B.1.3.1 Muscle Types and Functions in Human Movement

Muscle Types

Skeletal, cardiac, and smooth muscles serve distinct functions.

Skeletal Muscle

Voluntary muscles responsible for body movement.

Cardiac Muscle

Involuntary muscle that makes up the heart.

Smooth Muscle

Involuntary muscle found in internal organs.

Muscle Functions

Movement, stability, heat production, and posture maintenance.

Contractility

Ability of muscle to shorten and generate force.

Extensibility

Ability of muscle to stretch without damage.

Elasticity

Ability of muscle to return to original length.

Neuromuscular Function

Process involving neurons triggering muscle contractions.

ATP Metabolism

Energy source required for muscle contraction.

Motor Units

Functional groupings of muscle fibers and neurons.

All-or-None Principle

Muscle fibers contract fully or not at all.

Muscle Fiber Types

Types I, IIa, and IIx vary in function.

Hypertrophy

Increase in muscle size due to training.

Atrophy

Decrease in muscle size from disuse.

Contraction Types

Isometric, isotonic concentric, isotonic eccentric, isokinetic.

Reciprocal Inhibition

Muscles work in pairs: agonist and antagonist.

Origin and Insertion

Muscle attachment points for movement leverage.

Type 1 motor units

slow twitch muscle fibers, slow nerve transmission speeds, small forces, and maintain contractions for a long time

Type IIa

fast-twitch muscle fibers (anaerobic-aerobic) with more capillaries surrounding them. fast neural transmission times and strong contraction forces, are also resistant to fatigue

Type IIx

last twitch muscle fibers,generate greatest force but fatigue at a high rate

isometric muscle contraction

develops tension without changing length

important in postural muscle function and antagonistic muscle joint stabilization

isotonic muscle contraction

muscle changes in length with no change in tension

isotonic eccentric muscle contraction

force generated by muscle is less than load, muscle lengthens

Isokinetic Motion

Muscle contracts so that the body segment to which it is attached moves at a constant speed around the joint

Agonist (mover)

The muscle contracts concentrically to move the bone relative to the joint

Antagonist muscle

The muscle opposite the agonist, which must relax and lengthen during contraction of the agonist.

Fixator

muscle that prevents movement of bone

synergist (neutralizer) muscle

Muscles that oppose unwanted joint motions created by the prime mover and/or synergists, and/or muscles that prevent unwanted ancillary motion

Insertion

The attachment of a muscle tendon to a moveable bone or the end opposite the origin

Origin

attachment of a muscle that remains relatively fixed during muscular contraction

pectoralis major

Adducts and flexes humerus

flexor carpi group

flexes hand at wrist

external oblique

Compresses abdomen; laterally flexes and rotates vertebral column

lliopsoas

flexes thigh or trunk

quadriceps femoris

Four muscles of the anterior thigh

vastus intermedius

extends knee

Gastrocnemius

plantar flexes foot

extensor digitorum

Extends fingers and the wrist

extensor digitorum

Extends fingers and the wrist

Extensor carpi group

straightens wrist and hand

biceps femoris

extends thigh and flexes leg

Semitendinosus

Flexes leg at the knee and extends thigh at the hip; belongs to the hamstring group

Semimembranosus

Flexes leg at the knee and extends thigh at the hip; belongs to the hamstring group

Gastrocnemius

plantar flexes foot

Trapezuis

Upper center back muscle

deltoid

abducts arm

triceps brachii

extends forearm at elbow

biceps brachii

Flexes and supinates forearm

latissimus dorsi

Extends, adducts, and medially rotates the arm; draws the shoulder downward and backward

rectus abdominis

flexes and rotates vertebral column

flexor digitorum

flexion of wrist and digits

gluteus medius

abducts and medially rotates thigh

gluteus maximus

extends hip

adductor longus

adducts, flexes, and medially rotates thigh

Sartorius

Flexes, abducts, and laterally rotates thigh at the hip; flexes knee

vastus lateralis

extends leg at knee

Peroneus Longus

Plantar flexion and eversion of foot; stabilizes the lateral ankle and arch of the foot

tibialis anterior

dorsiflexes and inverts foot