Chapter 5
Connective Tissue Adaptations to
Training
Copyright © 2012 American College of Sports Medicine
Stimuli for Connective Tissue Adaptations
• Mechanical Stress
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Connective tissue (CT) adaptation via progressive overload by
increasing stress
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Internal force divided by cross-sectional area of CT structure
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CT increases tolerance for loading by:
• Increasing size
• Altering structural properties
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Important ramifications for:
• Injury prevention in sports
• Force transmission from muscle to bone
Copyright © 2012 American College of Sports Medicine
Stimuli for Connective Tissue Adaptations
(cont’d)
• Types of Stress
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Tension stresses
• Pulling forces on tissue
• Stretching or elongation occurs
–
(with tendons during muscle contraction)
Compression stresses
• Push structure inwardly
• Compressing longitudinal length
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Shear stresses
• Skewing
• Oblique force
Copyright © 2012 American College of Sports Medicine
Stimuli for Connective Tissue Adaptations
(cont’d)
• Stress-Strain Relationship
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Stress: level of force encountered by a tissue
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Strain: magnitude of deformation in proportion to stress applied
• Linear strain
• Compressive/tensile stresses that change tissue length
• Quantified as % relative to resting length
• Shear strain
• Bending of tissue (bone)
• Quantified by angle of deformation
• Poisson’s ratio: ratio of longitudinal to lateral strain
Copyright © 2012 American College of Sports Medicine
The Stress-Strain Relationship in a
Ruptured Achilles Tendon
Copyright © 2012 American College of Sports Medicine
Skeletal System
• Overview
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206 bones (177 of which involved in voluntary movement)
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Provides:
• Support
• Area for muscular attachment
• Protection to several organs
• Storage site for minerals
–
Produces:
• Movement upon skeletal muscle contraction
• Red blood cells
Copyright © 2012 American College of Sports Medicine
Skeletal System: Two Divisions
• Axial Skeleton
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• Appendicular Skeleton
80 bones in skull & trunk:
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126 bones in:
• Vertebral column
• Limbs
• Ribs
• Shoulder
• Sternum
• Pelvic girdle
• Sacrum
• Coccyx
Copyright © 2012 American College of Sports Medicine
The Axial and Appendicular Skeletons
Copyright © 2012 American College of Sports Medicine
The Skeletal System Roles:
• Provides support
• Area for muscular attachment
• Protection for several organs
• Produce movement upon skeletal muscle contraction
• Bones are a storage site for minerals when dietary intake is
low
• Bones produce red blood cells (for transporting oxygen)
Copyright © 2012 American College of Sports Medicine
Skeletal System (cont’d)
• Bone Anatomy (5 forms)
1. Long bones: femur & humerus
2. Short bones: carpals & tarsals
3. Flat bones: ribs, scapula, skull, sternum
4. Irregular bones: vertebrae
5. Sesamoid bones: patella
Copyright © 2012 American College of Sports Medicine
Anatomy of a Long Bone (Femur)
Copyright © 2012 American College of Sports Medicine
Internal Anatomy of a Long Bone
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Skeletal System (cont’d)
• Bone Remodeling
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Process of bone being constantly broken down & built up again
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Osteoblasts
• Cells that secrete a collagen-rich ground substance that aids
in bone formation
• Secreted by periosteum & endosteum
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Osteoclasts
• Cells involved in bone resorption or breakdown
• Digest mineralized bone matrix via acid & lysosomal enzymes
Copyright © 2012 American College of Sports Medicine
Skeletal System (cont’d)
• Bone Growth
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Longitudinal bone growth (developmental years)
• Intramembranous ossification: bone growth from CT
membranes
• Endochondral ossification: bone growth from cartilage
• Takes place at growth plates
• Epiphyses enlarge, diaphysis extends
• Some bones reach full length in 18 years, others in 25 years
–
Appositional bone growth (widening)
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Model for Bone Adaptation to Loading
Copyright © 2012 American College of Sports Medicine
Skeletal System (cont’d)
• Bone Adaptations to Exercise
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Minimal Essential Strain (MES)
• Minimal threshold volume & intensity needed for new bone
formation (increased bone mineral density [BMD])
• Depends on athlete’s training status & age
• 1/10th of force needed to fracture bone
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Dynamic, high-intensity loading to bones is paramount
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Weight-bearing exercise more effective than non-weight-bearing
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Athletes have higher BMD than non-athletes
Copyright © 2012 American College of Sports Medicine
Skeletal System (cont’d)
• Training to Increase Bone Size and Strength: Necessary
Components
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Specificity of loading
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Speed & direction of loading
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Volume
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Proper exercise selection
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Progressive overload
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Variation
Copyright © 2012 American College of Sports Medicine
Skeletal System (cont’d)
• Training to Increase Bone Size and Strength: General
Recommendations (Skeletal Loading)
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Multijoint exercises preferred
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Loading should be high with moderate to low volume (≤10 reps)
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Fast velocities of contraction preferred
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Rest intervals should be moderate to long (≥2-3 min)
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Variation in training stress is important for altering stimuli
Copyright © 2012 American College of Sports Medicine
Components of Dense CT
• Tendons and Ligaments
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Dense fibrous CT structures
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Composed of:
• Water (60-70% of content)
• Fibroblasts: collagen-producing cells
• Fibrocytes: mature cells
• Elastin: protein with elastic quality
• Collagen: great tensile strength, most abundant protein in the
human body-2 types: Type I in skin, bones, tendons and ligaments
and Type II in cartilage
• Ground substances: structural stability
Copyright © 2012 American College of Sports Medicine
• Fascia: CTs that surround and separate different organizational levels
within skeletal muscle.
• Fascia contains bundles of collagen fibers arranged in different planes
to provide resistance to forces from different directions.
• Fascia within skeletal muscle converges to form a tendon through
which the force of muscle contraction is transmitted to bone.
Copyright © 2012 American College of Sports Medicine
Structure of Collagen
Copyright © 2012 American College of Sports Medicine
Components of Dense CT (cont’d)
• Tendon, Ligament, and Fascial Adaptations to Training
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Mechanical loading
• Major stimulus for growth
• Leads to cascade of events leading to hypertrophy
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Degree of adaptation is proportional to intensity of exercise
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Sites where CT can increase strength
• At junctions between the tendon/ligament & bone surface
• Within the body of the tendon/ligament
• In the network of fascia within skeletal muscle
Copyright © 2012 American College of Sports Medicine
Components of Dense CT (cont’d)
• Cartilage Adaptations to Training
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Types
• Articular (hyaline) cartilage
• Fibrous cartilage
• Elastic cartilage
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Lacks its own blood supply & must receive nutrients from
synovial fluid
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Long recovery from injuries
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Potential for degeneration, leading to osteoarthritis
Copyright © 2012 American College of Sports Medicine