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 clavicle

Middle Deltoid:

Acromion

Process of

Scapula

Posterior

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 Extension

Agonist or Prime Mover:

• Triceps Brachii

– Triceps Brachii is a Biarticulate Muscle

Muscle Origin

• Scapula and Humerus

Muscle Insertion

• Ulna

Muscle Action

• Elbow and Shoulder Extension

Putting It TogetherSynergist

• Anconeus

Antagonist

• 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