ATP: Your Muscles’ Source of Energy

Alright, we all agree we want to lower that 5k time. We are going to train with some proven science. What is the next step? To me, the next step is understanding just what we are trying to do with each workout. Workouts go better when we know why we are doing them. So, let’s get started.

Just to get this out of the way first, I am assuming that the vast majority of readers are more interested in distance running as opposed to sprinting. This is for you. ATP (or adenosine triphosphate)  is what powers your muscles. But what about carbs or fats? The carbs and fats and to a lesser extent, protein, are broken down to let your body form ATP. How do we best form this indispensable molecule? Without it you are at a standstill. Without it, your legs don’t move, your heart stops beating, etc. Bummer! Fortunately, there are several ways to make ATP.

ATP being used to run

The simplest way, and also your muscles favorite way to make ATP, is by breaking down carbohydrates, glucose in particular. Glucose is readily available in most cases. Glucose is stored as glycogen in the body. The body has different ways to break it down. It can be done aerobically or anaerobically. Aerobic means in the presence of oxygen. Anaerobic means without oxygen. Which is better? If you break down glucose aerobically, you generate 38 molecules of ATP for each molecule of glucose. Anaerobic breakdown of glucose gives you only 2 molecules of ATP. For you science nerds the term for the breakdown of glucose is glycolysis. Glycolysis is latin for “I like to toss around big scientific sounding words for the breakdown of glucose”. A third way to get ATP is with a molecule called creatine phosphate. We won’t worry about creatine phosphate because it only gives you enough ATP to last about 5 to 7 seconds.

Let’s think this through. Thirty-eight or two ATP’s? After much deliberation, I have decided that I would prefer to make 38. How do we do make sure we are breaking down our glucose aerobically? The easy answer is that you can do that as long as your effort isn’t too great. So, if I want to average 19 minutes per mile for my next 5k, that will be all aerobic. I’m not overly interested in completing a one-hour 5k. If I want a faster time, I have to increase the intensity of my run. Once it  goes past a certain point my effort starts to become anaerobic. Where is the cutoff in intensity between aerobic and anaerobic? There is no cutoff. No matter how fast you run, you are still taking in and using oxygen. Therefore, you are making some ATP aerobically. But you have a limit as to how much oxygen you can take in and use at any particular time. So, now we add in some anaerobic glycolysis (yes, I said glycolysis, I admit I’m a science nerd). We get that extra boost with more ATP but there is a downside. The dreaded lactate or lactic acid!

The two molecules only differ by one hydrogen atom and are both part of the same chain of events.

For our purposes, we can use the terms interchangeably. If you talk to a real honest to goodness exercise physiologist, they can explain that it’s really a lot more complicated than this and that lactic acid has an undeserved bad reputation. But for our purposes, think of it as evil.

Note how evil these actual pictures of lactate molecules are. They don’t even smile.

Too much lactic acid eventually brings you to a screeching halt. You are making lactic acid right now. Just being alive makes you generate ATP and without going deep into the chemical reactions, that ultimately results in lactic acid production as a by-product of the process. The good news is that until you are doing something that requires a more intense effort, you can turn that lactic acid back into something useful again and you don’t even realize it was there. As your effort increases, let’s say from a walk to a slow jog, you start increasing your lactic acid production. Now you step up to a faster pace and your lactic acid production steps up with it. Luckily, your body is removing that lactic acid to the best of its ability as you go. The pace increases again and again and again. At some point, the effort is making enough lactic acid that your body can’t keep up with it and it starts to build up. The point where your production of lactic acid surpasses your ability to remove it is called your LACTATE THRESHOLD. Note the bold lettering for that term. It is to remind you this is something important and will be critical to your training.

Back to where we were, trying to figure out how to use our glucose aerobically instead of anaerobically and therefore generate more ATP per glucose molecule and run a faster 5k. A slower pace is one option but not if you are trying to run fast times. Better options are to increase your available oxygen, raise your lactate threshold or learn to run more efficiently on a given amount of oxygen. These are known as VO2 max, lactate threshold and running economy. Each will be the subject of one of the next three entries on this site from me. Enough science for now. Now, get out there and keep running my friends!


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