Metabolism for Endurance Athletes, Part 3

Jumping back into my series on physiology, I wanted to cover the other side of the coin to my last post. My last post covered the reasons why hydration can affect aerobic performance; the rate limiting step in aerobic metabolism is oxygen movement in the blood, and thinner blood can move faster because it flows easier. Once aerobic metabolism is complete, oxygen and glucose become water and carbon dioxide. Water isn’t much of a concern, but is there anything interesting about carbon dioxide in the body?

There are a few things to know about carbon dioxide in exercise metabolism as an endurance athlete. One is that carbon dioxide does not have a molecule like hemoglobin to facilitate its movement in the blood. Carbon dioxide is a gas at atmospheric pressure, but it readily dissolves in liquids (like in soda). Carbon dioxide remains dissolved in the liquids of our cells after metabolism, and is transported back to the lungs dissolved in blood; when carbon dioxide dissolves in blood, the molecule CO2 has an affinity for hydroxyl groups (OH), forming Bicarbonate.

The water in our blood is H20, but some amount of that water is broken into hydroxide and a free hydrogen ion. When carbon dioxide levels in the blood increase, as happens during exercise, some of the hydroxide groups become tied up, so to speak, with the carbon dioxide in blood. That leaves free Hydrogen ions in the blood and muscles, turning them acidic. Strong enough acids can actually cook food, as in ceviche, and much of the discomfort felt during strained aerobic exercise is attributed to this acidification of the muscle cells, interstitial fluid, and blood.

The question is, what can you do about this acidification? Basically, just breathe. The main way that the body addresses the acidification of blood is through exhaling the dissolved carbon dioxide. The feeling of needing to breath faster is actually regulated by parts of the brain which sense acidity in the blood.

So when you push hard during your next interval, to get the pain to stop, focus on making the exhaling portion of your breath just a bit longer than the inhale. By giving your body more time to diffuse carbon dioxide out of the blood, you’ll manage the acidity in your blood, and make everything hurt a bit less. Instead of trying to breathe very quickly, breathe steadily; if you’re on a bike try two pedal strokes in, three pedal strokes out.

If you want more tips like these, subscribe to this blog. If you’re interested in taking your training to the next level, shoot me an email at brycoward@gmail.com.