Final answer:
The end product of glycolysis in fast-twitch FG muscle fibers is lactic acid, which is produced during short, intense activities and leads to muscle fatigue.
Step-by-step explanation:
The end product of glycolysis in fast-twitch (FG) muscle fibers during anaerobic metabolism is lactic acid. FG fibers, also known as fast glycolytic fibers, generate energy quickly through the process of glycolysis, utilizing the stored glycogen within the muscle. During intense, short bursts of activity, these fibers produce ATP speedily for muscle contraction, but this leads to the quick accumulation of lactic acid, resulting in muscle fatigue. Therefore, FG fibers are essential for rapid and forceful muscle actions such as sprinting or weight lifting but are limited to short durations of exertion due to their rapid fatigue rate.