In the last episode we took a look at the anaerobic breakdown of a glucose molecule. In this episode will take a look at one of the most controversial terms in sports science: lactate. The goal of this episode is to clarify the necessity of lactate, and to make you really understand the important role this molecule plays in the energy systems.
As you hopefully remember from last episode, the end products of the Anaerobic glycolysis are ATP, pyruvate and NADH. Besides the end products, we also mentioned that NAD is an absolute necessity to make the anaerobic glycolysis pathway work. In other words: we need to break down NADH to NAD again to keep the anaerobic glycolysis working.
To keep it simple, we can divide the faith production of NADH in two different systems, that both work under different circumstances.
1. Oxidizationof NADH (low to moderate intensity). This is the ideal faith of NADH. In this situation, NADH is shuttled via two mechanisms over the mitochondrial membrane into the mitochondria (remember that the anaerobic glycolysis where NADH is build happens in the cytosol, thus outside the mitochondria). Inside the mitochondria, it enters the Electron Transport Chain (ETC) where it is reduced to NAD, including the release of ATP. This reaction however requires oxygen, in other words: it is aerobic. The NAD that is released from this reaction, can enter the anaerobic glycolysis again.
2. Lactate production (moderate to high intensity)In case intensity of a workout goes up, there is an increase in NADH and H+, as the anaerobic glycolysis needs to work harder. At a certain point, the shuttles from point 1 are not to able to bring all these products over te mitochondrial membrane anymore, and they accumulate in the cell cytosol. This results in two things: a lack of NAD because NADH is not broken down in the mitochondria and a burning sensation. However, the muscle cells have an extremely cool mechanism to deal with this situation: the pyruvate molecule (the other end product of anaerobic glycolysis) will offer itself and bind NADH, which forms Lactate + NAD. In formula form: NADH + Pyruvate <—> Lactate + NAD. With this newly formed NAD the anaerobic glycolysis can keep on turning.
So: lactate is the most important helper-molecule to keep energy production going! Lactate is not the substance that burns.
Naturally the production of lactate can not go on forever: as you see in the formula, the reaction can go two ways, back and forth. This means that when there is more lactate than pyruvate, production will go towards the left, which is the wrong direction! The body tries to prevent this from happening by getting the lactate out of the muscle and into the bloodstream, so that the reaction keeps going towards the right side of the equilibrium. Even cooler side-note: the heart, liver and brain can remove lactate from the bloodstream by producing energy from it!
The fact that lactate is driven into the bloodstream is also ideal for measuring purposes: rising lactate levels indicate that the muscles are predominantly working anaerobically and harder than the “ideal” or aerobic mechanisms allow for.
Through high intensity interval training (CrossFit) your muscles learn to shuttle NADH over the membrane more efficiently, which results in sustaining anaerobic glycolysis for longer durations through higher NAD availability, without the need to produce lactate.
In the next episode, we will take a look at aerobic glycolysis. In other words: the breakdown of pyruvate when it is not combined with NADH