Weight-bearing, muscle loading and bone mineral accrual in pubertal girls--a 2-year longitudinal study

Muscle strength deficits are associated with low bone mineral density in young pediatric cancer survivors: The iBoneFIT project

BACKGROUND

Pediatric cancer survivors are at increased risk of muscle weakness and low areal bone mineral density (aBMD). However, the prevalence of muscle strength deficits is not well documented, and the associations of muscle strength with aBMD are unknown in this population. Therefore, this study aimed to investigate the prevalence of upper- and lower-body muscle strength deficits and to examine the associations of upper- and lower-body muscle strength with age-, sex, and race-specific aBMD Z-scores at the total body, total hip, femoral neck, and lumbar spine.

METHODS

This cross-sectional study included 116 pediatric cancer survivors (12.1 ± 3.3 years old, mean ± SD; 42.2% female). Upper- and lower-body muscle strength were assessed by handgrip and standing long jump test, respectively. Dual‑energy X‑ray absorptiometry was used to measure aBMD (g/cm2). Associations between muscle strength and aBMD were evaluated in multivariable linear regression models. Logistic regression was used to evaluate the contribution of muscle strength (1-decile lower) to the odds of having low aBMD (Z-score ≤ 1.0). All analyses were adjusted for time from treatment completion, radiotherapy exposure, and body mass index.

RESULTS

More than one-half of survivors were within the 2 lowest deciles for upper- (56.9%) and lower- body muscle strength (60.0%) in comparison to age- and sex-specific reference values. Muscle strength deficits were associated with lower aBMD Z-scores at all sites (B = 0.133-0.258, p = 0.001-0.032). Each 1-decile lower in upper-body muscle strength was associated with 30%-95% higher odds of having low aBMD Z-scores at all sites. Each 1-decile lower in lower-body muscle strength was associated with 35%-70% higher odds of having low aBMD Z-scores at total body, total hip, and femoral neck.

CONCLUSION

Muscle strength deficits are prevalent in young pediatric cancer survivors, and such deficits are associated with lower aBMD Z-scores at all sites. These results suggest that interventions designed to improve muscle strength in this vulnerable population may have the added benefit of improving aBMD.

Bone Turnover Markers and Osteokines in Adolescent Female Athletes of High- and Low-Impact Sports Compared With Nonathletic Controls

This study examined differences in resting concentrations of markers of bone formation and resorption, and osteokines between female adolescent (12-16 y) swimmers, soccer players, and nonathletic controls. Resting, morning blood samples were obtained after an overnight fast from 20 swimmers, 20 soccer players, and 20 nonathletic controls, matched for age. carboxyl-terminal cross-linking telopeptide of type I collagen (CTX), amino-terminal propeptide of type I collagen (P1NP), total osteocalcin (OC), sclerostin, osteoprotegerin (OPG), and receptor activator of nuclear factor kappa B ligand (RANKL) were analyzed in serum. After controlling for percent body fat, there were no significant differences between swimmers and nonathletic controls in any of the measured markers. In contrast, soccer players had significantly higher P1NP (89.5 [25.6] ng·mL-1), OC (57.6 [22.9] ng·mL-1), and OPG (1052.5 [612.6] pg·mL-1) compared with both swimmers (P1NP: 66.5 [20.9] ng·mL-1; OC: 24.9 [12.5] ng·mL-1; OPG: 275.2 [83.8] pg·mL-1) and controls (P1NP: 58.5 [16.2] ng·mL-1; OC: 23.2 [11.9] ng·mL-1; OPG: 265.4 [97.6] pg·mL-1), with no differences in CTX, sclerostin, and RANKL. These results suggest that bone formation is higher in adolescent females engaged in high-impact sports like soccer compared with swimmers and controls.

Positive association of lean mass and negative association of protein intake on bone mass and bone geometry of adolescent soccer players

OBJECTIVE

The aim of this study was to evaluate the association of food consumption and body composition on bone parameters in adolescent soccer players.

METHODS

There were 148 male soccer players 12 to 18 y who participated in the study. Body composition was assessed by dual energy x-ray absorptiometry, comprising bone mineral density (BMD) and bone mineral content (BMC) of total body without head (TBLH), lumbar spine (L1-L4), and right femoral neck (RFN). The bone geometry variables measured were femoral strength index (FSI), buckling ratio (BR), section modulus (Z), cross-sectional moment of inertia (CSMI), and cross-sectional area (CSA). Food intake was analyzed using the 24-h food recall. Somatic maturation was estimated by the peak height velocity equation. For the statistical analysis, the stepwise multiple linear regression was used, with P < 0.05.

RESULTS

Regarding food consumption, there was a high protein intake and low calcium intake. Lean mass was a predictor of BMC of TBLH (R² = 0.524), L1-L4 (R² = 0.492), and RFN (R² = 0.405); BMD of L1-L4 (R² = 0.407) and RFN (R² = 0.27); Z (R² = 0.683), CSMI (R² = 0.630), and CSA (R² = 0.640). There was a negative correlation between protein intake with bone mass and bone geometry parameters.

