by Evie Ullman, DPT
Many of you avid exercisers out there complain of muscle soreness post workout and blame it on lactic acid hanging around in the muscles. “I need a massage to clear out the lactic acid,” you may say. This is actually a myth. I will give you the scoop on lactic acid.
In a nutshell, we derive our energy from a molecule called Adenosine Triphosphate, aka ATP. Our bodies use three basic energy systems to replenish ATP and the use of them varies depending upon the intensity of exercise. The three systems are the Phosphagen system, the Oxidative system and Glycolysis. The Phosphagen system comes into play during short high intensity activity such as weight lifting and sprinting, but it is also active at the start of all exercise, regardless of intensity. The Oxidative system serves as a source of ATP when our bodies are at rest or performing lower intensity, long-term activity such as long distance jogging. Lastly, Glycolysis works during moderate to high intensity and medium to short duration of exercise. This is the only energy system that produces what was once thought of as lactic acid.
In reality, lactic acid cannot even really exist in the body because blood pH is too neutral, (around 7) and acids require very low pH. As soon as lactic is produced in the body, it dissociates into lactate and hydrogen. Really what we are talking about when we say “lactic acid” is lactate. So you should not use the words “lactic acid” and “muscles” in the same sentence!
Now, what exactly is lactate, and does it make our muscles sore? During Glycolysis, carbohydrates are broken down to resynthesize ATP- remember, that is the molecule we need for energy. In short, multiple chemical reactions occur in our muscle cells during Glycolysis and an eventual end product is pyruvate, which either goes through the Krebs Cycle, where oxygen is required to synthesize ATP, or it gets converted to lactate. It is true that lactate levels increase as our muscles fatigue and burn from exercise. But lactate is not the cause of this fatiguing, burning sensation during exercise, nor is there any evidence that it is the cause of Delayed Onset Muscle Soreness (DOMS) after exercise. In fact, lactate is shuttled out of the muscles to the liver, where it is in turn converted back into carbohydrate and reused as an energy source. Lactate is helpful to us! If the lactate is not needed, it is transported away in the blood and oxidized. You may wonder, would massage help the transport of lactate from the muscles? A study performed at Queen’s University in Kingston Ontario concluded that massage actually impeded blood flow to the muscles and lactate removal was impaired. Massage has benefits, but lactate clearance is not one of them.
So there you have it. Lactic acid disappears as soon as it is formed in the body, and it is not the cause of muscle soreness.
- Wiltshire EV, Poitras V, Pak M, Hong T, Rayner J, Tschakovsky ME. “Massage impairs postexercise muscle blood flow and “lactic acid” removal.” Med Sci Sports Exerc. 2010 Jun;42(6):1062-71.
- Baechle, Thomas R and Roger W. Earle. Essentials of Strength Training and Conditioning 3rd Ed. Chicago: Human Kinetics, 2008.
Dr. Ullman is a Physical Therapist at Boston Sports Medicine