Explain why lactic acid builds up in muscles and blood during vigorous exercise causing Excess Post-exercise Oxygen Consumption (EPOC) or an ‘oxygen debt’

Sourav PanNovember 3, 2024

Answered

During vigorous exercise, the body often requires more energy than can be supplied through aerobic respiration, leading to a reliance on anaerobic respiration. This shift results in the production of lactic acid, which contributes to what is known as Excess Post-exercise Oxygen Consumption (EPOC) or “oxygen debt.”

Why Lactic Acid Builds Up

1. Increased Energy Demand: During high-intensity activities, muscles demand more energy quickly. When the intensity exceeds the capacity of the cardiovascular system to deliver oxygen, the body resorts to anaerobic respiration, which does not require oxygen but produces lactic acid as a byproduct.
2. Anaerobic Respiration Process: In anaerobic conditions, glucose is broken down through glycolysis into pyruvate, which is then converted into lactic acid instead of being fully oxidized in the presence of oxygen. This process yields only 2 ATP molecules per glucose molecule, significantly less than aerobic respiration.
3. Lactate Threshold: As exercise intensity increases, there comes a point known as the lactate threshold where lactate production exceeds its clearance from the bloodstream. This accumulation of lactate and accompanying hydrogen ions leads to increased acidity in muscle cells, causing fatigue and discomfort.

Effects of Lactic Acid Accumulation

• Muscle Fatigue: The buildup of lactic acid can lead to a burning sensation in the muscles and decreased performance due to fatigue. This occurs because the acidic environment affects muscle contraction efficiency.
• Oxygen Debt (EPOC): After intense exercise, the body enters a recovery phase where it continues to consume oxygen at elevated rates. This is necessary to convert accumulated lactic acid back into pyruvate and eventually into glucose or to be fully oxidized into carbon dioxide and water. The term “oxygen debt” refers to this additional oxygen requirement post-exercise to clear lactic acid and restore normal metabolic function