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Musculoskeletal Concepts
Dr. Suzan Ayers
Western Michigan University
Lecture Overview

Bone functions & structure

Joint classification and functions

Muscle structure & function/contractions

Synergistic/Antagonistic muscle roles

Components of muscular fitness
Bone Functions

Mechanical functions
– Support for weight bearing
– Protect internal organs
– Sites for muscle attachment

Physiological functions
– Heal/Maintain integrity
– Store essential minerals (i.e., calcium, phosphate)
– Immune system (marrow produces blood cells)
Bone Structure

Composition
– Calcium and phosphorous
– Collagen: toughness, flexibility (1/3)
– Calcium salts: hardness, rigidity (2/3)
Bone Structure

Bone cells
– Osteocytes (mature bone cells)
– Osteoblasts (build bone)
– Osteoclasts (remodel bone)

Bone types (1° difference is organization)
– Spongy: irregular latticework; releases Ca
easier, more like a trampoline
– Compact: concentric ring structure; provides
protection/support; more like concrete

Factors influencing bone composition
– Bone shape (femur vs. vertebra)
– Function (skull vs. foot bones)
Pg. 18-21: Bony Architecture Relative to Functions
Joint Classifications
Synovial
– Joint cavity; bones joined by articular capsule and
often ligaments; most familiar major joints (knee, ankle)
 Articular cartilage
 Joint capsule
 Synovial membrane (lubrication, protection, nutrition)
 Ligaments (major source of joint stability)
– Ball and socket: circular motion (hip, shoulder)
– Hinge: back & forth motion (ankle, knee, elbow)
– Biaxial/Saddle: motion in 2 planes (knuckles)
Joint Functions

Movement planes
– Sagittal/Longitudinal
(vertical: left/right)
run
 Flexion (angle decreases)
 Extension (angle increases)
– Coronal/Frontal jjax
(vertical: front/back)
– Transverse swing bat
– (horizontal: top/bottom)
Muscular Structure

Muscles cross bones

Muscle-tendon unit
– bone-tendon-muscle-tendon-bone

Relationship between direction of muscular pull
and joint axis of rotation determines resulting
joint action
Smooth muscle (digestive system, blood vessels)
 Cardiac muscle
 Skeletal muscle (p. 26)

– Cells are elongated w/ many nuclei, ergo fibers
– Actin(thin) & myosin(thick) create striated appearance
– Motor unit: a nerve & associated muscle fibers
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5 main properties of muscle
– Excitability from neural stimulation
– Contractility in response to neural stimulation
– Conductivity of electrical signals to coordinate motion
– Extensibility shape distortion
– Elasticity return to original shape
Muscular Function/Contractions

Muscular contraction
(pull only, no push):
– cock-connect-pull-release (cross-bridge cycling)
– http://www.sci.sdsu.edu/movies/actin_myosin_gif.html
Calcium essential for muscular contraction
 Types of contractions

– Concentric (shortening): produce movement
– Eccentric (lengthening): control movement
– Isometric (same length): maintain posture/stability
– Isokinetic (same speed)
– Isotonic (same tension)

Speed of movement: 2-1-4 (conc/ecc relationship)

Muscle types relative to joint actions
– Monoarticular (muscle crosses one joint brachialis)
– Biarticular (muscle crosses 2 joints hamstring)
– Polyarticular (muscle crosses >2 joints forearm)
Muscular contraction produces all joint actions
of which it is capable
 Limitations to ROM

– Joint capsule tension on stretching side of joint
– Flexibility of associated muscles/tendons
– Soft tissues on compressed side of joint
– Proximity/Contact of bony parts forming joint
Synergistic/Antagonistic Roles

Synergistic
– Contributing to desired motion, often by stabilization

Antagonistic
– Opposing desired motion

Examples of each
– Biceps: deltoids (s), triceps (a)
– Pectoralis: triceps (s), lats (a)
– Quadriceps: gluteals (s), hamstrings (a)
Role of synergistic/antagonistic muscle groups
 Need for appropriate training sequence

Little Ditties About Muscular Fitness
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Motor unit
– Motor nerve & all muscle fibers it innervates

Contractile force
– Depends on # & size of motor units recruited

Table 4.1
(Sharkey, p. 46)
– Slow-twitch/-oxidative (SO)
– Fast-oxidative glycolytic (FOG)
– Fast-glycolytic (FG)
– SO recruited first, then FOG then FG (size principle)

DOMS
– Micro-tears, edema, inflammation, enzyme leakage
Components of Muscular Fitness

Strength
– Max force exerted in 1 effort
– Unrelated to fiber type
– Fiber type differences based on rate of force
production
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Power
– Strength x speed

Muscular Endurance
– Ability to sustain sub-maximal contractions
– Small not large muscle groups (more CV endurance)

Power Endurance
– Repeated performance of a skill w/ adequate speed

Reaction Time
– Time between stimulus & response (processing &
signaling)

Quickness
– How an athlete reacts within a small area
– Combination of reaction time & speed of movement
– Has learned, trained and genetic components

Speed
– Final product of reaction time & quickness
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Balance
– Maintenance of equilibrium (dynamic or static)

Flexibility
– ROM through which joints move
– Influenced by gender, habitual use and stretching of
joint and associated structures
– Sport-specific & inversely related to joint stability

Agility
– Rapid change of speed & direction while ↔ balance