Structural Organization of Skeletal Muscle

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Structural Organization of Skeletal Muscle

• Approximately 434 Muscles In Human Body
• 40-45 Of Body Weight
• About 75 Muscle Pairs Are Responsible For
  Movement and Posture
• Force, Speed and Magnitude of Force of a Muscle
  Are Dependent of Anatomical and Physiological
  Characteristics of the Muscle

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Muscle Fibers

• Single Muscle Cell - Fiber
• Surrounded byMembrane - Sarcolemma (Cytoplasm) -
  Sarcoplasm
• Containing nuclei, mitochondra and threadlike
  myofibrils

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Myofibrils

• Contain Two Types of Protein Filaments
• Appearance - Striated Pattern

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Within The Myofibril

• Sarcomere
• Alternating Light and Dark Bands Made Up Of Actin
  and Myosin Proteins
• Compartmentalized By The Z Lines.

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Image Of Sarcomere

• From An Electron Microscope
• Notice the Band Widths
• These Widths Change Upon Nervous Innervation.

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Cross-bridge Theory

• During Muscle Contraction
• Actin Filaments From Either End Of The Sarcomere
  Slide Toward Each Other (The Z Lines Move Toward
  the A Bands)
• Projections From The Myosin Filaments Called
  Cross-bridges Form Physical Linkages With The
  Actin Filaments.
• The Number of Linkages Are Proportional To
• Force Production
• Energy Expenditure

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Network Channels In FiberProvide Transportation
of Electromechanical Mediators

• Sarcoplasmic Reticulum
• Associated With Each Fiber Externally
• Transverse Tubules
• Transect Completely Through The Fiber and Only
  Open Externally

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Motor Unit Defined

• Single Motor Neuron and All Fibers It Innervates.
• The Axon Of Each Motor Unit Subdivides So That
  Each Individual Fiber Is Supplied With a Motor
  End Plate (1/fiber).
• 100 to 2000 Motor Units Per Fiber

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Fiber Types

• Muscle Fiber Types Vary In Structure, Chemical,
  and Behavioral Characteristics.
• Functions Of Differing Types Of Great Interest To
  Exercise Physiologist and Biomechanists.
• Divided Into Categories
• Fast Twitch (FT - Type II)
• Slow Twitch (ST - Type I)
• Peak Tension Of FT Can Be Achieved In 1/7th Of
  The Time It Takes A ST fiber.
• Generally, FT Has Higher Amplitude (force) But
  Fatigues More Quickly.

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MORE RECENT SPECULATIONS ON STRENGTH

• Caused By A Change In Structural Nature Of Type
  II Muscle Fiber
• Type IIb (Fast Twitch) Fiber Type
• Type IIa - Fatigues Less
• Note Type IIb - Fatigues Very Quickly

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QUESTION

• What Are The Factors Which Contribute To
  Increases in Muslce?
• How Could These Be Understood For Future
  Development In Teaching or Coaching?
• Are Their Differing Ways To Increase Strength
  Depending On The Sport Or Activity?

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STRENGTH DEFINED

• Max Ability To Apply Or Resist Force.
• One Who Curls 150 lbs. Has Twice The Strength Of
  One Who Curls 75 lbs.
• How Measured?

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POWER DEFINED

• The Ability To Quickly Produce Force Over A
  Distance
• PwForce x Distance / Time
• Example Pushing A Sled In The Bobsled Race
• One person of equal strength pushes the sled ten
  feet further than another, the first person
  displayed more power.
• How Measured?

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OTHER ACTIVITIES REQUIRING A HIGH DEGREE OF
REPETITIVE MOVEMENTS OVER TIME

• Muscular Endurance
• Defined As The Ability To Sustain Contractions
  Over Time At Near Maximum Force
• How Measured?

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HOW DOES ONE COACH AND/OR DEVELOP POWER, STRENGTH
AND MUSCULAR ENDURANCE

• Before Neuromuscular Adaptation Occurs, What Must
  Be Accomplished?
• Answer Stress To The Muscle (Overload Principle)
• Just lifting or running at low intensity will not
  build muscle strength and power. ie yoga,
  stretching, lifting without sufficient enough
  stimulation.

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WHAT RESEARCH SHOWS

• Programs Where Stress In Loaded To Muscle
• Increases Strength Very Quickly
• Increases Neuromuscular Changes Vary Quickly
• How Quickly?
• In As Little As 3 to 6 Months.

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CAN STRENGTH BE LOST AS QUICKLY?

• Yes, Once Levels of Strength Or Adaptations
  Occur, It Can Be Quickly Lost.
• Atrophy.
• How Many Bouts Of Training Are Needed To Maintain
  Strength Power.
• Minimum 1-2 Bouts / Week - Sufficient

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SO WHAT ARE THE MECHANISMS CONTRIBUTING TO
STRENGTH GAINS

• A Change In Motor Unit Recruitment
• Neurons To Muscle Produce Two Types Of Responses.
• a. Inhibitory Impulses
• b. Excitatory Impulses

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INHIBITORY IMPULSES

• Natures Way Of Protecting Muscle From Over
  Exertion.
• Called Autogenic Inhibition Reflex (AIR)

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Training Possibly Decreases The Inhibitory
Impulses.

