1. Copyright © 2012 American College of Sports Medicine Chapter 3 The Skeletal-Articular System Ronald F. Zernicke, Gregory R. Wohl, and Jeremy M. LaMothe

2. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Physiology Overview –Low cellularity –Extracellular matrix (EM) constitutes majority of volume –EM of soft connective tissues is 70-75% water –Collagen comprises 60-70% of dry mass –Muscle microfibrils form subfibrils, which form fiber bundles –Muscle fiber bundles are collated into fascicles

3. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Physiology (cont’d) Ligaments –Tether bones across a joint –Control relative motion of joint Tendons –Connect muscles to bones –Transmit muscular forces to bones

4. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Physiology (cont’d) Menisci –Maintain joint components in appropriate position –Reduce joint stress by bearing load –Enhance rotation in synovial joints Bones –Mechanical support –Center for hematopoiesis –Largest calcium reservoir

5. Copyright © 2012 American College of Sports Medicine Frontal Section of Knee

6. Copyright © 2012 American College of Sports Medicine Fiber Pattern of Meniscus

7. Copyright © 2012 American College of Sports Medicine Structural Hierarchy of Tendon Organization

8. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Tissue Turnover Fine balance of extracellular matrix components Turnover of damaged matrix Repairing or building new matrix after injury or mechanical stimuli Fibroblasts: primary cells in ligaments & tendons Fibrochondrocytes: primary cells of menisci

9. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Tissue Turnover (cont’d) Characteristics of fibrous connective tissue: –Limited vascularity –Restricted metabolic capacity of cells during matrix turnover –Less vigorous adaptive response to stimuli than in bone –Poor response to injury –Optimized for mechanical function

10. Copyright © 2012 American College of Sports Medicine Skeletal-Articular Tissue Turnover (cont’d) Characteristics of bone: –Most dynamic of skeletal-articular tissues –Can completely turnover in as little as 3 years –Types of cells: Osteoblasts Osteocytes Osteoclasts –Modeling –Remodeling

11. Copyright © 2012 American College of Sports Medicine Bone Modeling and Remodeling

12. Copyright © 2012 American College of Sports Medicine Factors in Tissue Adaptation Bone mineral density –Genetics (80%) –Environmental conditions Bone strength –Bone mass –Bone density –Bone size –Bone geometry

13. Copyright © 2012 American College of Sports Medicine Tissue Response to Mechanical Stimuli Ligament & Tendon –Catabolic stimuli –Anabolic stimuli Meniscus –Catabolic stimuli –Anabolic stimuli

14. Copyright © 2012 American College of Sports Medicine Tissue Response to Mechanical Stimuli (cont’d) Bone –Positive effects of exercise Increase in bone cross-sectional area Reduction in bone mechanical stresses Increase in BMD Increase in bone strength Increased resistance to bending or torsion Increased intestinal & renal calcium absorption & secretion

15. Copyright © 2012 American College of Sports Medicine Relation Between Exercise and Bone Mass

16. Copyright © 2012 American College of Sports Medicine Tissue Response to Mechanical Stimuli (cont’d) Bone –Negative effects of very strenuous exercise Microdamage from prolonged bouts of extremely intense exercise Stress reactions Stress fractures Female athlete triad Interruption of normal growth with extremely strenuous exercise

17. Copyright © 2012 American College of Sports Medicine Tissue Response to Mechanical Stimuli (cont’d) Interactions With Exercise –Genetics –Diet Minerals (calcium) Vitamin D Protein Fat –Hormones: growth hormone & estrogen –Development & aging

18. Copyright © 2012 American College of Sports Medicine Mechanisms of Bone Adaptation Proposed Strain Components –Magnitude –Frequency –Rate –Gradient

19. Copyright © 2012 American College of Sports Medicine Strain Threshold Required for Osteogenesis

20. Copyright © 2012 American College of Sports Medicine Mechanisms of Bone Adaptation (cont’d) Mechanical Transduction –Cell populations (signal pathways) –Transduction mechanisms Bone cell strain/stretch receptors, cytoskeleton Piezoelectricity Fluid flow Shear flow Ion flow Nutrient flow

21. Copyright © 2012 American College of Sports Medicine Section of Bone in Bending