Why Athletes Measure Lactate

Intensity control is the foundation of a quality training process, and lactate is a precise marker of workload level. Regardless of the sport, the winner is the one who can handle more workload at the intensity that brings maximum benefit.

Let's look at several reasons why athletes measure lactate.

Lactate: A Marker of Glycolytic Activity

Lactate is always the end product of glycolysis (also called the anaerobic energy system). Thus, the rate of lactate production tells you something about how active the anaerobic energy system is.

Lactate: A Marker of Fatigue

Lactate itself does not cause fatigue. However, blood lactate concentration is a good marker of fatigue. For example, when an athlete shows a constant increase in lactate concentration, you can be confident that they will fatigue.

Fatigue markers such as heart rate are not always accurate, especially during dehydration. Lactate, on the other hand, directly reflects how you are currently loading yourself, which energy system you are using, and consequently which training objectives you are addressing.

Lactate: A Marker of Carbohydrate Use

The lactate production curve resembles the carbohydrate burning curve. We cannot quantify exactly how many carbohydrates you are burning using lactate, but we can definitely say that the higher the lactate, the more carbohydrates you are using as an energy source during exercise. If you have metabolic testing data, you can easily link it to your lactate profile and quantitatively assess expenditure.

Intensity, Duration, and Lactate Levels

Blood lactate concentration changes depending on exercise intensity. At higher exercise intensities, you will ultimately get higher blood lactate values.

Blood lactate concentration can also change over time, even when exercise intensity remains the same. If your intensity is above the lactate threshold 2 (OBLA) level, you will continuously accumulate lactate up to your maximum possible level, and the higher the intensity, the faster you will accumulate it and will have to slow down.

Imagine, for example, an athlete running 10 km. The running pace will remain roughly the same. However, the lactate concentration at the finish will be higher than at the midpoint of the race. In other words: lactate concentration increases even if the pace remains constant. There is a term — lactate accumulation rate: the lower this indicator is for you, the better.

Lactate concentration depends on both time and intensity. Each person will respond differently to these two factors. Therefore, if you want to know how you respond to workload, it may make sense to use different durations and different exercise intensities in your lactate testing protocol.

This also clarifies that you cannot compare results from two different (in duration and/or intensity) linear or step protocols.

Error Models

Blood lactate units are mmol/L, and plasma volume itself can expand and contract with fitness, heat stress adaptation, and other circumstances. During the off-season, it can decrease quite quickly, which may lead to higher measured lactate concentrations. Thus, for the same power output between two tests of a person with the same fitness level, we expect the same absolute mmol of lactate to be produced. In testing, we have found this to be very reproducible.

Let's see what happens when we change plasma volume. At rest, if an athlete has a blood lactate concentration of 1 mmol/L with a blood volume of 5 L, the athlete's blood contains a total of 5 mmol of lactate. During training, if the volume increases to 5.5 L, the concentration drops to 5 mmol / 5.5 L = 0.91 mmol/L, which seems insignificant. If a test results in blood lactate of 15 mmol/L with a blood volume of 5 L, then the total lactate is 75 mmol. If the same test is performed with 5.5 L of blood, the resulting value is 75 mmol / 5.5 L = 13.6 mmol/L. Dehydration can significantly affect lactate readings.