CONCLUSION

In adolescent soccer players, lean mass was a predictor of bone parameters, and high protein intake was negatively associated with bone mass and geometry.

Testing the Functional Model of Bone Development: Direct and Mediating Role of Muscle Strength on Bone Properties in Growing Youth

This study examines the functional model of bone development in peri-pubertal boys and girls. Specifically, we implemented a mixed-longitudinal design and hierarchical structural models to provide experimental evidence in support of the conceptual functional model of bone development, postulating that the primary mechanical stimulus of bone strength development is muscle force. To this end, we measured radial and tibial bone properties (speed of sound, SOS), isometric grip and knee extensors strength, bone resorption (urinary NTX concentration), body mass index (BMI), somatic maturity (years from peak height velocity) and skeletal maturity (bone age) in 180 children aged 8–16 years. Measurements were repeated 2–4 times over a period of 3 years. The multilevel structural equation modeling of 406 participant-session observations revealed similar results for radial and tibial SOS. Muscle strength (i.e., grip strength for the radial and knee extension for tibial model) and NTX have a significant direct effect on bone SOS (β = 0.29 and −0.18, respectively). Somatic maturity had a direct impact on muscle strength (β = 0.24) and both a direct and indirect effect on bone SOS (total effect, β = 0.30). Physical activity and BMI also had a significant direct impact on bone properties, (β = 0.06 and −0.18, respectively), and an additional significant indirect effect through muscle strength (β = 0.01 and 0.05, respectively) with small differences per bone site and sex. Muscle strength fully mediated the impact of bone age (β = 0.14) while there was no significant effect of energy intake on either muscle strength or bone SOS. In conclusion, our results support the functional model of bone development in that muscle strength and bone metabolism directly affect bone development while the contribution of maturity, physical activity, and other modulators such as BMI, on bone development is additionally modulated through their effect on muscle strength.

Resistance Training for Children and Adolescents

Resistance training is becoming more important as an integral part of comprehensive sport training regimens, school physical education classes, and after-school fitness programs. The increasing number of youth who are involved in sport activities, coupled with the health problems of inactivity and being overweight, have resulted in increased interest in resistance training. Secular declines in measures of muscular fitness in modern-day youth highlight the need for participation in youth resistance training for nonathletes as well as athletes. Parents often ask pediatricians to offer advice regarding the safety, benefits, and implementation of an effective resistance-training program. This report is a revision of the 2008 American Academy of Pediatrics policy statement and reviews current information and research on the benefits and risks of resistance training for children and adolescents.

Is Muscular Fitness Associated with Future Health Benefits in Children and Adolescents? A Systematic Review and Meta-Analysis of Longitudinal Studies

BACKGROUND

No previous systematic review has quantitatively examined the association between muscular fitness during childhood and adolescence and health parameters later in life.

OBJECTIVE

The aim was to systematically review and meta-analyze the current evidence for a prospective association between muscular fitness in childhood and adolescence and future health status.

METHODS

Two authors systematically searched MEDLINE, EMBASE and SPORTDiscus electronic databases and conducted manual searching of reference lists of selected articles. Relevant articles were identified by the following criteria: apparently healthy children and adolescents aged 3-18 years with muscular fitness assessed at baseline (e.g., handgrip, standing long jump, sit-ups, among others), and a follow-up period of ≥ 1 year. The outcome measures were anthropometric and adiposity measurements and cardiometabolic, bone and musculoskeletal health parameters. Two authors independently extracted data.

RESULTS

Thirty studies were included in the meta-analysis, yielding a total of 21,686 participants. The meta-analysis found a significant, moderate-large (p < 0.05) effect size between muscular fitness at baseline and body mass index (r = - 0.14; 95% confidence interval (CI) - 0.21 to - 0.07), skinfold thickness (r = - 0.32; 95% CI - 0.40 to - 0.23), homeostasis model assessment estimated insulin resistance (r = - 0.10; 95% CI - 0.16 to - 0.05), triglycerides (r = - 0.22; 95% CI - 0.30 to - 0.13), cardiovascular disease risk score (r = - 0.29; 95% CI - 0.39 to - 0.18), and bone mineral density (r = 0.166; 95% CI 0.086 to 0.243) at follow-up.

CONCLUSION

A prospective negative association was observed between muscular fitness in childhood/adolescence and adiposity and cardiometabolic parameters in later life, together with a positive association for bone health. There is inconclusive evidence for low back pain benefits.

Strategies for Addressing Mouth-Breathing Treatment with an “Adequate” Nose

Now that we have discussed and analyzed strategies to surgically achieve an adequately functioning and appearing nose, additional treatments are still required in many cases to achieve jaw closure due to limited musculoskeletal tone of the maxilla and mandible, as we described in Chaps. 4 and 5. From surgical jaw expansion, orthodontic treatments to jaw closure straps and appliances, these strategies are considered and evaluated in this chapter.

