Blood lactate testing for speed athletes; sprinters to endurance, has been used successfully for at least the last 20 years.

However, there is not much written about it for an athlete on a ketogenic low-carb diet.

This article will attempt to answer some questions and lay a framework for a ketogenic low-carb athlete to consider using blood lactate to improve performance through proper training of the two main energy fuel systems. The Interaction of the Two Fuel Systems

Lactate curve
As the speed increases the blood lactate increase and thus the shape of most “Lactate Curves”

Lactate is the by-product of unused pyruvate not used for energy by the working muscle. As your intensity increases the more energy your muscles need to fuel the rate of contractions. The harder your intensity the more lactate is produced because the working muscle can only use so much oxygen and pyruvate to fuel the production of adenosine triphosphate or ATP. Lactate also is present with a hydrogen ion, a highly acidic molecule. Therefore, the more lactate present in the blood the more your muscles get painful and shut down. At higher intensities, you are also gasping for oxygen. Oxygen is needed to react with the pyruvate to produce ATP. When there is not enough oxygen, i.e., you’ve reached your maximum intensity (VO2Max), the excess pyruvate that could not be converted to ATP is converted to lactate and the dreaded acidic hydrogen ion.  As you probably have experienced with extream high exercise intensity, you can’t breathe enough oxygen and your muscles feel like painful piercing lead weights.

The lactate curve is therefore upward sloping; i.e., with an athlete’s higher intensity they will need to produce more energy to fuel ATP and thus the higher amount of lactate will be produced and be present in the blood. In the example of the swimmer above, there was 2 mmol (2nd Swim) of lactate swimming at a speed of 1.43 m/second and 3 mmol (3rd Swim) of lactate swimming faster at 1.52 m/second.

In comparing two testing time frames, one earlier and perhaps one six weeks later, the curve is either going to move to the right to illustrate fitness improvement through training or it will move to the left, a decrease in fitness. The desire is to move the curve to the right. If this swimmer was tested again after 6 weeks of training and their lactate production at 2 and 3 mmol produced 1.54 m/second and 1.67 m/sec respectively, the curve moved to the right. In other words, the swimmer got faster at the same energy production (@ 2 mmol was 1.43 m/s in the first test and 1.54 m/s after 6 weeks of training).

Position of Lactate Curve
This graph illustrates the interaction of the two main fuel systems on the position of the lactate curve

The above graph explains how the swimmer in the example above improved their lactate curve to the right and at 2 mmol of lactate increased their speed from 1.43 m/s to 1.54 m/s.

An athlete has two main fuel systems that explain performance and fitness:

According to Jan Olbrecht,

Anaerobic capacity = The anaerobic capacity is the maximum amount of pyruvate that can be produced per second by the glycolysis. It is frequently called VLamax (in some literature also PLamax). Since the conversion from pyruvate into lactate and vice versa occurs very quickly, the ratio between the muscle concentrations of lactate and pyruvate is described as being 1/1. You may, therefore, find in literature on the subject the label “production of lactate” for what we refer to as “the production of pyruvate”. You may further find that the units of the anaerobic capacity are expressed in “mmol of lactate per liter and per second” instead of “mmol of pyruvate per liter and per second”. This may sound confusing but is in fact quite simple since they are counterparts. The anaerobic capacity can change as the athlete goes through the training cycle. It is thought that each individual has an innate maximum anaerobic capacity that is genetically determined. However, some coaches and sports scientists have observed growth in this capacity after years of training. (1)

Note: This term has many other meanings. The definition we provide is not common by many in the academic literature. The anaerobic capacity is also used to refer to the amount of anaerobic energy that is released during maximum activity as opposed to the highest possible rate of glycolytic energy release. (1)

Aerobic capacity =  the maximum amount of oxygen one can consume per minute. It is also called VO2max. Some sources in literature consider VO2max as a parameter of power and not of capacity. With respect to its unit of measure (VO2max is expressed per unit of time), it can indeed be seen as a parameter of power. According to its physiological meaning, however, it refers to a capacity. We join in the last argumentation and define, in line with Hollmann and Hettinger (1990), VO2max as a parameter of capacity. The higher the aerobic capacity, the better the performance in competition “can” be and the faster the regeneration process after training and competition will start. The aerobic capacity is constantly changing as an athlete goes through the training cycle. It is however thought that each individual has an innate maximum aerobic capacity that is genetically determined. (1)

(1) Olbrecht, Jan. The Science of Winning (Kindle Locations 4063-4064). F&G Partners. Kindle Edition.

