Lactate Metabolism

Lactate Metabolism and Maximum Lactate Steady State (MLSS) as it Affects Training Structure

Background

Different types of masters swim programs have different ways of doing things. Different types of sets target different sorts of adaptations, understanding the purpose of the sets will help you in following set design and making sure the workout you do is similar to the workout the coach had in mind. In other cases if you need to deviate from the coaches' plan you can do so intelligently.

In terms of physiology, much of what we do can be seen through the lens of lactate metabolism, so before starting the discussion of training sets, a bit about lactate metabolism and maximum lactate steady state.

MLSS

As will be seen later, some types of workouts are meant to create aerobic adaptations, others are aimed at anaerobic adaptations. Before addressing aerobic and anaerobic Adaptations, a little bit to explain the difference. Aerobic (with oxygen) and Anaerobic (without oxygen) are misnomers to a degree. Your body always uses oxygen for energy, it is simply that the system by which oxygen is used for energy is rate-limited. It can only be delivered so quickly. If your need for energy is outpacing the rate at which you can use oxygen for energy, then intermediate chemicals build up in your system. It’s like there is a logjam and all the logs are stacking up on the upstream side.

In energy metabolism, the first large substep is called glycolysis, it turns a glucose molecule in two lactate molecules¹ and creates energy in the process; this first step does not require oxygen. The glycolysis step can happen much faster than the next step in the chain. In normal, everyday situations, the lactate intermediary is then swept up and it goes to two separate subcycles that require oxygen and create MUCH more energy from that lactate molecule. It is these last two steps that are rate-limited.

This is where the logjam happens, if there is a signal to go all out, for example a starting gun, the glycolysis process can create lactate much more quickly than the aerobic metabolism can take it away and use it. I also like to use a bathtub analogy, in figure 1 lactate (water) is being delivered into the tub but is being swept away as quickly as it comes in and there is no net buildup of water in the tub (lactate). In this case the equilibrium is about halfway up the sides of the tub. The bathtub analogy goes even one step further, on your bathtub there is an overflow drain about halfway up the side of the tub. In the case of a muscle cell, something similar exists. In a working muscle cell, when the lactate concentration inside the cell gets too high, some of the lactate is taken out of the cell and enters the bloodstream. Once it enters the bloodstream, the lactate is taken to other organs to be used as fuel for aerobic metabolism in those organs. The lactate is used in other muscles that might not be working as hard, your liver, and actually is used as a fuel for your brain as well.

If instead of using a bathtub spigot to fill the tub, we use a firehose then the situation is a bit different. In this case there is no steady state, the firehose turns on and even though some of the water is being taken away through the drain, the water accumulates. If this situation persists, the bathtub will overflow, even taking into account the overflow drain in the tub halfway up, if the firehose is big enough it will overflow. In the muscle cells, instead of a firehose it is glycolysis that is running wide open and pouring lactate into the cell, even though the aerobic metabolism is dragging away some of the lactate, it is still accumulating in the cell.

As the lactate builds up too high, then bad things start to happen. Actually several different things and there is actually some debate about exactly how it works. For example, as part of all this when lactate is created, acid is created as well. It has been shown that when your muscles get too acidic, they do not want to fire, some coaches have claimed this is the “tying up” sensation that comes with high intensity exercise. There are others who say that you have acidity sensors and when they fire your brain will stop recruiting muscles; these are only two of many different ideas on exactly what is happening. Even though it is not exactly settled, what matters is that short term fatigue is closely associated with increased lactate levels at exercise, even if the exact mechanism how is not certain.

And what is “Maximum Lactate Steady State (MLSS)?” MLSS is the highest effort level that can be performed without the bathtub overflowing. It is just at the point where the tub is completely full and the water going down the drain and out the side drain is exactly equaled by the water coming in through the firehose. Think about your bathtub and how quickly water flows out of the drain when there is very little water in it, the water drains out pretty slowly. However when the tub is full, the amount of water flowing out per second is higher. If you leave the drain open and turn on the water just a bit, the tub will fill up just a bit until the water draining out equals the water coming in. Turn it on just a bit more and the water will build up higher still to make the water coming in and draining out equal.

You can continue doing this until you reach the point where having the tub filled to brim makes the water flowing in and flowing out equal. In cellular terms, this is the MLSS. This is the usual breakpoint between aerobic and anaerobic exercise. Exercise that is done where you stay under the MLSS effort is usually termed aerobic and exercise performed at an effort higher than MLSS effort is termed anaerobic.

In practical terms MLSS is something close to the pace you can maintain for a 30 minute max effort.

And what about Lactate Threshold?

In the vast majority of cases, when a coach says “Lactate Threshold” he really means MLSS. When a scientist says “Lactate Threshold” he means the effort at which your blood lactate is 1 mmol/L higher than resting level. So for most times you hear “Lactate Threshold” in popular literature or discussions² think MLSS.

So what?

The next question is “What can be done about it? Can I change the size of my tub? Can I make a bigger drain?” That will be covered in the next article.

1. Actually pyruvate is the intermediate chemical, however it is quickly converted back and forth from lactate to pyruvate depending on if there is oxygen to take the pyruvate away. No oxygen, then it gets converted to lactate until a later time when it can be converted back to pyruvate and taken away by the aerobic metabolism. 

2. Everyone talks about lactate metabolism in normal discussions right?