Clinical Correlations

Why is muscle testing performed?

To assess muscle strength and help diagnose nerve injuries.

How are muscles usually tested during a physical examination?

By comparing the same muscle on both sides of the body (bilaterally).

What are the two common methods of muscle testing?

1. The patient moves against resistance applied by the examiner.

2. The examiner moves against resistance provided by the patient.

Why are muscles tested in bilateral pairs?

To compare strength between the affected and unaffected sides.

During active muscle testing, who applies the force?

The patient contracts the muscle while the examiner provides resistance.

During passive resistance testing, who applies the force?

The examiner moves the limb while the patient resists.

Why can muscle testing help identify nerve injuries?

Because muscles lose strength when the nerves supplying them are damaged.

What is electromyography (EMG)?

A test that records the electrical activity of muscles.

How is EMG performed?

Surface electrodes are placed over a muscle while the patient performs specific movements.

What does a normal resting muscle show on EMG?

Baseline electrical activity (muscle tone).

When does baseline muscle activity disappear?

• Sleep

• Paralysis

• General anaesthesia

What happens to EMG activity during muscle contraction?

Large electrical action potentials (phasic activity) are recorded.

Why is EMG useful?

t helps assess muscle function and diagnose neuromuscular disorders.

Besides diagnosis, how else is EMG used?

As part of rehabilitation to help restore muscle function.

What is muscular atrophy?

Wasting (decrease in size) of muscle tissue.

What are three causes of muscular atrophy?

• Muscle disease

• Nerve injury

• Prolonged immobilisation

Why does immobilisation cause muscle atrophy?

Because unused muscle fibres gradually shrink.

Why does nerve damage cause muscle atrophy?

Because muscles require nerve stimulation to maintain normal size and function.

What is compensatory hypertrophy?

An increase in muscle cell size in response to increased workload.

How does the myocardium respond to increased workload?

Cardiac muscle fibres enlarge (hypertrophy).

Why does cardiac hypertrophy occur?

To generate greater force when the heart has to work harder.

Do cardiac muscle cells increase in number during hypertrophy?

No.

They increase mainly in size, not number.

What is a myocardial infarction (MI)?

Death (necrosis) of cardiac muscle due to loss of blood supply.

What happens to damaged cardiac muscle after an MI?

It is replaced by fibrous scar tissue.

Why doesn’t cardiac muscle regenerate after an MI?

Because cardiac muscle has very limited regenerative capacity.

What is myocardial necrosis?

Death of heart muscle tissue.

Why can an MI permanently reduce heart function?

Scar tissue cannot contract like healthy cardiac muscle.

Besides hypertrophy, how do uterine smooth muscle cells adapt during pregnancy?

They undergo hyperplasia (increase in cell number).

What is hyperplasia?

An increase in the number of cells.

How is hypertrophy different from hyperplasia?

Hypertrophy	Hyperplasia
Cells become larger	Cells increase in number

Give an example of hyperplasia.

Increase in uterine smooth muscle cells during pregnancy.

Compare muscle atrophy and hypertrophy.

Atrophy	Hypertrophy
Muscle decreases in size	Muscle increases in size
Reduced workload	Increased workload

Compare hypertrophy and hyperplasia.

Hypertrophy	Hyperplasia
Bigger cells	More cells

Compare normal myocardium and myocardial infarction.

Normal	MI
Healthy muscle	Necrotic muscle
Contracts	Replaced by scar tissue

Why does a muscle become weaker after weeks in a cast?

Because prolonged immobilisation causes muscular atrophy.

Why doesn’t exercising one arm make the muscles in your other arm larger?

Because hypertrophy occurs only in muscles exposed to increased workload.

Why can a person survive after a myocardial infarction?

Because the remaining healthy myocardium continues to pump blood, although less efficiently.

Why is scar tissue unable to replace the function of cardiac muscle?

Because scar tissue cannot contract.

Why does pregnancy cause enlargement of the uterus?

Because uterine smooth muscle undergoes both hypertrophy and hyperplasia.

Why is muscle atrophy visible on medical imaging?

Because prolonged muscle wasting reduces muscle bulk, which can be seen on imaging studies such as MRI and CT.

Why is knowledge of muscle hypertrophy useful in imaging?

Because enlarged muscles may represent normal adaptation or underlying pathology.

Why is recognising myocardial infarction important in medical imaging?

Because imaging helps identify areas of damaged myocardium and assess cardiac function.