What substance is produced in muscles during rapid exercise due to insufficient oxygen supply?

During rapid exercise, when the demand for oxygen in the muscles exceeds the supply, the body shifts from aerobic metabolism to anaerobic metabolism to produce energy. In this anaerobic environment, glucose is broken down to produce energy quickly, but because oxygen is limited, the end product of this process cannot be fully converted into carbon dioxide and water. Instead, the process produces lactic acid.

Lactic acid accumulates in the muscles and is often associated with the burning sensation experienced during intense physical activity. This buildup is a direct result of the conversion of pyruvic acid (which is produced from glucose breakdown) into lactic acid when oxygen is not available. Hence, latic acid serves as a temporary energy source in the absence of sufficient oxygen, allowing the muscles to continue functioning for a short duration despite the anaerobic conditions.

In contrast, glucose, ATP, and pyruvic acid are all part of the energy production process but do not represent the immediate substance produced under the stress of insufficient oxygen during intense exercise. Glucose is the fuel, ATP is the energy currency used by muscles, and pyruvic acid is an intermediate product before lactic acid is formed in the anaerobic pathway. The critical understanding is that lactic acid is the specific substance