Muscle Fibre Recruitment

Question 1

The ‘all-or-nothing’ principle for muscle activation

Answer 1

If the impulse meets or exceeds the threshold, the muscle fibre contracts fully.

If the impulse is below the threshold, no contraction happens.

This follows the All-or-Nothing Principle, meaning there’s no partial contraction—it’s either on or off.

Question 2

MOTOR UNIT

Answer 2

is one motor Neuron and the muscle fibres it stimulates

• A motor unit can include fast OR slow twitch fibres.
• More force can be generated with more motor units activated.

Question 3

ONE SMALL motor neuron may be responsible for:

Answer 3

stimulating ONE or TWO muscle fibres for fine movement.

producing low muscle force,
Examples - finger, facial and eye movements using small muscles

Question 4

ONE LARGE motor neuron may be responsible for:

Answer 4

stimulating THOUSANDS of muscle fibres for gross movement.

Require more stimulation from the nervous system to contract.

Example - kicking a ball, using the large quadricep muscle group.

Remember: larger motor units need more stimulus to activate!

Question 5

Sarcolemma

Answer 5

cell membrane surrounding each muscle fibre.

Question 6

Sarcoplasm

Answer 6

gel-like fluid contained by the sarcolemma

Question 7

Inside a MUSCLE CELL (MUSCLE FIBRE)

Answer 7

Mitochondria: site for aerobic energy production.

Myoglobin: carries O² (oxygen) to mitochondria.

Fat, glycogen (carbohydrates & protein): energy nutrients.

Phosphocreatine (AC) and Adenosine triphosphate (ATP): energy sources.

Enzymes: chemicals that speed up energy production.

Question 8

Type 2: Fast twitch fibres:

Answer 8

Stronger due to larger cell body and more axons.

These muscle fibre types are best suited to
short duration, high intensity anaerobic work.

Question 9

Type 2a Fast twitch

Answer 9

Fast-twitch Oxidative →

They have a combination of the benefits of both Type 1 and Type 2b fibres.

Question 10

Type 2b fast twitch

Answer 10

Anaerobic → fast-twitch glycolytic

They produce high force, power and speed, however have low endurance.

Question 11

Type 1 Slow twitch fibres:

Answer 11

Smaller cell body and fewer axons.

Type 1:
These muscle fibre types are best suited to low-intensity, long duration, aerobic, endurance work.

They produce low force, power and speed, however have high endurance.