- Lactate is produced whenever your body burns carbohydrates. Even at rest.
- It is not a waste product but a fuel that the body goes on to use.
- What matters is not the single value but how it changes as the workload increases.
- Two thresholds divide this curve into three zones. You base your training on them.
Hardly any value in endurance sport is mentioned as often, and misunderstood as often, as lactate. This chapter explains what lactate is, where it comes from and what the number on your meter tells you.
What lactate is
Your body draws its energy from two stores: fats and carbohydrates. Fats deliver energy slowly and need oxygen to do so. In return, they are in plentiful supply. Carbohydrates deliver energy quickly, even when oxygen runs short. Their store is limited, however. In practice, the body always uses a mix of the two.
Lactate is produced when carbohydrates are broken down, and this happens all the time: in every working muscle, even at rest. It passes into the blood and from there is put to further use, for example in the heart muscle, in the liver and in muscles that are working less hard. So lactate is a fuel that travels around the body.
Why the value rises
During easy exercise, the body clears lactate just as quickly as it is produced. The level in the blood stays low and stable. The harder you work, the more carbohydrates you burn and the more lactate is produced. Above a certain intensity, clearance can no longer keep up. The level then keeps rising, even if you merely hold your pace.
During very hard work the concentration rises sharply, the muscle becomes acidic and at some point can no longer work at full strength. This protects it from overload. That also makes lactate a signal: it shows how hard your metabolism is being pushed at that moment.
Two thresholds, three zones
If you plot the lactate values from a step test against the workload, you get the lactate curve. It runs flat at first and then bends upwards more and more steeply. Two points on this curve are particularly important for your training.
Values as a table
| Speed | Lactate | Heart rate |
|---|---|---|
| 8 km/h | 1.4 mmol/L | 128 |
| 10 km/h | 1.3 mmol/L | 142 |
| 12 km/h | 1.6 mmol/L | 155 |
| 14 km/h | 2.4 mmol/L | 167 |
| 16 km/h | 4.3 mmol/L | 178 |
| 18 km/h | 8.2 mmol/L | 187 |
- Aerobic threshold (LT1): This is where the lactate value starts to lift away from its baseline. Below it you are training easy and can keep going for a long time.
- Anaerobic threshold (LT2): The highest workload at which production and clearance are still just in balance. Specialists call this the maximal lactate steady state. Above it, lactate keeps rising and you can sustain the effort only for a limited time.
The threshold is not an exact point but a narrow range. And it lies somewhere different for every person. That is why it is measured rather than estimated. In older German-language texts you will also find the abbreviations IAS and IANS for the two thresholds.
What the values tell you
Lactate is given in millimoles per litre of blood, mmol/L for short. The following ranges help you put a value into context.
| Situation | Typical range |
|---|---|
| At rest | around 1 mmol/L |
| Easy exercise | 1 to 2 mmol/L, stable |
| Aerobic threshold | about 2 mmol/L |
| Anaerobic threshold | individual, usually between 3 and 8 mmol/L |
| After maximal effort | from below 8 to above 20 mmol/L, depending on the sport |
Values for orientation. Your own values may differ from them without anything being wrong.
Why not simply use heart rate?
In a step test, heart rate rises fairly evenly with the workload. It shows how hard your heart is working, but not the point at which your metabolism starts to lose its balance. It also varies with temperature, how you feel on the day and body position. Lactate shows more directly what is happening in your metabolism.
In practice, the two work together. The step test gives you the thresholds as a pace or power output, along with the heart rate you had at those points. In training you then go by pace, watts or heart rate. You do not need to measure lactate every time for that.
What affects the value
- Nutrition: A carbohydrate-rich meal shortly before the test raises the values.
- Preceding training: Hard training in the days before the test changes the curve.
- Test protocol: The faster the workload increases, the lower the lactate at the same power output.
- Environment: Heat pushes the values up.
- Sampling: Sweat in the drop of blood or squeezing the puncture site distorts the measurement.
- Meter: Different devices give slightly different values.
The conclusion is simple: always test under the same conditions, with the same protocol and the same device. Then you can compare your tests with one another.
Why a single value says little
3 mmol/L can still be below the threshold for one athlete and already above it for another. A single value without context is therefore of little help to you.
Lactate becomes meaningful over time: across the stages of a test and across several tests. If your curve shifts to the right, you can manage a faster pace or more watts at the same lactate value. How to set up a test like this is explained in Chapter 4.
This guide explains the basics for training. It is no substitute for a sports medical examination. If you have any questions about your health, talk to your doctor before an exercise test.