What is a significant byproduct of anaerobic metabolism during intense exercise?

During intense exercise, the body may not have sufficient oxygen available to meet its energy demands, leading to anaerobic metabolism predominating for energy production. In this process, glucose is broken down without oxygen, resulting in the production of ATP (the energy currency of the cell) and lactic acid as a significant byproduct.

Lactic acid is produced when pyruvate, a key intermediate in the metabolic pathway of glucose, is converted due to the lack of oxygen. This conversion allows for the continuation of ATP production even in anaerobic conditions, but it also leads to the accumulation of lactic acid in the muscles. This accumulation can contribute to feelings of fatigue and muscle soreness during and after intense physical activity.

In contrast, carbon dioxide is a byproduct of both aerobic and anaerobic respiration, whereas oxygen is a reactant rather than a product in energy production. Glycerol, typically associated with fat metabolism, does not play a significant role during high-intensity anaerobic exercise. Therefore, lactic acid stands out as the major byproduct of anaerobic metabolism during such activities, making it the correct answer.