Nathan Swan, DPT
Lactic acid has been a term thrown about in exercise circles for many years now. You can probably remember a coach or gym teacher use the term lactic acid all the time. For instance, “You need to get moving and work out the lactic acid in your muscle,” as if your muscles are coated in something like battery acid after you exercise. It all sounds believable and it sure would explain why those muscles are so sore after heavy exercise.
However, lactic acid does not really have anything to do with why you are so sore. It is a myth that goes way back to an experiment on frogs in the 1920’s. It was misunderstood by scientists for decades, which has resulted in a deep seated misunderstanding in the exercise community. Let’s put this topic “under further review” and settle the score on lactic acid.
After high intensity exercise such as a 200 meter dash or a series of intense plays in football, your muscles do become acidic, which contributes to fatigue, but the acidity is not because of lactic acid production. The acidity is produced from the body’s attempt to keep adequate levels of oxygen in your muscles to continue to work out at that high intensity. The production of H+ (a positive hydrogen ion), which causes acidity, is usually balanced by other reactions in your muscles. In the case of high intensity exercise, those other reactions can’t keep up with the production of H+ and your muscles lose their pH balance and become acidic. The acidity then contributes to the burning and fatigue you feel in your muscles, and is one of the reasons you feel out of breath. After five minutes of catching your breath and resting, the acidity levels normalize. Muscle acidity may contribute to fatigue, but it does not cause soreness, and it is not cause by lactic acid.
Lactic acid, or more correctly termed lactate, is a byproduct of one form of energy system in your muscles, namely glycolysis. Lactate accumulation in muscle peaks when you try to do a high intensity exercise for a long period, which is about the same time your acid levels are getting high. This is one reason researches blamed lactate for the acidity. However, lactate production actually decreases muscle acidity.1 Therefore, lactate correlates to the acid levels but does not cause them. This is a case of being in the wrong place at the wrong time.
So we now know the production of lactate actually does not cause acidity or fatigue but what about the leftover lactate? That shouldn’t be sitting around in muscle. Right? Lactate is actually a good thing. Your body can recycle this byproduct and use it in the production of more energy. It is actually very important for your body. Some energy drinks even contain lactate. So in reality neither the production nor lactate itself contributes to your fatigue and soreness. In fact, you would be more tired and sore without it. It is estimated you would only be able to sustain about 10-15 seconds of high intensity exercise without the production of lactate.2
So why am I sore after I exercise? Most researchers agree that post-exercise soreness is due to the micro-trauma your muscles sustain during your heavy work-out routine. Basically, you are creating little injuries to your muscle fibers when you exercise. Your body responds by remodeling the muscle tissue, and you get stronger as a result.
For me, this makes being sore after a good work-out so much more enjoyable instead of worrisome. With this knowledge, you can be encouraged your body is healing itself and actually getting stronger. It also displays the importance of exercise recovery in the 24-48 hours following a heavy work-out. Recovering quickly and effectively allows you to maximize the benefits of exercise. Without adequate recovery, you may produce more damage than your body can handle, as is the case with repetitive injury and participating in multiple sports practices on the same day in consecutive days. Make sure you have adequate time to heal and recover, and be thankful for the lactate in your muscles that allows you to push yourself harder and improve your endurance during high intensity exercise to improve your overall performance.
1. Robergs, Robert A. Farzenah, Ghiasvand, and Daryl Parker. "Biochemistry of exerciseinduced metabolic acidosis." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 287.3 (2004): R502-R516.
2. Baker, Julien S., Marie Clare McCormick, and Robert A. Robergs. "Interaction among skeletal muscle metabolic energy systems during intense exercise." Journal of nutrition and metabolism 2010 (2010).