Oxygen Debt

You have probably noticed that you breathe heavily not only during a strenuous exercise but also for several minutes afterwards. This is because your body accrues an oxygen debt that must be "repaid." Oxygen debt is the difference between the resting rate of oxygen consumption and the elevated rate following an exercise; it is also known as excess postexercise oxygen consumption (EPOC). The total amount of extra oxygen consumed after a strenuous exercise is typically about 11 L. It is used for the following purposes:

  • Replacing the body's oxygen reserves that were depleted in the first minute of exercise. These include 0.3 L of oxygen bound to muscle myoglobin, 1.0 L bound to blood hemoglobin, 0.25 L dissolved in the blood plasma and other extracellular fluids, and 0.1 L in the air in the lungs.
  • Replenishing the phosphagen system. This involves synthesizing ATP and using some of it to donate phosphate groups back to creatine until the resting levels of ATP and CP are restored.
  • Oxidizing lactic acid. About 80% of the lactic acid produced by muscle enters the bloodstream and is reconverted to pyruvic acid in the kidneys, the cardiac muscle, and especially the liver. Some of this pyruvic acid enters the aerobic (mitochondrial) pathway to make ATP, but the liver converts most of it back to glucose. Glucose is then available to replenish the glycogen stores of the muscle.
  • Serving the elevated metabolic rate. As long as the body temperature remains elevated by exercise, the total metabolic rate remains high, and this requires extra oxygen.
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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