FNES 340 - Kinesiology: The Muscular System Study Notes

FNES 340 - Kinesiology: The Muscular System

Types of Muscles

  • Smooth (Visceral) Muscle

    • Location: Vessels and hollow organs

    • Innervation: Involuntary nervous system

  • Cardiac Muscle

    • Location: Heart

    • Innervation: Involuntary nervous system

  • Skeletal (Striated) Muscle

    • Characteristics: Regularly spaced parallel stripes and multinucleated

    • Innervation: Somatic (voluntary) nervous system

    • Quantity: More than 400 skeletal muscles in the human body

Functions of Skeletal Muscle

  • Conduct movement

  • Maintain posture

  • Generate heat

  • Assist venous return of blood

Macrostructure of Skeletal Muscles

  • Muscle Belly > Fascicle > Fiber > Myofibril

    • Epimysium (deep fascia surrounding muscle belly)

    • Perimysium (surrounds fascicles)

    • Endomysium (between fibers)

    • Sarcoplasm (cytoplasm of muscle cell)

    • Sarcolemma (cell membrane of muscle fiber)

    • Tendon (connects muscle to bone)

Microstructure of Skeletal Muscles

  • Muscle Fiber

    • Definition: A single muscle cell

  • Sacrolemma

    • Definition: Thin cell membrane covering the muscle fiber

  • Endomysium

    • Role: Connective tissue between fibers and tendon

  • Myofibril

    • Description: Lie parallel to each other, run the full length of the fiber, number varies from less than 100 to 1000

  • Sarcomere

    • Definition: The repeating unit of myofibril, basic contractile unit of muscle

    • Contains: Thick filament (myosin), Thin filament (actin)

Sarcomere Structure

  • Z-line

  • Myofilaments (cross sections)

    • Actin filament

    • Myosin filament

  • A-band

  • I-band

  • M-line

  • H-zone

  • State of Muscle

    • Resting state: Involves interactions between actin and myosin

    • Components: Head, Tail, Backbone, Tropomyosin, Troponin

Muscle Contraction: Huxley’s Sliding Filament Theory

  • Mechanism: Connections between myosin and actin (cross-bridge) facilitate sliding, causing shortening of the sarcomere and muscle.

  • Trigger: Calcium ions (Ca²⁺) released promote cross-bridge formation

  • Note: Video reference provided for further illustration (https://www.youtube.com/watch?v=BVcgO4p88AA) (for information only)

Fiber Organization

  • Fusiform Muscles

    • Characteristics: Parallel muscle fibers and fascicles, run the length of the muscle parallel to the line of pull

    • Advantage: Large amount of shortening and high velocity

  • Penniform Muscles

    • Characteristics: Muscle fibers run diagonally relative to a central tendon (featherlike)

    • Advantage: Can produce more strength

  • Note: Video reference for illustrations (https://www.youtube.com/watch?v=X9luereuw7Y&t=40s) (very important)

Muscle Contraction Force

  • Physiological Cross-Sectional Area

    • Increasing sarcomeres in series or parallel increases strength

    • Diameter and cross-sectional area of myofibrils and myofilaments contribute to strength

  • Tensile Force

    • Human muscle during isometric contraction: can produce about 30 N/cm² if all fibers are active

    • Formula for maximal isometric force:
      Fm=AmσmFm=Amσm

    • Where:

    • $Fm$: maximal isometric force

    • $Am$: cross-sectional area

    • $σm$: maximum stress by isometric muscle contraction

Force Calculation Examples

  • General formula:
    Fm=(AmcosΘ)σmFm=(Am cos Θ)σm

  • Calculation examples:

    • For $23.08 ext{ cm}^2$:
      Fm=23.08extcm2x0.886x30extN/cm2=613extNFm=23.08 ext{ cm}^2 x 0.886 x 30 ext{ N/cm}^2=613 ext{ N}

    • For $10 ext{ cm}^2$:
      Fm=10extcm2x30extN/cm2=300extNFm=10 ext{ cm}^2 x 30 ext{ N/cm}^2=300 ext{ N}

