What is That Burning Sensation?: A Primer on Lactic Acid

What is the Burning Sensation--- (1)As with most of us, I have a love-hate relationship with training. Yes, it gives me an outlet for stress on the weekends, and it is satisfying in the end, but I continue to have trouble with quick fatigue, especially when doing hill or speed work. This has led me to look more into lactic acid, how it behaves, and how to best deal with it. I have a number of resources on this but was struck most by an article written by Thomas Fahey, Ed.D., Professor of Exercise Physiology, California State University at Chico, at the link below. I posted below the majority of that article, along with some of my thoughts on a few of the points. I don’t pretend to understand all of it, neither do I agree with some of his points related to the need for carbohydrates while exercising, but I am trying, so any further input is appreciated. Referenced material can be read HERE:

Lactic acid is formed from the breakdown of glucose

During this process the cells make ATP (adenosine triphosphate), which provides energy for most of the chemical reactions in the body. Lactic acid formation doesn’t use oxygen, so the process is often called anaerobic metabolism. Lactate-related ATP production is small but very fast. This makes it ideal for satisfying energy needs anytime exercise intensity exceeds 50% of maximum capacity.

Since lactic acid is produced by a lack of oxygen, deep breaths can at times alleviate the burning you are feeling. A fellow blogger recommended this to me after another post where I was complaining about the burning I always felt in my legs. The problem with this is that during extreme efforts your breath gets shallow, so even the act of forcing air from your lungs to fill it with fresh oxygen can be almost impossible. Other methods, which seem to make sense and are noted in a number of online references, are increased hydration intake, and slowing down.

Lactic acid doesn’t cause muscle soreness and cramps

Delayed onset muscle soreness, the achy sensation in your muscles the day after a tough workout, is caused by muscle damage and post-exercise tissue inflammation. Most muscle cramps are caused by muscle nervous receptors that become over-excitable with muscle fatigue. Many athletes use massage, hot baths, and relaxation techniques to help them rid their muscles of lactic acid and thus relieve muscle soreness and cramping. While these techniques probably have other benefits, getting rid of lactic acid isn’t one of them. Lactate is used rapidly for fuel during exercise and recovery and doesn’t remain in the muscles like motor oil.

This was news to me, and I guess by now I should know better. When I was playing football and running track and weight lifting all you ever heard the coaches telling us was to take hot showers to avoid the lactic acid build up. One more accepted truth from my youth (right there with “if you burn more calories than you eat you will lose weight”) blown out of the water.

The body produces lactic acid whenever it breaks down carbohydrates for energy

The faster you break down glucose and glycogen the greater the formation of lactic acid. At rest and submaximal exercise, the body relies mainly on fats for fuel. However, when you reach 50% of maximum capacity, the threshold intensity for most recreational exercise programs, the body “crosses over” and used increasingly more carbohydrates to fuel exercise. The more you use carbohydrates as fuel, the more lactic acid you produce.

Here it is, the argument for staying in Zone 2 during long workouts so that you use fat instead of sugar, which if you’re like me, helps you lose weight. The more you do this type of exercise the more your body becomes fat adapted, burning fat as a preferred energy source. Pushing over this threshold requires sugar be pumped into your system to maintain the effort, which is why you see cyclists with their jersey’s packed with an assortment of gels and gu’s.

Lactic acid can be formed in muscles that are receiving enough oxygen

As you increase the intensity of exercise, you rely more and more on fast-twitch muscle fibers. These fibers use mainly carbohydrates to fuel their contractions. Whenever you break down carbohydrates for energy, your muscles produce lactic acid. The faster you go, the more fast-twitch muscles you use. Consequently, you use more carbohydrates as fuel and produce more lactic acid. Increased blood lactic acid means only that the rate of entry of lactic acid into the blood exceeds the removal rate. Oxygen has little to do with it.

Many tissues, particularly skeletal muscles, continuously produce and use lactic acid

Blood levels of lactic acid reflect the balance between lactic acid production and use. An increase in lactic acid concentration does not necessarily mean that the lactic acid production rate was increased. Lactic acid may increase because of a decreased rate of removal from blood or tissues.

Lactic acid production is proportional to the amount of carbohydrates broken down for energy in the tissues. Whenever you use carbohydrates, a significant portion is converted to lactate. This lactate is then used in the same tissues as fuel, or it is transported to other tissues via the blood stream and used for energy. Rapid use of carbohydrate for fuel, such as during intense exercise, accelerates lactic acid production. Temporarily, lactic acid builds up in your muscles and blood because it can’t be used as fuel fast enough. However, if you slow down the pace of exercise or stop exercising, the rate of lactate used for energy soon catches up with the rate of lactate production.

