The Lactic Acid Boogeyman

Lactic Acid gets blamed for all kinds of problems in sports. From fatigue, to soreness, to pulled muscles, this boogeyman gets a lot of blame.  What is Lactic Acid and why is understanding what it does important to us in cross country? In this post, I plan on laying out for you exactly what this mystery substance comes from, what it does in your body, and how we can use our knowledge about it to our advantage.

Lactic Acid (LA)is a waste product that is continuously produced in the cells.  It is produced as a byproduct of the normal process of turning blood sugar into ATP (energy). As we work out at levels of increasing intensity, the level or LA in our blood rises.  Rising levels of LA are most closely associated with anaerobic exercise. Anaerobic exercise is exercise at a level that the heart and lungs cannot supply enough oxygen to the muscles for them to produce ATP optimally.  There is some debate as to whether LA causes muscles to fatigue or is merely present in the muscles as they fatigue.  Whether LA actually causes fatigue is unimportant, however.  What is important is that certain levels of  LA are associated with well identified levels of fatigue. 

Many coaches and physiologists will mistakenly say that LA is only produced as a result of anaerobic exercises such as sprinting.  It is incorrect to say this.  LA only BUILDS UP as a result of anaerobic exercise, but it is always being produced.  When the body is at rest or performing easy exercise, LA is converted back to a molecule called pyruvate that can then be used to make ATP. At rest or during easy exercise, the LA is converted and used in the same cells in which it was produced.

It is when we start exercising harder that interesting things begin to happen with Lactic Acid in our bodies.  Please refer to the chart below.

The stair step line across the bottom of the graph represents work intensity
The blue line represents Blood Lactic Acid levels at that given intensity.
Intensity is represented on the X axis and Lactic Acid levels are on the Y axis.
LTP1 stands for Lactic Acid Turnpoint 1
LTP2 stands for Lactic Acid Turnpoint 2

This graph is only hypothetical but it illustrates a couple of very important concepts:

1. At exercise intensity from resting to 40% max effort, no LA accumulates in the blood, because it is being converted in the muscle cells that produced it. If we were running, we would call this "very easy" or "shake out" or "cool down" type of intensity.
2. At exercises from 40% to 75% max intensity, the muscles that make us move are producing more LA than they can remove and some of the excess LA leaks out into the blood and circulates to other parts of the body (such as the liver). These other parts of the body then clear it from the blood stream.  As you work harder in this "Zone II" intensity, blood LA levels gradually rise with increasing workload, but if you exercise at a constant workload, LA levels will stay steady.  Zone II is known as "Steady State".  At the low end of Zone II, exercise will still feel very easy.  At the high end of Zone II, exercise will feel pretty tough.  The bulk of your easy mileage will be in zone II
3. At LTP2, your systems are working at maximum efficiency when it comes to removing LA from your blood.  Once you cross LTP2, you begin to surpass your body's ability to clear LA from the blood.  Even if you keep running at a steady pace, LA levels in your blood will begin to rise and eventually, when they get high enough, you will be forced to stop or slow down.  

For high performance training, some of the most important paces are those that are right around LTP2.  If you are a well trained marathoner, you should theoretically be able to run just below LTP2 for over 2 hours.  You should also be able to run right at LTP2 for about an hour.  At levels just above LTP2, you can still maintain effort for 30-40 minutes.  A little faster and you can only hold that pace for 20 minutes.  The faster you go, the less time you can hold that pace....you get the picture.  Sprint as fast as you can and you can only maintain that pace for a few seconds.

Our goal in training is to spend as much time as possible at a pace that will bring you very close to LTP2.  As you do work at that pace, your body will adapt and soon you will be able to run faster without crossing LTP2.  Working at paces much beyond LTP2 can have a counter productive effect because the most important variable we are trying to manipulate is TIME at the right intensity

For further discussion of how to choose the right pace for you, I will be posting another article that explains our HHS pace charts.  

Paces by Distance

Paces by Time