The Biochemistry of Alactic + Aerobic Training - Glycolytic Pathway
[This is part 4 of many about the details of Alactic + Aerobic training and why you should be doing it.]
Last time, I talked about the phosphagen system where we can regenerate our ATP with Creatine Phosphate. This happens super quick for explosive power, but can only last for a few seconds. What happens when you need to work for longer?
The glycolytic pathway is the oldest (evolutionarily speaking) pathway - going all the way back to single-celled critters. It also is pretty darn inefficient - it only gets a few percent of the available energy out of the sugar. But, it works and it's reasonably simple - or at least it was the first method that did work in our evolutionary milieu, and there was nothing significantly better to displace it.
There are two ways to make this happen. You can burn sugar (glucose) directly
Sugar -> 2ATP + acid + some other stuff
Or your can burn muscle glycogen which is usually stored nearby
Glycogen -> 3ATP + less acid + some other stuff
So burning Glycogen will give you more ATP and less acid as a by product. That's good. But when you run out of muscle glycogen, you need to burn sugar directly. So this might point to the need to do a small amount of carbohydrate before a workout (the night before so that you have time to create glycogen out of it). If you are pure keto, you might not have much muscle glycogen lying around and you'll be burning sugar which makes more acid. At least, that's my take-away from this.
Generally, we have the idea that glycolysis can last for a few minutes. The question is why? If we keep shoving sugar in there, can't we keep making more ATP? Well, not quite. All of that acid that's created starts to build up and creates a backward pressure on the reaction. You cannot keep shoving acid into the cell with no penalty.
That's where the lactate molecule come in. Contained in that "some other stuff" up there, is pyruvate. That can eat up some acid and turn into lactate. The body can get rid of that lactate. There are two places for that, it can be sent out of the cell and into the blood - this is when people start talking about lactate threshold. They have reached the point where they can measure lactate in the blood. And the other is that it can be stuffed into the mitochondria and used as a fuel source in the aerobic pathway to make some more ATP. An ancient form of recycling.
Two comments on that:
1 - If you start to see lactate in the blood, I'd argue you went too far. No need to do "lactate training," just train in a regime that doesn't produce much acid and thus the need for lactate to buffer it
2 - I've had folks argue with me that since lactate is used as a fuel source, it's a good thing. I don't agree. I think it's like burning your trash to generate heat. Sure it's better than freezing to death in the winter, but surely there are better fuels to burn to keep you warm.
Since it's not a good idea to have too much acid lying around in our cells, we've come up with a couple of ways to buffer it. We try to burn it up elsewhere and get it into the blood and out of the body the other way. Regardless, the rate at which you can buffer that acid is the rate at which you can continue with glycolysis. So it starts off great when the cell is fresh - you get lots of power for a few minutes. Then the rate has to slow down as we're limited by the acid buffering rates. It all comes down to chemical kinetics - my advisor would be proud!
In the context of A+A training: we don't want to dig too deep or too long into glycolysis. It's a good idea to hit it a little so that we're training those pathways (and the detox pathways too!), but there's no need to turn the acid load to 11 to get the training effect. That's why 10-15 second repeats are the best, and sometimes (rarely) we'll push it to 30 seconds to just stress it a little more. No long 7 minute non-stop metcons acidifying our entire body!