Muscle Fiber Types

  • Type I: Slow-Twitch Oxidative (SO)

    • Characteristics: Highly aerobic, fatigue-resistant, smaller in diameter, less tension generated

  • Type IIA: Fast-Twitch Oxidative-Glycolytic (FOG)

    • Characteristics: High aerobic and anaerobic capacities, develop tension quickly and sustain it

  • Type IIB: Fast-Twitch Glycolytic (FG)

    • Characteristics: High anaerobic, generate high tension but fatigue quickly

  • Note: Video link with explanations (https://www.youtube.com/watch?v=8x8H-GFtwyU) (very important)

Summary of Muscle Fiber Types

  • Fatigue Resistance Ability: Type I > Type IIA > Type IIB

  • Force Generation Ability: Type IIB > Type IIA > Type I

  • Speed of Force Generation: Type IIB > Type IIA > Type I

  • Note: Critical information for understanding muscular functions (very important)

Roles of Muscles in Movement

  • Prime Mover vs Assistant Mover

  • Agonist Muscle

    • Definition: Creates force in the same direction of the joint action

    • Role: Primary muscle responsible for movement

  • Antagonist Muscle

    • Definition: Creates force opposite the joint action

    • Role: Helps control smooth movement

  • Stabilizer

    • Definition: Active isometrically to keep a limb from moving

    • Function: Allows specific movements at adjacent joints

  • Neutralizer

    • Function: Creates torque to oppose undesired muscle action

  • Synergy

    • Definition: Muscle assisting in producing the desired action

Examples of Muscular Roles

  • Shoulder Abduction

    • Agonist: Deltoid (responsible for abduction)

    • Antagonist: Latissimus dorsi (resists abduction)

    • Stabilizer: Trapezius (holds scapula in place)

    • Neutralizer: Teres minor (neutralizes internal rotation)

  • Note: For illustrative purposes only, not for testing.

Types of Muscular Actions

  • Concentric Contraction

    • Definition: Muscle active and attachments closer

  • Eccentric Contraction

    • Definition: Muscle active and attachments drawn farther apart

  • Isometric Contraction

    • Definition: Muscle active but attachments do not move

  • Note: Video link for further details (https://www.youtube.com/watch?v=YIYhrj4QBWU) (very important)

Efficiency of Muscular Actions

  • Eccentric Action

    • Efficiency: More efficient, same force with less oxygen consumption and EMG activity

    • Comparison: Eccentric > Isometric > Concentric

  • Graphical Illustration: Eccentric action produces the highest force compared with isometric and concentric actions (very important)

Muscle Length and Active Tension

  • Active tension ranges: about 60% to 160% of its resting length

  • Key Components in Tension Development:

    • Actin, Z-line, Myosin

    • Lengths regarding force production:

    • Minimum length for active tension

    • Maximum length for active tension

Relationship Between Muscle Length and Tension

  • Passive Tension

    • Developed in sarcomere and connective tissues (sarcolemma, endomysium, perimysium, epimysium, tendon)

  • Multiple Joint Muscles

    • Unlike single joint muscles, they are less constrained within a specific range and can engage beyond 160%.

One and Two Jointed Muscles

  • One Jointed Muscle

    • Example: Deltoid (contraction causes movement of one joint)

  • Two Jointed Muscle

    • Example: Hamstring (can cause movement of two joints)

    • Note: Actions depend on position and external interactions; more prone to injury due to overstretching potential.

Force-Velocity Relationship

  • Trade-off: As the velocity of muscle contraction increases, the amount of force generated decreases.

  • Graphical Illustration: Shows the inverse relationship between force and velocity (for information only)

Other Factors Influencing Maximum Force

  • Prestretch

  • Stimulus Duration

    • Optimal time: >0.001 to 0.300 seconds

  • Fatigue

    • Impact: Decreased ATP supply reduces force generation

  • Fiber Type Influence

    • Type I, Type IIA, Type IIB mentioned above as they relate to fatigue resistance, tension generation, and overall performance