VO2max says how much oxygen you can process at maximum effort. It says nothing about how much of that ceiling you can hold for an hour. That second part is what your thresholds answer, and that is where training control begins.
Why a single VO2max value is half the story
Engine size versus usable shareThink of two properties. The first is the size of the engine : your VO2max, set mainly by oxygen delivery, meaning cardiac output, stroke volume and haemoglobin. The second is the usable share : the percentage of that maximum you can sustain over a long effort. Sports science calls this fractional utilisation, and it depends on the periphery, on mitochondria and capillaries in the working muscle.
Two people can share the same VO2max and still perform very differently, because one of them can hold a much higher share of that ceiling. The VO2max value alone does not show this difference. The thresholds do.
The four thresholds in plain words
Two from the breath, two from the bloodDuring a step test your load rises in defined stages. Two systems react to that, and both can be measured. Breath gas analysis records how ventilation and carbon dioxide output change. A blood sample from the fingertip per stage records how lactate behaves. Each route yields two turning points.
| Threshold | Measured in | What it marks |
|---|---|---|
| VT1 | Breath gas | First turning point in the breathing pattern. Marks the upper limit of the base endurance range. |
| LT1 | Blood | First clear rise of lactate above the resting value. The aerobic threshold and the counterpart to VT1. |
| VT2 | Breath gas | Respiratory compensation point. Breathing rises disproportionately to buffer the acidosis. Not sustainable for long. |
| LT2 | Blood | Highest load at which lactate production and clearance are still balanced. The anaerobic threshold and the counterpart to VT2. |
The ventilatory turning points go back to the classic work of Wasserman and colleagues, the lactate thresholds to lactate step testing. Both are model concepts, not anatomical landmarks.
Schematic · The curve shows the typical shape : flat for a long time, a gentle rise from LT1, a steep rise from LT2. Axis values are deliberately omitted, because the actual positions are individual and only come out of a real step test. Do not read any numbers into this drawing.
The two routes describe the same physiological events from different angles, which is why VT1 and LT1 as well as VT2 and LT2 usually sit close together. Close together is not the same as identical. Where a threshold ends up depends on the test protocol, on the sport, on your glycogen status on the test day and on the evaluation model.
Schematic · Both curves run over the same load axis. The shaded corridors show the aerobic pair (VT1 and LT1) and the anaerobic pair (VT2 and LT2). They validate each other : if breath gas and blood point into the same corridor, your zones rest on two independent signals instead of one.
The individual anaerobic threshold
Your value instead of a fixed valueFor a long time the anaerobic threshold was pinned to a fixed lactate concentration. That is simple, and for many people it is roughly right, but it ignores the fact that resting lactate, the shape of the curve and the clearance capacity differ from person to person. The individual anaerobic threshold (IAT) is therefore not read off a fixed value but derived from the shape of your own curve, from the point at which production and clearance stop being balanced.
The idea behind it is the highest load you can hold in a steady state over a longer period. That is what makes the IAT practical : it is the anchor for tempo work, it separates what is still controllable from what is only sustainable for a short time, and it is the value that moves most clearly when your endurance base improves.
And the limits, plainly : the IAT is a model value, not a measured constant. Different evaluation models place it at slightly different points, the step length of the protocol shifts it, and a low-carbohydrate day before the test shifts it as well. It is a good working anchor, not a law of nature. That is exactly why the second measurement route matters.
What you actually steer with it
Zones, volume, intensityTwo thresholds split the entire load range into three ranges. That sounds trivial and it is the most useful result of the test, because almost every training mistake is a mistake of allocation between these three.
Schematic · The widths of the sections are drawn, not measured. Where your own boundaries sit and how wide your transition range is only comes out of your test. In practice the boundaries are handed over as heart rate, watt or pace corridors.
Most of the volume stays below LT1
In world-class distance runners the clear majority of training volume sits in the low intensity range. That is not a fashion, it is what makes the hard sessions repeatable.
The middle only on purpose
The range between LT1 and LT2 is useful when you choose it deliberately. It becomes a problem when your easy sessions drift into it and your hard sessions never leave it.
Concretely, the test gives you three things that go straight into your week : boundaries for your easy sessions so they really stay easy, a corridor for tempo work around your individual threshold, and a reference point above LT2 for interval sessions. The intensity distribution across the week becomes a decision instead of an accident.
Why both routes together
Mutual validationEvery single measurement has its own weak spots. Breath gas analysis reacts to breathing technique, to talking during the test and to the evaluation method for the turning points. Lactate testing reacts to step length, sampling timing, carbohydrate status and contamination at the sampling site. The error sources of the two have little in common, and that is exactly the point.
- One route alone : a shifted threshold looks plausible and stays undetected.
- Two routes : if breath gas and blood point into the same corridor, the zone is solid.
- Two routes that disagree : that is information as well, and a reason to check the protocol before the training plan.
- Neither route : training by feel, and the middle range quietly swallows the week.
On top of that, the combination gives you two things a lactate test alone cannot : the absolute value of your VO2max as the ceiling, and the share of that ceiling at which your thresholds sit. That share is the figure that tells you whether your next block needs more volume or more intensity.
Retest and trend
Same setup, otherwise not comparableA single measurement is a snapshot. The value of the diagnostic only appears in the second and third test, when you can see whether a threshold has moved. That only works with an identical setup : same protocol, same step length, same device, comparable time of day, comparable load in the days before, comparable carbohydrate intake. Changing the protocol between tests produces a difference that says nothing about your training.
Also worth knowing : the two adaptations run on different time scales. The central side, the heart, responds comparatively quickly. The peripheral side, mitochondria and capillaries, needs more time and above all volume. So do not expect both to move in the same retest.
Measure both, not just one
Spiroergometry and lactate step test in one appointment, with your zones handed over afterwards. In Tübingen and the greater Stuttgart area.
Sources (primary literature)
- Bassett DR, Howley ET (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc 32(1):70-84. doi:10.1097/00005768-200001000-00012
- Wasserman K, Whipp BJ, Koyal SN, Beaver WL (1973). Anaerobic threshold and respiratory gas exchange during exercise. J Appl Physiol 35(2):236-243. doi:10.1152/jappl.1973.35.2.236
- Beaver WL, Wasserman K, Whipp BJ (1986). A new method for detecting anaerobic threshold by gas exchange. J Appl Physiol 60(6):2020-2027. doi:10.1152/jappl.1986.60.6.2020
- Faude O, Kindermann W, Meyer T (2009). Lactate threshold concepts : how valid are they? Sports Med 39(6):469-490. doi:10.2165/00007256-200939060-00003
- Beneke R, Leithäuser RM, Ochentel O (2011). Blood lactate diagnostics in exercise testing and training. Int J Sports Physiol Perform 6(1):8-24. doi:10.1123/ijspp.6.1.8
- Seiler S (2010). What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform 5(3):276-291. doi:10.1123/ijspp.5.3.276
- Haugen T, Sandbakk Ø, Seiler S, Tønnessen E (2022). The training characteristics of world-class distance runners. Sports Med Open 8:46. doi:10.1186/s40798-022-00438-7
- Mølmen KS, Almquist NW, Skattebo Ø (2025). Effects of exercise training on mitochondrial and capillary growth in human skeletal muscle. Sports Med 55:115-144. doi:10.1007/s40279-024-02120-2
This article is educational and does not replace medical advice. StoaVita provides longevity and performance coaching, not medical treatment. The figures on this page are schematic and contain no measured values.