Each of these fuel systems contributes to the amount of energy the athlete can produce. The more energy an athlete can produce (anaerobic system) AND be used (aerobic system), generally faster they will be.

Note on the graph the unique interplay with these two systems. Let’s take our swimmer above who’s lactate curve improved to the right in our hypothetical example. Their VO2Max improved at a higher rate than their anaerobic capacity either improved or declined.

It’s important to get a feel for this interplay before going on and explaining the difference between the fuel systems of a HIGH Carb athlete vs a LOW Carb athlete.

The HIGH Carb Athlete

The high carb athlete is depending more on glucose to create energy than they are fat. Glucose is the creator of pyruvate and thus the main fuel for the production of ATP is carbohydrate. A high carb athlete that is using glucose as their fuel is also using more oxygen, i.e., it takes more oxygen to create a unit of energy from glucose than it takes to create a unit of energy from fat.

Because there are so few speed athletes, either from sprinters to endurance, that are low-carb, there has been, to my knowledge, very few training studies using blood lactate testing for a low-carb athlete. Using blood lactate, on the other hand, for a glucose high-carb athlete is commonplace.

The LOW Carb Athlete

The low-carb athlete has chosen this method of nutrition fueling for various reasons. Many enjoy the benefit and ease of maintaining a lean body composition. Other endurance athletes who race at 70-85% of their V02Max enjoy the benefit of relying on their own fat to fuel their energy needs. And because fat metabolizes slower than glucose their is less a need for oxygen.

Blood Lactate Testing and the LOW Carb Athlete

According to Jeff Volek, Ph.D., RD and Stephen D. Finney, MD, Ph.D. in their book, The Art and Science of Low Carbohydrate Performance (Kindle Locations 508-511). Beyond Obesity LLC. Kindle Edition they report:

Lactate Metabolism. An increased reliance on fat and a corresponding decrease in glycolysis during exercise are associated with less accumulation of lactate (a surrogate for hydrogen ion accumulation). As cellular lactate and hydrogen ion levels increase at higher intensities of exercise, there are several events that cause force production and work capacity to decrease. A key contributor in this process is the acidity (i.e., decreasing pH) associated with hydrogen ion buildup. Along with maximal oxygen consumption, lactate threshold (the exercise intensity where blood lactate begins to accumulate) is a major determinant of endurance performance. With the enhanced ability to oxidize lipid [burn fat] associated with keto-adaptation, there is less lactate production at any one workload, and thus an elevation in the threshold exercise intensity associated with increased acidity.

Ventilatory Drive. There are two primary drivers of your respiration. The first is the blood oxygen level – you breathe harder if the brain perceives a low oxygen content in the blood. The second driver is carbon dioxide, which drops the blood pH (makes it more acid) when CO2 accumulates, and this reduced blood pH increases respiration. This is also why having lactic acid build up in the blood during intense anaerobic exercise causes such intense hyperventilation because its buildup also contributes to a drop in blood pH. Once you are adapted to a low carb diet, two things influencing your respiratory drive change. First, your respiratory quotient (RQ) at most workloads is lower, which means you make less CO2 per calorie burned, so there’s less of a pH drop and less respiratory drive. Ditto that for lactate as well – at most workloads all the way to your max output, lactate levels are also lower. Obviously, you still need to breathe hard enough to get the oxygen you need into your blood to perform the work, but under most circumstances, you are protected from that intense sense of ‘air hunger’ that comes from having dropped your blood pH into the basement.