See Dr. George Brooks “Lactic Shuttle Theory” which describes the central role of lactic acid in carbohydrate metabolism and it’s importance as a fuel for metabolism.

During endurance races, such as marathons and triathlon, blood lactic acid levels stabilize even though lactic acid production increases

This occurs because your capacity to produce lactic acid is matched by your ability to use it as fuel. Early during a race, there is a tremendous increase in the rates that muscle uptake and use glucose and breakdown glycogen. The increased rate of carbohydrate metabolism steps up production of muscle lactic acid, which also causes an increase in blood lactic acid.

As your body directs blood to your working muscles, you can shuttle the lactate to other tissues and use it as fuel. This reduces lactic acid levels in your muscles and blood, even though you continue to produce great quantities of lactic acid. However, you often feel better during the race or training. This relief is sometimes called “second wind”. Scientists use radioactive tracers to follow the use pattern of fuels in your blood and muscles. Their studies show that during exercise, lactic acid production and removal continue at 300-500 percent of resting rates, even though oxygen consumption has stabilized at submaximal levels.

Lactic acid is a very fast fuel that can be used to athletes’ advantage during exercise

The concentration of both glucose and lactic acid rise in the blood after a carbohydrate-rich meal, but the blood lactic acid concentration does not rise much because it is removed so rapidly. The body converts glucose, a substance removed from the blood only sluggishly, to lactate, a substance removed and used rapidly. Using lactic acid as a carbohydrate “middleman” helps you get rid of carbohydrates from your diet, without increasing insulin or stimulating fat synthesis. During exercise, you won’t want an increase in insulin because it decreases the availability of carbohydrates that are vital to high performance metabolism.

Including lactate as part of a fluid replacement beverage provides a rapid fuel that can help provide energy during intense exercise. The rationale for including lactate in athletic drinks is simple- since the body breaks down so much of dietary carbohydrates to lactate anyway, why not start with lactate in the first place? Lactate in the drink can be used rapidly by most tissues in the body and serves as readily available building blocks for restoring liver glycogen during recovery.

I am not sure about adding lactate to a recovery drink but will look into this. If anyone has heard about this before please let me know how you feel about this recommendation.

Proper training programs can speed lactic acid removal from your muscles

This can be achieved by combining high intensity, interval, and over-distance training. Athletes and coaches must learn to deal effectively with lactic acid. Fortunately, most training programs incorporate elements necessary to speed lactate removal. Training programs should build your capacity to remove lactic acid during competition. Lactic acid formation and removal rates increase as you run, bike or swim faster. To improve your capacity to use lactate as a fuel during exercise, you must increase the lactic acid load very high during training. Training with a lot of lactic acid in your system 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.

Over distance training causes muscular adaptations that speed the rate of lactate removal. Over distance training in running, swimming, or cycling increases muscle blood supply and the mitochondrial capacity. Mitochondria are structures within the cells that process fuels, consume oxygen, and produce large amounts of ATP. A larger muscle mitochondrial capacity increases the use of fatty acids as fuel, which decreases lactate formation and speeds its removal.

The author goes on to suggest that a diet high in carbohydrates is essential for athletes. Since I am not a believer in this I edited that part out, but since converting to a No Sugar No Grain way of eating, and hitting the wall a number of times on loner rides and runs, I can see the point in needing to replenish carbs during this specific training style. What needs to be pointed out, however, and the underlying reason I chose to edit that portion, is that carbs does not mean sugar. Carbs in the forms of fruits and vegetables  are real food and should not be removed from a diet in my opinion. Sugar, itself, in the form of processed varieties, have been shown to have a direct relationship to health issues, including obesity.

So What Does This all Mean?

Lactic acid is an important fuel for the body during rest and exercise. It is used to synthesize liver glycogen and is one of our most important energy sources. Lactate is the preferred fuel source in highly oxidative tissues, such as heart muscle and slow-twitch skeletal muscle fibers. It is used rapidly by the body and is a valuable component in athletic fluid replacement beverages.

Lactic acid also is a powerful organic acid, and its accumulation can cause distress and fatigue during exercise. Athletes need both high intensity and over-distance training to improve the capacity to use lactic acid as a fuel during exercise and recovery. High intensity training develops cardiovascular capacity that reduces lactic acid transport to tissues that can use it as fuels. Over distance training causes tissue enzymes adaptations that increase use of fatty acids for energy. This helps slow lactic acid production from carbohydrates and to enhance tissues ability to use lactic acid as fuel.

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