Back when I was training for triathlons, my coach gave me workouts specifically designed to raise my lactate threshold. Lactate was believed to be a nuisance. It was assumed to be a waste product of glycolysis (a fundamental energy system during exercise), and the cause of muscular fatigue during strenuous exercise. If you were better able to clear lactate, you could perform at higher intensities before the fatigue and burn set in, forcing you to slow down or stop.
Active recovery days and post-workout stretching and foam rolling were also part of my regimen as ways to “minimize lactic acid buildup.” This was important to prevent, or lessen, the soreness that set in a day or two after a tough training session.
Or so we thought.
Common, but Not True
It’s still common knowledge that lactic acid and muscle soreness go hand in hand. But what if I told you that although this knowledge is common, it’s incorrect.
Let’s ruffle some feathers.
According to one of the many research abstracts I scoured, “lactate science is far from being completely understood; therefore, it is still an exciting area to study.” (Source)
This explains why finding consistent information on this topic was challenging. But I did my best to cut through the noise and present here the most recent, accurate findings on lactic acid and lactate.
Lactic acid and lactate are often used interchangeably. However, while they do belong in the same bucket, they aren’t the same thing.
Lactate was first discovered in 1780, and since then has been in a constant state of change. Lactate, along with its protonated form (one extra hydrogen ion in the molecular structure), lactic acid, was “unfairly seen as primarily responsible for muscular fatigue during exercise and a waste product of glycolysis.” (Source)
Yes, unfairly seen!
However, over the last twenty years, lactate’s status (and therefore lactic acid’s status as well) has slowly changed from a byproduct of exercise to an energy source for muscles.
We will uncover the longstanding and prevalent myth that lactic acid causes muscle soreness, denote the difference between lactate and lactic acid, and discuss the real reasons we get fatigued during intense exercise and why we get sore afterwards.
Lactic acid vs Lactate
Myth: lactic acid and lactate are the same thing
Reality: they have different molecular structures and play different roles in the body
Lactic acid and lactate are often used interchangeably, but they’re not the same thing.
From a chemistry standpoint, lactic acid has the same molecular structure as lactate, but with an extra hydrogen ion.
Lactic acid: C3H6O3
Lactate: C3H5O3
From a functional standpoint, lactic acid is produced by our muscles, red blood cells, skin, brain, and GI tract, and has many functions. But it never really builds up in the muscles or in the blood. That’s right, it never builds up.
Specifically,
“During exercise glycogen and glucose are broken down to pyruvate to produce ATP.
Pyruvate can either enter the mitochondria for oxidation (aerobic metabolism requiring O2) for more ATP or can be reduced to lactic acid (anaerobic metabolism).
Lactic acid … rapidly dissociates into lactate and hydrogen ions, so there’s never much lactic acid in the muscle and even less in the blood.” (Source)
So, since lactic acid doesn’t stick around for very long in the body, separates into lactate, and doesn’t really have much affect on exercise or recovery, the terms lactic acid and muscles don’t belong in the same sentence.
Myth: lactic acid buildup causes muscle soreness
Reality: lactic acid buildup isn’t a thing
“In reality, lactic acid cannot even really exist in the body because blood pH is too neutral, (around 7) and acids require very low pH. As soon as lactic acid is produced in the body, it dissociates into lactate and hydrogen. Really what we are talking about when we say ‘lactic acid’ is lactate. So. You should not use the words ‘lactic acid’ and ‘muscles’ in the same sentence!” (Source)
Muscle Burn/Fatigue During Exercise
You’re on a run and get to a hill. As you’re climbing the hill your heart rate climbs as well, and within seconds your legs are on fire. You have no choice but to slow down to a walk. The burning subsides and you’re able to pick up the pace again.
You’re at the gym lifting weights. The first 8 reps of squats feel great, but then as you climb higher in reps, so does the pain in your legs. You stop, shake it out, and after a minute are able to do another set.
If this has happened to you, you may be tempted to blame it on lactic acid. But over the past 20-30 years, research has evolved and there’s a new understanding of the role of lactate (which is what lactic acid turns into) in energy metabolism. However, many of the old misconceptions continue.
