That Exercise Burn Is Not Lactic, Here’s What It Really Is

The doc steps up to the plate to tell you all about lactic acid and why you're wrong.


Dr. Mike Posthumus |

I’m on the edge of my seat, watching the thrilling stage 17 of the 2018 Tour de France. The organisers have shortened this day of the race, to try and spice up the action; the start was a let-down, but now – up the final climb, the Col de Portet – the excitement is rising as the battle for overall GC really starts heating up. Nairo Quintana, Geraint Thomas, Tom Doumalin, Primoz Roglic and Chris Froome are all there, exchanging blows.

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But unlike in boxing, the pain is delivered through very hard surges or short sprint-like efforts – while they’re going as hard as they can, up a climb that takes the top riders in the world around an hour to summit.

My opinion? That hurts as much (if not more) than a punch from Tyson.

The commentary is just a dull white noise in the background as I focus fully on the race. The pain on each rider’s face is evident as he pushes himself. As a cyclist, I know this pain all too well.

Suddenly the white noise clears, as a phrase jumps out that sends shivers down my spine: “Lactic Acid”. Now, let me explain my reaction…

If I could dispel only one myth relating to exercise physiology, it would be this villain – “Lactic Acid”.

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It’s become a very convenient explanation for that burning sensation you may feel while going hard, in the gym or on the sports field. How often have you heard, “I can feel the lactic acid burn”, or “I can feel the acid building up in my muscles”?

And yet us scientists can’t seem to get the news out there: there is No. Such. Thing.

Firstly, your muscles don’t produce lactic acid. In fact, those little energy factories in your muscle cells (the mitochondria) produce lactate, a very useful fuel source – and through a process that actually decreases the acidity in your muscles.

Yes, that’s right. Lactate increases your pH – the exact opposite to what an acid would do!

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would do! So while the Tour de France GC contenders are battling it out up Col de Portet, they’re producing very high levels of lactate; but this is just their muscles’ mechanism for trying to create even more energy.

Because your little energy factories are highly intelligent – they know that a build-up of lactate will block their energy production chain. So they pump the lactate into your bloodstream, so that it can be transported to other muscles, where it’s used as fuel. (Interestingly, lactate is your heart’s primary fuel source.)

It’s common knowledge that when your exercise intensity increases past a moderate level, lactate starts appearing in your blood supply. So it’s all too easy to blame the appearance of lactate on increased exertion.

However, these two phenomena – lactate appearance, and increased exertion and fatigue – are not directly linked. The sad truth is, this is not news; scientists have known it for more than 50 years. Clearly (and unfortunately) it takes decades for misconceptions to be dispelled.

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So please: spread the word, and help us dispel this myth once and for all. And next time you “feel the burn”, remember: it’s not the lactic acid!

*Dr. Mike Posthumus has a PhD in exercise science, is head of the high-performance division at SSISA, the co-owner of Science to Sport, and an elite MTB rider and cycling coach.

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