S. Norman
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Skeletal Muscle—attached to the bones of the
skeletal system
◦ Voluntary muscle—contraction of skeletal muscle is a
result of conscious voluntary control
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Smooth Muscle—primarily lines hollow internal
structures (blood vessels and digestive tract)
◦ Involuntary muscle—contraction and relaxation phases
are automatic
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Cardiac Muscle—found only in the heart
◦ Involuntary
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A motor nerve coming from the brain or spinal cord
causes a muscle to contract or a gland to secrete
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A motor unit consists of a single motor nerve and all
the muscle fibers to which it sends impulses
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A motor nerve is connected to many muscle fibers,
but each muscle fiber is controlled by only one motor
nerve
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Very fine movement, very few muscle fibers
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Large or heavy movement, many muscle fibers
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A muscle fiber contracts completely or not at
all.
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If a stimulus for contraction is below the
threshold value, the muscle does not contract
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If the stimulus is above the threshold value,
the muscle contracts completely
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All of the muscle fibers in a motor unit
contract completely or not at all.
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Muscle tissue can contract or relax—muscle can
pull on bones or stop pulling on bones
Muscle tissue can only pull—it cannot push
All exercises involve muscles pulling on bones
across a joint. The movement that takes place
depends upon the structure of the joint and
position of the muscle attachments involved.
Types of contraction are: isometric, isotonic,
concentric, eccentric, and isokinetic
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Iso means equal, metric refers to length or
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Muscle maintains an equal length
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Contracting a muscle and creating a force against
an immovable object
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Muscle contracts and tries to shorten but cannot
overcome the resistance
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Example: Pushing against a wall or trying to lift a
truck
measure
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Tonic means tone or tension.
Movement occurs but muscle tension remains
about the same.
Example: a complete barbell curl
External resistance remains constant, however,
the muscle does not maintain constant tone
throughout the exercise movement because of
the continuous change in its angle of pull on the
bone.
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Result in the muscle fibers shortening as
tension develops, causing motion in a joint
Muscle becomes shorter and overcomes
resistance
Example: lifting the weight upward during the
biceps curl, pushing outward on the leg press
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Lengthening contraction
Muscle contracts and tries to shorten but is
overcome by the resistance
Allow you to lower things smoothly and
slowly
Example: lowering weight in a smooth,
controlled manner during the biceps curl
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iso = same, kinetic = motion
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Constant-speed contraction
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Muscle can contract at 100% throughout the
full range of motion at a constant speed
Example: injury evaluation/rehabilitation
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Muscles that are not used will shrink to a size
that is adequate for the demands placed
upon them
Example: broken leg or arm put in a cast,
when the cast is removed the arm or leg will
be much smaller than the active arm or leg
Both limbs will be reduced in size gradually
(often unnoticed) when one does not train the
muscular system
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Muscles that are forced to work harder than
normal generally increase in size
Women < Men
Men have more testosterone and a larger
number of muscle fibers in a muscle
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Specificity—You must exercise the specific muscles
you want to develop, and follow specific exercise
guidelines to produce the specific type of change
you desire (strength, size, endurance)
Overload—The muscle to be developed must be
overloaded or forced to work harder than normal
Progression—The workload must be increased
progressively as the muscle adapts to each new
demand (written record)