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Myth-busting: lactic acid

The myth: Lactate is a waste product that slows you down mid-workout. 

The verdict: False.

By no means does lactate fall into this category, says de Mille. (Carbon dioxide, however, is a good example of a waste product, something your body needs to get rid of to function properly.)

Most of the lactate you make during exercise gets converted into energy to power your workout. “It helps you go a little bit further than you would otherwise,” Fournier says. 

In fact, a study from the University of California, Berkeley shows that exercise trains your muscles’ cells to more effectively use lactate for this purpose. The researchers believe that high-intensity intervals are the best way to improve your body’s ability to do it. To get the benefits, log at least two 20-minute HIIT sessions every week.

The myth: Lactate makes your muscles burn.

The verdict: False.

As you break down carbs for fuel, the resulting adenosine triphosphate (the source of energy for all the cells in your body) releases hydrogen ions. When these ions accumulate, the pH levels in your muscles drop, making them more acidic. That, combined with the heat that builds up in your muscles during demanding efforts, explains the burn—not lactate, says de Mille.

In fact, lactate eases the burn. To produce the substance, your body uses up some of those offending hydrogen ions, decreasing acidity.

The myth: Lactate contributes to muscle soreness. 

The verdict: False. 

People often think that because lactate goes hand in hand with tough workouts, the substance causes soreness. Instead, soreness sets in because of the inflammation and micro-tears that occur in the muscles during hard sessions, de Mille explains. 

“If lactate were responsible, you’d feel sore after every intense workout,” de Mille says. That’s not the case; chances are, you don’t feel aches after every single HIIT routine. But you probably do feel sore after a marathon even though lactate levels remain low during long, steady-state activity. 

The myth: You need to flush lactate out of your body with external stimuli. 

The verdict: False. 

It’s common to see people foam rolling after they train. Ask them why, and they might say it’s to flush the lactate out of their system. Foam rolling has many benefits (if you do it right), but they're unrelated to the exercise byproduct. “Even if you sat down and did nothing after a hard workout, your lactate levels would return to normal within thirty to sixty minutes,” de Mille says. 

The right cool-down will help increase circulation and reduce the acidity that’s associated with (but not caused by) lactate. To jumpstart recovery, use the stationary bike, elliptical, or treadmill at a low intensity for 5 to 10 minutes immediately after exercise, per de Mille. Doing the same types of movement for up to 30 minutes on days you feel sore can also speed up the process.

The bottom line: “Think of lactate as a helpful friend who just happens to hang out with a tough crowd of troublemakers: hydrogen ions, micro-tears, and inflammation,” she says.