Myth: lactate is what causes exercise fatigue
Reality: lactate is fuel for your muscles during exercise
“During the twentieth century, lactate was seen as a waste product of glycolysis and its production was associated with muscular fatigue. Early studies showed that lactate increased with exercise in an intensity-dependent manner; therefore, it was strongly correlated with fatigue levels.” (Source)
In other words, the predominant theory was that lactic acid converted to lactate due to the body’s pH, then caused a decrease in the pH, producing muscular acidosis. This was viewed as a probable cause of fatigue and muscle burning during high intensity exercise.
When actually…
…lactate is not responsible for acidosis.(Source)
Instead, it has many benefits during exercise, including being a fuel source.
The “lactate shuttle theory” was introduced in 1986 and suggests that lactate plays a role as an energy source during high intensity exercise. (Source)
As fatigue develops while you’re exercising, lactic acid (and subsequently lactate) is produced. But this is not what causes fatigue. Instead, lactate is a valuable fuel source for muscles and other organs.
You may be wondering, if lactate doesn’t cause muscle burn and fatigue at high workloads, then what does?
There are several reasons, dependent on the exercise intensity level and duration.
“Increases in phosphate, altered ratios of high energy phosphates, reactive oxygen species, amongst others are thought to be the culprits of fatigue at high workloads.” (Source)
Inorganic phosphate accumulation is now seen to be the main cause of the muscle fatigue that occurs during anaerobic exercise (when workload exceeds oxygen input).
The fatigue that happens during aerobic exercise (when ample oxygen is available) is more likely to be caused by carbohydrate depletion, dehydration, or simply a decline in muscle performance (in events such as a marathon).
What about the burn? Not only is lactate not the cause of muscle burn, but it actually helps prevent it by combatting muscle acidosis. Muscle burn happens because of a drop in pH (creating a more acidic environment) due to an accumulation of hydrogen ions and inorganic phosphate, as well as a buildup of other metabolites in the muscle cells.
Post-Workout Soreness
Myth: lactic acid is why you get sore after a workout
Reality: micro-tears and inflammation cause soreness
DOMS (delayed onset muscle soreness) is the pain and stiffness you feel in your muscles for 1-3 days after a workout. Doing things like stretching, foam rolling, and getting a massage can help, but not because of anything that has to do with clearing out lactic acid.
The theory that lactic acid causes DOMS was debunked in the 1980s.
It’s now known to be micro-tears in the muscles that is responsible for delayed onset soreness.
Exercise works by causing micro damage/trauma to our muscles. When the muscles rebuild, they build back stronger! Recovery-focused modalities are great for bringing fresh blood to damaged muscles, improving the healing process and reducing muscle soreness.
Benefits of Training at High Workloads (Plus two Sample Workouts)
Here are two workouts (thanks to Dr. Stacy Sims) that will set your fitness on fire by delivering major benefits such as:
- Increased cardio efficiency (a stronger heart)
- Improved metabolic health (blood sugar and insulin control)
- Increased power and strength
- Stronger bones
- Preventing muscle loss
Workout 1: HIIT
5 sets of 45 seconds to 3 minutes at 85-90% of max heart rate, equal rest after each set.
(Ex. 1 minute “on” and 1 minute “off” for 5 rounds)
Workout 2: SIT
5 rounds of 20-30 seconds at 100% (max effort), with 2-3 minutes rest after each set.
For both workouts, choose an activity that allows you to safely hit the prescribed effort. Examples are running, biking, rowing, burpees, thrusters, etc. And remember, the key is to hit the correct level of intensity!
Conclusion
There’s no shortage of misinformation out there on the topic of fitness. I hope you enjoyed this nerdy deep dive into lactate and lactic acid!
Above all, the best thing we can do to add quality to the years we have left is to exercise. Specifically, high intensity exercise like heavy lifting and sprint intervals.
“Don’t get caught up in the numbers on the scale. Body composition is what counts, especially how much muscle you have.” -Dr. Stacy Sims
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The Best Way to Build Muscle