Muscle Contraction

What is the origin of a muscle?

The attachment that usually remains fixed during contraction (typically the proximal attachment).

What is the insertion of a muscle?

The attachment that usually moves during contraction (typically the distal attachment)

Why are the terms "proximal attachment" and "distal attachment" (or medial and lateral) often preferred over "origin" and "insertion"?

Because some muscles can act in either direction depending on the movement being performed.

During a typical muscle contraction, which attachment moves?

The insertion (usually the distal attachment).

How much can muscle fibres shorten during contraction?

To approximately 70% of their resting length

Which muscle architecture shortens the most during contraction? What does this provide?

Parallel muscles. Provides considerable range of movement

Are parallel muscles powerful or not?

Not powerful

Which muscle architecture generates the greatest force? Why?

Pennate muscles. Muscle power increases as the total number of muscle cells increases, and wide pennate muscles that pack in the most fibre bundles shorten less but are the most powerful

Why can't muscles push?

Because muscle fibres can only contract (shorten), producing a pulling force.

What are the three main types of skeletal muscle contraction?

• Reflexive

• Tonic

• Phasic

What is a reflexive contraction?

An automatic contraction that is not under voluntary control.

Give an example of a reflexive contraction.

The patellar tendon reflex or normal breathing by the diaphragm

What causes a tendon reflex?

Stretching the muscle by tapping its tendon.

What is tonic contraction?

A slight continuous contraction (muscle tone) that does not produce movement.

What is muscle tone?

A slight continuous contraction that keeps muscles firm.

What are the functions of muscle tone?

• Maintains posture

• Stabilises joints

What are the two types of phasic contraction?

• Isometric

• Isotonic

What is an isometric contraction?

A contraction in which muscle tension increases but muscle length does not change.

Does an isometric contraction produce movement?

No.

Give an example of an isometric contraction.

Holding the arm abducted without moving it.

What is an isotonic contraction?

A contraction in which the muscle changes length to produce movement.

What are the two types of isotonic contraction?

• Concentric

• Eccentric

What is a concentric contraction?

An isotonic contraction in which the muscle shortens while producing movement.

Give an example of a concentric contraction.

The deltoid shortening to raise the arm into abduction.

What is an eccentric contraction?

An isotonic contraction in which the muscle lengthens while remaining under tension.

Why is eccentric contraction important?

It controls movement by allowing muscles to lengthen gradually rather than suddenly.

Give an example of an eccentric contraction.

The deltoid controlling the lowering of the arm.

Compare isometric and isotonic contractions.

Isometric	Isotonic
No movement	Produces movement
Muscle length unchanged	Muscle length changes
Tension increases	Tension produces movement

Compare concentric and eccentric contractions.

Concentric	Eccentric
Muscle shortens	Muscle lengthens
Produces movement	Controls movement
Example: raising arm	Example: lowering arm

Which contractions are isotonic?

• Concentric

• Eccentric

Which contraction does not involve movement?

Isometric contraction

Which contraction involves muscle shortening?

Concentric contraction.

Which contraction involves muscle lengthening?

Eccentric contraction.

Why does holding a heavy shopping bag become tiring even though your arm isn't moving?

Because your muscles are performing an isometric contraction, generating continuous tension without movement.

Why is lowering a heavy object usually easier than lifting it?

Because eccentric contraction controls the movement while gravity assists.

Why is standing upright possible without constantly thinking about it?

Because tonic contraction continuously maintains posture.

Why is the patellar tendon reflex useful during a neurological examination?

It tests the integrity of the reflex arc and associated nerves.

Why are eccentric contractions commonly associated with muscle soreness after exercise?

Because muscles generate force while lengthening, producing greater mechanical stress on the muscle fibres.

Why is understanding muscle contractions important in radiography?

Because muscle contractions influence joint position, fracture displacement, and patient positioning during imaging.

Why is knowledge of muscle attachments important when interpreting fractures?

Because muscles can pull on bone fragments, altering their position after a fracture.

How can understanding muscle actions help explain fracture displacement on an X-ray?

The direction of pull of attached muscles often determines how fractured bone fragments are displaced.

Complete the sequence:

Reflexive → ______ → ______ → Concentric/Eccentric

Reflexive → Tonic → Phasic → Concentric/Eccentric