Last week we talked about why we breathe heavy during the initial stages of exercise. This week I want to examine the other end of the spectrum. Have you ever noticed that after a long run, or an intense workout, that you’re still out of breath for a few minutes??? Well, once again, you may be out of shape, but that’s not the underlying reason as to why you’re breathing heavy.
Excess Post-exercise Oxygen Consumption (EPOC), sometimes known as “afterburn”, is essentially the time it takes for the body to transition from exercise back to a resting state. Sounds simple, but there is a lot that is going on during this time period. Some of the events taking place during this period of oxygen consumption:
- Restoration of fuel sources
- Replenishing of Myoglobin and Hemoglobin (oxygen-carrying molecules)
- Replenishing glycogen stores
- Removal and/or oxidation of lactate
- Heart and respiratory muscles working harder than rest periods
Two of the more important events occurring here are the restoration of fuel sources and removal/oxidation of lactate. Adenosine triphosphate (ATP) is a chemical needed for all cellular activity within the human body. It transports chemical energy for metabolism, which becomes very handy during activity being that we are metabolizing all kinds of chemical within the body. It makes sense that sense ATP is necessary for all cellular activity, that it becomes depleted during exercise. This is the primary substance that is replenished during EPOC. Also replenished here is Phosphocreatine (CP). This molecule serves as a rapid source of energy in skeletal muscle and the brain, and is used heavily during activity.
During EPOC, lactate is also a major player. It can either be removed through ventilation in the lungs, or oxidized back into pyruvic acid. Pyruvic acid, in short, is a major chemical player in the metabolism of fatty acids within the body. When we exercise, we produce lots of lactate, and we have to do something with it. So, we either get rid of it altogether, or we recycle it back into a useful substance. It’s important to note that the longer oxygen consumption is elevated, the more lactate we can turn into pyruvic acid. With more of that substance, we can burn more fat!! That is one reason for the increasing popularity of short, intense workouts. More oxygen deficit at the beginning leads to a higher oxygen consumption after exercise, which in turn leads to more fat metabolism.
Last week we focused on the blue portion of the graph. Now were looking at the green portion. As you can see, exercise stops at the 5 and a half-minute mark, but, as the red line indicates, oxygen consumption stays elevated. Oxygen consumption remains elevated for hours after exercise, but is simplified for the sake of illustration. There is a steep, rapid decline which is thought to be when we replenish the majority of our fuel sources (ATP and CP). The slower decline, lasting for hours at a time, is the removal of lactate and other chemicals produced during exercise.
I hope this article hasn’t been too scientific for you guys. I have had plenty of people ask me why this happens, both at the beginning and end of exercise. I think it’s a pretty fascinating process within the human body, but I’m a physiology nerd.
Take Away Message: Train Hard. Increase your oxygen deficit initially. Increase your post-exercise oxygen consumption. Burn more fat.