Which muscle fiber type is best suited for endurance activities due to oxidative metabolism?

• A. Fast-twitch glycolytic fibers
• B. Fast-twitch oxidative fibers
• C. Slow-twitch oxidative fibers
• D. Intermediate fast-twitch fibers

Answer: (C)

Endurance relies on energy produced through oxidative metabolism. Slow-twitch oxidative fibers, also known as Type I, are built for this. They’re packed with mitochondria, have a high capillary density, and contain a lot of myoglobin to store and deliver oxygen. This setup supports continuous aerobic ATP production, mostly from fats and glucose, using oxygen. Because they contract slowly and generate less force, they fatigue very slowly, making them ideal for long-duration activities like distance running or cycling.

In contrast, fibers that rely more on glycolysis can generate quick power but fatigue quickly due to lactic acid buildup, which isn’t favorable for sustained effort. Fibers with mixed oxidative and glycolytic capabilities exist as well, but they don’t match the sustained endurance efficiency of slow-twitch oxidative fibers.