What role do branched chain amino acids (BCAA) primarily serve during prolonged exercise?

Branched chain amino acids (BCAAs), which include leucine, isoleucine, and valine, play a significant role in energy production during prolonged exercise. When the body is under the stress of extended physical activity, glycogen stores become depleted, and the body starts to utilize amino acids for energy. BCAAs can be oxidized within the muscles to produce energy, especially during endurance activities.

As exercise continues, the body's demand for energy intensifies, and BCAAs help to bridge the gap when carbohydrate stores are low. This is particularly important for maintaining performance and delaying fatigue. While BCAAs are certainly involved in muscle repair and protein synthesis, their immediate contribution during prolonged exercise centers around being utilized for energy, thus enhancing endurance and stamina.

The other options, while relevant to BCAAs in a broader context, do not capture their primary function during extended activity as effectively. For example, the building of muscle mass and stimulating protein synthesis are more long-term effects associated with BCAAs, whereas reducing fatigue relates to subjective feelings of tiredness rather than their biochemical role during prolonged exertion.