The relationship between muscle size and bone geometry during growth and in response to exercise☆
Introduction
Muscle and bone are inextricably linked by common genes regulating body size and a shared loading environment [1]. Growth, in the presence of unloading, results in both a bone that lacks the specific shape that is unique for its function and a muscle that lacks functional capacity [2]. Thus, while the development of muscle and bone during growth is influenced by gravitational forces associated with body weight and physical activity, it is proposed that forces produced by muscle contractions dominate the skeleton's postnatal structural adaptation to loading [3], [4], [5]. Therefore, as muscles become larger and stronger during growth or in response to increased loading (exercise), bones should adapt to increased loads imparted by muscles by adding mass, size, and strength [3]. This biomechanical link between muscle and bone supports the concept of a ‘functional muscle–bone unit’, in which changes in muscle mass and strength should affect bone mass, size, and strength predictably and correspondingly [2]. While this concept of a ‘muscle–bone unit’ is supported by indirect evidence, there is little direct evidence to support the notion that an exercise-induced increment in muscle size and strength are associated with the adaptive response of the skeleton to loading during growth. The aim of this study was to investigate the relationship between muscle and bone during different stages of growth and in response to additional loading. More specifically, in this unilateral model, we tested the hypothesis that (1) the relationship between muscle size and bone mass and geometry (nonplaying arm) would not change during different stages of puberty and (2) exercise would not alter the relationship between muscle and bone, that is, additional loading would result in a similar unit increment in both muscle and bone mass, bone size, and bending strength during growth.
Section snippets
Subjects
Forty-seven pre-, peri-, and post-pubertal competitive female tennis players aged 8–17 years were recruited from tennis clubs located within metropolitan Melbourne, Australia. Players were included if they had been playing competitive tennis for a minimum of 2 years, and were currently playing at least 3 h/week. Thirty-four players were competing at a national, state and regional level, and 13 at a high standard club level. Forty girls were right-handed, and 33 girls used a double-handed
Muscle–bone relationship during growth (nonplaying arm)
In this unilateral model, the nonplaying arm represents the relationship between muscle and bone as developed during growth in the presence of loading due to everyday living. At all stages of puberty, there was a linear relationship between muscle area and BMC, total, medullary and cortical area, and Ip (r = 0.56–0.81, P ranging 0.09 to < 0.001). These relationships remained after adjusting for age and humeral length. Despite a trend for the slopes of the relationship between muscle and bone
Discussion
Muscle and bone are inextricably linked by common genes regulating size, their physical connection, and the shared loading environment. Thus, it is often assumed that an increase in muscle mass and strength results in a corresponding increase in bone mass and strength [2], [5]. In this study, we report that an exercise-induced increment in muscle size during growth was positively correlated with changes in bone mass, size, and strength. However, the greater muscle size accounted for only 12–16%
Acknowledgements
The authors would like to thank radiographers Amanda Hunt and Glenn Rush for their technical assistance, and Rinske Miller for her assistance with the MRI analysis. The authors are grateful to Associate Professor Damien Jolley for his statistical advice and Dr Cameron Blimkie for his helpful comments and suggestions. We would also like to thank the players and their parents for their time contributions to the study.
References (24)
Muscle–bone interactions, revisited
Bone
(2000)- et al.
Gender-related differences in the relationship between densitometric values of whole-body bone mineral content and lean body mass in humans between 2 and 87 years of age
Bone
(1998) - et al.
Estrogen and bone–muscle strength and mass relationships
Bone
(1998) - et al.
Bone mineral and soft tissue measurements by dual-energy X-ray absorptiometry during growth
Bone
(2002) - et al.
Influences of skeletal mineralization in children and adolescents: evidence for varying effects of sexual maturation and physical activity
J. Pediatr.
(1994) - et al.
Do genetic factors explain associations between muscle strength, lean mass, and bone density? A twin study
Am. J. Physiol.
(1996) - et al.
The “muscle–bone” unit in children and adolescents: a 2000 overview
J. Pediatr. Endocrinol. Metab.
(2000) Muscle strength, bone mass, and age-related bone loss
J. Bone Miner. Res.
(1997)On our age-related bone loss: insights from a new paradigm
J. Bone Miner. Res.
(1997)- et al.
The effect of mechanical loading on the size and shape of bone in pre-, peri-, and postpubertal girls: a study in tennis players
J. Bone Miner. Res.
(2002)
Cadaver validation of skeletal muscle measurement by magnetic resonance imaging and computerized tomography
J. Appl. Physiol.
Measurement of midfemoral shaft geometry: repeatability and accuracy using magnetic resonance imaging and dual-energy X-ray absorptiometry
J. Bone Miner. Res.
Cited by (0)
- ☆
This study was funded by grants from the Australian Research Council Grant and the School of Health Sciences, Deakin University.