Transcript Types of Muscle Contractions Roles of Muscles

TCCD MASSAGE THERAPY PROGRAM: KINESIOLOGY
SOUTH CAMPUS SHPE 1230A
SECTION 4
GOALS FOR THE STUDENT MT:
1. Define the key terms of this chapter and state the meanings of the
word origins of this chapter.
4. Describe the relationships among the force of a muscle’s
contraction, the force of resistance to the muscle’s contraction,
and which type of muscle contraction results.
5. Define and give an example of a resistance exercise.
6. Give an example of each of the three types of muscle
contractions.
7. Relate the sliding filament mechanism to each of the three
types of muscle contractions.
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3. Describe the relationships among the terms mover, antagonist,
concentric contraction, and eccentric contraction
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2. State and define the three types of muscle contractions
(concentric, eccentric, and isometric).
8. Define the term muscle contraction.
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Three Types of Muscle Contractions:
●
If the force of the muscle’s contraction is less than the
resistance to the muscle’s contraction, the muscle will lengthen
instead of shorten as it contracts. This is called an eccentric
contraction.
●
An isometric contraction is one wherein the muscle
contracts and stays the same length. The force of the muscle’s
contraction is exactly equal to the resistance force.
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●
A concentric contraction is the type of contraction
wherein a muscle contracts and shortens. The muscle generates
the force that moves a body part to create the joint action that is
occurring. It is therefore termed the mover.
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~ Concentric contractions
~ Eccentric contractions
~ Isometric contractions
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Eccentric Contraction
●
Concentric contraction of the brachialis muscle is shown
here on the left. The arm is fixed and the forearm is mobile. The
arrow within the brachialis shows the line of pull of the muscle.
The red curved arrow represents the strength and direction of
pull of the brachialis acting upon the forearm; the straight brown
arrow represents the strength and direction of pull of gravity
acting on the forearm.
●
In the eccentric contraction scenario on the right, the
force of the contraction of the brachialis is less than the
resistance force of the weight of the forearm. Therefore, the
forearm extends with gravity, causing the brachialis to lengthen.
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Concentric Contraction
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●
In this scenario, the force of the contraction of the
brachialis is exactly equal to the resistance force of the weight of
the forearm. The brachialis, therefore, does not succeed in
shortening and flexing the forearm, nor does gravity succeed in
lengthening the brachialis and extending the forearm. This
illustrates isometric contraction of the brachialis.
● During isometric contraction, no joint action takes place
and therefore no mover or antagonist exists.
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Isometric Contraction
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● Figure a demonstrates an
example of resistance exercise
by adding resistance to flexion of
the forearm at the elbow by
placing a weight in the person’s
hand.
● Figure b shows added resistance
by using rubber tubing that must
be stretched for the person to be
able to flex the forearm at the
elbow joint.
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KINESIOLOGY
● Resistance exercises add to the
force of resistance that the
contracting muscle must work
against.
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Resistance Exercises
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●
As the musculature shortens, the arm is lifted up into the
air in which plane?
The arm is lifted up into the air in the frontal plane.
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●
One example of concentric contraction is shown here
with the person abducting the right arm at the shoulder joint
against the force of gravity. This force of abduction is created by
concentric contraction of the abductor musculature.
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●
Why is it necessary to slow down the force of gravity in this
type of movement?
It is necessary to slow down the force of gravity to prevent
the arm/forearm/hand from slamming into the side of the body.
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●
This same person is now adducting the arm at the shoulder
joint. Gravity is the mover force that creates adduction in this case,
but the abductor musculature is eccentrically contracting to slow
down the force of gravity.
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●
Does the musculature change in length during this type of
contraction?
No, the musculature of the joint does not change in length
because no joint action is occurring.
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●
In this illustration the person is statically holding the arm in
a position of abduction. In this case the abductor musculature is
isometrically contracting, equaling the force of gravity so that no
motion occurs.
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Muscle structure
Nervous system control
●
The central nervous system sends a signal through
neurons to every sarcomere of every myofibril of the muscle
fiber to cause a muscle contraction.
●
The sliding filament mechanism explains how actin and
myosin filaments slide along each other. When cross-bridges
form and create a pulling force toward the center of the
sarcomeres, the muscle is defined as contracting.
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KINESIOLOGY
●
A muscle is an organ composed of thousands of muscle
fibers that attaches from one bone to another (via its tendons),
thereby crossing the joint that is located between the two
bones.
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Sliding filament mechanism
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●
If the bending force of the myosin cross-bridges is
successful in pulling the actin filaments in toward the center, the Zlines are drawn toward the center of the sarcomere and the
sarcomere shortens.
●
The message for contraction is given to every muscle fiber
of a motor unit, so every muscle fiber of that motor unit will
shorten. What type of contraction will result?
A concentric contraction is the result of the successful
shortening of a muscle.
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Concentric
Contraction
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●
The myosin cross-bridges will not be successful in bending
and pulling the actin filaments in toward the center if the force of
resistance to the muscle shortening is greater than the force of the
muscle contraction.
●
What happens to the actin filaments when the force of the
resistance is greater than the muscle contraction force?
The resistance force will actually pull the actin filaments
away from the center of the sarcomere and each sarcomere
will actually lengthen.
●
An eccentric contraction is a lengthening contraction.
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Eccentric
Contraction
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●
If the muscle can equal the strength of the resistance
force, the myosin filaments do not succeed in shortening the
sarcomere, nor do they get pulled apart and have to reattach
farther from the center of the sarcomere; instead, they stay at the
same binding site locations. This is an isometric contraction.
