The fuel for a 12RM bench press will primarily come from ______.

In a 12-repetition maximum (12RM) bench press, the primary source of fuel for the muscles performing the exercise is sugar, specifically in the form of glucose derived from carbohydrates. This activity relies on the anaerobic glycolysis pathway, which breaks down glucose to produce energy quickly for short, intense efforts.

During resistance training such as a 12RM bench press, the body does not have enough time to utilize fat as a significant energy source due to the intensity of the exercise and the relatively quick transition of energy demands. While ATP and creatine phosphate play a crucial role in the initial seconds of high-intensity activity, their stores are limited and are depleted quickly, typically within the first 10 seconds of exertion.

As the set continues beyond this period, the body increasingly relies on anaerobic glycolysis to continue producing ATP, leading to the breakdown of glucose, which ultimately becomes the primary energy substrate. In contrast, fat metabolism is more suited for endurance activities that occur at lower intensities and for longer durations, making it irrelevant in the context of high-repetition strength training.

Thus, for a 12RM exercise like the bench press, carbohydrate utilization through glycolysis is the best fuel source to support performance effectively.