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. 2. State and define the three types of muscle contractions (concentric, eccentric, and isometric). 3. Describe the relationships among the terms mover, antagonist, concentric contraction, and eccentric contraction 9/21/2018 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. 8. Define the term muscle contraction. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY

Overview of the Types of Muscle Contractions Three Types of Muscle Contractions: ~ Concentric contractions ~ Eccentric contractions ~ Isometric contractions 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● 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.

Overview of the Types of Muscle Contractions Concentric Contraction Eccentric Contraction 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Overview of the Types of Muscle Contractions Isometric Contraction 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Overview of the Types of Muscle Contractions Resistance Exercises ● Resistance exercises add to the force of resistance that the contracting muscle must work against. ● 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. 9/21/2018 TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● Resistance exercises add to the force of resistance that the contracting muscle must work against. ● Figure 12-3a 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 12-3b 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.

Concentric, Eccentric, and Isometric Contraction Examples 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● 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.

Concentric, Eccentric, and Isometric Contraction Examples 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● 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.

Concentric, Eccentric, and Isometric Contraction Examples 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● 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.

Relating Muscle Contraction and the Sliding Filament Mechanism Muscle structure Nervous system control Sliding filament mechanism 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 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. ● 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.

Relating Muscle Contraction and the Sliding Filament Mechanism Concentric Contraction 9/21/2018 ● If the bending force of the myosin cross-bridges is successful in pulling the actin filaments in toward the center, the Z-lines 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● If the bending force of the myosin cross-bridges is successful in pulling the actin filaments in toward the center, the Z-lines 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.

Relating Muscle Contraction and the Sliding Filament Mechanism Eccentric Contraction 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Relating Muscle Contraction and the Sliding Filament Mechanism Isometric Contraction 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

GOALS FOR STUDENT MTS: 1. List and describe the three scenarios in which a concentric contraction occurs. 2. Define the term gravity neutral, and describe its relationship to muscle contractions. 3. List and describe the three scenarios in which an eccentric contraction occurs. 9/21/2018 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY

Concentric Contractions—More Detail Scenario 1—Against Gravity 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Concentric Contractions—More Detail Scenario 2—Gravity Neutral 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Concentric Contractions—More Detail Scenario 3—With Gravity 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Concentric Contractions—More Detail ● 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. ● Figure a shows a car moving uphill or vertically upward against gravity. ● 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. 9/21/2018 TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● Figure a shows a car moving uphill or vertically upward against gravity. ● 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.

Eccentric Contractions—More Detail 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY 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.

Eccentric Contractions—More Detail Scenario 1— “Slowing Gravity’s Vertical Downward Motion” 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Eccentric Contractions—More Detail Scenario 2 “Slowing Momentum of a Horizontal Motion” 9/21/2018 ● 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). TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● Figure 12-10a 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).

Eccentric Contractions—More Detail Scenario 3: “Slowing Momentum of a Vertical Upward Motion” 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Eccentric Contractions—More Detail ● 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. ● Figure a shows the car moving downhill (vertically downward) and slowing down by pressing on the brakes. ● 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). 9/21/2018 TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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. ● Figure 12-11a shows the car moving downhill (vertically downward) and slowing down by pressing on the brakes. ● Figure 12-11b shows the car moving on level ground (i.e., gravity neutral) and slowing down by pressing on the brakes. ● Figure 12-11c 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).

Isometric Contractions—More Detail Scenario 1— Against Gravity ● An isometric contraction is a contraction in which the muscle stays the same length. ● 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. 9/21/2018 TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● An isometric contraction is a contraction in which the muscle stays the same length. ● 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.

Isometric Contractions—More Detail Scenario 2— Against Any Force Other Than Gravity 9/21/2018 ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY ● 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.

Movement versus Stabilization Mobility ~ Movement Stability ~ Fix or stabilize 9/21/2018 ● 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. ● 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. TCCD MASSAGE THERAPY PROGRAM: MSSG 2012 KINESIOLOGY

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