 0.30 ± 1.19, p = 0.006) and legs (-0.14 ± 1.00 vs. 0.35 ± 1.06, p = 0.026) compared to highly physically active youths. Multiple linear regression showed a positive linear relationship between legs BMD and PA in boys (β = 0.72 [95% CI = 0.09; 1.36]). Conclusion: In boys, low PA levels are associated with lower BMD in arms and legs.

A 9-Month Jumping Intervention to Improve Bone Geometry in Adolescent Male Athletes

PURPOSE

Sports have different effects on bone development and effective interventions to improve bone health of adolescent athletes are needed. The purpose of the study was to investigate the effect of a 9-month jumping intervention on bone geometry and metabolism in adolescent male athletes.

METHODS

Ninety-three adolescent (14.1 yr old) male swimmers (SWI), footballers (FOO), and cyclists (CYC) were randomized to intervention and sport (INT-SWI = 19, INT-FOO = 15, and INT-CYC = 14) or sport only (CON-SWI = 18, CON-FOO = 15, and CON-CYC = 12) groups. Cross-sectional area, cross-sectional moment of inertia (CSMI), and section modulus (Z) at the femoral neck were assessed using hip structural analysis and trabecular texture of the lumbar spine using trabecular bone score. Bone mineral content (BMC) at femoral neck and lumbar spine was assessed using dual-energy x-ray absorptiometry. Serum N-terminal propeptide of procollagen type I, isomer of the carboxy-terminal telopeptide of type 1 collagen, total serum calcium, and 25-hydroxyvitamin D were analyzed.

RESULTS

INT-CYC acquired significantly higher lumbar spine BMC (4.6%) and femoral neck BMC (9.8%) than CON-CYC. INT-CYC acquired significantly higher cross-sectional area (11.0%), CSMI (10.1%), and trabecular bone score (4.4%) than CON-CYC. INT-SWI acquired significantly higher femoral neck BMC (6.0%) and CSMI (10.9%) than CON-SWI. There were no significant differences between INT-FOO and CON-FOO in any bone outcomes. N-terminal propeptide of procollagen type I significantly decreased in CON-SWI, INT-FOO, CON-FOO, and CON-CYC. Carboxy-terminal telopeptide of type 1 collagen significantly decreased in CON-SWI and CON-CYC. The 25-hydroxyvitamin D significantly increased in INT-CYC, CON-CYC, INT-FOO, and CON-FOO.

CONCLUSIONS

A 9-month jumping intervention improved bone outcomes in adolescent swimmers and cyclists, but not in footballers. This intervention might be used by sports clubs to improve bone health of adolescent athletes.

Best Practices for Conducting Observational Research to Assess the Relation between Nutrition and Bone: An International Working Group Summary

Diet is a modifiable factor that can affect bone strength and integrity, and the risk of fractures. Currently, a hierarchy of scientific evidence contributes to our understanding of the role of diet on bone health and fracture risk. The strength of evidence is generally based on the type of study conducted, the quality of the methodology employed, the rigor and integrity of the data collected and analysis plan, and the transparency and completeness of the results. Randomized controlled trials (RCTs) are considered to be the gold standard from a clinical research paradigm, but there is a dearth of high-quality diet-related intervention trials with bone as the primary outcome, forcing the use of observational research to inform research and clinical practices. However, for observational research to be of the most utility, standardization and optimization of the study design, accurate and reliable measurement of key variables, and appropriate data analysis and data reporting are paramount. Although there have been recommendations made in relation to RCTs in the field of nutrition, no clear rubric exists for best practices in conducting observational research with regard to nutrition and bone health. Therefore, the purpose of this paper is to describe the best practices and considerations for designing, conducting, analyzing, interpreting, and reporting observational research specifically for understanding the role of nutrition in bone health, amassed by a global panel of scientific experts with strengths in bone, nutrition epidemiology, physical activity, public health, clinical and translational trials, and observational study methods. The global panel of scientific experts represents the leadership and selected participants from the 10th annual International Symposium for the Nutritional Aspects of Osteoporosis. The topics selected and best practices presented reflect expert opinion and areas of scientific expertise of the authors rather than a systematic or comprehensive literature review or professional reporting guidelines.

Effects of High-Fat Diet and Body Mass on Bone Morphology and Mechanical Properties in 1100 Advanced Intercross Mice

Obesity is generally protective against osteoporosis and bone fracture. However, recent studies indicate that the influence of obesity on the skeleton is complex and can be detrimental. We evaluated the effects of a high-fat, obesogenic diet on the femur and radius of 1100 mice (males and females) from the Large-by-Small advanced intercross line (F₃₄ generation). At age 5 months, bone morphology was assessed by microCT and mechanical properties by three-point bending. Mice raised on a high-fat diet had modestly greater cortical area, bending stiffness, and strength. Size-independent material properties were unaffected by a high-fat diet, indicating that diet influenced bone quantity but not quality. Bone size and mechanical properties were strongly correlated with body mass. However, the increases in many bone traits per unit increase in body mass were less in high-fat diet mice than low-fat diet mice. Thus, although mice raised on a high-fat diet have, on average, bigger and stronger bones than low-fat-fed mice, a high-fat diet diminished the positive relationship between body mass and bone size and whole-bone strength. The findings support the concept that there are diminishing benefits to skeletal health with increasing obesity. © 2019 American Society for Bone and Mineral Research.

