electromyograms

Question 1

What is the purpose of electromyography? (2)

Answer 1

Measures the electrical activity in muscles during contraction and fatigue;

The resulting trace is called an electromyogram

Question 2

How is an electromyogram recorded? (3)

Answer 2

Two electrodes are placed on the muscle (e.g., bicep);

A third electrode is placed on an inactive point (e.g., bony wrist area) as a control;

The electrodes are connected to an amplifier and a computer

Question 3

What should an electromyogram show when the muscle is relaxed? (1)

Answer 3

A straight line should be seen on the electromyogram

Question 4

What happens to the electromyogram when the muscle is contracted? (2)

Answer 4

Spikes should appear on the tracers;

As motor units are activated to contract the muscle

Question 5

What happens to the electromyogram when a weight is lifted? (2)

Answer 5

The amplitude of the trace will increase;

As more motor units are recruited to lift the weight

Question 6

How does the electromyogram change when the muscle begins to fatigue? (3)

Answer 6

The amplitude increases even further;

Because the brain activates more motor units;

In an attempt to maintain the force required to hold the weight