Debunking the Lactic Acid Myth

Cyclists on road, single file, pine trees in background

Athletes often refer to lactic acid when talking about the side effects of a hard and strenuous workout. Lactic acid has played an essential role in the traditional theory of muscle fatigue and the limitation of endurance exercise performance. It has been referred to as a waste by-product of anaerobic metabolism and was believed to be responsible for muscle soreness, the burn felt during exercise, or a buildup in the muscles that causes an athlete to have to slow down.  Lactic acid cannot be found in muscles or blood but is actually found in fermented foods like cheese and dairy. The body produces lactate which is an intermediate link between anaerobic and aerobic muscle metabolism and instead of a toxin, it is actually beneficial.

The Science of Lactate

Lactate or, as it was habitually known, 'lactic acid' was one of the first molecules to attract the notice of early exercise scientists.  At that time, scientists found that blood lactate concentration could be measured and was shown to increase with increasing exercise intensity (Cairns, 2006).  Since then, scientists have found that lactate acts as a buffer.  Muscles produce lactate continuously and it is generated during the breakdown of glucose as an energy source (Brooks, 2018). When an athlete is at rest or moving slowly, most of the lactate is further broken down to pyruvate and goes into aerobic energy pathways in the mitochondria. When an athlete moves faster and needs to produce energy quickly to keep up with loads, the aerobic pathways are too slow, and more energy is generated anaerobically, producing lactate.  At high levels of intense exercise glycogen or glucose is broken down to lactate without oxygen, and then lactate is broken down to carbon dioxide and water with oxygen.

Benefits of Producing More Lactate

George Brooks of the University of California-Berkeley has conducted numerous research products regarding the production of lactate in the body (Brooks, 2018).  In his later research, he specifically looked at the role of lactate in cell signaling. He found that intense exercise high levels of intracellular lactate stimulate some of the positive fitness adaptations that occur in reaction to such training (Brooks, 2018).  Notably, high concentrations of lactate trigger the production of free radicals in genes that are associated with mitochondrial biogenesis (Brooks, 2018).  When an athlete works at high intensities and accumulates intracellular lactate, he or she stimulates the muscle cell to produce more mitochondria which enhances the body to burn lactate and other fuel more efficiently in the future. Research indicates that the highest lactate exposures take place in workouts consisting of three to five at VO2max velocity separated by two to three active recoveries. An athlete’s VO2max velocity is approximately the fastest speed he or she can maintain for 10 minutes.

When it comes to exercise, lactic acid should no longer be cited as a viable reason for muscle soreness, the burn felt during exercise or a buildup in the muscles that causes an athlete to have to slow down.  Athletes should instead work towards incorporating high-intensity workouts in their training regime to aid in triggering performance-boosting muscle adaptations.


Brooks, G. A. (2018). The science and translation of lactate shuttle theory. Science Direct, 27(4), 757-785.

Cairns, S. P. (2006). Lactic acid and exercise performance. Sports Medicine, 36(4), 279–291.

Kristen Hench

Kristen Hench, Ph.D., is a certified coach through USAT, USAT Para, ACE, USAC, ASCA, ASFA Yoga certified, and is a RRCA certified race director. She has trained beginner through elite athletes helping many to reach podium finishes as well as meet their personal goals in triathlon, running, track, and swimming. Kristen coaches adaptive sports with the USAF AFW2 program as a cycling coach and also works with a variety of able-body and parasport athletes through TRIMotion3. She enjoys helping children and youth get healthy, learn new life-long skills, and build confidence. She has coached internationally and was selected to coach in the 2018 and 2020 Invictus games. Kristen has also directed numerous family races and competed in several triathlons herself, including the Ironman distance events. She placed in the top three for her age group in the inaugural year of the Mountaineer Half Ironman and was one of the top swimmers in the 2004 Lake Placid Ironman. Besides triathlons, Kristen also enjoys marathons (with a PR of 3:15), triathlon, swimming, and a multitude of boot camp activities.