Lactic Acid – The Lie

I spent 2 years studying for an A level in PE, learning all about lactic acid and how it is detrimental to performance. I get to Uni, sit in my first physiology lecture and I find out that it is all a massive LIE!

Your body can prefer lactate as an energy source compared to glucose.


Attitudes towards lactic acid have changed drastically over the years:

2005: Argh, I hate the burn of lactic acid in my muscles after hard workouts!

2010: What’s that you say? Lactic acid doesn’t cause muscle soreness? And it’s actually “lactate,” not lactic acid, that accumulates during hard exercise?

2015: I love lactate so much. I wish I could figure out how to produce more of it.

George Brooks is the researcher responsible changing the perceptions of lactic acid. He summaries:

Overall use of lactate: You get about 1/3 of your total carbohydrate energy from lactate; the rest is from blood glucose and muscle glycogen.

Direct vs. indirect lactate oxidation: To use lactate as fuel for muscles, you can either “burn” it directly, or turn it into glucose and then burn it. In untrained subjects, about 75% of the lactate used is directly oxidized. In trained subjects, about 90% is directly oxidized. Trained subjects also burn significantly more lactate overall. This shows that endurance training stimulates adaptations to use more lactate, and to use it more efficiently — in fact, Brooks writes, “these findings suggest that in trained subjects, lactate is a preferred substrate over glucose.” Who’d have guessed that? If you train enough, you actually prefer lactate to sugar!

The consequence: the more lactate you’re able to use during exercise, the less muscle glycogen you have to use, which means your glycogen stores will last longer. Isn’t lactate wonderful?

So, to clarify, lactic acid doesn’t cause next day muscle soreness, in fact, the activities that are more likely to cause soreness are the activities less likely to produce lactate. Cooling down to flush lactate doesn’t solve soreness, it speeds up the movement of lactate out of the muscle but even if you didn’t cool down it would still leave your muscles within a couple of hours.


Also, blaming the “lactate threshold” on insufficient oxygen is confusing correlation with causation. The difference between aerobic and anaerobic energy sources isn’t just the presence or absence of oxygen — it’s also about how quickly the energy can be made available. Aerobic energy is slow, so when you’re working really hard you have to rely on anaerobic (and lactate-producing) energy. That would be true even if your muscle cells had an infinite supply of oxygen! So the lactate threshold does signal the transition to anaerobic energy sources, but not necessarily because of a shortage of oxygen.

So lactate is good, now go and spread the word!

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