10 Truths About Lactic Acid
10 Truths About Lactic Acid by Aaron Ivey
Many misunderstandings exist about lactic acid, even among fitness professionals and exercise physiologists. Here is a list of 10 things you should know about lactic acid. The terms lactic acid and lactate will be used interchangeably in this article. However, the truth is that lactic acid, as the acid form, is not likely to exist in the blood. Please refer to “The Real Truth About Lactic Acid.”
1. Breaking down glucose in muscles results in the production of lactic acid.
Muscle cells break down glucose to for ATP (adenosine triphosphate), which provides the high energy bonds that are used for most chemical reactions in the body. The byproduct lactate does not require the use of oxygen (anaerobic metabolism). ATP production from lactate happens quickly but produces very little ATP. It is ideal for high intensity activity that exceeds 50% of maximum capacity such as interval training.
2. Lactic acid is not responsible for muscle soreness or cramps.
Delayed onset muscle soreness, also known as DOMS is soreness that most people feel a day or two after a tough workout or a change in your workout routine. Though some have attributed this soreness to lactic acid, research suggests that the soreness is more likely caused by damage done by the workout as well as post-exercise inflammation. Muscle cramps may be caused by dehydration or overexcitable nerve receptors in the muscle due to fatigue.
It is common to use massage, hot baths, and other relaxation techniques to rid the muscles of “built up” lactic acid. These remedies for muscle soreness may be beneficial for getting rid of the soreness but they have noting to do with getting rid of lactic acid build up. Your body clears the lactate out of the blood and converts it to pyruvate, another chemical that can be used to produce ATP.
3. Lactic acid is a byproduct of carbohydrate break down for energy.
During exercise that does not rely primarily on oxygen, anaerobic exercise, such as interval training, glycogen (muscle glucose) is broken down quickly to produce ATP. The greater the rate of glycogen breakdown the greater the production of lactate. As the intensity of exercise increases, a greater proportion of the energy is derived from muscle glycogen which in turn produces a greater amount of lactate.
4. Lactate production occurs all the time. It can occur even when the majority of the energy produced comes from fat sources.
Lactate production occurs during low intensity activities also. However, the body is able process the lactate fast enough so that the levels of lactate in the blood rises only minimally. As the intensity of exercise increases, you rely more and more on fast-twitch muscle fibers which are very efficient at burning carbohydrates. As lactate production increases, it exceeds the rate at which the body can process lactate and convert it to pyruvate to continue the energy production process. This increase in blood lactate levels simply means that those fast twitch muscles you have been using for your interval training are producing more lactate than the body can process. Oxygen has little to do with it.
5. Lactic acid is continuously produced and used by many of the body’s tissues.
A delicate blood lactate balance is maintained between lactic acid production and utilization. An increase in lactic acid concentration may simply mean a decrease in the rate of removal from blood or tissues not necessarily that the lactic acid production rate was increased.
Lactate production is proportional to the amount of carbohydrate that is used for energy production. A portion of the carbohydrate is converted to lactate as a byproduct and then utilized by the same tissue or others in the body to produce more ATP. Rapid break down of carbohydrates, as with interval training, accelerates production of lactate. This lactate may temporarily build up in the muscle because it is not able to utilize it as quickly as it is produced. Some of it may even end up in the blood stream. However, once you lower your intensity, like during your rest phase of interval training, your body is able to clear out and use the lactate that built up. It doesn’t take days for this clearing out to occur.
6. Lactic acid is used by the body to continue anaerobic metabolism.
Carbohydrates are digested, broken down to glucose, and enter the blood stream. Sometimes glucose travels to the liver and is converted to muscle glucose known as glycogen. Sometimes glucose goes directly to the muscles and is converted to lactate. The lactate then travels to the liver where it is converted to liver glycogen. Much of the glycogen in the liver is produced from lactate. This is known as the “Glucose Paradox.”
7. During long steady state exercise such as endurance races, blood lactate levels stabilize though production continues to increase throughout the event.
As blood flow increases to the muscles that are being used the most and producing the most amount of lactate, you are able to shuttle the increased lactate to other tissues. This in turn reduces the lactate levels in your muscles even though you continue to break down carbohydrates into lactate. As you become more conditioned your body increases its ability to clear out lactate, increased lactate threshold.
Radioactive tracers are used to discovery patterns of fuel usage in the blood and muscles. These studies suggest that lactate production and removal continue at 300-500% of resting rates.
8. Slow twitch muscles, the heart, and respiratory muscles prefer lactate as primary fuel source.
The uptake of lactate increases in the heart as the intensity of exercise increases while the usage of glucose remains unchanged.
9. Lactic acid is a very fast fuel that is actually an athlete’s friend during intertense exercise.
After eating a meal high in carbohydrates. the concentration of glucose and lactate increase in the blood. Lactate is cleared out and processed pretty quickly so its concentration does not rise to high levels. However, glucose is processed and removed from the blood much more slowly. The body’s ability to use lactate as a fuel source actually helps to keep insulin levels lower. Less insulin in the blood stream means that your body won’t freak out and go in to fat storage mode.
So why is lactic acid so important for regulating metabolism? We aren’t totally sure. However, there are a few physiological reasons that seem to make sense. Because lactic acid is a smaller substance than glucose and some other fuel sources, it is able to be transported more readily into the cells through a process called facilitated transport. Other fuels such as glucose depend more on slower processes to get them into the cells such as with insulin. Lactate can also be produced rather quickly from high intensity muscle activity as was mentioned previously. It is easier for the muscles to release lactate into the blood than to convert glycogen (muscle glucose) into glucose for mass distribution in the blood.
Some fluid replacement drinks are including lactate as part of their formulation. The rationale for that is that since glucose is converted to lactate anyways and lactate can provide a faster energy source during intense exercise, why not use it in a drink? Lactate in the drink can also provide a great source of building blocks to restore glycogen levels in the muscle.
10. Specific training can help the body become more efficient removing lactate from your muslces.
High intensity interval training is perfect for training your body to use lactate more efficiently. This is critical for an athlete to compete at their best. It is also important for coaches to know how to train their athletes to most effectively prepare them for their sport or event. Fortunately, most training programs incorporate elements necessary to speed lactate removal. Training programs should build your capacity to remove lactic acid during competition.
Training programs should aim to tax your body’s ability to process lactic acid production. Increased intensity and training at a level that exceeds the body’s ability to remove lactate (lactate threshold) will help it to become more efficient. Training at or above your lactate threshold stimulates your body to produce enzymes that speed the use of lactic acid as a fuel.
High intensity interval training will cause cardiovascular adaptations that increase oxygen delivery to your muscles and tissues. Consequently, you have less need to breakdown carbohydrate to lactic acid. Also, better circulation helps speed the transport of lactic acid to tissues that can remove it from the blood.
