Lactic Acid: Semantics or Misunderstanding?

I always find the sections on energy pathways to be interesting, as I have learned about these “systems” in several running and fitness certification courses and each uses slightly different terminology to describe the same phenomena occurring in the human body. Some refer to them as immediate, non-oxidative, and oxidative. Other texts refer to them as the ATP-CP, glycolytic, and oxidative pathways. Again, regardless of the terms, they are describing the same systems. And if we want to look at these with gnat’s ass detail, calling them “systems” is insufficient. Describing a series of biological processes as a “system” is helpful in understanding what is happening, but the body does not know systems, it is an adaptable organism with a highly complex set of interdependent and interrelated cells and organs that respond in a specific way to stimulus.

But one distinction to want to bring to light is the use of the term “lactic acid”. This substance is commonly understood as the source of fatigue when working out at high intensity, however this traditional understanding is based on  correlative research, not experimental research findings. Recent research has uncovered a new understanding of the actual sources of fatigue and muscle burn; what is actually happening at the cellular level inside your muscles during high intensity training. As I make my way through another fitness certification course through the International Sports Sciences Association (ISSA), I consistently see the term lactic acid as the by-product of carb metabolism and the culprit for the perceived burn and fatigue. This is more than satisfactory for the level of explanation that a trainer would give a client, but it is not technically correct. To be accurate, there is an important distinction. During high intensity exercise carbohydrates (glucose) are used to meet energy demands. A by-product of this reaction is pyruvate, as well as the formation of Hydrogen ions (H+) in the muscle. Pyruvate begins to absorb the H+ to keep local acidity in check. As pyruvate absorbs the H+, lactate forms. Lactate is a fuel source for the muscles and acts as a buffer against an overly acidic environment within the muscles. The semantic misunderstanding stems from lactate and hydrogen ions being present together in the muscles, which is incorrectly called “lactic acid.” Regardless of what we call it, the important thing is to understand what is actually happening so we can design training that improves clients’ ability to process the lactate that their muscles produce, thus reducing fatigue and improving performance levels.


Fahey, Thomas. Strength and Conditioning. International Sports Sciences Association (ISSA), 2016. Course material.

Fitzgerald, Matt. The Lactic Acid Myths. 1/26/2010.

Yu, Christine. Fuel, Not Foe? The Truth about Lactic Acid, 7/18/2016.


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