Which of the following is the most readily available form of fuel used by the...

In NASM’s Exercise Metabolism and Bioenergetics section, glucose is defined as “the simplest form of carbohydrate used by the body for energy.” The Study Guide clearly states that carbohydrates are broken down into glucose, which is the most readily available form of fuel for the brain, nervous system, and muscles. Glucose can be rapidly metabolized through glycolysis to produce ATP, making it essential during both rest and high-intensity activities. Glycogen—its stored form—is limited, but glucose in the bloodstream is immediately accessible, especially to tissues that rely heavily on carbohydrate metabolism, such as the brain (which cannot use fat directly as fuel). The guide also notes that “the fuels used to create ATP are glucose from carbohydrates, free fatty acids from fat, amino acids from protein, and ketone bodies,” but fat oxidation is slower and protein is typically reserved for structural and enzymatic roles. Fiber is a non-digestible carbohydrate and thus not a fuel source. Therefore, glucose is the correct answer as the “most readily available” substrate for immediate energy needs across the nervous and muscular systems, supporting rapid ATP regeneration during movement and cognitive tasks.