Which fibre type is primarily aerobic in energy supply?

Which fibre type is primarily aerobic in energy supply?

• A. Type 2a
• B. Type 2b
• C. Type 1
• D. Type 2x

Answer: (C)

The main idea here is which fibre type relies most on oxygen to keep producing energy over a long period. Type I fibres are slow-twitch and are packed with mitochondria, have high myoglobin content, and a dense network of capillaries. This setup fuels oxidative metabolism, so ATP is produced mainly through the aerobic system using oxygen. That makes these fibres ideal for endurance activities, where energy must be supplied continuously and fatigue slowly sets in. In contrast, the fast-twitch fibres (IIa and IIx) lean more on anaerobic energy pathways to deliver quick bursts of power, and they fatigue more quickly. Type IIa has some oxidative capacity but still shifts toward glycolysis during high-intensity effort, while Type IIx is primarily glycolytic. So the fibre type that is primarily aerobic is the slow-twitch Type I.

The main idea here is which fibre type relies most on oxygen to keep producing energy over a long period. Type I fibres are slow-twitch and are packed with mitochondria, have high myoglobin content, and a dense network of capillaries. This setup fuels oxidative metabolism, so ATP is produced mainly through the aerobic system using oxygen. That makes these fibres ideal for endurance activities, where energy must be supplied continuously and fatigue slowly sets in.

In contrast, the fast-twitch fibres (IIa and IIx) lean more on anaerobic energy pathways to deliver quick bursts of power, and they fatigue more quickly. Type IIa has some oxidative capacity but still shifts toward glycolysis during high-intensity effort, while Type IIx is primarily glycolytic. So the fibre type that is primarily aerobic is the slow-twitch Type I.