Physical Activity and Bone Accretion: Isotemporal Modeling and Genetic Interactions

PURPOSE

This study aimed to determine if replacing time spent in high- and low-impact physical activity (PA) predicts changes in pediatric bone mineral density (BMD) and content (BMC).

METHODS

We analyzed data from the longitudinal Bone Mineral Density in Childhood Study (N = 2337 with up to seven visits). The participants were age 5-19 yr at baseline, 51.2% were female, and 80.6% were nonblack. Spine, total hip, and femoral neck areal BMD and total body less head (TBLH) BMC Z-scores were calculated. Hours per day spent in high- and low-impact PA were self-reported. Standard covariate-adjusted (partition model) and time allocation-sensitive isotemporal substitution modeling frameworks were applied to linear mixed models. Statistical interactions with sex, self-reported ancestry, age, and bone fragility genetic scores (percentage of areal BMD-lowering alleles carried) were tested.

RESULTS

In standard models, high-impact PA was positively associated with bone Z-score at all four skeletal sites (e.g., TBLH-BMC Z-score: beta = 0.05, P = 2.0 × 10), whereas low-impact PA was not associated with any of the bone Z-scores. In isotemporal substitution models, replacing 1 h·d of low- for high-impact PA was associated with higher bone Z-scores (e.g., TBLH-BMC Z-score: beta = 0.06, P = 2.9 × 10). Conversely, replacing 1 h·d of high- for low-impact PA was associated with lower bone Z-scores (e.g., TBLH-BMC Z-score: beta = -0.06, P = 2.9 × 10). The substitution associations were similar for each sex and ancestry group, and for those with higher and lower genetic scores for bone fragility (P-interactions > 0.05), but increased in strength among the older adolescents (P-age interactions < 0.05).

CONCLUSIONS

Time-sensitive models suggest that replacing low-impact PA for high-impact PA would be beneficial for the growing skeleton in the majority of children.

Bone Accrual in Children and Adolescent Nonelite Swimmers: A 2-Year Longitudinal Study

OBJECTIVE

To examine differences in bone mass between children and adolescents swimming competitively at nonelite levels (locally and regionally) and nonathletes and to assess changes in bone mass in these 2 groups over 24 months after taking into consideration several known confounders of bone mass.

DESIGN

Observational prospective study.

PARTICIPANTS

White nonelite swimmers (n = 128) and nonathletes (n = 106) 8 to 18 years of age from Memphis, Tennessee, USA.

MAIN OUTCOME MEASURES

Participants underwent dual-energy x-ray absorptiometry to assess total body and hip bone mineral content (BMC) at baseline and 12 and 24 months later.

RESULTS

At baseline, swimmers had 4.2% and 6.1% higher adjusted BMC for the total body and hip, respectively, compared with nonathletes (P values < 0.027). Averaging across assessment points, swimmers had 73.5 and 2.2 g higher BMC for the total body and hip, respectively, than nonathletes. Although there was a significant annual increase in total body and hip BMC in both groups (33.5 and 0.7 g, respectively), there was no difference in annualized bone accrual between swimmers and nonathletes for either total body BMC (swim by time effect; P = 0.213) or hip BMC (P = 0.265).

CONCLUSIONS

Competitive swimming at nonelite levels during childhood and adolescence does not seem to compromise bone accrual.

The interactions of physical activity, exercise and genetics and their associations with bone mineral density: implications for injury risk in elite athletes

Low bone mineral density (BMD) is established as a primary predictor of osteoporotic risk and can also have substantial implications for athlete health and injury risk in the elite sporting environment. BMD is a highly multi-factorial phenotype influenced by diet, hormonal characteristics and physical activity. The interrelationships between such factors, and a strong genetic component, suggested to be around 50-85% at various anatomical sites, determine skeletal health throughout life. Genome-wide association studies and case-control designs have revealed many loci associated with variation in BMD. However, a number of the candidate genes identified at these loci have no known associated biological function or have yet to be replicated in subsequent investigations. Furthermore, few investigations have considered gene-environment interactions-in particular, whether specific genes may be sensitive to mechanical loading from physical activity and the outcome of such an interaction for BMD and potential injury risk. Therefore, this review considers the importance of physical activity on BMD, genetic associations with BMD and how subsequent investigation requires consideration of the interaction between these determinants. Future research using well-defined independent cohorts such as elite athletes, who experience much greater mechanical stress than most, to study such phenotypes, can provide a greater understanding of these factors as well as the biological underpinnings of such a physiologically "extreme" population. Subsequently, modification of training, exercise or rehabilitation programmes based on genetic characteristics could have substantial implications in both the sporting and public health domains once the fundamental research has been conducted successfully.