What type of muscle fiber is also known as fast-twitch?

Fast-twitch muscle fibers, commonly referred to as white muscle fibers, are designed for quick bursts of power and activity. These fibers are anaerobic, meaning they primarily use glycogen for energy and are highly effective in short-term, high-intensity activities such as sprinting or heavy lifting. They have a lower concentration of myoglobin, which gives them a lighter appearance compared to red muscle fibers. This lack of myoglobin translates to a quicker fatigue rate but enables them to contract rapidly and generate significant force.

In contrast, red muscle fibers, known as slow-twitch muscle fibers, are more geared towards endurance and sustained aerobic activities. They contain a higher amount of myoglobin and have a greater number of mitochondria, enabling them to utilize oxygen effectively for longer durations. Cardiac muscle fibers serve a completely different purpose, being specialized for the heart's rhythmic contractions, and are not categorized as either fast or slow-twitch. Thus, the identification of white muscle fibers as fast-twitch is clearly accurate.