Bonus Content: Lactic Acid

So, if you have been thinking that lactic acid is both the reason for muscle fatigue AND for DOMS (delayed onset muscle soreness), you’re in for a shock. This is going to be one of those times where I ask you to suspend your disbelief for a few minutes while you read the below content. It might turn a few things upside down.

I’ll also start by saying that there are still elements of the role that lactic acid plays in the body that are unconfirmed and still under scrutiny.

What Does Lactic Acid Do?

Lactic acid or lactate has long-since been named the culprit for muscle soreness and fatigue. It has also long-since been shown to not actually be the culprit, however it seems a bigger challenge to change someone’s mind once they’ve had the original seed planted, than it was to plant the initial seed.

Reduction in fatigue

Contrary to popular belief, research shows us that actually the production of lactic acid actually decreases fatigue. In other words, it allows you to perform your chosen activity for a longer period of time without getting tired. This has been demonstrated three main ways:

? There is a rare medical condition known as McArdle’s disease, and it essentially leads to the inability to produce lactate. Given previous interpretations of lactic acid science, we would assume that these people would therefore have a substantial advantage in performance because they wouldn’t fatigue… right? Well, the exact opposite occurs – people with this condition are unable to sustain exercise beyond a few minutes at a time without experiencing pain, weakness, fatigue, cramping and other spasmodic actions of muscles. This alludes to lactic acid actually being important in the continuation of exercise and a delay of fatigue onset.

? Starting back in the 1960’s, experiments done by Depocas and associates showed that lactate was also being used by a lot of cells as a fuel for metabolism. [Not only locally within the cell, but also transported around the body and utilized by other cells]. This means that it is actually a fuel source that can compare to the utilization of glucose directly, and this once again means that lactic acid actually staves-off fatigue, enabling you to continue to perform your activity for longer periods of time with adequate energy supply.

? We’ve found that not only does training improve our ability to actually produce more lactic acid for longer periods, it also improves the ability to cycle that lactate out of the muscle. The reason this is important is because if lactate is allowed to build up in a muscle, it slows the production of it, and therefore no “new” lactate is being brought in to “help”. So with exercise training we actually produce MORE lactic acid, but the more we train for something the later we feel fatigue. Once again strongly opposing the idea that lactic acid is the cause of fatigue. (more can be read on this here, in a study from 1997)

No correspondence to DOMS

Not only does lactate actually increase your capacity for exercise by reducing/delaying fatigue, it also doesn’t make you sore.

? To build on the second point from above, if lactic acid caused DOMS, we should expect that an increase in production of the substance would lead to an increase in pain/discomfort of DOMS. To the contrary, we’ve already discussed that training adaptations include an increased ability to produce lactate, and move it out of the cell for more to be made. It’s also well documented (and you’ve likely experienced) that with training, you experience less and less DOMS for the same activity. This opposes the idea of lactate causing muscle soreness.

? Additionally, if we look at blood lactate levels post exercise, and if we’re assuming that it causes DOMS, we would anticipate that lactic acid concentrations peak between 24 and 48 hours post-exercise. This is not the case. In fact, whether we warm-down from our activity or not, our blood lactate levels return to normal after about 2 hours post-exercise. So by the time we feel sore, the lactic acid is looooong gone.

So what causes fatigue and DOMS then?

The short answer is “no one knows for sure”.
The longer answer is: for fatigue a lot of research is focusing efforts on understanding the role of protons (acid) and central mechanisms (CNS) for understanding fatigue, whereas DOMS is being closely studied through the lens of “microtrauma” to the muscle…which is getting weaker support, and neurotrophic factors…which is gaining stronger support.

So rather than fearing the lactic acid, we should actually be thanking it!