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The "muscle-bone unit" in children and adolescents: a 2000 overview
1Department of Orthopaedic Surgery, Southern Colorado Clinic, Pueblo, CO 81008-9000, USA.
Insights
Children's bone strength primarily depends on muscle strength, not just hormones or vitamins. This Utah paradigm highlights the crucial interplay between bone and muscle development for skeletal health.
Area of Science:
- Pediatric skeletal physiology
- Bone and muscle biology
Background:
- Traditional views emphasized hormones, calcium, and vitamin D for bone strength.
- Emerging evidence suggests mechanical loads are critical for skeletal development.
Purpose of the Study:
- To present the Utah paradigm of skeletal physiology.
- To explain the interplay between bone and muscle strength in children and adolescents.
Main Methods:
- Review of existing evidence on skeletal physiology.
- Integration of mechanical loading concepts into bone health models.
Main Results:
- Muscle-generated mechanical loads are the primary determinants of bone strength.
- Bone strength is strongly influenced by the development of muscle strength and bone's response to it.
- Hormones and other non-mechanical factors modulate, but do not replace, the bone-muscle relationship.
Conclusions:
- Bone and muscle function as an integrated unit in determining skeletal strength.
- The Utah paradigm offers a comprehensive understanding of pediatric bone health.
- Implications for pediatric endocrinologists include focusing on muscle development for bone health.
Abstract:
In former views hormones, calcium, vitamin D and other humoral and nonmechanical agents dominated control of postnatal bone strength (and "mass") in children and adolescents. However later evidence that led to the Utah paradigm of skeletal physiology revealed that this control depends strongly on the largest mechanical loads on bones. Trauma excepted, muscles cause the largest loads and the largest bone strains, and these strains help to control the biological mechanisms that determine whole-bone strength. That makes the strength of children's load-bearing bones depend strongly on growing muscle strength and how bones respond to it. Most hormones and other nonmechanical agents that affect bone strength can help or hinder that "bone strength-muscle strength" relationship but cannot replace it. In addition some agents long thought to exert bone effects by acting directly on bone cells, affect muscle strength too. In that way they could affect bone strength indirectly. Such agents include growth hormone, adrenalcorticosteroid analogs, androgens, calcium, genes, vitamin D and its metabolites, etc. Thus bone and muscle do form a kind of operational unit. It is part of the Utah paradigm that supplements earlier views with later evidence and concepts. The paradigm explains how the "bone strength-muscle strength" relationship works. This article provides an overview of that physiology, and some of its implications for pediatric endocrinologists.