Relationship between the changes over time of bone mass and muscle health in children and adults: a systematic review and meta-analysis

Background

Various cross-sectional studies provide an abundance of evidence that shows a relationship between bone quantity and muscle health. However, one question remains, less-often studied: is their development - or decline – associated? The aim of the research was to conduct a systematic review and meta-analysis to summarize the studies exploring the association between changes in bone mineral density (BMD) and changes in muscle parameters (registration CRD42018093813).

Methods

We searched for prospective studies, both in children and adults, by consulting electronic databases (Ovid-MEDLINE, Ovid-AMED, Scopus). Each review steps were performed by two independent reviewers. For outcomes reported by less of 3 studies, we synthetized the results narratively. In other cases, a meta-analysis was performed, giving an overall r coefficient and its 95% confidence interval (CI).

Results

Fifteen papers were included. In connection with the change of BMD, 10 studies concerned the parallel change of lean mass, 4 were about grip strength, and 1 was about physical performance. Children were the population of interest for 5 studies, while the aging population was the focus of the other studies. The correlation between hip BMD and lean mass was significant, with an overall coefficient r = 0.37 (95% CI 0.23–0.49). High heterogeneity was observed between studies but the length of follow-up, sex and study quality did not seem to significantly influence results. The systematic review allowed some other highlights: a significant link between changes in BMD and changes in muscle strength was observed (p-value < 0.05 in the 4 studies), in addition to changes in performance (1 study, r = 0.21, p-value = 0.004).

Conclusion

Despite the heterogeneity between studies, we highlighted a significant association between the change of BMD and the change of various muscle parameters. Future studies should investigate preventive and therapeutic strategies that are based on a single entity: the ‘muscle-bone unit’.

Mechanical, biochemical, and dietary determinants of the functional model of bone development of the radius in children and adolescents

This study examined the degree to which various mechanical, biochemical, and dietary factors are related to nonweight bearing bone properties in 172 healthy peri-pubertal children (age, 11.7 ± 2.0 years). Dominant radial speed of sound (rSOS) was measured by transaxial quantitative ultrasound at distal radius. Potential modulating factors included somatic maturity offset (years from age of peak height velocity), grip strength, forearm lean cross-sectional area (CSA), physical activity, nutritional intake, and amino-terminal cross-linking propeptide (NTx), reflecting bone resorption. In a hierarchical regression, grip strength adjusted for CSA was the second most important predictor of rSOS after the maturity offset (β = 0.22 and β = 0.33, respectively; R² = 0.16). When relative grip strength was added to the model the contribution of sex was no longer significant. Calcium intake was a significant predictor of rSOS only after NTx was accounted for in the model (β = 0.17, R² = 0.21). This may suggest that calcium's effects on the muscle-bone unit may be modulated through bone resorption. In the final model, relative grip strength together with maturity offset, dietary calcium, and NTx explained up to 21% of the variance in rSOS in this cohort of children. Therefore, during the peri-pubertal stage, size-adjusted forearm muscle strength is related to radial bone strength after controlling for maturity, with calcium intake having a potential indirect association through NTx.

The effects of weight loss approaches on bone mineral density in adults: a systematic review and meta-analysis of randomized controlled trials

We assessed the impact of weight loss strategies including calorie restriction and exercise training on BMD in adults using a systematic review of randomized controlled trials. Weight reduction results in reduced BMD at the hip, but has less effect on the spine. Both calorie restriction and a combination of calorie restriction and exercise result in a decrease in hip bone density, whereas weight loss response to exercise training without dietary restriction leads to increased hip BMD.

INTRODUCTION

Findings are not consistent on the effect of weight loss on bone mineral density (BMD). We conducted a systematic review on the randomized controlled trials to assess the effect of weight loss strategies, including calorie restriction and exercise programs on BMD in adults.

METHODS

A structured and comprehensive search of MEDLINE and EMBASE databases was undertaken up to March 2016. Study-specific mean differences (MD) were pooled using a random-effects model. Subgroup analysis and meta-regression were used to find possible sources of between-study heterogeneity.

RESULTS

Thirty-two randomized controlled trials met predetermined inclusion criteria. The meta-analysis revealed no significant difference on total BMD (MD 0.007, 95 % CI -0.020-0.034, p = 0.608). In contrast, the pooled data of studies showed a significant effect of weight loss on hip BMD (MD -0.008, 95 % CI -0.09 to -0.006 g/cm(2), p < 0.001) and also lumbar spine BMD (MD -0.018 g/cm(2), 95 % CI -0.019 to -0.017, p < 0.001). BMD in the hip site decreased after more than 4 months, especially in those who were obese. Moreover, calorie restriction interventions longer than 13 months showed a significant decreased in lumbar spine BMD.

CONCLUSION

Weight loss led to significant decreases at the hip and lumbar spine BMD but not at the total. Weight loss response following calorie restriction resulted in a decrease in hip and lumbar spine bone density especially more than 1 year; whereas an exercise-induced weight loss did not.

