Final answer:
Fast glycolytic (FG) fibers contract quickly and primarily use anaerobic glycolysis, leading to rapid fatigue. Slow oxidative (SO) and fast oxidative (FO) fibers mainly use aerobic metabolism but differ in fatigue resistance and contraction speed. Exercise type affects the proportion of these muscle fibers.
Step-by-step explanation:
Types of Muscle Fibers and Their Characteristics
Muscle fibers can be classified based on their contraction speed and how they produce ATP. Fast glycolytic (FG) fibers have a fast form of myosin ATPase, which allows them to break down ATP more rapidly, resulting in quick contractions. These fibers primarily rely on anaerobic glycolysis for their energy needs, have a high glycogen storage, and are large in diameter which provides quick, powerful movements but leads to fast fatigue.
Slow oxidative (SO) fibers are rich in mitochondria, myoglobin, and capillaries, allowing them to sustain aerobic activity and contract for longer periods without fatigue. Fast oxidative (FO) fibers, on the other hand, contract rapidly and primarily use aerobic respiration but can switch to anaerobic, meaning they fatigue more quickly than SO fibers.
Most muscles are a mix of all three types, with the predominant fiber type correlating with the muscle's primary function. The proportions of these fibers can be influenced by the type of exercise performed—endurance exercise boosts SO fibers, while resistance training favors FG fiber hypertrophy.