Have you ever felt a burning sensation in your muscles after an intense sprint, or maybe peddling up a hill on a bicycle?
The common belief is that this burning sensation is caused by lactic acid build up in our muscles, which eventually forces us to stop exercising.
But does lactic acid really cause muscle burn?
The answer is a resounding “No”, it doesn’t. In fact, lactic acid build up helps reduce the burn.
While this article is a bit technical, it will help you understand the true dynamics of why you feel muscle burn during exercise and what lactic acid really is.
How Lactic Acid Build Up Works
Your body needs energy to function and glucose is its primary fuel source during exercise. Under a process called glycolysis, your body breaks down the glucose into a substance called pyruvate.
Then, within the cell, the pyruvate can be converted into (1) water and carbon dioxide through the Krebs cycle (a series of chemical reactions that occur using pyruvate to generate energy) and (2) oxidative phosphorylation (process for the creation of ATP – adenosine triphosphate – that cells use for energy). This requires oxygen.
So, during times when there is not enough oxygen, such as when you are exercising intensely, the cell cannot keep up production of ATP to meet its energy demands, leading to increased glucose break down into pyruvate, Now the pyruvate, instead of going through the Krebs cycle, is converted to lactate.
Even when there is adequate oxygen, in some cells, lactate is still made continuously. Note that lactate is created and not lactic acid.
While lactate is actually the salt of lactic acid, there is a big difference in what they do.1
Lactate, as the salt, is missing a hydrogen ion or proton. Therefore, their properties inside the cell differ. A measurement of the amount of the protons tells you how acidic something is. Lactate, not having any protons, is not acidic. Lactate, because it is not acidic, is NOT the cause of the burning sensation in your muscles.
OK, Then What Causes Muscle Burn?
If neither lactate, nor lactic acid causes muscle burn, then what does?
Remember ATP, that substance used as an energy source by your cells? During exercise, your body uses large quantities of ATP to meet your muscle cells’ high energy demand. When you use this ATP, it produces a proton.
And what happens when protons are produced? The area becomes more acidic. As the protons increase in number they come into contact with nerves near the muscles, creating the sensation known as muscle burn. As you continue to work your muscles, you use more ATP, producing protons and increasing the acid in the muscles.
None of this involves lactate or lactic acid.
Lactic Acid Build Up Reduces Muscle Burn
It might be hard to believe, with the bad rep given to lactic acid & lactate over the years, but they’re actually beneficial.2 Lactate in the cell can act as a buffer by reducing the cell’s acidity.
But the most benefit comes when lactate leaves the cell. At this point, it can either enter other cells, like your heart cells, to generate energy for them. Or, it can undergo the Cori cycle, where it is taken from the muscles and brought to the liver to be turned back into glucose and recycled.
Lactic acid is not your enemy, but a perfect fuel source for your muscles. Helping to reduce the acidity that comes from exercising, it is also used as a vast energy source for muscles to work on endurance.
So, next time you exercise, you can thank lactic acid for keeping your muscles moving!
Well what causes the burn and how can we reduce the ache? It is nice to know that lactic acid build up is a myth but what are the protons attached to? Most important is what can we do to minimize muscualr discomfort after a tough workout?
ATP usage is the cause muscle burn. As ATP is being used up, acid is being produced in the muscles. In order to reduce muscular comfort after a tough workout, good nutrition and hydration is key as they are what your muscles use to repair, grow, and function properly. Techniques such as foam rolling, epsom salt baths, and icing can be effective after a workout. Note that the eccentric portion of an exercise or movement (lowering the bar on the benchpress, going down during a squat, walking down a flight of stairs) causes the most soreness so reducing that part of the exercise can lead to less soreness. While muscle soreness and discomfort can be irritating, they are a natural part of exercising.
@Hank – Great question. Peter gave you a solid answer. I have a monster muscle soreness post coming up soon that’s 2000 words long, so it should answer any and all questions you have about muscle soreness and how to reduce it.
Very Interesting, thanks Marc.
These are the type of articles that I enjoy. Do you think you could do a scientific breakdown of how fat loss really occurs?
