If you want to make a physiologist wince, tell them how much "lactic acid" you felt in your muscles after a hard workout. "Lactic acid" has unfortunately been pinned as the culprit behind muscle fatigue and the limitation of endurance exercise performance. What is actually being talked about is lactic acid's conjugate base called lactate. Lactate is in fact one of your most valuable and trusted allies in improving endurance performance.
Common misconceptions about lactate are:
1. That it should be avoided during exercise
2. That it inhibits muscle contractions
3. That it's a waste byproduct
Far from being a waste-by-product that inhibits muscle contractions, it is in fact the exact opposite. It is a valuable fuel resource for our working muscles and brain. By consuming lactate, we conserve carbohydrates, our most scarce and valuable fuel source.
The Science of Lactate
Lactate 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. Since then, scientists have found that lactate acts as a buffer to increase the efficiency of anaerobic energy production (Brooks, G.A. (1985).
Muscles produce lactate continuously and it is generated during the breakdown of glucose as an energy source (Brooks, 2018). When an athlete is at an intensity lower than VT1, most of the lactate is broken down aerobically in the mitochondria. As we increase our effort beyond a resting state, energy production eventually increases to the point where the aerobic pathways don't have enough capacity to consume all of the lactate that is being created. This excess lactate ends up being sent to the bloodstream where it can be measured by a blood lactate meter as the first "uptick" in blood lactate concentration signaling that the athlete has traversed their LT1.
As exercise intensity continues to increase, so too does anaerobic muscle activation which creates even more lactate that our aerobic pathways can't absorb. This results in a runaway production of lactate that streams into the blood causing an inflection point in blood lactate concentration known as LT2.
Benefits of Producing More Lactate
George Brooks of the University of California-Berkeley has conducted numerous research studies 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 during 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 causes excess lactate to be produced, they are stimulating the muscle cell to produce more mitochondria which enhances the muscles' ability to efficiently burn fuel aerobically, including excess lactate. Research indicates that the highest lactate exposures take place in workouts consisting of three to five minutes at VO2max separated by two to three active recoveries of equal duration. An athlete’s VO2max velocity is approximately the fastest speed they can maintain for 10 minutes (Matt Fitzgerald, PodiumRunner, 2010).
When it comes to lactate in exercise and endurance performance, we should learn to love, and rely on our lactate. It is not a toxin that slows us down, it is a fuel that keeps us going and sends signals to our muscles to build back better and stronger so we can go further for longer in the future.
Cairns, S. P. (2006). Lactic acid and exercise performance. Sports Medicine, 36(4), 279–291.