You may be familiar with the feeling known as “the burn”—the tingling soreness emanating from deep within your muscles, telling you to stop what you’re doing and rest. The burn can appear during the last few reps at the gym, the end of a long jog or even during the last few twists while screwing in a lightbulb. You’ve likely heard the phrase “feel the burn,” but what exactly is it? And should we be thanking it rather than just feeling it?

What is “the burn?”

When you think of “the burn,” you might conjure up vague memories of gym class and the term “lactic acid.” You may even recall something about fermentation. The truth is the phrase “lactic acid” is a bit of a misnomer. When we exercise, we produce lactate by breaking down sugar to fuel our muscles. Coincidentally, our muscles also produce acid through a separate process. Although the two are completely separate, when early researchers studied exercising muscle, they found both lactate and acid—leading to the idea of “lactic acid.” While the acid is the real culprit behind “the burn,” lactate has taken the bulk of the blame—it’s a classic case of being guilty by association.

A misunderstood molecule

In recent decades, lactate has received some bad press. Its unfortunate association with acid has led some people to characterize it as a waste product, acid or metabolic poison. These statements could not be further from the truth. Lactate is, in fact, an active force for good.

The science behind lactate

Far from a metabolic poison, lactate acts as a helper in several key physiological functions. Studies have shown that lactate serves as an alternative fuel source for our brains, hearts, muscles and other organs during times of stress. It’s been found to be beneficial in many situations ranging from exercise to traumatic brain injury and even doing mental math. Lactate also serves as a signaling molecule helping our blood vessels relax, altering gene expression and letting our bodies know where extra fuel is needed.

So next time you “feel the burn” remember, it’s not the enemy—it’s here to help!