This originally appeared on February 21st, 2012 at NikeRunning.com.

“Lactate is not a dead-end metabolite.”

Those were the words my undergraduate exercise physiology professor loved to share during our discussion of the anaerobic metabolism. He rarely used the term “lactic acid” but rather referred to “lactate.” You should too. Your muscles don’t produce “lactic acid” but rather, they produce a compound called “lactate” in response to intense exercise, exercise where the energetic need in the working muscle is higher than can be produced by aerobic metabolism alone. But the cool thing about lactate is that your body can use it as a fuel source. Another professor of mine used remind us that “the heart loves lactate” as an energy source (just as the muscles love using stored glycogen). And what you’re probably thinking is, “Wait – I thought the muscle soreness I feel after a hard workout is from the lactic acid?” Nope. The soreness is primarily due to a mechanical breakage at the cellular level of the muscle. You end a track workout with a certain percentage of your muscle cells literally broken (and you’ll need some recovery time to allow them to repair…which they will).

So why all of this exercise physiology? Simple. I want you to embrace lactate, and workouts that introduce lactate, as part of the path to becoming a better runner. I love to assign athletes fartlek workouts where the “on” portion is run faster than threshold pace. Running faster than threshold pace will bump up the amount of lactate in the system. This is followed by running the “off” portion slower than threshold pace (still at a steady pace), allowing the body to deal with the lactate and make a physiological adaptation. The bottom line is that you can teach your body to become better at dealing with lactate and this efficiency helps runners from 800m runners to marathon runners.