This is the first installment of Physiology of Cycling where I explain the inner workings of the body and how it relates to cycling training and performance. This article will explain what lactate is, ways we can test it, and how we can use that information to create precise workouts to target specific metabolic systems in the body.
What Is Lactate?
Lactate is a product of anaerobic respiration, therefore is created mostly during high intensity exercises. Above a critical point (often referred to as lactate turnpoint, lactate threshold, or by extension FTP), respiration begins to switch from mainly aerobic to anaerobic respiration. If we go back to high school biology we may remember that anaerobic respiration is done with the absence of oxygen, starting with glycolysis converting glucose to pyruvate, and then into lactic acid through fermentation. This lactic acid is then reduced into lactate and a hydrogen ion. It is this reduction and liberation of hydrogen ions that is responsible for the decrease of blood PH during exercise, as well as cellular damage that occurs from oxidative stress. Lactate is produced at all times in the body, however, as resting blood lactate values can range anywhere from 0.5 to 2.0 mmol. This non-zero value indicates that anaerobic respiration occurs at all times throughout the body, even at rest.
Lactate is not only a metabolic byproduct, but is also used as a fuel source. Just like anaerobic respiration turns glucose into pyruvate, then eventually lactate, the liver can reverse this process. Hepatic gluconeogenesis is what this process is called; hepatic meaning in the liver, gluco- meaning pertaining to glucose, and -neogenesis meaning creation of, so this is the creation of new glucose in the liver. This cycle of anaerobic respiration creating lactate from glucose, followed by hepatic gluconeogenesis is referred to as the Cori cycle, and it is a way the body is able to recycle waste products to create new fuel when that fuel is limited.
Lactate During Exercise
Many endurance athletes seek tests to determine their individual lactate turnpoint, and it can be reliably measured using graded exercise tests (often referred to as ramp tests in the cycling community) where the athlete performs exercise at a specific intensity for a specific amount of time, before the intensity is increased by a known amount. These steps will continue until the athlete reaches exhaustion, or they reach a specific physiological marker depending on the type of test. While performing this test, the athlete will either have their blood sampled at regular intervals to directly measure the blood lactate concentration, or the athlete will wear a mask/ mouthpiece so gas exchange can be measured (Usually referred to as a VO2 Max test). These two tests measure completely different things, but will give nearly identical results due to them both measuring products of the same process: anaerobic respiration.
blood lactate does begin to rise, we can determine the point at which anaerobic respiration begins in measurable and significant amounts (Lactate Threshold 1), and additionally when lactate values begins to increase more significantly still,
usually at an exponential rate, we can conclude this is the point where anaerobic respiration begins to take over compared to aerobic respiration (Lactate Threshold 2). Recall back to when I stated that as lactate is being produced, the blood becomes more acidic, we know that there is a proportional relationship between lactate produced and hydrogen ions in the blood, so therefore we know there is a relationship between the amount of anaerobic respiration that occurs in the cells and the PH of the blood. The body attempts to lower this PH through a process called the bicarbonate buffer system, and this system increases the amount of CO2 we breathe out. Therefore, we can correlate a sharp increase in expired co2 with that same point at which anaerobic respiration begins to take over. Additionally, breathing rate will increase at this same point in order to help expel the additional CO2 being produced.
Why Is The Second Threshold Important?
