Mechanics of movement i muscle force and action across joints
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Mechanics of Movement I: Muscle Force and Action Across Joints. Review muscle force generation Muscle Mechanics --force versus cross section --length versus strain Lever mechanics and agonist/antagonists Stabilizing the joint—isometric and eccentric contraction.

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Mechanics of Movement I: Muscle Force and Action Across Joints

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Mechanics of movement i muscle force and action across joints

Mechanics of Movement I: Muscle Force and Action Across Joints

Review muscle force generation

Muscle Mechanics

--force versus cross section

--length versus strain

Lever mechanics and agonist/antagonists

Stabilizing the joint—isometric and eccentric

contraction

Frolich, Human Anatomy, Mechanics of Movement


Muscle structure review

Muscle Structure Review

  • Muscle fiber = muscle cell

  • Fibers lined up = direction of pull

  • Tendon attaches to bone

  • Muscle pulls on bone

Frolich, Human Anatomy, Mechanics of Movement


Muscle origin and insertion

Muscle Origin and Insertion

  • Origin

    • Proximal

    • Fixed

  • Insertion

    • Distal

    • Moves

  • (usually!!)

Frolich, Human Anatomy, Mechanics of Movement


Mechanics of contraction

Mechanics of Contraction

  • Muscle fiber is one cell made up of myofibrils, each filled with myofilament proteins actin and myosin, all lined up along length of muscle cell.

  • Action potential or depolarization of membrane releases calcium

  • Calcium changes shape of actin so myosin cross-bridges form and “row” or pull in to center of sarcomere.

Frolich, Human Anatomy, Mechanics of Movement


Visualizing muscle contraction

Visualizing muscle contraction

How actin-myosin complex (sarcomere)

shortens muscle

Frolich, Human Anatomy, Mechanics of Movement


Summary of muscle organization function

Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement


Summary of muscle organization function1

Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement


Summary of muscle organization function2

Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement


Mechanics of movement i muscle force and action across joints

Levels of Muscle Organization

Frolich, Human Anatomy, Mechanics of Movement


Muscle mechanics cross section versus force

Muscle Mechanics: Cross section versus force

  • Cross sectional area is proportional to Force of muscle

Frolich, Human Anatomy, Mechanics of Movement


Muscle mechanics length versus force

Muscle Mechanics: length versus force

  • Force generation depends on current length of muscle or overlap in actin/myosin of sarcomeres

  • Muscle force strongest between 80-120% of normal resting length—WHY? (don’t forget role of cross-bridges)

  • Most muscles arranged to work in this range

Frolich, Human Anatomy, Mechanics of Movement


Muscle mechanics length versus total shortening

Muscle Mechanics: length versus total shortening

  • Length of muscle is proportional to ability to shorten (strain)

    • Number of sarcomeres in series gives shortening ability

  • Short, fat muscles

    • Lots of force

    • Less shortening range

  • Long, skinny muscles

    • Less force

    • More shortening range

Frolich, Human Anatomy, Mechanics of Movement


Types of fascicle arrangements

Types of fascicle arrangements

  • Affects length and cross section of muscle

  • Thus affects force and shortening properties of muscle

  • See Muscle Mechanics if this doesn’t make sense

Frolich, Human Anatomy, Mechanics of Movement


Long thin straight muscle versus short fat pinnate muscle

Gastrocnemius (calf muscle)

Short and bulky

Pinnate fibers

Great force, low shortening distance

Pushes off each step—”spring-loaded”

Sartorius

Tailor’s or hackey-sac muscle

Longest muscle in body’

Thin and straight fibers

Low force, great shortening distance

Long thin straight muscle versus short fat pinnate muscle

Frolich, Human Anatomy, Mechanics of Movement


Muscle movement across joints is like lever system

Muscle movement across joints is like lever system

Frolich, Human Anatomy, Mechanics of Movement


Agonist antagonist muscles

Agonist/Antagonist muscles

Frolich, Human Anatomy, Mechanics of Movement


Stabilization and control around joint

Stabilization and Control Around Joint

  • Antagonist often “fires” or contracts or is stimulated simultaneously with agonist to stabilize around joint during movement

  • NOTE: Muscle “contraction” or stimulus to “fire” does not always result in muscle shortening

Frolich, Human Anatomy, Mechanics of Movement


Relation between muscle contraction or firing and shortening

Relation between muscle contraction (or “firing”) and shortening

  • Concentric contraction—muscle contracts and shortens to cause movement across joint

  • Isometric contraction—muscle contracts but stays same length to hold joint or body in same position

  • Eccentric contraction—muscle contracts while lengthening to stabilize joint during movement (most common in antagonist to slow movement caused by agonist)

Frolich, Human Anatomy, Mechanics of Movement


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