@Nick – we are working on researching that article as I write this comment! In fact, my man Peter who wrote this article is working on the research. It’s a major challenge to simplify fat loss in a way that can make sense for someone without a PHD in biochemistry, or into an article less than 1000 words, but we are trying our best to be scientifically accurate while keeping the information relevant and useful like usual. Very happy you liked the article.
My knowledge is limited when it comes to helping with the ache, but warm-downs and post training active and passive recovery (depending on the excercise) will help prevent you from getting the burning sensation in the first place.
Thanks for the amazing website Marc, since I signed up for your emails I’ve lost about 8kg of fat and gained about the same in muscle mass!
You’ve also inspired me to change the field I wish to study when I finally finish my last year of high school to sports science or something similar!
@Branden – That’s huge news! Super happy to hear that! If you have any before/after photos to share, shoot them over to support (at) builtlean.com. They will remain confidential unless you indicate otherwise.
So lactic acid turns out to be a good sound term. I honestly don’t know how to reduce the paint after a good workout for the next couple or few days. I try to intake as much protein as i can from meats to recover that broken muscle tissue bigger or again, Isnt that the reason why we feel sore, because we want muscle growth. i currently maintaining so i keep my reps high and low weights but still getting that good sore feeling the next day. if you feel it on your butt that means that leg press and squads are good.
very interresting study…i remember my ISSA fitness course .i always admire your articles..
great trainer mark..god bless you..john aouad,cft,beirut,lebanon
Thanks, John. Have to hand it to Peter for digging deep and writing a great article.
Hi Marc, this article on muscle burn is extremel
Hi Marc, this article is extremely informative. It has just ignited a thought process in my mind and maybe you can do some further research. Just to inform you, I am a pharmaceutical sales rep and my company launched a Coenzyme Q10 supplement, a couple of years ago. Not to get too technical, but CoQ10, is an electron carrier that sits in the mitochondria, and its key function is to convert ADP to ATP. This is our main source of energy. My company’s main target group was for patients who experience muscle cramps on cholesterol lowering medications. This is due to the fact that certain cholesterol lowering agents significantly lower the levels of CoQ10, and hence pts experience muscle cramps or muscle burn. However, there is a million benefits of CoQ 10, even in healthy individuals, and I have personally been taking CoQ 10 as a general supplement. Its uses range from reducing fatigue to having ani ageing properties. In my case, it definitley made a significant impact in reducing muscle burn and aiding in musle recovery. Two key points; the dose must be over 100mg a day and most CoQ 10 supplements on the pharmacy shelves are TOO SMALL a dose, so please be aware of this, and secondly, it takes 4 to 6 weeks to see results, and has to be a long term daily part of one’s supplementation routine. You may want to look further into this. Hope it helps all my fellow Builtlean brothers and sisters. I didn’t mention my company brand here for ethical reasons, but if required, I’m quite happy to supply you the info.
Is there no need to refer doctor to use CoQ10?
We recommend consulting with your primary care physician before taking any new supplements to ensure that those supplements are appropriate and safe for you. That includes supplements you could find at your local pharmacy or grocery store.
-Kristin Rooke, BuiltLean Coach & Managing Editor
I have muscle burn & chills with ANY exertion because of my Myalgic Encephylolimitis. Any suggestions? I use to be a HUGE exerciser!
I would highly recommend speaking with your primary care physician or a physical therapist to determine the best exercise approach for you. Myalgic encephalomyelitis (also known as chronic fatigue syndrome), is characterized by profound fatigue, pain, sleep abnormalities, and other symptoms, and is aggravated by exertion. A physician or physical therapist (especially one that specializes in chronic fatigue syndrome) will be the best resource to help you be active while mitigating the symptoms you experience.
Good luck! And if you ever need more advice, feel free to contact us at [email protected].
-Kristin, BuiltLean Coach & Managing Editor
Do you have any resources on the effect asthma would have on this process?
That’s a good question, ‘m not aware of any offhand, if you find them, please leave a comment and let us know.