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Knowing power and heart rate levels at lactate threshold may help train and race effectively, and knowing how the body uses lactate may be an incentive to train with a bit more intention.

Pedaling into the wind at the ACA state time trial, my legs were starting to feel that slow burn. I looked down at my power meter and I was over my lactate threshold. I backed it off 10 watts, and within a minute the burning disappeared and my speed increased. I mentally took note to pace a bit more conservatively, and continued on. Later in the time trial, as I began to suffer a bit more, I kept it dialed to the wattage I knew I could produce and hold, and tried to ignore the fatigue creeping into various parts of my body.

Lactate is produced in our muscles at low exercise intensities, and at much higher ones. In fact, it’s present in the body at rest. Lactate is created during the breakdown of glucose (glycolysis) which is one chemical process that helps our body create energy. Pyruvic acid is produced through this process, and as it accumulates, it is converted to lactate. Under moderate-to-high exercise intensities (tempo, for instance) lactate is converted back to pyruvic acid and re-used for energy production.

In terms of improving the use and re-use of lactate in our muscles, lactate threshold (LT) intervals encourage fast-twitch muscles to produce an enzyme (MCT-1) which is important to transport lactate into muscle cells where it is converted into pyruvic acid for further exercise. The more MCT-1 you have, the greater the rate of lactate conversion and the greater the muscle endurance. LT intervals also increase the number of mitochondria (cellular energy power plants) and capillaries (blood highways).

Despite their benefits, LT intervals have earned a bad reputation due to the discomfort associated with the efforts that are required to produce more energy. Actually, lactate doesn’t cause the discomfort. If it did, my fingers would be in pain from typing (one might say I type at a “painfully” slow rate, but I digress…). Lactic acid is formed from pyruvic acid as a result of insufficient oxygen at the muscle cells during high rates of exercise. It then converts back into lactate once in the blood stream, in the presence of more oxygen. Once the lactic acid is converted back to lactate, the lactate in turn is converted and re-used as pyruvic acid. Lactic acid, however, may cause loss of muscle power and pain in the working muscles if it builds-up past the point that the muscles can clear it into the blood stream for conversion back to Lactate. The latest (but unproven) theory on this is that the changed pH from accumulated and un-cleared lactic acid causes the discomfort and slows muscle contractions.

So, what about that NY Times (NYT) article that people have been calling and e-mailing about? On May 16th the NYT ran an article titled “Lactic Acid is not Muscles’ Foe, it’s Fuel”. As I illustrated above, it’s lactate that is the fuel, and lactic acid that is a by-product. Neither is a waste product, as we may have come to believe. Both are essential for producing the results that you want, both during exertion and for recovery. In fact, fifty-percent of the lactate produced during a moderate-to-high level workout is used for replenishing muscle glycogen stores during recovery. (In this case, I’m talking about lying on the couch eating chips, and I’m referring to recovery from higher intensity workloads). When lactate is released into the blood stream, the liver uses it to produce glucose and glycogen, which are then used by the working muscles.

What is the big deal about testing then? If lactate is a fuel then why care how much is in the bloodstream at any given time? The value of a test is to discover at what workload (watts and/or heart rate) your body is accumulating lactate to the extent that glycolysis is proceeding with less oxygen and muscle action becomes inhibited. By identifying this level, one can target training zones specifically to facilitate the muscle adaptations (more MCT-1, mitochodria and capillaries) that are required to produce more energy at this level. LT testing doesn’t predict performance, but if the LT test protocol includes a section where the rate of lactate clearing is determined, then one can also adjust training to maximize clearing as well as power production at higher levels.

The bottom line is that lactate is a product of carbohydrate metabolism during exercise, and is valuable part of the body’s energy production. Rather than dreading the “burn”, know that your muscles are working hard to produce power, and that you are benefiting your recovery as well. One final note, as lactate is processed rather quickly, it doesn’t cause that lingering soreness several days later. More on that in a future article.

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Jonathan Siegel, Director of Coaching
JDS Sportcoaching, LLC

Jonathan Siegel, CSCS is an USA Cycling certified expert coach. His finest moment of coachability came after flailing in deep powder. If you have a comment about this article or a training question, send an email or call 303.744.2766.