Lactate Threshold and Blood Lactate Testing

Last Friday, I was fill in for one of Krista Schultz’s blood lactate tests after her client canceled because he was sick. She needed a test subject and I was curious what my power output at Lactate Threshold (LT) was.

What is lactate?

First, let’s start with pyruvate.

Pyruvate is a byproduct of anaerobic glycolysis, which is the breakdown of glycogen (or carbohydrate) for energy by the muscles without requiring oxygen during the process.

Pyruvate then either:

1. Enters the mitrochondria in a muscle’s cells for conversion to Acetyl-CoA and entry into the Kreb’s cycle (i.e. oxidative phosphorylation or what we typically refer to as the “aerobic system”) or
2. Is converted to lactate, some of which is released in to our blood. Other muscles, the liver, the heart and other tissues can utilize lactate as a fuel source.

At rest and at lower exercises intensities, lactate levels in the blood are at steady state such that the low levels of lactate being produced are equal to the level of lactate being cleared away.

As exercise intensity increases, more and more pyruvate is converted to lactate, as the body depends more and more on the faster anaerobic glycolysis system to provide energy more quickly (the conversion of pyruvate to lactate helps “prime the pump” of anaerobic glycolysis).  The “slower” aerobic system just can’t keep up with the intense demands placed on it.

As more lactate is produced than our body can clear away, our blood lactate levels increase.  Correspondingly, our blood is also becoming more acidic from the increased concentration of [H+] hyrdogen ions (pH is going down).  If your blood is too acidic, you’ll have to slow down until it becomes less acidic.  If you’ve heard the term “lactic acid burn” that’s what this is referring to.

What is a blood lactate test?

A blood lactate test measures the concentration of lactate [La] in the blood typically via a finger prick at increasing levels of intensity while exercising (I was on a exercise bike).  The purpose of the test is to determine Lactate Threshold (LT), which this particular test protocol defines as 4.0 mmol/L of lactate.  LT is essentially the point above which lactate begins to accumulate exponentially (see chart below).

After I warmed up for about 15 minutes with easy pedaling, the test began.  Starting at a moderate intensity, Krista increased the resistance on my bike every 3 minutes.  At the end of each 3 minute period, she pricked my finger then used her lactate analyzer to measure my blood lactate levels (see picture on right) while noting my both power level and heart rate.  The test continued until I exceeded 4.0 mmol/L of lactate.

Here are my test results:

The dots on the chart represent sample [La] data points taken every 3 minutes at corresponding power outputs (x-axis).  The curved line is a polynomial curve mathematically fit to the data points.

As you can see from the chart my blood lactate level was fairly constant for the first two data points then started to increase at the third point, which was about 275 Watts. At the third point (200W), I was just below the threshold of 4 mmol/L, which I then exceeded at the final point at 320 W.

Per the test, my LT is currently at 305W of power.

Why is knowing Lactate Threshold important to an endurance athlete?

Bassett, et al.¹ state that there are three major variables related to the maximal velocity that can be maintained in distance races:

1. VO₂ max,
2. % VO₂ max at LT and
3. Economy

VO₂ max is somewhat trainable, especially for an untrained individual, but not much increase can be expected for an athlete already highly endurance trained (see my blog article “Understanding VO2 Max: What Exactly Is It?“).  LT and Economy, however, are both very trainable.

As an endurance athlete, it’s helpful for me to know my LT today so that I know how to structure my training in order to both:

• Increase my power (bike) and velocity (run) at lactate threshold
• increase the amount of time I can sustain near lactate threshold intensity

When I test again in the future, I expect my power at LT to have increased, as well as my ability to sustain a higher training intensity for longer amount of time below lactate threshold.

Ultimately, as endurance athletes, we want to be able sustain as fast a speed as possible over the duration of our events - in my case, a 140.6-mile Ironman race.  Knowing LT is a power tool to help me do that more effectively.

Interested in finding out your LT?  Please visit Krista’s website www.totalperformanceinc.net for more information and to sign up for a blood lactate test.

Live strongly and boldly!

David

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David B. Glover, MS, CSCS
Author of Full Time and Sub-Nine: Fitting Iron Distance Training into Every Day Life
Triathlon Coach, Athlete and Writer
Web: enduranceworks.net

© 2010 David B. Glover

References:

1. Bassett, D.R., Jr. and E.T. Howley. Maximal oxygen uptake: “classical” versus “contemporary” viewpoints. Med. Sci. Sports Ecerc. 29: 591-603, 1997.