Six Lies You Were Taught About Lactic Acid

Lactic acid is nasty stuff. Your muscles produce it during intense exercise. It’s a metabolic byproduct that makes no contribution to exercise performance. It causes muscle fatigue and post-exercise muscle soreness. No wonder the best endurance athletes don’t produce as much lactic acid.

Actually, none of the above statements is true. Recent research has demonstrated that lactic acid is not what we once though it was, in almost every way. Read on, and learn the truth behind the lies you’ve been told.

Lie 1: Muscles Produce Lactic Acid During Exercise

The muscles do not produce lactic acid during exercise. They produce a very similar compound called lactate. Whatever you call it, this substance is not produced as a waste product of anaerobic metabolism, as once believed. It’s actually an intermediate link between anaerobic and aerobic metabolism.

Lie 2: Lactic Acid Causes Muscle Fatigue

Most athletes believe that lactate (as we’ll call it from now on) causes muscle fatigue by making the muscles too acidic to contract effectively. This is not true. While the muscles do become more acidic during exercise, lactate is not the cause. In any case, far from hastening fatigue, lactate accumulation in the muscles actually delays fatigue by mitigating the effects of a phenomenon known as depolarization. During intense exercise, your muscles lose power in the same way a battery does: by becoming depolarized. The accumulation of lactate in muscle tissue during intense exercise partly counteracts the effect of depolarization.

Lie 3: Lactic Acid Causes Soreness

Lactate does not cause post-exercise muscle soreness. The simplest proof of this is the fact that very little lactate is produced during highly prolonged, low-intensity exercise, and yet it is this very type of exercise that leaves the muscles sorest in the following days. Post-exercise muscle soreness is actually caused by simple mechanical damage to muscle fibers, free radical damage, and inflammation.

Lie 4: Lactic Acid Does Not Contribute To Exercise Performance

Without lactate, you would not get fitter in response to training to the same degree you do with it. Lactate production during intense exercise stimulates a phenomenon called mitochondrial biogenesis after exercise. The mitochondria are little factories inside the muscle cells where aerobic metabolism occurs — that is, where oxygen is used to break down fats and glucose to yield energy. An increase in the concentration of mitochondria inside muscle cells is one of the major adaptations to training that improve endurance performance. And lactate makes it happen. This is one of the reasons high-intensity interval training is such a potent performance booster.

Lie 5: Muscles Do Not Use Lactic Acid For Fuel

Some athletes are aware that lactate produced during exercise can be “recycled” into glucose and used as fuel by the muscles, heart, and brain. But few are aware that lactate is also metabolized aerobically in the mitochondria as a direct fuel for muscle contractions. In fact, it has been estimated that roughly 75% of the lactate produced inside the muscle cells is used in this way, and only 25% leaks out into the bloodstream, where it can be measured through blood lactate testing.

Lie 6: Better Athletes Produce Less Lactic Acid

Some of the world’s best endurance athletes, such as Michael Phelps, appear to produce significantly less lactate during intense exercise than less successful athletes. This makes sense if you believe that lactate is a toxic waste product that causes fatigue and does not help exercise performance in any way. But it doesn’t makes sense in the light of current knowledge about the effects of lactic acid. And it’s also very unlikely to be true.

In all likelihood, the reason there is less lactate in the blood of the likes of Meb Keflezighi and Michael Phelps during intense exercise is not that their muscles produce less, but rather that they use more. If, in the average endurance athlete, 75 % of lactate is burned in the mitochondria and only 25% escapes into the bloodstream, in come very special athletes, perhaps 85% of lactate is burned and only 15% escapes.