7.10—Skeletal muscle fibre and twitch types

Fast-twitch fibres contract rapidly and suit short, high-intensity activity; slow-twitch fibres contract more slowly and resist fatigue during sustained activity. Their structure and metabolism support those roles.

Fast fibres rely more on anaerobic ATP supply and have fewer capillaries and less myoglobin; slow fibres have greater aerobic capacity, blood supply and oxygen storage.

A sprint uses fast fibres for rapid force, whereas prolonged walking recruits more slow fibres. A muscle usually contains a mixture rather than only one fibre type.

“Fast” does not mean stronger in every task, and fibre type alone does not determine performance. Link the claim to ATP pathway, fatigue and activity duration.