• So Gains In Strength May Well Be Due to Decreased
  AIR.

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OTHER REASONS FOR STRENGTH GAINS

• Hypertrophy Of The Muscle.
• What Causes Hypertrophy?
• a. Increased Testosterone Hormone
• Females Have However Shown Increased Strength
  Without Hypertrophy.

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Hypertrophy Alone Does Not Account For Increased
Strength.

• DIFFERENCE BETWEEN ACUTE AND CHRONIC HYPERTROPHY
• Acute or Transient Hypertrophy - Caused By
  Intramuscular Fluid
• Chronic or Long Term - Caused By Structural
  Changes

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CONFLICTING EVIDENCE

• Hyperplasia - A Splitting Of Muscle Fiber - 10
  In The Research.
• Increased Sarcoplasm
• Increased Connective Tissue and Size
• Enlargement In Size Of Fiber - Myofibrils

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PROCESS OF STRUCTURAL CHANGE

• Through Later Repetitions Cramping Occurs In Type
  II Fibers.
• Additional Reps Tears The Fibers From The
  Connective Tissues At Their Weakest Links
• Damage Remodeling In Three Phases
• Inflammation Phase
• Clean-Up Phase
• Adaptive Growth

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MOST WIDELY ACCEPTED THEORY FOR INCREASED MASS

• INCREASE IN MYOFIBRIL AND FILAMENTS
• Providing More Crossbridges and More Contractile
  Force.

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Question With Weight Training, Is There A Change
In The of Myofibrils Or Of Muscle Fiber?

• Small Increases In of Muscle Fibers Are
  Present, But Not Significantly

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CAN MUSCLE FIBER TYPES CHANGE?

• Possibly Across Type II Fibers, But Not From Type
  II to Type I Fibers.
• Neither Strength Of Endurance Training Seems To
  Change Type I to II Or In Vise Versa.

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HOW DOES ONE INCREASE POWER?

• Since Power Is A Product Of Speed and Strength,
  It Is Obvious That Strength Increases Encourages
  Increases In Power.

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HOW DO WE INCREASE MUSCULAR ENDURANCE?

• Increase Repetitions
• Decrease Resistance
• Muscle Endurance Has Been Shown To Improve With
  Strength Gains.
• Direct Correlation Between Absolute Muscular
  Endurance and Strength

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WHY DO WE SEE INCREASED MUSCLE ENDURANCE AS A
RESULT OF STRENGTH GAINS?

• Increased Vascularization Within The Muscle
  Yielding
• Better Circulation
• Increased Removal of Waste
• Increased Availability of Fuels For Energy ie
  Glucose
• Increased Availability Of Oxygen

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TYPES OF CONTRACTIONS

• Static
• Example Isometrics
• (Iso Same) (Metric Change In Length)

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STATIC CHARACTERISTICS

• Energy Is Still Being Utilized - Due To
  Contractions
• Fatigue Can Still Be Met
• LA H ion Build Up Is Still Present
• Neural Activity Continues During Contraction

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MEASUREMENT OF STATIC STRENGTH

• Hand Grip Dynamometer - Measured in Kilograms
• How Can We Explain Isometrics In Terms Of Work?
• Work Force x Distance / Time
• Research - Mueller (1950) showed that 6-7
  bouts/week significantly improves strength

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DYNAMIC STRENGTH

• Strength Exercises Using Movement
• Example
• Isotonic
• Isokinetic

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ISOTONIC

• Weight or Resistance Is The Same During The
  Entire Range Of Movement
• Points
• Contraction Occurs During Lifting
• Mechanical Advantages Play A Role Throughout
  Range Finding One's Max Can Be A Complex Matter

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ISOKINETIC

• Speed Is Utilized Throughout The Entire Range Of
  Motion
• Points
• Speed Is Consistent
• Degrees Of Motion Can Be Regulated.
• The Slower The Velocity That Movement Is
  Occurring Through A Range, the More Recruitment
  Of Muscle Fiber
• Greater The Force, The Greater The Resistance
• Theoretically, This Method Should Lead To Greater
  Strength Improvement.

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MEASUREMENT OF ISOTONIC ISOKINETIC

• Isotonic - Free Weights, Max Lift
• Isokinetic - Hydraulic Lifts, Leaper Machine.

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POWER

• How Does Power Differ From Strength?
• Power Work (F x D) / Time
• There Is A Time Frame
• Tests On Power Were Developed To See If Subjects
  Could Move With Resistance Over A Time Period.

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TYPES OF POWER TESTS

• S.J. Sargent Jump Tests - Curvilinear
  Relationship Between Vertical Jump Force.
  Learning Does Take Place.
• M.K. Force Power Test - Has The Aspect Of
  Learning Also, Relates To Skill.
• Wingate Power Test - Intermittent Power Test -
  Revolutions/Time _at_ 7 Body Weight Resistance
• Most Reliable

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MUSCLE ENDURANCE

• Defined The Ability To Sustain At High Levels Of
  Contraction Over Time
• Associates Well With Muscle Metabolism
• Test Of Endurance Using Less Resistance But
  Maximum Repetitions
• Assessment
• Push Up Test Over Time
• Sit Up Test Over Time

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COMPARATIVE DIFFERENCES IN FORMS OF WEIGHT
TRAINING.