Lactic Acid and Exercise: Friend or Foe?

Lactic Acid and Exercise: Friend or Foe?

(Last Updated On: April 4, 2019)


Lactic Acid and Exercise: Friend or Foe?

Lactic acid – isn’t that something bad? You experience the effects of it every time you lift weights to the point of fatigue – and it burns! Lactic acid gets a bad rap. In fact, it often gets blamed for causing muscle soreness. Still, poor, misunderstood lactate may actually have benefits when you’re trying to build muscle.

What is Lactic Acid? 

Lactic acid is an acid that builds up in your muscles when you do strenuous exercise. Let’s use sprinting or lifting a heavy weight as an example. During the first few seconds of a sprint, your muscles use stored ATP as well as ATP from the creatine phosphate system to fuel exercise. Once that’s depleted, it uses another system called anaerobic glycolysis. This system generates more ATP than the creatine phosphate system and also produces a compound called pyruvate.

What happens next?  If there’s enough oxygen available, pyruvate can enter the mitochondria of the cell. It’s here, through a process called oxidative phosphorylation, that cells can generate the most ATP. Ideally, your cells want to use oxidative phosphorylation since it produces the maximal amount of ATP. Yet, when you’re sprinting or doing another near maximal exercise, including heavy weight lifting, energy demands are high and you have to meet those demands quickly – so what do you do?

To send more oxygen to your cells, you breathe faster. Yet, due to the intensity of the exercise, despite your best efforts, you can’t get oxygen to your muscles and tissues fast enough to use oxidative phosphorylation. Instead, cells have to revert to anaerobic glycolysis, which literally means “in the absence of oxygen.” Through anaerobic glycolysis, cells can make ATP and generate pyruvate but can’t send pyruvate into the mitochondria for oxidative phosphorylation. Instead, in the absence of oxygen, cells convert pyruvate to lactic acid and then into lactate. By converting pyruvate into lactic acid and lactate, anaerobic glycolysis can continue despite low levels of oxygen.

Unfortunately, anaerobic glycolysis and conversion of pyruvate to lactic acid and lactate is only a temporary measure. Within one to three minutes, lactic acid starts to build up. As lactic acid starts to accumulate in the muscle, the pH of the cell drops. This drop in pH likely explains why your muscles burn during intense exercise. Plus, the drop in pH due to the accumulation of lactic acid causes anaerobic glycolysis not to function as well. These changes make it hard to keep exercising and you have to slow down or stop. That’s when your muscles burn and your legs or arms feel like they’re going to give out. You’re probably well acquainted with this feeling.

Once you stop, you begin to clear some of the lactic acid out of your muscle tissue. Energy demands drop after you slow down or stop exercising and you’re able to deliver enough oxygen to meet those demands. As a result, oxidative phosphorylation can take over and help meet the energy needs of cells without the build-up of lactic acid.  That’s what happens during recovery.

Where Does It Go?

When lactic acid builds up in muscle tissue, some of it leaks out into your bloodstream – but where does it go once it leaves the muscle? Part of it goes to your liver where your liver can use it to remake glucose through a process called gluconeogenesis. Believe it or not, some parts of your body can use lactate as a fuel. For example, your heart can harness it as can your red blood cells. So, contrary to popular belief, lactic acid isn’t just a waste product. It’s a source of fuel for some organs, particularly your heart.

Other Myths about Lactic Acid 

A popular belief among bodybuilders that should be dispelled is that lactic acid causes muscle soreness. You’ve probably felt the effects of delayed-onset muscle soreness, also known as DOMS, many times. It’s the achy muscles and stiffness you get after a workout that’s more intense than you’re accustomed to, particularly one that emphasizes eccentric contractions. However, research shows that it is not the cause of DOMS. The reason you feel sore is that you’ve damaged muscle fibers. The muscle fibers that are damaged elicit an inflammatory response and it’s the inflammation that makes it so hard to walk after a tough lower body workout.

Training Your Body to Handle Lactic Acid 

Here’s the good news. You can train your body to deal with lactic acid more efficiently. As research at the University of Berkeley shows, high-intensity interval training generates lactic acid. This makes sense since you’re working out at an intensity that makes it hard to deliver enough oxygen to the muscles. In response to the build-up of lactate, cells adapt so that they can clear lactate faster. As a result, less lactic acid builds up. When this happens, you can exercise longer without experiencing severe muscle burn or fatigue. It just goes to show that your body is an extraordinary adaptation machine!

Can Lactic Acid Help You Get Stronger and Leaner? 

Lactic acid has its good points too. According to a study published in the British Journal of Sports Medicine, lactate may give you a leg up on building muscle tissue. This study showed lactate build-up is a stimulus for the release of growth hormone, a hormone produced by your brain that boosts muscle protein stimulus. Growth hormone also aids in fat burning. When you lift a weight past the point that you feel the burn, your body responds by releasing more growth hormone. So, maybe lactic acid isn’t such a bad guy after all.

The Bottom Line 

Now you know why lactic acid builds up – because you’re exercising so hard that you can’t deliver oxygen to your muscles fast enough. Therefore, cells use anaerobic glycolysis as a fallback and that, after a few minutes, causes lactic acid to build up and enter your bloodstream. As it turns out, lactic acid or lactate entering your bloodstream isn’t such a bad thing. Your heart can use it as a fuel, in fact, it prefers lactate. Plus, with regular training, your body becomes better at handling lactate. Finally, at least one study shows lactic acid is a stimulus for growth hormone release. So, you may actually get benefits from lactate. Maybe it’s not such a bad guy after all.



Sports Med. 2006;36(4):279-91.

UC Berkeley News. “If you “feel the burn,” you need to bulk up your mitochondria”

Br. J. Sports Med. 2009 Jul: 43(7): 521-5.

IDEA Health and Fitness Association. “Revisiting Energy Systems”


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