Factoid: RQ is the ratio of CO2 expired to O2 consumed. Burning exclusively carbs results in equal amounts of CO2 expired to O2 consumed, and thus an RQ = 1.0. Burning exclusively fat results in an RQ of 0.7(i.e., only 70% as much CO2 expired as when burning glucose). In a keto-adapted athlete, most endurance exercise is done at RQ values less than 0.75.”

Blood Lactate Testing for the Low-Carb Athlete

It is my opinion that blood lactate testing is viable to identify the results of training for a low-carb athlete. Because all coaches and athletes are attempting to produce a positive fitness benefit from their training, using blood lactate testing will give the coach and athlete insight into how well the two energy systems are being trained and progressing.

For example, the swimmer in our hypothetical example moved their lactate curve to the right, exactly what the coach was attempting to do and thus the swimmer got faster at his/her same intensity level. Yet, without blood lactate testing, the coach has no way of really knowing if the athlete’s aerobic capacity improved greater than their anaerobic capacity. In this exact example, this athlete slowed down their intensity in training to purposely reduce their anaerobic system while increasing their aerobic system.

As stated by Volek and Phinney, all things being equal, a low-carb athlete will have lower concentrations of blood lactate than a high-carb athlete. Because each athlete will have their own upward sloping lactate curve, using blood lactate testing is just as valid a fitness testing protocol for low-carb athletes as high-carb athletes.

Final Note

I’ve had well-meaning athlete friends effectively disagree with my use of lactate testing because I’m a low-carb endurance athlete. Their argument is based on their false assumption that a low-carb endurance athlete doesn’t need a high VO2Max because I’m relying on mostly fat as my fuel and they only associate performance with the burning of glucose at the higher intensity. Also, it’s my observation, very few people understand the second graph above and the interrelationship of anaerobic and aerobic capacity. Blood lactate testing is the only way to test this interdependent relationship and thus be able to train for it.

As a low-carb athlete, I want to have a very high VO2Max. While it’s true I’ll never approach that intensity in an Ironman triathlon, I want my lactate curve as far to the right as possible BECAUSE I want to go faster (thus the higher rate of fat oxidation to produce ATP) as I can at my race intensity. For example, if I’m racing at 80% of my VO2Max, it will feel the same for me at 80% of a VO2Max of 38 as it will at 80% of a VO2Max of 50 (80% of 38 = 30.4. 80% of 50 = 40. 40 > 30.4).

Blood lactate testing answers another question for me; Where is my anaerobic threshold (AT)? In other words, the intensity level that my blood lactate does not rise but stays constant. If my lactate begins to rise, so will the acidic hydrogen ion and eventually, I’ll have to slow down or stop once lactate reaches higher levels. Racing just below my AT keeps me fast the entire race. Knowing this intensity will also help me answer the question; How much carbohydrate will I need to consume during the race to maintain my race intensity? I can have my RQ (see factoid above) level tested and determine the amount of fat versus glucose I’m burning at my AT.

Because I’m not producing as much lactate my curve is relative to me and therefore I can track fitness using the blood lactate testing protocol.

bike lactatetreadmill running lactate

The results of my most recent blood lactate tests. My lactate curve is similar in shape to the swimmers above. The faster I went the more lactate I produced.

What’s interesting is the reduction in blood lactate when I went all out on the bike compared to the test before it. Notice that riding for 7 minutes at 221 watts (7.6 mmol of lactate) I produced more blood lactate than my aerobic capacity (VO2Max) 90-second test where I produced less blood lactate (6.4 mmol at 301 watts).

In 6 to 8 weeks I’ll retest and see if my training plan is producing better fitness and moving my curve to the right.

Where I Ordered My Testing System


They have a great discussion for triathletes.

About the Author Michael Lantz (Big Papa)

The Wellness Warrior™; Health & Leadership/Business Coach, Speaker, Blogger, Author, Ironman Triathlete Helping others live with more health and joy, paying for their dreams and make a difference in the world! Learn more: