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Muscles: Actions, Movements, and Terminology
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Overview• Muscle 101• Role of Skeletal Muscle• Muscle Terminology• Muscular Contractions
– Concentric– Eccentric– Isometric
• Muscle Movement Classification or Defining a Muscle’s Role in Producing Movement – Agonist or Prime mover – Antagonist– Synergist – Stabilizer
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Muscles• Three types of muscle in the human body
– Skeletal• Voluntary
– Cardiac (heart)
– Smooth (internal organs)
• Consists of contractile cells (muscle fibers)
• Muscles can only pull; they can not push
• Tendons attach muscles to bone– ligaments attach bone to bone
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Role of Skeletal Muscle• Gives form to the body• Provides heat• Produces skeletal movement • Assists in maintaining joint stability • Maintains posture • Maintains balance over center of gravity
–55% of height in women–57% of height in men
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Muscle TerminologyUniarticulate• A muscle that
crosses one joint
• Ex: Brachioradialis crosses the elbow joint
Biarticulate• A muscle that
crosses two joints
• Sartorius
Triarticulate• A muscle that
can move three joints
• Ex: Wrist Flexors
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Muscle Terminology• Muscle Action:
– Specific movement of the joint • Flexion, Extension, Ad/Abduction, etc.
• Muscle Origin: – The end of the muscle attaching to the
relatively fixed (or least moveable) bone of its joint.
– The more proximal attachment site• Muscle Insertion:
– The end of the muscle attaching to the freely moving bone of its joint.
– The more distal attachment site of the muscle.
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Origin:Anterior Deltoid: Lateral 1/3 of clavicleMiddle Deltoid: Acromion Process of ScapulaPosterior Deltoid: Spine of Scapula
Insertion: Deltoid tuberosity of humerus
O:Medial Epicondyle of Humerus (2 heads medial and posterior)I: Pisiform, Hammate, and Base of 5th metacarpal
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Muscle Terminology• Nerve Innervation: The segment of the
nervous system responsible for providing a stimulus to muscle fibers.
• Muscle Palpation: Examination by touch
• Muscle length: The distance between bony attachments
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Muscular Contractions• Muscular Contractions
–Isotonic (Movement with constant external resistance-Bicep Curl)• Concentric
• Eccentric
–Isokinetic (Movement with varying external resistance/control for velocity-Tubing?)
–Isometric (no joint movement)
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Concentric Muscle Contraction• Muscle shortens in length while
developing tension– Muscle tension is greater than the load
• Examples: – The upward phase of a bicep curl– The upward phase of a bench press– The upward phase of an abdominal
crunch– The upward phase of a squat– The downward phase of a lat pull-down
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Eccentric Muscle Contraction• Muscle lengthens under tension.
– Resistance is greater than muscle tension.
• Examples:
– The downward phase of a biceps curl
– The downward phase of a squat
– The downward phase of a lunge
– The upward phase of a lat pull-down
• Eccentric muscle contractions are what makes you sore
• Most injuries occur in the eccentric phase
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Isometric Muscle Contraction• No movement
– Tension equals the load.
• Examples:
– Wall Sit
– Plank
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Isometric
Concentric
Eccentric
Deltoid holds arm in ________________
Deltoid shortens to move arm into ________________ Deltoid lengthens
to lower arm into ________________
Types of contraction
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Muscle Movement Classification
A muscle’s role in producing movement can be defined as that of the:
• Agonist or Prime Mover
• Antagonist
• Synergist
• Stabilizer
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Agonist or Prime Mover• A muscle or group of muscles that causes a
motion– Muscle contracts concentrically or eccentrically
• Examples:
– Knee Extension
• Quadriceps, through concentric contraction, extend the knee
– Elbow Flexion
• Biceps work concentrically to bend arm
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Antagonist• “The Opposer”• Resists the motion caused by the prime mover• Contracts to prevent, slow or control a motion
– Helps protect the agonist
• Examples: – Knee Extension
• Hamstring muscles, through eccentric contraction, help to slow the rate of knee extension
– Elbow Flexion• Triceps work eccentrically to slow the rate that
the arm is bent – Rotator Cuff Muscles
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Synergist• Assists the movement of a prime
mover but is less effective– These muscles are considered to have a
functional relationship with the prime mover
– However, the assisting muscle cannot perform the motion at a functional level.
• Example: As a portion of the quadriceps crosses the hip joint, it can help produce hip flexion. However, it is incapable of producing hip flexion alone.
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Stabilizer• Muscles contract (frequently by an isometric
contraction) to hold a body part immobile while another body part is moving. – Your wrist while doing a dumbbell bench press– Core muscles
• Proximal Stabilization: In most normal activities, the proximal joint is stabilized while the distal joint performs the action.– To perform isolated elbow flexion the proximal
shoulder joint must be stabilized by flexors/extensors, abductors/adductors and internal/external rotators.
– The quadriceps may stabilize the knee in an extended position to permit plantar flexion of the ankle
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Putting It Together
starting position ending position
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Putting It TogetherExercise• Standing Cable Triceps ExtensionAgonist or Prime Mover: • Triceps Brachii
– Triceps Brachii is a Biarticulate Muscle
Muscle Origin• Scapula and HumerusMuscle Insertion• UlnaMuscle Action• Elbow and Shoulder Extension
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Putting It TogetherSynergist• AnconeusAntagonist• Elbow Flexors (Biceps Brachii, Brachialis and
Brachioradialis)Stabilizers: • Latissimus Dorsi • Teres Major • Pectoralis Major• Deltoid• Rotator Cuff Muscles• Erector Spinae • Rectus Abdominis • Obliques • Wrist Flexors
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Putting It TogetherConcentric Contraction Eccentric Contraction• Down phase of exercise Up phase of exercise
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Breathing • Exhale during the working phase of a
movement
• You are moving against the force of resistance
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Direction of Movement
Agonist-Contraction
Antagonist-Contraction
Progravity Eccentric Concentric
Antigravity Concentric Eccentric
Gravity Eliminated
Concentric Eccentric
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Take Home Points• Skeletal muscle plays many roles in the
body including producing skeletal movement, heat and joint stability
• Muscles can be uni, bi or triarticulate• Muscle action is the specific movement of
the joint• A muscles origin is proximal and relatively
fixed while the insertion is more movable and distal
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Take Home Points• There are three key types of muscular
contractions–Concentric, eccentric and isometric
• A muscle’s role in producing movement can be defined as that of the: –Agonist/prime mover, antagonist,
synergist or stabilizer