The health benefits of muscular fitness for children and adolescents: a systematic review and meta-analysis

BACKGROUND

Physical fitness during childhood and adolescence has been identified as an important determinant of current and future health status. While research has traditionally focused on the association between cardio-respiratory fitness and health outcomes, the association between muscular fitness (MF) and health status has recently received increased attention.

OBJECTIVE

The aim of this systematic review and meta-analysis was to evaluate the potential physiological and psychological benefits associated with MF among children and adolescents.

METHODS

A systematic search of six electronic databases (PubMed, SPORTDiscus, Scopus, EMBASE, PsycINFO and OVID MEDLINE) was performed on the 20th May, 2013. Cross-sectional, longitudinal and experimental studies that quantitatively examined the association between MF and potential health benefits among children and adolescents were included. The search yielded 110 eligible studies, encompassing six health outcomes (i.e., adiposity, bone health, cardiovascular disease [CVD] and metabolic risk factors, musculoskeletal pain, psychological health and cognitive ability). The percentage of studies reporting statistically significant associations between MF and the outcome of interest was used to determine the strength of the evidence for an association and additional coding was conducted to account for risk of bias. Meta-analyses were also performed to determine the pooled effect size if there were at least three studies providing standardised coefficients.

RESULTS

Strong evidence was found for an inverse association between MF and total and central adiposity, and CVD and metabolic risk factors. The pooled effect size for the relationship between MF and adiposity was r = -0.25 (95% CI -0.41 to -0.08). Strong evidence was also found for a positive association between MF and bone health and self-esteem. The pooled effect size for the relationship between MF and perceived sports competence was r = 0.39 (95% CI 0.34-0.45). The evidence for an association between MF and musculoskeletal pain and cognitive ability was inconsistent/uncertain. Where evidence of an association was found, the associations were generally low to moderate.

CONCLUSION

The findings of this review highlight the importance of developing MF in youth for a number of health-related benefits.

Physiology of Mechanotransduction: How Do Muscle and Bone "Talk" to One Another?

The complexity of cell interactions with their microenvironment and their ability to communicate at the autocrine, paracrine, and endocrine levels has gradually but significantly evolved in the last three decades. The musculoskeletal system has been historically recognized to be governed by a relationship of proximity and function, chiefly dictated by mechanical forces and the work of gravity itself. In this review article, we first provide a historical overview of the biomechanical theory of bone- muscle interactions. Next, we expand to detail the significant evolution in our understanding of the function of bones and muscles as secretory organs. Then, we review and discuss new evidence in support of a biochemical interaction between these two tissues. We then propose that these two models of interaction are complementary and intertwined providing for a new frontier for the investigation of how bone-muscle cross talk could be fully explored for the targeting of new therapies for musculoskeletal diseases, particularly the twin conditions of aging, osteoporosis and sarcopenia. In the last section, we explore the bone-muscle cross talk in the context of their interactions with other tissues and the global impact of these multi-tissue interactions on chronic diseases.

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

PURPOSE

Muscle forces influence the development of bone mass and structure, but dynamic loading via impact exercise is considered particularly osteogenic. We hypothesized that indices of local muscle function and physical activity exposure would predict femoral neck (FN) structure in premenarcheal females.

METHODS

We tested this hypothesis in 76 healthy, premenarcheal girls (46 gymnasts and 30 nongymnasts). Height, weight, Tanner breast stage, and prior year nonaquatic, organized physical activity level (PAL) were recorded semiannually. Hologic dual-energy x-ray absorptiometry scans (whole body, left FN) yielded total body nonbone lean mass and bone outcomes, including narrow neck (NN) hip structural analysis data. Dynamometers assessed nondominant hand grip and left hip flexion/extension indices. Parsimonious regression models tested the following as predictors of bone outcomes: local muscle function, PAL, gymnast status, and lean mass, accounting for Tanner breast stage and height, as appropriate.

RESULTS

Hip flexion indices were significantly correlated with indices of FN mass, density, structure, and strength (P < 0.05). However, the entry of PAL, gymnast status, and lean mass into regression models supplanted local muscle function explanatory value. In contrast, for many variables, the significant association of gymnast status persisted after accounting for physical maturity, body size/lean mass, and PAL. For all skeletal indices except FNArea, NNwidth, NN endosteal diameter, and NN buckling ratio, gymnast status was more strongly associated with bone outcomes than PAL.

CONCLUSIONS

Greater activity doses and exposure to extreme dynamic loading provide independent benefits to FN structure during growth. Furthermore, weight-bearing activity and high-impact exercise exposure appear superior to local muscle force measures for prediction of FN structure.

Serum interferon gamma concentration is associated with bone mineral density in overweight boys

Childhood obesity has recently been linked to low-grade inflammation. Overweight children have slightly different processes of bone accumulation than normal weight children. The possible links between inflammation and bone accumulation have not previously been assessed in overweight children.

AIMS

An exploratory study to assess whether common inflammatory markers are associated with the development of obesity and bone accumulation in childhood.

