Lactic Acid Explained

What most people think they know about lactic acid is actually a myth, misnomer, and is basically wrong. We blame it for the burning muscle sensation during intense exercise and for the muscle soreness (DOMS) the next day, but in reality there is no ‘lactic acid’, there is lactate and metabolic acidosis. The reason for the confusion was that back in the 1920’s scientists found high levels of lactate and high levels of hydrogen ions (reason for acidosis) present in the muscles during high intensity exercise and fatigue, and believed them both to be the reason – hence the name Lactic Acid. This went unchallenged for about 80 years, and in that time, the myth had become deeply imbedded into coaches, trainers and most fitness literature.

Ok, so I’m going to try and keep this as simple as possible.

For our muscles to work and contract they need energy, and they get this energy by the breakdown of a molecule called ATP – this subsequent breakdown for energy is called hydrolysis (because it also requires one molecule of water). The letters ATP stand for Adenosine Triphosphate, which basically means its composed of one part adenosine, and three phosphates (hence the ‘Tri’….in phosphate). When ATP is broken down it releases one of its phosphates, and that in turn produces energy and a hydrogen ion (proton). Leaving the once named ATP, to now be called ADP, because of the loss of the phosphate, it has now only got two phosphates so is called Adenosine Diphosphate. (Di for two, instead of the Tri).

Because muscle cells store ATP in only limited amounts, and activities/sports require a constant supply of ATP – there are three energy systems that exist to replenish ATP in the human body. These systems are: The Phosphagen system, Glycolysis, and the Oxidative System. All three energy systems are active at any given time; however the system that gets the lion’s share of the overall work is primarily dependent on the intensity and duration of the activity involved.

For now, I am only going to discuss Glycolysis, which is the breakdown of carbohydrate to resynthesize ATP - either glycogen stored in the muscle or glucose delivered in the blood. (Nb. all carbohydrates you eat get broken down by the body into glucose, and glucose is stored as glycogen). One of the end results of glycolysis apart from energy resynthesis, is pyruvate.

Pyruvate once created can go in two different directions depending on exercise intensity. If the exercise intensity is high, then the pyruvate is converted into lactate.

So now I have discussed and mentioned two end products: lactate and hydrogen ions. I’m now going to backtrack and revisit those hydrogen ions (protons) which are a by-product of the hydrolysis of ATP to produce energy. It is the inevitable hydrogen ion accumulation that reduces the PH level and inhibits glycolytic reactions that is known as metabolic acidosis and is responsible for the fatigue and burning sensation during high intensity exercise. Moreover, it is the production of lactate that actually works to decrease metabolic acidosis rather than accelerate it, by each molecule absorbing two hydrogen ions (protons), which in turn alkalises the cells.

Once lactate is formed it can be cleared from the system in the blood to be reused by the cells as energy, or sent to the liver to be turned into glucose.

When we train we want to push ourselves to the lactate threshold and beyond, so our bodies become more adept at producing and clearing lactate to flush out the hydrogen ions. The problem exists when hydrogen ions build up, and there’s not enough to clear it from the system.

Athlete’s have low concentrations of lactate in their bodies, not because they don’t produce a lot of it, as that would be counterintuitive of what’s been discussed above, but because they produce more of it and clear more of it, which in turn gets rid of a lot of hydrogen ions, and thus the acidosis/muscle fatigue quicker than non-athletes do.

So to summarise, Lactate is actually the good guy trying to get rid of the acid-causing hydrogen ions, whilst making the tissues more alkaline – he’s just got a lot of unnecessary bad press over the years.

Reference Material:

-NSCA – Essentials of Strength Training and Conditioning. G. Gregory Haff & N. Travis Triplett

-Discovery Learning Course Notes