ENERGY SYSTEMS DEVELOPMENT - PART 2

ENERGY SYSTEMS DEVELOPMENT - PART 2

After discussing energy systems as a whole and briefly introducing the phosphagen system - read about it again here if you missed it - we move onto part 2. This, in my own opinion is where things get confusing. Our main priority here will be to introduce the glycolytic system. This series of reactions happens WITHOUT the presence of oxygen. Here's where we introduce the famed lactate for the first time properly and talk about it - it is your friend not your enemy. If you can get a handle on this section, the rest of it is easy. This article is a bit biochemistry heavy so if you're not a fan of it, I suggest you look away now!

Glycolysis:

The glycolytic system is the system that uses either glycogen (stored in the body) or glucose from your diet to produce energy. It all starts with one glucose molecule. This glucose molecule is converted into glucose 6-phosphate. This is where the glycolytic system starts. There are several steps that are undertaken to break this molecule down from glucose 6-phosphate, into 2 pyruvate molecules. This whole process gives us a net gain of 2 ATP molecules. So, one glucose molecule, gives us 2 ATP molecules. Who doesn't love biochemistry???

As mentioned before, glycolysis happens under anaerobic conditions. When exercise intensity is extremely high, we are not able to get oxygen to the cells fast enough and therefore we undergo anaerobic glycolysis as shown above. When utilising stored glycogen for this process, it is first converted to glucose 1-phosphate and then to glucose 6-phosphate so that this whole process starts again, still giving us 2 ATP molecules. Now, you're probably still wondering where the pyruvate and lactate come into all this, I'm getting to it. The end result of glycolysis is 2 ATP molecules and 2 pyruvate molecules. For those nerdy people like myself, below is an image of all the steps undergone through glycolysis to leave us with our end products. What happens next is dictated by the exercise duration, intensity and oxygen availability.

​At this point, we stand at a crossroads completely dictated by exercise intensity, duration and the individuals training history of course. The end of glycolysis gives us 2 pyruvate molecules. In the absence of oxygen, these molecules are reduced to lactate molecules by using an enzyme called lactate dehydrogenase. The body works extremely hard under these conditions to remove lactate from the cells as it used in key reactions to produce more energy during recovery times. This process is the start of what's known as The Cori Cycle. You see, it's not necessarily lactate, or lactic acid that's the bad man. It's your individual ability to delay the formation of lactate from pyruvate during energy production and the ability to tolerate higher levels of lactate in the cells as well. A big part of the training process takes this into account. Can you train yourself to delay the production of lactate during exercise so that you can operate at higher intensities for longer?

Remember, everything you've read up to this point has been under extremely intense conditioning without the presence of oxygen. This is part of the reason why higher intensity activities can only be maintained for up to a minute or so. There's only so much your body can do with the tools that it has available to it. Once you run out of the fuel to provide your cells with to produce more energy, exercise intensity has to suffer (slow down) or you need to completely finish. So, our rate limiting factors for glycolytic energy is the amount of stored glycogen, the amount of carbohydrates in our diet leading up to that session and our ability to remove lactate from the cells for entry into The Cori Cycle. 

Once you deplete these energy stores, this is where the oxidative system comes into play. Still with us? Next up is the oxidative system. Little bit more biochemistry to go with this but we're nearly there. Hopefully, by the time you've finished reading you'll understand that lactate isn't the enemy, training as close to 100% all the time probably isn't a smart idea, doing lower intensity aerobic activity is necessary and should be encouraged and that there's also so much we don't know still!