Distinguish between slow-twitch (Type I) and fast-twitch (Type II) muscle fibres and relate each to endurance and power sports.

• A. Type I are fast, fatigue quickly; Type II are slow, fatigue-resistant; endurance uses Type II.
• B. Type I are slow, fatigue-resistant and rely on oxidative metabolism; Type II are fast, high force but fatigue quickly; endurance uses Type I, power uses Type II.
• C. Type I are anaerobic; Type II are aerobic; endurance uses Type II.
• D. Type I are not present in humans; Type II control all movements; endurance and power not related.

Answer: (B)

Muscle fibre types differ in how quickly they contract and how they generate energy for activity. Slow-twitch fibres contract slowly, are highly fatigue-resistant, and rely on oxidative (aerobic) metabolism to provide energy over long periods. Fast-twitch fibres contract quickly, can produce high force, but fatigue more rapidly because they rely more on anaerobic pathways and have a lower oxidative capacity. Because of this, endurance activities—long, steady efforts—primarily use slow-twitch fibres to sustain contractions. Power or sprint activities—short, explosive efforts—rely on fast-twitch fibres to deliver rapid, high-force outputs, though they tire quickly. There are subtypes within fast-twitch fibres that vary in oxidative capacity, but the general pattern remains: endurance toward Type I, power toward Type II.