●
Do the attachments and body parts move during
isometric contraction?
No, the muscle remains the same length and the body
parts do not move.
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Isometric
Contraction
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3. List and describe the three scenarios in which an eccentric
contraction occurs.
4. State the most usual circumstances when an eccentric
contraction occurs.
5. Define, describe, and give an example of internal forces
and external forces.
6. List and describe the two scenarios in which an isometric
contraction occurs.
7. Describe the relationship between joint mobility and joint
stability.
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2. Define the term gravity neutral, and describe its relationship
to muscle contractions.
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1. List and describe the three scenarios in which a concentric
contraction occurs.
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●
The brachialis is concentrically contracting in this
illustration.
●
What motion is occurring?
The forearm is flexing at the elbow joint. The motion is
vertically upward, against gravity.
●
Gravity is a force that pulls downward caused by the
mutual attraction between the earth and our bodies.
● The force that gravity exerts on the mass of an object is
then defined as the weight of that object.
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Scenario 1—Against Gravity
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●
This illustration shows the scapula retracting at the
scapulocostal joint.
●
This motion is horizontal and gravity neutral; therefore, the
muscles of scapular retraction must contract as movers to create this
motion.
What muscle is seen contracting in this figure?
The trapezius (and especially the middle trapezius) is seen
contracting in this figure; however, any scapular retractor might
concentrically contract to create this motion.
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Scenario 2—Gravity Neutral
●
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●
Figure c shows the arm adducting at the shoulder joint. This is a
downward motion.
●
Do any muscles need to concentrically contract to create this
motion?
No, they do not, unless the arm needs to be adducted faster
than would happen by gravity.
●
Figure d illustrates the arm adducting against the resistance of
rubber tubing. Even though this motion is downward and aided by
gravity, because of the resistance of the tubing, shoulder adductors
must concentrically contract to overcome the resistance and adduct
the arm.
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Scenario 3—With Gravity
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●
Figure b shows the car moving
on level ground, or gravity neutral.
●
Figure c illustrates the car
moving downhill (faster than coasting
with gravity), or vertically downward
and faster than gravity would create.
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●
Figure a shows a car moving
uphill or vertically upward against
gravity.
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●
Comparing the motor of a car
to a concentrically contracting muscle
is a helpful analogy to use when
learning why and when concentric
contractions occur.
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●
During an eccentric
contraction, instead of the myosin
heads bending toward the center of
the sarcomere, they are overpowered
by the resistance force to contraction
and they are bent in the other
direction. As a result, the actin filaments
slide away from the center and the
sarcomere lengthens.
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●
An eccentric contraction is defined as a lengthening
contraction (i.e., a muscle contracts and lengthens).
●
When a muscle lengthens, its attachments are moving
away from each other. This is usually not caused by muscle
contractions within our body, but by an external force.
●
In this illustration of a person lowering a glass of water,
the flexor muscle of the forearm at the elbow joint must contract
to oppose the elbow joint extension force that is being caused
by gravity. Without control of the muscular system, the glass
would come crashing down to the table and break.
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Scenario 1— “Slowing Gravity’s
Vertical Downward Motion”
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●
Figure a shows a person who has just hit a ping-pong ball
with a forehand stroke. What movement is taking place?
The person is horizontally flexing the arm at the shoulder
joint.
●
What motion must take place to slow down the motion of
the arm to prevent it from moving too far?
The person must eccentrically contract the muscles that do
the opposite action of the forehand stroke (i.e., horizontal extension).
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Scenario 2 “Slowing Momentum
of a Horizontal Motion”
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●
In this illustration the girl has just thrown a ball up into the
air by flexing the arm at the shoulder joint. This motion was
initiated by muscular contraction.
●
What motions take place in this scenario?
Upward motion of flexion of the arm aids in throwing the
ball up into the air. Eccentric contractions of the muscles on the
other side of the joint (i.e., the antagonistic shoulder joint
extensors) act to slow the upward motion.
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Scenario 3: “Slowing Momentum
of a Vertical Upward Motion”
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●
Figure b shows the car
moving on level ground (i.e., gravity
neutral) and slowing down by pressing
on the brakes.
●
Figure c shows the car
moving uphill (i.e., vertically upward)
and slowing down by pressing on the
brakes (slowing more quickly than it
would have due to gravity alone).
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●
Figure a shows the car
moving downhill (vertically downward)
and slowing down by pressing on the
brakes.
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●
Comparing the brakes of a
car to an eccentrically contracting
muscle is a helpful analogy to use when
learning why and when eccentric
contractions occur.
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●
What force is gravity
exerting on the arm?
It is pulling the arm
downward toward extension.
●
How is this man able to
hold his arm in a position of
flexion?
The shoulder joint
musculature must isometrically
contract with enough force to
equal the force of gravity.
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●
An isometric
contraction is a contraction in
which the muscle stays the
same length.
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Scenario 1— Against Gravity
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●
Isometric contractions can not only hold a body part up
against the force of gravity, but can also hold a body part in position
against any force other than gravity. This other force could come
from another muscle contracting within the body or from an external
force.
●
When a person arm wrestles and the force of the person’s
isometric contraction is exactly equal to the opposing force from the
other individual, neither force is capable of moving a body part, so
the parts remain statically still.
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Scenario 2— Against Any Force Other Than Gravity
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●
A muscle that contracts to create a force that
holds a body part in a static position is said to fix or
stabilize that body part.
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●
A muscle can create a force that can cause
or modify movement of a body part at a joint; it can
also create a force that can entirely stop movement of
a body part at a joint.
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Mobility
~ Movement
Stability
~ Fix or stabilize
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