Lactic acid has a bad reputation. Many feel it’s responsible for their fatigue, muscle pains and cramps. They believe that because it is considered a metabolic waste, its production should be avoided in any way.
Scientific research has shown that lactic acid plays an important role in energy production during exercise. Rather than accusing it as the “bad kid” of our metabolism, let us consider that its presence provides energy to several tissues. It helps our body to use carbohydrates as fuel, and is a source of energy for the liver to produce glucose and glycogen. In fact, lactic acid is the way for our body to cope with stressful situations.
But lactic acid also has its dark side. When produced, it breaks down into lactate ions and hydrogen ions. Hydrogen ions are the acid contained in lactic acid. These are interfering with electrical stools in the muscles and nerves, which reduce energy reactions and prevents muscle contraction. The known “burning” sensation experienced by someone during intense exercise is due to the accumulation of hydrogen ions and not to lactic acid that is finally unfairly accused. In addition, we should say that our body loves lactate, which is a quick source of energy that you prefer from the heart and other muscles during exercise. Its presence is the guarantee that our body provides a steady stream of carbohydrates even when the exercise lasts for a long time. If we could consume it as a liquid before, during and after exercise, we would achieve performance improvements and accelerate the rate of recovery.
The following 7 points (myths and realities) should be considered important in the understanding of lactic acid:
1. Lactic acid is produced by the decomposition of glucose
During this process cells produce ATP (adenosine triphosphate) that is used as energy in most chemical reactions in our body. Lactic acid production does not require the presence of oxygen, so the process is called anaerobic metabolism. ATP production in the above case is small but extremely fast and is used whenever energy requirements exceed 50% of maximum performance.
2. Lactic acid does not cause muscle aches and cramps
The late onset of muscular pains, the next day of an intense workout, is due to muscle fiber destruction and inflammation of these fibers.
Most cramps are due to the fact that neuromuscular receptors are over-stimulated by muscle fatigue. Most athletes resort to grueling, warm bathing and other relaxation techniques to remove lactic acid from the muscles and so alleviate muscular disorders. Although these techniques have potential beneficial effects in alleviating pain, the possibility of removing lactate, however, fails. This is because lactic acid when produced is rapidly used as a fuel during exercise and restoration and does not remain in the muscles.
3. The body produces lactic acid each time carbohydrates are cleaved to produce energy
The faster the decomposition of glucose and glycogen, the more lactic acid is produced. During rest and low-intensity exercise the body produces energy from fat metabolism. When the intensity exceeds 50% of the maximum capacity, the body seeks energy from other sources – carbohydrates – to produce the required energy. The more carbohydrates are used to produce energy, the more lactic acid is produced.
4. Lactic acid can also be produced in muscle tissue that is fed with enough oxygen
As the intensity of exercise increases, both the body uses more and more white (rapid contraction) muscle fibers. These muscle fibers mainly use carbohydrates as a fuel for energy production. Therefore, the more the tension increases, the faster the rapid muscle fibers are involved, so more and more carbohydrates will “take care” for the energy required. The result will be increased lactic acid production. The increased presence of lactic acid in the blood means that the rate of production is faster than the rate of removal. The presence of oxygen in the above process does NOT play a role.
5. Several tissues, especially skeletal muscles, are constantly producing lactic acid
The levels of lactic acid in the blood reflect the balance between production and use of lactic acid by the body. An increase in the concentration of lactic acid does not necessarily mean that its production has increased. Elevated values may mean that its rate of removal from blood or tissues has decreased. Lactic acid production depends and is enhanced by increased carbohydrate decomposition during energy production. Whenever carbohydrates are used in energy production, a significant amount of carbohydrates is converted to lactic acid. This lactic acid is used in the same tissues as a fuel for energy production, or it is transported through blood circulation for the same purpose to other tissues. The rapid rate of use of carbohydrates for energy production (eg, intense exercise) also results in accelerating lactic acid production. For a short time, the concentration of lactic acid in the blood increases because it can not be used at the same rate as a fuel to produce energy. However, if the pace of exercise is reduced or stopped altogether, this balance will be restored. Dr. George A. Brooks (Department of Integrative Biology, Berkley University, SF, California) described in detail the dynamics of the production and use of lactic acid in metabolism in the theory of “Lactate Shuttle Theory” . This theory describes the central role of lactic acid in carbohydrate metabolism and its importance as a fuel for energy production for metabolism.
6. The body uses lactic acid as a “biochemical mediator” to metabolize carbohydrates
Carbohydrates in our diet are absorbed and introduced into the circulation during digestion and through the liver mainly in the form of glucose. However, instead of entering the liver as glucose and turning it directly into glycogen (carbohydrates), most of our glucose (derived from carbohydrates) does not pass through the liver and is introduced into the circulation and eventually muscles to convert to lactic acid. This lactic acid comes back into circulation and ends up in the liver where it is used as a raw material in the construction of hepatic glycogen. The body produces a lot of hepatic glycogen indirectly from lactic acid instead of directly from blood glucose. This process is called by the scientists “Glucose Paradox”. The theory was first mentioned by the well-known biochemist Dr. J.D. Mc Garry  and his colleagues and shows the importance of lactic acid in carbohydrate metabolism.
7. During endurance (marathon, triathlon, etc), the lactic acid in the blood stabilizes, although its production is increased
This is because the production of lactic acid is balanced by its consumption as a fuel for energy production. At the beginning of the race, the needs for using glucose and breaking it into glycogen are enormous. This increased rate of carbohydrate metabolism also increases the production of lactic acid, which in turn will present an increased blood concentration. The body, however, will channel the blood around the periphery and of course those working most where the lactic acid will be used as a fuel for energy production. This reduces the concentration of lactic acid in the muscles and blood despite its continued increased production.
However, the athlete often feels better later during the exercise or competition if he continues and persist the effort. This relief is also called the “second wind”. Scientists have used radioactive labels to track the process of producing energy in the blood and muscles. The results of their research show that during the exercise lactic acid production and its removal can reach 300 to 500% of the corresponding production and resting even if the oxygen consumption has stabilized to a sub-maximum level.
1. Lactate shuttles in Nature G. A. Brooks’ Exercise Physiology Laboratory, Department of Integrative Biology, University of California, Berkeley, U.S.A. 2002 Biochemical Society Transactions (2002) Volume 30, part 2 p.258-263
2. Katz, J; McGarry, J D (1984-12-01).”The Glucose paradox. Is glucose a substrate for liver metabolism?” Journal of Clinical Investigation. 74 (6): 1901–1909. ISSN 0021-9738 . PMC 425376. PMID 6392338