Muscles: Actions, Movements, and Terminology

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

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

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

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

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.

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

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

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)

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

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

Isometric Muscle Contraction• No movement

– Tension equals the load.

• Examples:

– Wall Sit

– Plank

Isometric

Concentric

Eccentric

Deltoid holds arm in ________________

Deltoid shortens to move arm into ________________ Deltoid lengthens

to lower arm into ________________

Types of contraction

Muscle Movement Classification

A muscle’s role in producing movement can be defined as that of the:

• Agonist or Prime Mover

• Antagonist

• Synergist

• Stabilizer

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 

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

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.  

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

Putting It Together

starting position ending position

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

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

Putting It TogetherConcentric Contraction Eccentric Contraction• Down phase of exercise Up phase of exercise

Breathing • Exhale during the working phase of a

movement

• You are moving against the force of resistance

Direction of Movement

Agonist-Contraction

Antagonist-Contraction

Progravity Eccentric Concentric

Antigravity Concentric Eccentric

Gravity Eliminated

Concentric Eccentric

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

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