Final answer:
Type-IIb muscle fibers, also called fast glycolytic or white muscle fibers, have the least amount of mitochondria. These fibers are suited for short, anaerobic, high-intensity activities, contrasting with slow oxidative fibers which have more mitochondria for prolonged contractions.
Step-by-step explanation:
The muscle fiber type with a very small amount of mitochondria is the Type-IIb fiber, also known as the fast glycolytic (FG) or white muscle fiber. This type of muscle fiber primarily uses anaerobic metabolism to produce ATP for short bursts of high-intensity activity, making it less dense in mitochondria compared to the other muscle fiber types.
Muscle cells in general require a high concentration of mitochondria due to their energy demands for contraction. However, the number of mitochondria varies across different types of muscle fibers. The oxidative fibers, such as slow oxidative (SO) fibers, contain many more mitochondria as they rely on aerobic metabolism which occurs in the mitochondria, allowing for sustained muscle activity over long periods.