Muscle fibre types

Question 1

What are the two main fibre types of skeletal muscle?

Answer 1

Slow and fast twitch fibres.

Question 2

What are the proportion of slow and fast twitch fibres in each muscle?

Answer 2

Fats twitch and slow twitch fibres vary in different muscles and in different individuals these portions tend to be inherited.

Question 3

What are the characteristics of slow twitch fibres?

Answer 3

Red, contract slowly, aerobic, endurance based, can contract repeatedly, exert less force (sub maximal).

Question 4

What are the characteristics of fast twitch fibres?

Answer 4

White, contract rapidly, anaerobic, speed/strength based, easily exhausted, exert great force

Question 5

What are type 2a fast twitch fibres?

Answer 5

Called fast oxidative glycolytic fibres (FOG) pick up certain type 1 characteristics through endurance training. They therefore tend to have greater resistance to fatigue. Activities that are high in intensity and of relatively short duration rely on 2a fibres.

Question 6

What are type 2b fast twitch fibres?

Answer 6

Called fast twitch glycolytic (FTG), they are used in activities that are intense and have much stronger force of contraction. This is because the motor neuron that carries the impulse is much larger, there are generally more fibres within a fast twitch motor unit, and the muscle fibres are generally larger and thicker. We could expect a power lifter or sprinter to possess large proportion of FTG fibres.

Question 7

What are mitochondria?

Answer 7

These organelles are responsible for ATP generation for cellular activities and are the place that allow aerobic respiration to take place. Hence, many mitochondria in aerobic and hence type 1 muscle fibres.

Question 8

What is myoglobin?

Answer 8

It is a form of haemoglobin that occurs within the muscle cell that transports oxygen to the mitochondria in order to produce energy via the aerobic pathway. Slow twitch fibres possess more myoglobin due to their need for oxygen. Myoglobin gives the red colour. Endurance training can increase muscle myoglobin content up to 80%.

Question 9

What are the structural features of slow twitch fibres?

Answer 9

Small in size, many mitochondria, many capillaries, a lot of myoglobin, low PC stores, low glycogen stores, high triglyceride stores

Question 10

What are the structural features of FOG?

Answer 10

Large in size, moderate mitochondria, capillaries and myoglobin, high PC stores, glycogen stores, moderate triglyceride stores

Question 11

What are the structural features of FG?

Answer 11

Large in size, little mitochondria, capillaries, low myoglobin content, high PC stores and glycogen stores, low triglyceride stores

Question 12

What are the aerobic capacities of the fibres?

Answer 12

Slow twitch - high
FOG - low
FG - lowest

Question 13

What are the anaerobic capacities of the fibres?

Answer 13

Slow twitch - low
FOG - high
FG - highest