Does lactic acid exist in humans and, if not, where does that burn come from?
We all remember the gym coach who roared about how you weren’t working until you felt that lactic acid burn. The phrase “lactic acid” is part of our sports lingo. How many times have we heard “gotta clear the lactic acid”? Well, it turns out that the coach was slightly misinformed. More and more, I have endurance athletes asking me the truth about lactic acid: 1) Are lactic acid and lactate different and which one do we have in our bodies? 2) Does lactate have a purpose?
There is considerable power behind the lactic acid myths, but the reality is that they are just that — myths. Let’s dispel them now.
Does lactic acid exist in humans?
According to Professor Matthew Hickey, head of the Human Performance Research Lab at Colorado State University, “The bottom line is, no. There is no lactic acid in human beings.”
To explain why, a brief lesson about acids is necessary. Every acid has an alternate base (alkaline) form — a sort of yin and yang. For example, lactate is a base and lactic acid is, well, an acid. Acids and bases frequently exist as mixes and are able to change back and forth between one another.
So how do we measure these acid/base mixes? Enter “pH value,” which is simply a measure of acidity/alkalinity. The pH ranges on a scale from 0 to 14. The lower the number, the more acidic the fluid. Our blood, for example, has a pH slightly above seven.
As the pH drops, more and more base molecules transform into acid molecules. There is a critical point at which there is a perfect 50/50 mix. Hickey points out that for lactic acid/lactate, that “occurs at a pH of 3.87.“ That, of course, is well below our blood pH of seven. This is why we don’t ever have “lactic acid” in our system. According to Hickey, lactic acid really doesn’t start appearing until “you have a pH under six,” and even then “you’d have 99 percent as [lactate] and one percent as lactic acid. During intense exercise, you can drive [pH] down into the high sixes,” Hickey said. This is well above the pH required to produce true lactic acid. If you had lactic acid in your blood, you’d have to have a pH under six, and you’d be getting rushed to the hospital.
Why then do we still talk about lactic acid in our bodies? Because of “simple historical inertia,” said Hickey. “It has stuck in the minds of lay audiences, coaches, athletes, etc. But it is based on a misunderstanding about the chemistry.”
But if we don’t have lactic acid, then what do we have? What causes the burn? Our muscles do produce acid, but that acid is simply positively charged hydrogen, not lactic acid as we once believed. Scientists were long fooled because hydrogen and lactate exit the cell together — in fact one can’t leave without the other. So when we measure lactate levels, it correlates with hydrogen ions. We thought we were measuring lactic acid, but it is merely a coincidence that when we measure a rise in lactate it happens to match with a rise in painful acid levels.
Does lactate serve a purpose?
Our misunderstanding about lactate gave it a bad rap. It was believed that lactate was just a nasty waste product that made our legs scream 50 meters from the finish. In reality, lactate serves many important roles. For example, “it is the principle fuel for the heart during vigorous exercise,” Hickey said. And the liver can recycle it, “releasing a brand new glucose molecule as if you’d been drinking a sports drink.”
The reality is that we are constantly producing lactate in our bodies. “There’s a misunderstanding that until you get to threshold you’re not making lactate. That’s not the case,” Hickey said. “You’re making lactate 24/7 all your life.”
The same goes for acid, those hydrogen ions. The reason our blood lactate levels are low most of the time is because our bodies clear and use it as quickly as we produce it. Our lactate threshold is simply the point where our bodies produce both lactate and acid faster than it can clear them. This makes our ability to clear lactate and acid a critical part of sustaining high-end power. And that brings us to our next big myth.
The myth that leaves you breathless
When you’re cranking up that 15 percent grade and gasping for air, it’s not the need for oxygen that’s driving you to breathe hard. It’s the struggle to breathe out. According to Hickey, we have sensors that constantly sample our blood and tell the brain when to increase respiration. “They are far more sensitive to rises in carbon dioxide in our blood than a drop in oxygen.”
Humans are one of the few mammals to have overbuilt lungs. We only require two thirds of their capacity to fully oxygenate our blood. So taking in enough oxygen is rarely a problem (unless you happen to be on the slopes of Mount Everest.) The reason we breathe hard “goes back to all of this pH threshold stuff,” Hickey said. If we can buffer the acid, “we can delay that pH threshold and get up to a higher and higher exercise intensity.”
Our best immediate buffer is a molecule called bicarbonate. Bicarbonate binds to acid to produce harmless water and CO2. However, “that process is only as good as the last step, which is breathing off the carbon dioxide.” If we don’t breathe it off fast enough, the CO2 is converted back to acid, and we lose the race.
The takeaway? Concentrate on exhaling.
Trevor Connor is a long-time cycling coach and researches both exercise physiology and nutrition at Colorado State University.