Did you know that even after you're done exercising, your body continues to require more oxygen than it did before your workout? This is referred to as excess post-exercise oxygen consumption, or EPOC. You may have wondered why your body continues to feel weak or why you feel a little light headed or out of sorts for a while after your work out. You're still requiring the same amount of oxygen that you did while you were exercising!
This isn't a new concept. In 1922, two men named A. V. Hill and H. Lutpon hypothesized that people continue to need more oxygen a while after exerting themselves. They first referred to it as an "oxygen debt". They hypothesized that the body can't bounce right back to just needing the same amount of oxygen as before, and that it takes a while for it to go back to its resting state. Much more recently, researchers can break EPOC down into a few different events, or the stages the body undergoes on its way back to homeostasis.
Since your oxygen is being used up at a higher rate, it also means you're still burning a higher amount of energy. Here is what happens when your body is in this state:
Your body is replenishing its natural fuel, which is what it creates and converts from oxygen and other things your body needs, like water and nutrients. You muscles are working to restore the muscle glycogen, you used while working out. Muscle glycogen is a form of carbohydrates that your muscles have stored away, which powers them during your workouts. Other fuels your body creates are also being stored away again.
The circulatory hormones that were amped up during exercise are being slowly returned to normal. Your body is also working hard to re-oxygenate your blood, which has been depleted to deliver oxygen to the different parts of your body.
Your body is returning back to its normal temperature, and your body is using energy to achieve that.
Your heart rate and breath rate are quickly returning to normal, and it needs energy to do this, as well, and more energy means more oxygen.
Recent studies have concluded that there is a higher EPOC response after a strength training workout than an aerobic workout. After lifting some weights or resistance exercises, your muscles will need to work harder to get back to normal, since they were being pushed harder.
When muscle fatigue occurs, it's because these fuels in the muscles have been used up, and the body has to work even harder to replenish them. Using weights to help you work out, even light ones on your wrists and ankles while you walk, will give you an advantage to losing weight, because your body is still rapidly burning energy, which is used from oxygen, as well as calories.
This is why your doctor might want you to use oxygen therapy while you exercise. If you already have less oxygen in your blood, you will definitely need more during and after your workout.