Slow-twitch muscle fibers, also known as type I fibers, are specialized for endurance activities. They contract slowly and can sustain activity for long periods without fatigue. These fibers are rich in mitochondria and myoglobin, which help them efficiently use oxygen for energy, making them ideal for activities like long-distance running or cycling. Due to their endurance capabilities, slow-twitch fibers are less powerful than fast-twitch fibers, which are designed for short bursts of strength and speed. Athletes who engage in endurance sports typically have a higher proportion of slow-twitch fibers, allowing them to perform better in prolonged physical activities.