That Burning Sensation

Lactic acid or lactate?

A common misconception among the general population and still within the scientific / fitness community is that the burning sensation we feel in our muscles during bouts of high intensity exercise is caused by our body producing lactic acid as a by-product of anaerobic respiration (burning fuel without the presence of oxygen).

This well meant yet inaccurate conclusion was reached because scientists noticed a build-up of lactic acid in athletes whose muscles were burning and at the point of failure.

The first point to note here is that it isn’t lactic acid that is produced, but lactate. So, what is the difference? Lactate is the conjugate base of lactic acid - which simply means that lactic acid has one more hydrogen ion than lactate. Although the two terms are often used interchangeably, it is lactate - and not lactic acid - that is being produced by your body.

Secondly, it isn’t the lactate that is causing the burning sensation. This sensation is caused by acidosis, a condition whereby our physiological environment becomes more acidic (a pH value of less that 7).

Metabolic acidosis describes a build-up of hydrogen ions within our body’s fluids. There are a few theories as to where the hydrogen ions that make the cell acidic come from and these generally involve the hydrolysis of a molecule called ATP (the universal currency of energy within cells). Energy is released when  ATP is broken down into ADP.

Respiratory acidosis is where Carbon Dioxide cannot be removed from the blood quickly enough and builds up, thereby increasing the acidity of the blood.

Surprisingly the truth is that lactate (lactic acid) actually protects against the acidosis it was accused of causing and as such is a helpful product that can actually allow muscles to contract for longer. When we look back at the literature it becomes evident that scientists have been questioning the misconception of lactate for decades (Wilkie 1979) so it is amazing how this myth still perpetuates.

Anyway, after all that heavy reading, the take away is that the build-up of lactate does not cause the burning sensation and actually allows us to exercise for longer.