Muscle Anatomy

1
Muscle Anatomy

• PE Theory 42
• Read 3, 6-13, 18-24
• Figures 1.1, 1.3, 1.4ab, 1.9, 1.10

2
Skeletal Muscle

• Skeletal muscles are muscles that are attached to
  bones to produce movement across joints
• Tendons attach the muscles to the bones allowing
  muscles to cause movement
• A muscle is made up of bundles of muscle fibers.

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Skeletal Muscle

• Muscle belly
• Fasciculus
• Single Muscle Fiber

4
Muscle Fibers

• Type I - Slow Twitch Fibers
• High aerobic capability for endurance
• Lower contractile force capabilities
• Type II- Fast Twitch Fibers
• High glycolytic capability for strength power
• High contractile force capabilities

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Muscle Fiber Types

• Type I II fibers very person to person
• Genetic (choose parents wisely)
• No differences in fiber type for men women
• Elite Athletes
• Can A Type I change become a Type II?

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X-Section of Muscle Fibers

• Each person has different genetically determined
  strength, power, and endurance capabilities

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Motor Unit

• Motor Unit- a motor neuron all the muscle
  fibers it stimulates
• The basis of muscle stimulation
• Composed of either all type I or type II
• Fibers are spread out within a muscle

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Motor Units

• When a muscle moves, those motor units that are
  not activated do not generate force they move
  passively through the range of motion.
• The size of motor units varies
• Human eye- 10 fibers to a motor unit
• Quadriceps- 450 or more fibers to a motor unit

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Size Principle

• Motor units are recruited from the smallest to
  the largest based on the force demands placed on
  the muscle
• Low threshold units
• High threshold units

10
Size Principle

• Lifting heavy resistances will start with
  recruiting low threshold motor units first, and
  progressively move up the line until enough motor
  units are recruited to produce the needed force.
  The process is rapid.
• If only a low resistance is used, the largest
  motor units will no be recruited

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Size Principle

• Selective activation of motor units difference
  in size of motor units allow for graded force
  production
• More precise control of body movements

12
All or None Law

• When a specific motor unit reaches its threshold
  level for activation, all of the muscle fibers in
  that motor unit are activated fully
• If the threshold is not reached, then none of the
  muscle fibers in that motor unit is activated

13
All or None Law

• If one motor unit in a muscle is activated, that
  muscle produces only a very small amount of force
• If several motor units are activated, muslce
  produces more force
• If all motor units in a muscle are activated,
  maximal force is produced by the muscle

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Muscle Activation

• Only the motor units that are actively recruited
  during an exercise produce force subsequently
  are subject to the adaptations from that exercise

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More on the Size Principle

• Very High Velocity movements are an exception
• The Type IIs are recruited first to allow faster
  movement, skipping type I activation
• Ensures low-threshold motor units are pred.
  Recruited for lower-intensity (endurance)
  activites, and Higher-threthold units for high
  force and power activites

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To Build Strength

• In order to recruit Type II Fibers and receive a
  training effect in these fibers, the exercise
  must consist of heavy loading or high power
  output.
• Body position change (vary the exercise)can
  change the order of recruitment and different
  muscle fibers can be recruited