METHODS

Thirteen different inflammatory markers in serum were measured in 38 boys with BMI >85th centile (overweight) and 38 boys with normal BMI (normal weight), aged 10-11 years. Total body (TB) and lumbar spine (LS) bone mineral density (BMD), bone mineral content (BMC) were measured by DXA. TB BMC for height, TB and LS bone mineral apparent density (BMAD) were calculated.

RESULTS

Overweight boys had higher mean TB and LS BMD, TB BMC and TB BMC for height, but lower mean TB BMAD (all p < 0.05) than normal weight boys. Serum interferon gamma (IFNγ) concentration was significantly (p < 0.05) correlated with TB BMD (r = 0.36), TB BMC (r = 0.38) and TB BMC for height (r = 0.53) in the broader overweight group (n = 38). In obese boys (BMI > 95 centile, n = 36) IFNγ was correlated with LS BMD (r = 0.38).

CONCLUSION

The positive correlation between serum INFγ concentration and BMD suggests that the inflammatory process, already involved in the early stage of obesity, may also affect bone accumulation. Further studies are needed to clarify the role of INFγ as a possible link between adipose tissue and bone health.

Site-specific variance in radius and tibia bone strength as determined by muscle size and body mass

PURPOSE

To investigate the predictive ability of muscle cross-sectional area (MCSA) and body mass on bone mineral content, compressive bone strength index (BSIc), and the polar stress-strain index (SSIp) of the forearms and lower legs of middle-aged adults.

METHODS

A total of 53 healthy adults (37 male, 16 female; mean age 50.4; SD 2.1 y) were scanned with peripheral quantitative computed tomography (pQCT) to measure radius and tibia total and cortical bone mineral content, BSIc, SSIp, and forearm and lower-leg MCSA (BSIc: 4% distal; SSIp and MCSA at 65% and 66% radius and tibia shaft sites, respectively). Multiple regression models adjusted for sex and height were used to assess the relative variance in radius or tibia bone outcomes predicted by body mass and/or forearm or lower-leg MCSA.

RESULTS

Forearm MCSA independently predicted total bone-mineral content, BSIc, and SSIp in radius (r partial=0.59, 0.56, 0.42). Body mass was a negative predictor of radius BSIc (r partial=-0.32) and did not predict other radius outcomes when both body mass and MCSA were forced in the models. In the lower leg shaft, MCSA, and body mass predicted bone content and strength similarly when independently added to the models with sex and height.

CONCLUSIONS

Forearm MCSA was a dominant predictor of radius bone content and estimated strength. In the tibia, both body mass and lower-leg MCSA contributed to predicting bone content and estimated strength.

Dystrophin and utrophin "double knockout" dystrophic mice exhibit a spectrum of degenerative musculoskeletal abnormalities

Duchenne muscular dystrophy (DMD) is a degenerative muscle disorder characterized by the lack of dystrophin expression at the sarcolemma of muscle fibers. In addition, DMD patients acquire osteopenia, fragility fractures, and scoliosis indicating that a deficiency in skeletal homeostasis coexists but little is known about the effects of DMD on bone and other connective tissues within the musculoskeletal system. Recent evidence has emerged implicating adult stem cell dysfunction in DMD myopathogenesis. Given the common mesenchymal origin of muscle and bone, we sought to investigate bone and other musculoskeletal tissues in a DMD mouse model. Here, we report that dystrophin-utrophin double knockout (dko) mice exhibit a spectrum of degenerative changes, outside skeletal muscle, in bone, articular cartilage, and intervertebral discs, in addition to reduced lifespan, muscle degeneration, spinal deformity, and cardiomyopathy previously reported. We also report these mice to have a reduced capacity for bone healing and exhibit spontaneous heterotopic ossification in the hind limb muscles. Therefore, we propose the dko mouse as a model for premature musculoskeletal aging and posit that a similar phenomenon may occur in patients with DMD.

Young age at diagnosis, male sex, and decreased lean mass are risk factors of osteoporosis in long-term survivors of osteosarcoma

BACKGROUND

Long-term survival of children with osteosarcoma has increased, but most suffer from osteoporosis in adulthood. The aim of this study was to investigate the prevalence and identify the risk factors of osteoporosis.

METHODS

Forty long-term survivors of osteosarcoma and 55 controls were enrolled. The mean age of the survivors was 21.8 ± 5.2 years. They were diagnosed at younger than 23 years of age (mean, 14.9 + 5.0 y). Bone mineral densities (BMD) and body compositions were measured by dual-energy x-ray absorptiometry.

