It has been theorized that muscles generate more force on bone than body weight alone and therefore it is likely that muscle contraction drives and sustains bone adaptation (Frost 1999). Purpose: To investigate the relationship between the timing and tempo of peak growth velocities of lean tissue (LT) and bone mineral content (BMC) in boys and girls at three sites using data derived from individual growth curves. Methods: 72 boys and 70 girls were fitted with growth curves that had a distinguishable peak. Height and weight were measured for each participant and tissue assessment was performed annually using DXA. Factorial ANOVAs were completed to analyse data for differences in age, while forward regression analyses was used between LT and BMC. Results: The peak growth velocity for lean occurred significantly (P<0.05) earlier than the peak growth velocity for bone at all locations except the legs. There was a difference (P<0.001) between genders in the age of peak for both lean tissue and bone tissue at all locations with females peak growth occurring before that of males. When aligned by PHV a significant difference (P<0.05) in the timing of PBMCV was found between the arms and the legs with the peak in bone growth in the legs occurring significantly before peak bone growth in the arms. PLTV was independently associated with PBMCV at the arms (r2= .71, p<0.001), legs (r2= .53, p<0.001) and trunk (r2= .52, p<0.001). Conclusion: In conclusion, LT growth precedes BMC growth and after controlling for gender, size and maturity the magnitude of LT growth is associated with BMC growth. The findings of this study are in support the Muscle-bone Unit (Frost and Schoenau, 2000), which theorizes that localised muscle action is a driving force for bone growth. Future studies are needed to analyse bone strength as it relates to local muscle strength and usage while controlling for confounding variables.

It has been theorized that muscles generate more force on bone than body weight alone and therefore it is likely that muscle contraction drives and sustains bone adaptation (Frost 1999). Purpose: To investigate the relationship between the timing and tempo of peak growth velocities of lean tissue (LT) and bone mineral content (BMC) in boys and girls at three sites using data derived from individual growth curves. Methods: 72 boys and 70 girls were fitted with growth curves that had a distinguishable peak. Height and weight were measured for each participant and tissue assessment was performed annually using DXA. Factorial ANOVAs were completed to analyse data for differences in age, while forward regression analyses was used between LT and BMC. Results: The peak growth velocity for lean occurred significantly (P<0.05) earlier than the peak growth velocity for bone at all locations except the legs. There was a difference (P<0.001) between genders in the age of peak for both lean tissue and bone tissue at all locations with females peak growth occurring before that of males. When aligned by PHV a significant difference (P<0.05) in the timing of PBMCV was found between the arms and the legs with the peak in bone growth in the legs occurring significantly before peak bone growth in the arms. PLTV was independently associated with PBMCV at the arms (r2= .71, p<0.001), legs (r2= .53, p<0.001) and trunk (r2= .52, p<0.001). Conclusion: In conclusion, LT growth precedes BMC growth and after controlling for gender, size and maturity the magnitude of LT growth is associated with BMC growth. The findings of this study are in support the Muscle-bone Unit (Frost and Schoenau, 2000), which theorizes that localised muscle action is a driving force for bone growth. Future studies are needed to analyse bone strength as it relates to local muscle strength and usage while controlling for confounding variables.

Introduction: Puberty is a crucial period for rapid changes in bone mineral, size, geometry, and microarchitecture. The mechanostat theory postulates that increased mechanical loading will affect bone phenotype and strength during development and in later life. Individuals with cystic fibrosis (CF) have an increased risk of developing osteoporosis and fragility fractures in young adulthood, which may be caused by poor growth. The aim was to investigate whether sex and disease status modified the relationship between: 1) puberty and bone, and 2) muscle and bone. This would contribute to the understanding of how sex (males vs. females) and disease group (CF vs.controls) alters the relationship between bone and muscle in children and adolescents as they transition through puberty and who, on a population level, differ in the prevalence of osteoporosis and risk of fracture in later life. Methods and Analyses: This observational study used novel imaging and muscle assessment techniques to measure bone and muscle parameters in White Caucasian children and adolescents, aged 8 to 16 years, living in the UK, with children with CF (n=65) and controls (n=151). Anthropometry and pubertal status were assessed. Dual energy X-ray absorptiometry, peripheral quantitative computed tomography (pQCT), high-resolution pQCT, and jumping mechanography were used to measure bone and muscle outcomes. ANCOVA with Scheffé post hoc and multiple linear regression tests were performed. Data were adjusted according to the research aims and included covariates; sex, disease group, pubertal stage, age, quadratic age, height, weight, maximum force (Fmax), and maximum power (Pmax). Data are presented as beta-coefficient (%) and p-value, with the significance level set to p < 0.05. Results: In height adjusted analyses, among healthy participants, females had smaller bones and lower bone density compared to males. With pubertal maturation, females had lower apparent gains in the distal and proximal total area (Tt.Ar and CSA), distal cortical porosity (Ct.Po) and proximal bone strength (SSI) but higher apparent gains in distal and proximal cortical bone density(Ct.BMD, Ct.TMD, vBMD). Females had consistently lower distal total area (total CSA) and density (total vBMD), distal trabecular density(BV/TV) and number(Tb.N), and proximal cortical area(CSA) compared to males, across all stages of puberty. With increasing muscle force (Fmax), females had higher apparent gains in total body less head bone mineral (TBLH BMC) and bone area(BA), distal total and trabecular density (total and trab vBMD) compared to males. In contrast, with increasing muscle power (Pmax), females had higher apparent gains in distal total and cortical densities (D100, Ct.BMD and Ct.TMD), and distal trabecular thickness (Tb.Th), and proximal cortical density (cortical vBMD) but lower apparent gains in distal cortical porosity (Ct.Po) and trabecular number (Tb.N) compared to males. In height adjusted analyses, participants with CF had smaller bones and lower bone density compared to controls. With increasing pubertal maturation, participants with CF had lower apparent gains in total body less head bone mineral and bone area, and in distal trabecular density, cortical porosity, and trabecular thickness compared to controls. Participants with CF had consistently lower distal total and cortical area, distal total and trabecular densities and proximal bone strength compared to controls, across all stages of puberty. With increasing muscle force, participants with CF had lower apparent gains in total body less head bone mineral and bone area, distal total density, trabecular density, and trabecular number. In contrast, with increasing muscle power (Pmax), participants with CF had higher apparent gains in distal trabecular density (BV/TV) and trabecular number (Tb.N) compared to controls. Conclusion: These findings suggests that sex and disease status do modify the relationships between puberty and bone, and between muscle function and bone. Skeletal adaptation to muscle differs between sexes and in populations with chronic disease, which may explain sex and disease group differences in risks of osteoporosis and fracture. Bone adaptation to muscle in children with CF is altered, which may lead to narrow, under-mineralised bones, with lower bone strength in later life. Understanding better impairments in muscle functions may provide targets for intervention to improve skeletal health in later life.