When you’re fit, your body actually prefers lactate to glucose as a fuel.

Seen on RunnersWorld and written By Alex Hutchinson

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.

It’s funny how attitudes change — but reassuring that new ideas (gradually) gain acceptance when they’re supported by good data. Certainly attitudes about lactate haven’t changed overnight, but I think the idea that it’s not an enemy is slowly taking over. The next step is to realize how important it is as a fuel during hard exercise. One of the challenges there is that the process is quite complex, so it’s hard to get an intuitive feel for it (for me, at least).

Anyway, there’s a new study from George Brooks — the researcher most responsible for “rehabilitating” lactate that has a few interesting details about how training ramps up the use of lactate as a fuel.

– 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?