RESULTS

Nineteen (47.5%) subjects had osteoporosis and 12 (30.0%) had osteopenia. The regions affected by osteoporosis were: femur neck of osteosarcoma site (47.5%), unaffected femur neck (12.5%), lumbar spine (12.5%), and total body (15.0%). Twelve subjects (30.0%) had 14 episodes of fractures. The identified risk factors of osteoporosis were young age at diagnosis, male sex, and low lean mass. Subjects diagnosed before attainment of puberty (male ≤ 16 y, female ≤ 14 y) were found to have a higher prevalence of osteoporosis (37.5% vs. 10.0%, P < 0.01). Males had a higher prevalence of osteopenia or osteoporosis than females (86.4% vs. 66.7%, P < 0.01). Total lean mass was positively correlated with unaffected femur neck BMD. Regional lean mass in affected limb was significantly reduced along with affected femur neck BMD.

CONCLUSIONS

In long-term survivors of osteosarcoma, prevalence of osteoporosis and fracture was higher than expected. Initial evaluation and regular follow-up of BMD should be performed in all osteosarcoma patients, especially in those who did not attain puberty, males, and those with a low lean mass.

Assessing bone health in children and adolescents

During normal childhood and adolescence, the skeleton undergoes tremendous change. Utilizing the processes of modeling and remodeling, the skeleton acquires its adult configuration and ultimately achieves peak bone mass. Optimization of peak bone mass requires the proper interaction of environmental, dietary, hormonal, and genetic influences. A variety of acute and chronic conditions, as well as genetic polymorphisms, are associated with reduced bone density, which can lead to an increased risk of fracture both in childhood and later during adulthood. Bone densitometry has an established role in the evaluation of adults with bone disorders, and the development of suitable reference ranges for children now permits the application of this technology to younger individuals. We present a brief overview of the factors that determine bone density and the emerging role of bone densitometry in the assessment of bone mass in growing children and adolescents.

Mechanical loading: bone remodeling and cartilage maintenance

Bone remodeling and cartilage maintenance are strongly influenced by biomechanical signals generated by mechanical loading. Although moderate loading is required to maintain bone mass and cartilage homeostasis, loading can cause deleterious effects such as bone fracture and cartilage degradation. Because a tight coupling exists between cartilage and bone, alterations in one tissue can affect the other. Bone marrow lesions are often associated with an increased risk of developing cartilage defects, and changes in the articular cartilage integrity are linked to remodeling responses in the underlying bone. Although mechanisms regulating the maintenance of these two tissues are different, compelling evidence indicates that the signal pathways crosstalk, particularly with the Wnt pathway. A better understanding of the complex tempero-spatial interplay between bone remodeling and cartilage degeneration will help develop a therapeutic loading strategy that prevents bone loss and cartilage degeneration.

Low bone density and bone metabolism alterations in Duchenne muscular dystrophy: response to calcium and vitamin D treatment

Boys with Duchenne muscular dystrophy often have reduced bone mass and increased fracture risk. In this prospective study on 33 patients, calcifediol (25-OH vitamin D(3)) plus adjustment of dietary calcium to the recommended dose reduced bone resorption, corrected vitamin D deficiency, and increased bone mass in about two-thirds of cases.

INTRODUCTION

Low BMC and BMD and bone metabolism alterations are frequent in boys with Duchenne muscular dystrophy (DMD), especially now that long-term glucocorticosteroid (GC) treatment is the standard of care. This prospective study was designed to evaluate the effects of a first-line treatment (25-OH vitamin D(3) [calcifediol] plus adjustment of dietary calcium to the recommended daily dose) on bone.

METHODS

Thirty-three children with DMD on GC treatment were followed for 3 years: one of observation and two of treatment.

MAIN OUTCOME

spine and total body BMC and BMD increase; secondary outcome: changes in bone turnover markers (C-terminal [CTx] and N-terminal [NTx] telopeptides of procollagen type I; osteocalcin [OC]).

RESULTS

During the observation year, BMC and BMD decreased in all patients. At baseline and after 12 months, serum CTx and urinary NTx were higher than normal; OC and parathyroid hormone at the upper limit of normal; 25-OH vitamin D(3) significantly lower than normal. After 2 years of calcifediol and calcium-rich diet, BMC and BMD significantly increased in over 65% of patients, and bone metabolism parameters and turnover markers normalized in most patients (78.8%). During the observation year, there were four fractures in four patients, while during the 2 years of treatment there were two fractures in two patients.

CONCLUSIONS

Calcifediol plus adequate dietary calcium intake seems to be an effective first-line approach that controls bone turnover, corrects vitamin D deficiency, and increases BMC and BMD in most patients with DMD. Lack of response seems related to persistently high bone turnover.

Is bone's response to mechanical signals dominated by gravitational loading?

During locomotion and exercise, bone is subjected to forces induced by gravitational loading and muscle loading. The inherent link between these modes of loading has confounded emergence of either one as the principal anabolic or anticatabolic signal in bone. A paradigm has emerged in the literature stipulating that muscle loading is the larger of the two, and therefore, bone morphology is predominantly determined by muscle loads. In spite of the intuitive appeal of a muscle-bone unit tuned to the magnitude of contractile forces, little evidence exists for the relatively few, large-magnitude muscle contractions arising during daily activities to dominate the mechanosensory input of bone. Moreover, a review of the literature raises several inconsistencies in this paradigm and indicates that the alternative--gravitational loading--can have a significant role in determining bone mass and morphology. Certainly, the relative contribution of each type of loading will depend on the specific activity, the location of the bone within the skeleton, and whether the bone is weight-bearing or not. Most likely, a more comprehensive paradigm for explaining sensitivity of bone to loading will have to include not only large-magnitude gravitational and muscle loads, but also other factors such as high-frequency, low-magnitude signals generated by the muscles during postural adjustments.

Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm

BACKGROUND

The influence of adiposity on upper-limb bone strength has rarely been studied in children, despite the high incidence of forearm fractures in this population.

OBJECTIVE

The objective was to compare the influence of muscle and fat tissues on bone strength between the upper and lower limbs in prepubertal children.

DESIGN

Bone mineral content, total bone cross-sectional area, cortical bone area (CoA), cortical thickness (CoTh) at the radius and tibia (4% and 66%, respectively), trabecular density (TrD), bone strength index (4% sites), cortical density (CoD), stress-strain index, and muscle and fat areas (66% sites) were measured by using peripheral quantitative computed tomography in 427 children (206 boys) aged 7-10 y.

RESULTS

Overweight children (n = 93) had greater values for bone variables (0.3-1.3 SD; P < 0.0001) than did their normal-weight peers, except for CoD 66% and CoTh 4%. The between-group differences were 21-87% greater at the tibia than at the radius. After adjustment for muscle cross-sectional area, TrD 4%, bone mineral content, CoA, and CoTh 66% at the tibia remained greater in overweight children, whereas at the distal radius total bone cross-sectional area and CoTh were smaller in overweight children (P < 0.05). Overweight children had a greater fat-muscle ratio than did normal-weight children, particularly in the forearm (92 +/- 28% compared with 57 +/- 17%). Fat-muscle ratio correlated negatively with all bone variables, except for TrD and CoD, after adjustment for body weight (r = -0.17 to -0.54; P < 0.0001).

CONCLUSIONS

Overweight children had stronger bones than did their normal-weight peers, largely because of greater muscle size. However, the overweight children had a high proportion of fat relative to muscle in the forearm, which is associated with reduced bone strength.

Geometry of a weight-bearing and non-weight-bearing bone in the legs of young, old, and very old men

Bone geometry is an important determinant of bone strength and is influenced by muscle pull and weight-bearing. Muscle mass and exposure to weight-bearing decrease with age and thus the purpose of the study was to compare bone geometry of the weight-bearing (tibia) and non-weight-bearing (fibula) bones of the leg in different age groups. Magnetic resonance images of the right leg were acquired in 13 young (26 yr), 13 old (66 yr), and 13 very old men (83 yr). Cortical, medullary and total cross-sectional areas (CSA) of the bones were measured at approximately one-third and two-thirds the length of the leg. Muscle CSA of the anterior, lateral and posterior compartments was measured at the proximal site. Cortical CSA was approximately 14 to 22% smaller in the elderly in the tibia but similar across age in the fibula. Medullary CSA was larger with age (approximately 5 to 65%) in both bones but approximately 15 to 440% greater in the tibia than fibula. Total CSA was similar across age in both bones. Muscle mass was similar between young and old but approximately 25% less in the very old and as a consequence, the magnitude of differences in bone geometry at proximal and distal sites varied in the two elderly groups. These findings indicate that there is a complex age-dependent interaction between muscle pull and weight-bearing. The greater age-related differences in bone geometry in the tibia suggest the weight-bearing role of the tibia makes it more susceptible than the fibula to the reduced activity typically associated with aging.

Peak lean tissue mass accrual precedes changes in bone strength indices at the proximal femur during the pubertal growth spurt

PURPOSE

We examined the timing of the age and the magnitude of peak lean tissue mass accrual (PLTV) relative to the age and magnitude of two variables of bone strength [peak cross sectional area velocity (PCSAV), and peak section modulus velocity, (PZV)] at the proximal femur in males and females during the adolescent growth spurt. We hypothesized that the age of PLTV would precede the ages of PCSAV and PZV and that there is a positive relationship between the magnitude of PLTV and both PCSAV and PZV in both genders.

METHODS

41 males and 42 females aged 8-18 years were selected from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-2005). Participants' total body lean tissue mass was assessed annually for 6 consecutive years using DXA. Narrow neck and femoral shaft cross sectional areas (CSA) and section modulus (Z) were determined using the hip structural analysis (HSA) program. Participants were aligned by maturational age (years from peak height velocity). Lean tissue mass, CSA, and Z were converted into whole year velocities and the maturational age of peak tissue velocities was determined using a cubic spline curve fitting procedure. A 2 x 3 (gender x tissue) factorial MANOVA with repeated measures was used to test for differences between age of PLTV and the ages of PCSAV and PZV between genders. Multiple regression analyses were used to examine the relationship between PLTV and both PCSAV and PZV.

