What substance accumulates in muscles during intense exercise?

During intense exercise, lactic acid is the substance that accumulates in muscles. This occurs due to the process of anaerobic metabolism, which is a way for the body to generate energy when oxygen levels are insufficient to meet the demands of prolonged or intense activity. When exercise intensity increases, the body switches from aerobic pathways to anaerobic pathways to produce energy quickly. One of the byproducts of this anaerobic energy production is lactic acid, which can build up in the muscles and lead to the feeling of fatigue or a burning sensation.

Understanding the role of lactic acid in exercise is crucial, as it indicates that the muscles are working hard and that the body's energy systems are engaged. The accumulation of lactic acid is often mistakenly thought to cause muscle soreness, but it is actually cleared from the muscle tissue relatively quickly after exercise.

While carbon dioxide is produced during both aerobic and anaerobic respiration and is expelled from the body through breathing, it is not the main substance that accumulates during intense physical activity. Sodium bicarbonate is sometimes used as a supplement to neutralize acidity in the body but does not accumulate in muscles during exercise. Creatinine is a waste product formed from muscle metabolism but is not directly related to the immediate energy production processes during intense exercise