Transcript Muscle Anatomy - West Valley College

Muscle Anatomy
PE Theory 42
Read: 3, 6-13, 18-24
Figures: 1.1, 1.3, 1.4a&b, 1.9, 1.10
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.
Skeletal Muscle
• Muscle belly
• Fasciculus
• Single Muscle Fiber
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
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?
X-Section of Muscle Fibers
• Each person has
different genetically
determined strength,
power, and endurance
capabilities
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
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
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
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
Size Principle
• Selective activation of
motor units &
difference in size of
motor units allow for
graded force
production
• More precise control
of body movements
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
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
Muscle Activation
• Only the motor units
that are actively
recruited during an
exercise produce force
& subsequently are
subject to the
adaptations from that
exercise
More on the Size Principle
• Very High Velocity movements are an exception
• The Type II’s 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
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