RESULTS

There were no sex differences in the ages at which tissue peaks occurred when aligned by maturational age. There were significant differences between the age of PLTV and both PCSAV and PZV at the narrow neck (p=0.001) and femoral shaft (p=0.03), where the age of PLTV preceded both PCSAV and PZV when pooled by gender. PLTV was a significant predictor of the magnitude of both PCSAV and PZV at all sites (p<0.05).

CONCLUSIONS

These findings support the hypothesis that the age of PLTV precedes the age of PCSA and PZV at the proximal femur. Results support the theory that muscle development is an important factor in affecting bone strength.

Eight months of regular in-school jumping improves indices of bone strength in adolescent boys and Girls: the POWER PE study

The POWER PE study was an 8-mo, randomized, controlled, school-based exercise intervention designed to apply known principles of effective bone loading to practical opportunities to improve life-long musculoskeletal outcomes. A total of 99 adolescents (46 boys and 53 girls) with a mean age of 13.8 +/- 0.4 yr (peri- to postpubertal) volunteered to participate. Intervention subjects performed 10 min of jumping activity in place of regular physical education (PE) warm up. Control subjects performed usual PE warm-up activities. Bone mass (DXA and QUS) was assessed at baseline and follow-up along with anthropometry, maturity, muscle power, and estimates of physical activity and dietary calcium. Geometric properties (such as femoral neck [FN] moment of inertia) were calculated from DXA measures. Boys in the intervention group experienced improvements in calcaneal broadband ultrasound attenuation (BUA) (+5.0%) and fat mass (-10.5%), whereas controls did not (+1.4% and -0.8%, respectively). Girls in the intervention group improved FN BMC (+13.9%) and lumbar spine (LS) BMAD (+5.2%) more than controls (+4.9% and +1.5%, respectively). Between-group comparisons of change showed intervention effects only for whole body (WB) BMC (+10.6% versus +6.3%) for boys. Boys in the intervention group gained more lean tissue mass, trochanter (TR) BMC, LS BMC, and WB BMC and lost more fat mass than girls in the intervention group (p < 0.05). Ten minutes of jumping activity twice a week for 8 mo during adolescence seems to improve bone accrual in a sex-specific manner. Boys increased WB bone mass and BUA, and reduced fat mass, whereas girls improved bone mass at the hip and spine.

Relationship of total body fat mass to bone area in New Zealand five-year-olds

Fat mass was recently shown to be a positive determinant of bone mass and size independently of lean mass in a birth cohort of British 9-year-olds. The present study was undertaken to investigate whether similar relationships are evident in younger, preschool children. Height and weight were measured, and a total-body dual-energy X-ray absorptiometric scan was performed on 194 preschool New Zealand children (81 girls, 113 boys) participating in the Dunedin birth cohort Family, Lifestyle, Activity, Movement, and Eating (FLAME) study close to their fifth birthday. Relationships of total-body fat mass and lean mass to total-body-less-head (TBLH) bone area and TBLH bone mineral content (BMC) were evaluated using linear regression. Girls had higher mean fat mass (3.9 vs. 3.2 kg) and lower lean mass (14.5 vs. 15.2 kg) than boys (P < 0.001), but their heights, weights, and TBLH bone area were similar. Although a given weight of lean tissue was associated with greater increases in TBLH area than a given weight of fat tissue, our results show that fat mass was an independent predictor of TBLH bone area (R (2 )= 0.79, P < 0.001) and TBLH BMC (R (2) = 0.74, P < 0.001) in data adjusted for socioeconomic status, ethnic group, lean mass, and height. We conclude that increased fat mass is associated with outward expansion of the TBLH skeletal envelope (wider bones) independently of height and lean mass in very young children.

Physical fitness effect on bone mass is mediated by the independent association between lean mass and bone mass through adolescence: a cross-sectional study

We studied 278 adolescents (169 females) aged 13.0-18.5 years to elucidate whether an independent effect of physical fitness and lean mass in the differences between male and female bones can be detected. Lean and fat masses and bone mineral content (BMC) were measured with DXA. Physical fitness was evaluated with six different tests included in the EUROFIT test battery (flexibility, isometric, dynamic and endurance strength, speed, and cardiovascular fitness). To test the independent relationship between physical fitness and bone mass, multiple regression analysis was applied, including lean mass, age, and Tanner development as covariates. The males had a 43% lower fat mass and 40% and 16% higher lean mass and total BMC compared with the females (all P < 0.05). After adjustment for differences in body size and lean mass, the females exhibited a 7.4% higher BMC than the males (P < 0.05). The multiple regression analysis showed that lean mass had an independent relationship with bone mass (P < 0.001), explaining 67% of the total variance in whole-body BMC. In males, change in R (2) was 0.658 for hand grip and 0.035-0.151 for the rest of physical fitness-related variables; but 0.019-0.042 in females (all P-0.001); however, the independent relationships between physical fitness and bone disappeared after controlling for lean mass. In conclusion, it is likely the differences between male and female in bone mass could be explained by differences in lean mass and physical fitness.