Lactic Acid's Role in Post-Workout Fatigue

It is like rain on your parade when that initial post-workout feeling of euphoria transitions into fatigue. It is even discouraging when your main goal of exercising is to increase your energy but instead you have crashed. How do you make sense of this lethargy? Popular theory points to lactic acid, scientifically named Sarcolactic Acid: a waste product that builds up in muscles during intense "anaerobic" workouts at a higher rate than the ability to metabolize or remove it. While lactic acid is labeled "acid of fatigue", recent studies insist that lactic acid is a factor but not a cause of muscle fatigue. With this in mind, let us explore the role of lactic acid in post-workout fatigue and ways to reduce lactic acid build up.

Role of Lactic Acid in Post-Workout Fatigue

The basic concept is that lactic acid increases with the intensity of a workout. Unlike moderate aerobic workouts (walking, running, cycling...) that use oxygen to metabolize stored fat into energy, high intensity workouts (sprinting), where oxygen runs low, use glycogen for energy. This occurs during anaerobic metabolism (glycosis) that releases the by-product lactic acid. According to Mayo Clinic, you are more likely to experience post-workout fatigue when you have a low lactate (anaerobic) threshold wherein too much lactic acid is released in your skeletal muscles when they are using oxygen and metabolizing glucose.

Ways to Reduce Lactic Acid Build Up

How can we increase our lactate threshold to reduce lactic acid build up? One recommendation by Chem-Online.org, which I can vouch for due to personal workout success, is to train well by means of stretching, interval training, endurance training, and cool-downs. Interval training involves alternating high bursts of intensity "turbo" exercises with low intensity exercises or rest. An example is sprinting short distances followed by jogging and walking. Endurance training is aerobic activity that increases stamina and decreases heart rate meaning that fewer beats per minute are needed to transport a fixed amount of blood. All of this training increases the metabolism of lactic acid. Further, lactic acid build up can be minimized by performing cool-downs: light, repetitive movements that gradually slow your breathing after an intense workout.

Another way to reduce lactic acid build up and fatigue after exercising is through nutrition. In her book, Foods & Nutrition Encyclopedia, Volume 1, Audrey H. Ensminger mentions that some trainers encourage their athletes to consume lactic acid based foods such as yogurt and buttermilk or to take lactic acid salts (lactates). Proper hydration and vitamins such as Vitamin D, Magnesium, and Thiamin (B1) are also known to combat lactic acid build up. In fact, a study by the Institute of Health Sport Sciences at the University of Tsukuba, Japan where 16 male athletes were given either Thiamin supplementation or a placebo revealed that Thiamin reduces exercise-induced fatigue.

In spite of the debate over whether lactic acid is directly responsible for post-workout fatigue, we can say that it is plays a key role. Noting that a higher lactate threshold means a lower release of lactic acid, we can take a variety of steps to increase our threshold. This includes training properly, staying hydrated, and getting essential vitamins through supplementation or better yet through wholesome foods.

Sources

Ensminger, A.H. "Athletics & Nutrition."Foods & Nutrition Encyclopedia, Volume 1- Google Books.

"Lactic Acid: CHEM-ONLINE.org."Chem-Online.org.

Reyes, A. "Mayo Clinic-Mayo Clinic on the Summer Olympic Games."Mayo Clinic.

Suzuki, M., Itokawa, Y. "Effects of Thiamine Supplementation on Exercise in...[Metab Brain Dis. 1996] - PubMed Result."NationalCenter for Biotechnology Information, U.S. National Library of Medicine.

Westerblad, H. "Muscle Fatigue: Lactic Acid or Inorganic Phosphate the Major Cause?"
American Physiological Society.