Hardly any value in endurance sport has as bad a reputation as lactate. "Acidosis", "waste product", "to blame for muscle soreness" — the half-truths persist stubbornly, even though training science moved on long ago. In fact lactate is an energy carrier that your body actively puts back to use, and a distinctly useful measurement: from the lactate curve you can derive thresholds and training ranges that no heart rate strap alone provides. In this article you will learn how lactate is formed and cleared again, what the aerobic and anaerobic thresholds mean, how a step test works and what you actually do with the numbers afterwards.
Lactate is not a waste product
Lactate arises in what is known as anaerobic glycolysis. In this process, glucose is broken down to pyruvate in the cell plasma, and part of this pyruvate is converted into lactate and H+. The body uses the energy released in the process to restore ATP — so the cell gains energy. One detail is important that is expressly emphasised in the training: the pathway is called "anaerobic" not because there is no oxygen present, but because none is needed for this reaction. A lack of oxygen in the muscle is not the precondition for lactate formation.
Just as wrong is the idea that lactate is simply disposed of. The body builds it back up into pyruvate and channels it back into energy supply; the liver can also make glucose from it again via gluconeogenesis. The heart muscle and the brain even use lactate directly as an energy carrier. So it does not leave the body via the kidney but is put to use — and continuously, because even at rest you produce small amounts of lactate. How the three energy systems work in parallel is shown in the article on how energy supply works in the body.
The most stubborn error: lactate and muscle soreness
Lactate does not cause muscle soreness. Muscle soreness arises from micro-injuries in the muscle fibre — the Z-discs of the sarcomeres are slightly torn apart during unaccustomed and intense, mostly braking (eccentric) movements. The small tears lead to fluid accumulation and repair processes that irritate pain-conducting nerve cells. That typically takes 24 to 48 hours. Lactate, by contrast, is broken down again within minutes to around an hour after an effort — in terms of timing alone it cannot be the cause. What really lies behind the phenomenon is covered in the article Muscle soreness — what does it really mean.
The burning sensation during a hard effort is also not due to the lactate itself but to the accompanying hydrogen ions. Lactate is the companion, not the culprit — but a companion that is easy to measure, and that is precisely what makes it valuable for diagnostics.
Aerobic and anaerobic threshold
Two points in the lactate curve are decisive for managing training.
- Aerobic threshold: up to this point, as much lactate is cleared as is formed, or more, so nothing accumulates. Only at the transition does the concentration in the blood rise measurably for the first time. For diagnostics this point is less spectacular, because hardly anything changes before it — for the training ranges it is decisive: it tells you where base training has to lie.
- Anaerobic threshold: the training defines it as the performance that can be maintained for over 20 minutes without the blood lactate concentration changing by more than 1 mmol. That is the maximal lactate steady state: exactly as much lactate is produced as is simultaneously put back to use. If it is exceeded, the value rises exponentially — the body can no longer keep up with clearance.
Why this second threshold says so much about your competition performance is explored in more depth in the article on the anaerobic threshold.
The four intensity zones used in the training
In update Akademie's training theory, the course of a step test is divided into four intensity zones — each with a guide value on the Borg scale for the subjective perception of effort:
- Base range — up to the aerobic threshold. Clearance keeps pace with new formation, no lactate accumulates. Borg 8 to 11.
- Transition range — between the aerobic and the anaerobic threshold. Anaerobic glycolysis contributes increasingly, but blood lactate does not yet rise disproportionately. At its upper end lies the highest possible lactate steady state. Borg 15 to 16.
- Sustained-effort range — from the anaerobic threshold to the end of the test. A large part of the energy comes from anaerobic glucose combustion, the oxygen deficit grows, lactate rises exponentially. Borg 17 to 20.
- Supramaximal range — not reachable in a step test at all, because the reserves have already been drawn on. Coming from full recovery, even higher outputs are possible here for 10 to 20 seconds, supported substantially by the creatine phosphate system.
This division matches what circulates internationally as a zone model. The calm base range corresponds to what many know as zone 2 training; the transition range is the much-discussed grey zone, in which most recreational athletes end up unintentionally.
How a lactate step test works
The step test is the standard procedure for determining the anaerobic threshold and assessing performance capacity in the aerobic as well as the anaerobic range. It works on a cycle, rowing or arm ergometer, on a treadmill, in the swimming pool and as a field test on the 400-metre track.
The principle: the load increases in steps — on the bike, for example, by 30 watts per stage, when running by 2 km/h. The duration of each stage stays constant, usually 2 to 3 minutes. Heart rate is recorded continuously; at the end of each stage a small blood sample is taken from the earlobe or fingertip for the lactate value. The load is increased until subjective exhaustion. In update Akademie's test protocol, women start at 80 watts after the warm-up and men at 100 watts; later the load is increased by 20 watts every two minutes, and heart rate and Borg value are also noted for each stage.
In the evaluation, heart rate and lactate are plotted together against power output. In the aerobic range, heart rate runs directly proportional to power output and flattens off slightly in the anaerobic range. Lactate first rises linearly and then bends into an exponential curve — that exact point graphically marks the anaerobic threshold.
The training also covers alternatives: spiroergometry measures VO2max via the respiratory gases. The Conconi test manages without a blood sample but is considered imprecise — in some people tested, the heart rate curve shows no usable inflection at all.
What you do with the values
The benefit of a step test lies not in the individual number but in the consequences for training:
- Training ranges become individual. Instead of calculating with "220 minus age", you get heart rate and power ranges that fit your metabolism. How to transfer them into everyday training is shown in the article on endurance training and heart rate.
- The grey middle becomes visible. Many only realise during the test that their "easy steady run" has long been in the transition range.
- Progress becomes measurable. If after a few months the threshold shifts to a higher output at the same lactate value, the training has worked — even if your time on your home loop is still the same.
- Fine-tuning becomes possible. With the Karvonen formula the ranges can be refined further using resting heart rate; how that works is explained in the article on the Karvonen formula.
A value nevertheless remains a value: daily form, nutrition, heat and sleep shift the lactate curve. That is why body awareness always belongs alongside it — more on this in the article Understanding training management.
Course tip from update Akademie: How a step test is carried out, evaluated and translated into a training plan is what you learn in the Athletikcoach programme at update Akademie — including a lactate step test that we carry out together on the first practical day. Alongside your job and close to practice.
Frequently asked questions about lactate
Do I need a lactate test as a recreational athlete?
It is not essential. The talk test and heart rate are enough to start with. A step test becomes worthwhile if you are training towards a goal in a structured way, have been stagnating for some time or want to know whether your easy sessions really are easy.
From which lactate value are you "in the red"?
Fixed limits in mmol per litre are misleading, because the individual threshold varies widely. What is decisive is not an absolute value but the point at which your personal curve bends into an exponential rise. That is precisely why it is tested rather than estimated.
How long does lactate stay elevated after training?
Depending on the effort and the cool-down, the value is back at resting level after about 30 to 60 minutes. Easy cooling down speeds up clearance, because the working muscles put the lactate to further use.
What does lactate steady state mean?
It describes the state in which exactly as much lactate is formed as is cleared. The highest possible steady state lies at the anaerobic threshold — the performance that can be held for over 20 minutes without the lactate concentration rising by more than 1 mmol.
Conclusion
Lactate is neither poison nor waste, but an energy carrier and above all a window into your metabolism. Anyone who understands where the aerobic and the anaerobic threshold lie knows how slow their base training really has to be and how hard the intensive sessions may be. A step test provides these limits individually instead of via rules of thumb — and makes progress visible long before the stopwatch shows it.
