What type of muscle fibers are characterized by high resistance to fatigue?

The correct answer is slow twitch fibers. These fibers, also known as Type I muscle fibers, are specifically designed for endurance and prolonged activities. They have a high density of mitochondria, allowing for efficient aerobic metabolism. This enables them to utilize oxygen effectively, making them less prone to fatigue during extended periods of exercise.

Slow twitch fibers are rich in myoglobin, which helps store oxygen and support sustained activity. This characteristic allows muscles composed predominantly of slow twitch fibers to contract for longer periods without tiring, making them well-suited for endurance activities such as marathon running or long-distance cycling. They generate less force compared to fast twitch fibers but maintain their function over extended periods, which is critical for endurance athletes.

On the other hand, fast twitch fibers, intermediate fibers, and Type IIb fibers do not have the same level of fatigue resistance. Fast twitch fibers, for example, are designed for short bursts of power and speed, while Type IIb fibers are particularly geared towards explosive movements and fatigue quickly. Intermediate fibers have a mix of characteristics but generally do not match the endurance capabilities of slow twitch fibers.