We have discussed what the second threshold is and why it occurs, but why is this important for increasing athletic performance? First, this is a physiological marker that we can base training zones and intensities around more objectively than simply stating an RPE, or percent of max heart rate, etc. The second threshold represents the point at which anaerobic respiration begins to take over the primary energy production, so we know that anything above it will be overwhelmingly anaerobic and the opposite for intensities below. Physiology is a complicated subject and no two people are likely to be the same. For example, two athletes may have the same VO2 max, so they have the same theoretical maximum aerobic fitness. However, athlete 1 may have his lactate turnpoint at 78% of their VO2 max, but athlete 2 might have his at 86%. Despite both athletes having the same theoretical max, athlete 1 will be able to produce a higher power output before anaerobic respiration takes over and he is unable to continue. This difference is precisely why it is important to determine this turning point and base threshold style work with it. If both athletes didn't know where their lactate turn point was, but both were asked to perform a 20 minute effort at 80% of their VO2 max, athlete 1 may have a perfect interval, but struggle; conversely athlete 2 may feel as if this intensity is too easy and his training is not as effective as it could be. By using the second threshold as an anchor point, we can more precisely prescribe exercise intensities to more effectively stress whichever energy system we are trying to improve. With this level of precision it is possible to prescribe workouts with the explicit goal to either increase the body’s ability to cope with high levels of blood lactate through an increase the effectiveness of the bicarbonate buffering system, or increase the body’s ability to turn that lactate back into fuel and increase the efficiency of the Cori cycle.
How to Use It
Two sports physiologists, Dr. Andrew Coggan and Hunter Allen are responsible for the term “Functional Threshold Power” which has become ubiquitous in the cycling training space, and for good reason. They were the first people to devise a relatively quick, simple, and cheap test to approximate this second threshold in a way that can be done in the field, or in a lab. Due to this simplicity, it has become the gold standard for approximating a cyclist's second threshold, but similarly with comparing two different athlete’s VO2 maxes is not necessarily indicative of either’s ability to perform, neither is FTP. Trying to condense the human body’s vast array of physiological processes into one single number will always result in inaccuracies especially as you begin to stray further from that set point. For this reason, FTP, nor the second threshold should be what you base all of your training off of, simply because it is extrapolating the performance of one specific physiological process across the entire width of usable training intensities, including ones that rely on other physiological processes. For example, two athletes may have the same FTP based on the 20 minute protocol, however the processes that occur that lead to that result may be vastly different. One athlete may be able to function at a much higher blood lactate level, and the other may be better at reutilizing that lactate. Although they will both have the same FTP, the first athlete may be able to produce higher powers slightly above the lactate threshold as he can function at higher peak values. However the second athlete may be able to hold his FTP for much longer than an hour as he is able to reutilize that lactate and keep his blood PH lower, in a more optimal range for steady state exercise.
These shortcomings are in no way a reason not to use the 20 minute protocol to approximate the second threshold, as it is still the cheapest, simplest, and most accessible way to determine it. Taking a blood lactate or gas exchange test will certainly be more precise and allow your training zones to be more precise, but is the added cost and complexity worth it? An additional shortcoming with both of these protocols is that it produces a static value to base all future training off of. Physiology is inherently volatile and constantly changing, so one day your actual measured second threshold may be different than the next just simply based on how biological processes occur. For this reason, I think you should look at your thresholds as “zones”. Don’t consume yourself with adding a watt or 2 here and there or even losing a watt or two here and there, the physiology is constantly changing and adapting. Are you planning on doing a workout that says, for example, perform a 20 minute interval “at threshold” or at 100% FTP? It is entirely possible that the day you performed your FTP test, your measured lactate threshold is equal to your actual lactate threshold. However, it is equally as likely that your measured lactate threshold on that day does not equal what your lactate threshold is a week later on the workout you intend to hold 100%. For that reason, allowing yourself soft ranges is incredibly beneficial to help with workout adherence and future, long term adaptations. I believe it is much more beneficial to perform your given workout a percent or two lower than planned, rather than being unable to complete the workout and 1, working above the intensity you were supposed to be working in so you aren’t stressing the correct systems, and 2, your total workload is lower since you cut the interval short which may not allow for optimal adaptations.
