The Lactic Acid Myth

There is no lactic acid in the human body. That said, the burn we feel during hard efforts has a lot to do with acid.

A triathlete dressed all in black grimaces while riding his bike
An athlete pushes through lactate buildup during the bike leg of the Sestroretsky A1 Triathlon. Photo: Shchukin

We’ve all had a gym teacher or coach who talked (or yelled) at us about that lactic acid burn. It’s in our lingo. “Gotta clear that lactic acid!”

But should it be? Let’s tackle that question head on: Does lactic acid exist in our bodies?

“The bottom line is no. There is no lactic acid in human beings,” says Professor Matthew Hickey, Head of the Human Performance Research Lab at Colorado State University. “It cannot exist as lactic acid at the pHs we operate at.”

What exists is lactate. All acids actually have both an acid and base form. Lactate is the base. So why do we only have lactate? To explain, we have to talk about something called pKa.

“The pKa value represents the pH at which you have 50 percent as the acid and 50 percent as the ion [base],” Hickey says. “For lactate, that pKa occurs at a pH of 3.87. Physiological pH most of the time is above seven. You’d have to have a pH under 6 before you’d have 99 percent as the ion and 1 percent as lactic acid—and you’re just not going to get that. During intense exercise you can drive it down into the high 6 range. You’d know it.”

So why, then, do we talk about lactic acid?

“It was simply historical inertia; we’ve had the term around for a long time and it has stuck in the minds of lay audiences, coaches, athletes, and so on,” Hickey says. “But it is based on a misunderstanding about the chemistry of that molecule.”

What’s behind the burn

Don’t worry though, that burn you feel as you’re sprinting to the line isn’t in your head. “The important thing to know is that the burn does come from what we might broadly call a metabolic acidosis,” Hickey says. The acid is simply hydrogen ions (hydrogen missing an electron).”

The lactic acid myth exists because of an ironic coincidence. According to Hickey, blood lactate and blood hydrogen ion concentrations correlate well because they leave the cell by virtue of the same mechanism. In fact, lactate can’t get out without a hydrogen ion getting out with it. That, in part, has added to the confusion.

This is why physiology labs continue to conduct lactate tests. “The point at which we see a sudden rise in lactate during exercise happens to correspond to the point where pH suddenly drops,” Hickey says. “Had we known we probably wouldn’t be talking about lactate threshold. We’d be talking about pH thresholds.”

It turns out, lactate is just a surrogate for what is really acting as the governor on race pace, which is pH.

Lactate as fuel

This distinction is important because lactate is not just the biological waste product that has us cringing at the end of a hard sprint. There’s a misunderstanding that until you get to that lactate threshold, an athlete isn’t making any. That’s not the case. In fact, you’re making lactate at every moment throughout life.

Indeed, lactate has many uses. “Probably the most important one is that it’s the principal fuel for the heart during vigorous exercise. If you think of any race pace intensity, between 60 and 80 percent of the heart’s energy is coming from oxidizing lactate that was produced by skeletal muscle just a few moments ago.”

The rise in lactate during a threshold test isn’t just about how rapidly we produce lactate but our ability to clear it as well.

“The lactate only starts to rise at a given point because it’s at that point where the rate at which we produce lactate exceeds the net or combined tissue ability to remove it,” Hickey says.

And here again, hydrogen ions and lactate correlate well. So, training your system’s ability to clear is a very critical part of sustainable high-end power.

How to improve lactate clearance 

Lactate buildup in muscle tissue is one of the primary limiters of high-end power. And clearance is as important as production in avoiding fatigue. Here are a few tips to help with both.

Work that blood flow

Since lactate is used as fuel, it helps to circulate it throughout our bodies. Our ability to deliver blood throughout our bodies is sometimes referred to as central conditioning. Nothing trains it better than base training—long slow miles in the winter.

Stay warm

Cold limbs and muscles also restrict blood flow and our ability to clear acid. Keep your legs and body covered when racing and training on cold days.

Burn that fat

Relying more on carbohydrates for fuel produces significantly more lactate and acid than relying on fats. Take advantage of the winter months to train your “fat-reliance.” Several studies have shown that time on the bike at any intensity and eating fewer carbs on your training rides can build this ability.

You can’t escape intensity

Ultimately, nothing trains your threshold like riding at threshold. “There are ways to train your heart, your less-used muscle, and your liver to better clear hydrogen ions,” Hickey says. “And, not surprisingly, one of the ways to do that is to bathe those tissues regularly in lactate.” Start with five-minute efforts and, then, as your clearance systems improve, build to 20- and even 30-minute efforts.