It is a common belief that lactic acid is what causes the burning sensation we feel when we do a hard bout of high intensity exercise, for example during higher rep weightlifting sessions or longer speed sessions (anaerobic glycolytic energy system). How many times have you heard someone say that they really felt the "burn of the lactic acid build up"? This is actually a false belief, but it is one that is shared by many.

What actually happens is the body breaks down ATP to produce energy to create a muscle contraction. During this process, hydrogen ions are released. Because muscle oxygen levels are low, the body can’t recycle hydrogen ions fast enough, so it begins to store up, and this creates an acidic environment that leads to the “muscle burn” we feel. At this point, it isn’t lactic acid that accumulates, it’s LACTATE.

During high intensity exercise (one to three minutes), our bodies rely on glycogen to supply energy for muscle contraction. As glycogen is broken down, also known as glycolysis, pyruvate molecules begin to accumalate, along with hydrogen ions. Pyruvate absorbs two hydrogen ions, forming lactate.

However, lactate provides us with many benefits. It acts as a buffer to the acidic nature of the hydrogen ion build up and without it, the accumulation of hydrogen ions would eventually cause mechanical failure to take place. It is extremely useful, as it is estimated that around 75% of lactate is recycled by our muscles cells to produce fuel (glucose). An additional benefit, is the build-up of lactate also counters muscle fatigue by delaying the depolarization of the muscle tissue.

Take Aways:

1- Lactic acid does not accumulate but lactate does

2- Lactic acid or lactate doesn’t cause muscle burn/ soreness

3- Build-up of hydrogen ions causes muscle burn that leads to mechanical failure

4- Lactate buffers against the acidic environment caused by hydrogen ions

5- Lactate counters depolarization of the muscle tissue.

6- Our bodies recycle lactate to produce more fuel (glycogen)

Definitions:

Depolarised: a loss of the difference in charge between the inside and outside of the plasma membrane of a muscle/ nerve cell due to a change in permeability and migration of sodium ions to the interior.