On a similar note, since these thresholds are constantly changing from training adaptations, nutrition, stresses, etc, I think it is important to test these relatively often. “Training is testing and testing is training” is a good motto to live by. This will keep your training zones and intensities as accurate as possible, while simultaneously confirming training adaptations or lack thereof. Tim Cusik of Trainingpeaks recommends testing the normalized residual, or in other words, whatever your weakness is. If you have a power meter and lots of historical data, this is easy to determine, as it will be the time durations where your actual recorded personal best power is lower than what the power-duration curve model predicts you can do. I like this approach as it gives some variety to training, and allows athletes different goals to strive for throughout a training block or season. Performing lab tests regularly would obviously be the most precise method, but you may begin reaching diminishing returns as far as cost to benefit goes. It is almost certainly the best method if you strive for absolute accuracy and precision, but remember that accuracy and precision becomes meaningless as adaptations begin to occur and day by day life stresses change the way your body functions on a cellular level. There is merit in a middle ground, with possibly annual or bi-annual formal lab testing, with the remainder of the year including less structured, less formal testing and possibly the occasional 20 minute protocol to re-confirm.
As training becomes more and more precise, and athletes are becoming more fit, they are looking for ways to increase their day-of performances and hopefully create larger long-term adaptations. We know that the bicarbonate buffering system is responsible for lowering blood PH, so it would be logical to assume having more bicarbonate to buffer this PH could allow us better performance. Scientific literature in this space is non-conclusive with many conflicting results. A 2021 study on 12 high level swimmers showed a very high variety in blood bicarbonate concentration after oral ingestion, some of which saw almost no change and some significant changes (Newbury et al., 2021). This would indicate that the ability to administer the buffering agent into the blood is very unpredictable and possibly ineffective. Another study took 25 rugby players, administered bicarbonate orally, and measured performance and blood PH. This study concluded that the bicarbonate did in fact increase the blood PH, but did not result in significant performance changes in repeated sprint training sessions. However, the incidence of GI distress, bloat, and gas was significantly higher in the bicarbonate group vs the control (Cameron et al., 2010). Specific for cyclists, a study concluded that bicarbonate did increase performance in a 4km time trial, but again resulted in quite significant GI distress (Hilton et al., 2020). However it should be noted this experiment only included 10 experimental trial participants. All of these studies used very small sample sizes which makes it difficult to make a definitive statement on its efficacy, especially given its polarizing results across the board. I think with its unvalidated efficacy along with its ability to cause GI distress, I wouldn't recommend it to athletes, especially those competing in longer endurance events.
Cameron, S. L., McLay-Cooke, R. T., Brown, R. C., Gray, A. R., & Fairbairn, K. A. (2010). Increased blood ph but not performance with sodium bicarbonate supplementation in Elite Rugby Union players. International Journal of Sport Nutrition and Exercise Metabolism, 20(4), 307–321. https://doi.org/10.1123/ijsnem.20.4.307
Hilton, N. P., Leach, N. K., Hilton, M. M., Sparks, S. A., & McNaughton, L. R. (2020). Enteric-coated sodium bicarbonate supplementation improves high-intensity cycling performance in trained cyclists. European Journal of Applied Physiology, 120(7), 1563–1573. https://doi.org/10.1007/s00421-020-04387-5
Jordan, M. (n.d.). Understanding lactate for track cyclists. Track Cycling Academy. Retrieved November 13, 2022, from https://www.trackcyclingacademy.com/blog/understanding-lactate-for-track-cyclists
Mazaheri, R., Schmied, C., Niederseer, D., & Guazzi, M. (2021). Cardiopulmonary exercise test parameters in athletic population: A Review. Journal of Clinical Medicine, 10(21), 5073. https://doi.org/10.3390/jcm10215073
Mlblevins. (2015, May 27). A brief explanation of the importance of Cori cycle in metabolism. Biology Wise. Retrieved November 13, 2022, from https://biologywise.com/brief-explanation-of-cori-cycle
Newbury, J. W., Cole, M., Kelly, A. L., Chessor, R. J., Sparks, S. A., McNaughton, L. R., & Gough, L. A. (2021). The time to Peak blood bicarbonate (HCO3–), ph, and the strong ion difference (SID) following sodium bicarbonate (nahco3) ingestion in highly trained adolescent swimmers. PLOS ONE, 16(7). https://doi.org/10.1371/journal.pone.0248456