Anyone who has ever picked up a magazine or watched a broadcast of a live sports event has undoubtedly heard of  lactic acid. Lactic acid is often considered an athlete’s worst enemy. But in reality, it is one of the most important substances in our metabolism, actually delaying fatigue rather than causing it.

This post marks the start of our first series – Unravelling Lactic Acid, in which we will dissect the physiology behind its production; separating facts from fiction and discussing its practical relevance in training.


Lactic acid, more correctly termed lactate, is a product of our anaerobic (glycolytic) metabolism, a sequence of chemical reactions which partially break down glucose without the use of oxygen. Contrary to popular belief, and for reasons which shall be addressed later in this series, our bodies are constantly using our anaerobic metabolism and therefore constantly produce lactate.

Given that lactate is produced when we use our anaerobic metabolism, the more anaerobically reliant we become, the more lactate will be produced. At times of rest, lactate will therefore be low, but as exercise becomes increasingly intense and anaerobic metabolism pulls more slack, lactate production increases.

Why do our anaerobic systems become more involved during higher intensity tasks? 
Our anaerobic systems are considerably less efficient than our aerobic systems, as they yield only a portion of the energy compared to that produced aerobically. However, they’re able to produce energy at a significantly faster rate. During high intensity exercise, our muscles require a quick energy turnover, and anaerobic systems become more important.

Very rarely do we turn to our anaerobic systems simply because we ‘lack oxygen’. Instead, we do so when our aerobic system is unable to deliver energy fast enough.



Lactate is actually a source of energy
As mentioned before, lactate is the product (or remains) of our anaerobic glycolytic metabolism, a process which only partially breaks down glucose. Partial/incomplete glucose breakdown is great for rapid energy supply, but, leaves over a substantial amount of unused energy. Fortunately, lactate holds this unused energy and is able to prevent it from going to waste.

Unlike glucose (which is too large), lactate can be exported from within a cell to the bloodstream and be uptaken by other muscles and organs (heart/liver/brain) and utilised for energy through aerobic metabolism. This is a highly notable feature of our metabolism, as the production of lactate essentially allows glucose to be partially used for energy within a cell, then shipping its remaining energy to another. This recycling helps prevent wasted energy.

Allows extended anaerobic metabolism to take place
For any reaction to repetitively take place there needs to be a restoration of the starting reactants/substances. When we repetitively use the anaerobic process glycolysis in a cell (i.e. during intense exercise), an important coenzyme (facilitates reactions) known as NAD+ (nicotinamide adenine dinucleotide) is protonated (gains hydrogen ions) to become inactive in the form of NADH. To begin glycolysis again, NADH needs to be restored to NAD+. The production of lactate fortunately deprotonates NADH into NAD+, to restore the coenzyme to function again. In doing so, lactate helps the extended use of our anaerobic metabolism. Figure 1 below annotates this.

Lactic Acid Metabolism



Many believe that lactate is a dead-end metabolite and fatigue inducing poison, but this simply isn’t true. Up to this point we’ve discussed how lactate is constantly produced by the body and is a valuable fuel source especially during times of energy crisis.

Lactate doesn’t cause fatigue, but is brought about as a result of it and is there to mitigate it. High lactate at the onset of fatigue is comparable to a full team of firemen present during a blazing fire – not there to cause the fire, but there to treat it.

This is not to completely throw the cat out of the bag, as although lactate itself is not the culprit of fatigue, its presence shares a linear relationship with the substances which do, and which are not as easily measurable. Lactate corresponds in particular with the presence of hydrogen ions, which when accumulated create a slightly more acidic environment (decreased pH). It must be noted that when we speak of an increased acidity, we’re talking about marginal changes in pH. An increase in blood acidity subsequently reduces muscle contractility and impairs our performance. It also will trigger a particular type of sensory receptor known as chemoreceptor which then causes us to feel the familiar burning sensation during intense work.


Just as our body always produces lactate, it also always clears it. So when we measure blood lactate levels, what we’re really doing is measuring the difference between how much is produced (and reaches the blood) and how much is cleared. Therefore the production of lactate is not an issue as long as it is cleared (thus fatiguing products cleared).

You may recall that lactate is a product of our fast acting anaerobic metabolism, which can assist distance runners in running fast. This is why coaches speak of utilizing lactate threshold training to deal with a higher lactate production by clearing more. It’s not that at race pace the best runners don’t produce lactate, it’s rather that they have the ability to deal with it better.

How runners can improve their ability to deal with lactate and corresponding fatiguing products is achieved through the following:

  • Improved ability to shuttle lactate = clear and utilize lactate effectively
  • Improved buffering capacity = ability of body to resist the effect of substances which change pH and can cause fatigue. We have several buffering systems, one of which is our bicarbonate buffering system which helps neutralize hydrogen ions from causing acidosis.
  • Improved lactate tolerance = ability to perform quality in an acidosis state (more relevant for 400m/800m runners)


Many believe that your post-race aching muscles are caused by lactate, which is why clearing lactate during a post exercise cool-down is important. Cooling-down is important, and can actually reduce DOMS (delayed onset muscle soreness), but for reasons that have nothing to with lactate. Lactate does not trigger any exercise related soreness, and anyways, returns to resting levels with about 1 hour after hard exercise, regardless whether you cool-down or not.

Instead, your aching muscles and DOMS sensation are likely due to micro-tears in your muscle caused by forceful contractions.



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