Lactic Acid: The Good, The Bad, And The Ugly

During a recent discussion with some co-workers, we determined that lactic acid, the bane of an athlete’s existence, is responsible for everything bad in this world. Burn! Creates muscle pain; It causes tight muscles, lack of strength, and lack of power. Just as “global warming” is blamed for any bad or unexplained climate change, lactic acid is the “global warming” of the exercise physiology world. If there is any negative response or discomfort during exercise, the lactic acid is most likely to blame.

Well, we are here to tell you that lactic acid is not all bad. It fulfills several important functions and is an essential component of human metabolism. Let’s take a closer look to dispel some of the myths surrounding this mysterious substance and give you a better appreciation and understanding of its function.

As most of us know, when you exercise a lot, your body requires immediate energy. This energy comes in the form of adenosine triphosphate (ATP). Two of the body’s energy systems can provide this ATP quickly, but at a cost. These systems are the immediate phosphate system, which uses high-energy phosphates for energy, and the glycolytic system, which breaks down sugar for energy. The phosphate system, also called the ATP/phosphocreatine system, can provide immediate energy for a few seconds; however, if high-intensity exercise continues, the glycolytic system becomes the predominant source of fuel. Without turning this into an advanced physiology lesson, after several more steps it produces a byproduct that affects the cellular environment. This final byproduct is lactic acid.

Lactic acid is a strong acid that builds up during intense exercise. Like all other acids, it readily dissociates (ie breaks down) into other compounds. In this case, lactic acid dissociates into lactate and a hydrogen ion. The result of giving up hydrogen ions is the lowering of the pH of the cellular environment. That is, the cellular environment becomes more acidic. It is through this mechanism that lactic acid gets much of its notorious reputation. You see, this reaction is responsible for that “muscle burn” you feel when you continue with high-intensity exercise.

Remember that lactic acid is always being produced, even as you read this article. However, as you read this article, you can use and/or delete everything it produces. If you start walking you will do more and again you will use it as fast as you do. Now if you start running fast, your lactic acid production will start to increase rapidly. It will build up so quickly that you won’t be able to get rid of it as fast as it builds up in your body. This point is often called the lactate threshold, anaerobic threshold, or onset of blood lactate accumulation (OBLA). The released hydrogen ions now begin to spill into the circulating blood. This increased level of hydrogen and the resulting low blood pH cause that familiar burn. If you want to keep running at this pace, you will have to tolerate a very uncomfortable feeling. The peak of this accumulation will arrive at 2-3 minutes. At this point, the high levels of lactic acid will cause your internal pH to drop so low that it will slow down. You might even stop and gasp for air! The normal amount of lactic acid circulating in the blood is about 1 to 2 millimoles/liter of blood. The onset of blood lactate accumulation (OBLA) occurs between 2 and 4 millimoles/liter of blood. In non-athletes, this point is around 50% to 60% VO2max. and in trained athletes, about 70% to 80% of VO2 max. These numbers can be significant as it is this VO2 Lactate Threshold, or “LTVO2” that is the primary limiter on performance, and not VO2 max.

Believe it or not, that uncomfortable burning sensation actually serves as a protective mechanism. Acidity must be well controlled in the human body and lactic acid ensures that you will not exercise to the point of poisoning your internal environment. If you continued to exercise at high levels, the pH of your system would drop so low that it would eventually kill you. By producing lactic acid and the resulting burning sensation, the body protects itself against the athlete’s excessive desire to continue high-intensity activity.

The mechanisms used to provide protection are two. As stated above, it will provide a level of discomfort (ie burning) throughout the body. This uncomfortable feeling stops most people. However, for hard core people (you know who they are) who don’t listen to reason, lactic acid goes right to the core of the problem, it stops muscle contraction. That’s right, if you don’t listen to the pain and discomfort, the resulting low pH will chemically interfere with the process that allows your muscles to contract. At this point, you have no power over the problem: you will slow down or stop! When you slow down, the body begins to switch to a slower metabolism (ie aerobic metabolism). As the rate of energy requirement continues to decrease, the lactic acid in the system can be converted into fuel that the body can use. All the accumulated lactic acid disappears in approximately 60 minutes after high intensity exercise ceases. It is a fail-safe system of protection and efficiency.

As stated above, muscles and some organs can also use lactic acid for fuel, or as a fuel precursor. The liver uses lactic acid to produce glucose (sugar) through the Cori cycle. The lactate extracted from the blood can also be used by slow skeletal muscle and the heart as fuel via the Lactate Shuttle. The decreased energy requirement allows enzymes to rapidly change lactic acid back to a compound called pyruvate that can be entered in the final cascade reaction of aerobic metabolism. This final stage (ie the electron transport system -ETS) is where most of your ATP comes from. The only problem is that it takes 39 steps to provide it, which is too slow to provide energy for short bursts of high-intensity activity.

The last mechanism of use is loss through sweat and urine. Although not as profound as the other mechanisms, small amounts are found in sweat and urine.

There are also several conditions that lactic acid does not produce. It does not cause the muscle soreness that is felt in the days after training. Remember that the body eliminates lactic acid within an hour of exercise, especially if you follow high-intensity exercise with a few minutes of light aerobic activity. Lactic acid also doesn’t make you weak after exercise. As stated above, the effects of lactic acid on the muscles are immediate and wear off within an hour. Finally, lactic acid does not tense the muscles. Muscles fill with blood due to intense resistance training. This influx of blood to the area gives you a feeling of tightness. This is strictly a mechanical phenomenon, like blowing up a balloon.

So how do you improve your lactate threshold and improve your body’s ability to deal with lactic acid? The goal is to saturate the muscles in lactic acid. This will educate the body’s buffering mechanisms to deal with this more effectively. Resistance training is one way to do this. Resistance training increases the capillary density of working muscles, allowing two different things to happen. Again, without turning this into an advanced physiology lesson, suffice it to say that oxygen will be used more efficiently and the need for sugar for fuel will be reduced. This, in turn, means that your body will produce less lactic acid at the same relative work rate.

So what have we learned here?

Good-Lactic Acid fulfills several important functions. Protects you from high levels of acidity; serves as a fuel source for muscles and organs; it is also a precursor to important energy compounds.

Bad lactic acid, or more specifically, low blood pH caused by the onset of blood lactate buildup, causes that uncomfortable burning sensation we all love to hate. To improve your lactate threshold, you need to get to this point and stay there…often!

The ugly: don’t listen to this pain reaction and you will pay one way or another. The burning sensation is often accompanied by nausea and vomiting. Worse than that, if you continue past this point, your body’s defense mechanisms will stop muscle contraction.

As you can see, there is more to lactic acid than meets the eye. We hope that you now have a better understanding of the characteristics of lactic acid; The good, the bad and the ugly!