Setting your training zones with a lactate test: the complete guide

Most training plans start from a guess. A heart rate zone from a formula, a pace from a friend, or simply "hard enough that it hurts". The problem: this way you often train your easy sessions too hard and your hard sessions too soft. Exactly the wrong way round.

A lactate test fixes that. Instead of estimating your training zones, we measure them. The result is training in which every session has a purpose and nothing goes to waste. In this guide we explain how a lactate test works, what your thresholds mean, and how you derive your zones from them.

What a lactate test actually measures

During exercise your muscles produce lactate (commonly called lactic acid). At an easy effort your body clears it away effortlessly. The harder you go, the faster it builds up, until you reach a point where production outpaces removal.

During the test you run or ride in stages that get progressively harder, usually of four to six minutes each. After each stage we take a small drop of blood, from a prick in your fingertip or earlobe, and measure your lactate value. For running we typically raise the pace by around 1 km/h per stage, for cycling by about 20 to 30 watts. From those measurements we draw your lactate curve, and the kinks in that curve reveal the two thresholds that define your zones.

The two thresholds: aerobic and anaerobic

Two physiological turning points matter.

The aerobic threshold (LT1). The point where your lactate first rises slightly above your resting value, often somewhere around 1.5 to 2 mmol per litre. Below it you can keep training for hours without lactate stacking up. This is your true base zone.

The anaerobic threshold (LT2). The point where your lactate starts to climb steeply because your body can no longer clear it fast enough. It's roughly the highest intensity you can still hold in a metabolic balance. The value of 4 mmol per litre is classically used for this, but in practice it lies individually somewhere between 3.5 and 4.5.

Worth knowing: those fixed values of 2 and 4 mmol are averages, not personal truths. Your real threshold can lie well above or below them. That's precisely why we read your thresholds off your own curve, instead of slapping on a fixed number.

From thresholds to training zones

Once your two thresholds are placed on the curve, we tie the matching heart rate, power and pace to them. We split the space around them into zones.

In the simplest model you get three zones: below the aerobic threshold (easy), between the two thresholds (the middle ground), and above the anaerobic threshold (hard). Many sports watches and coaches work with a finer five-zone split, which divides this same range further.

Watch out for one confusing detail: "zone 2" doesn't mean the same thing in both models. In the three-zone model, zone 2 is the middle ground around your threshold. In the five-zone model, and in the popular term "zone 2 training", zone 2 is actually the easy base zone below your aerobic threshold. We mean the latter when we talk about easy endurance training.

Why "220 minus your age" doesn't fit you

The well-known formulas for maximum heart rate and zones are averages across large groups. For an individual they're easily off by dozens of beats: 10 to 15 on average, and between two people of the same age the difference can run up to around 30 beats.

Train on those estimated zones and you're really training on someone else's physiology. A lactate test measures your body. Only once you know your real thresholds do you know whether an easy long run is actually easy, or secretly already too hard.

Heart rate, power or pace?

You can express your zones in three ways, and they complement each other:

• Pace (speed) works well for runners: it directly reflects what you're producing.
• Power (watts) is the most precise and direct for cyclists, and doesn't lag.
• Heart rate is intuitive and cheap, but reacts slowly and drifts with heat, fatigue, hydration and caffeine.

A lactate test ties your thresholds to all three at once. In training, it's best to cross-check them: they should track together. If they suddenly diverge, that tells you something about your fatigue or your form.

Zone 2 and the right training split

The bulk of your training belongs at low intensity, in your easy base zone below the aerobic threshold. That's where you build your aerobic base: your fat burning, your aerobic capacity and your ability to clear lactate, without piling up much fatigue. Many athletes run precisely those easy sessions too hard, which means they're never fresh for their hard sessions.

The exact split is still hotly debated in the science. Two models keep coming back: polarised (lots of easy, a solid chunk of hard, little in between) and pyramidal (lots of easy, some threshold work, a little hard). Both work, and what stands out is that just about all well-trained endurance athletes fill the lion's share of their volume with easy training, often around 70 to 80 percent. Which split works best for you depends on your goal, your level and your season. There's no universal recipe for it, only a plan tailored to you.

How often to retest, and who it's worth it for

Your zones shift as you get fitter, so a test isn't a one-off measurement. Once to three times a year is enough for most: a baseline at the start, a retest after a block of eight to twelve weeks, and possibly a check heading into your race. You'll often see measurable progress within four to six weeks of consistent training.

And no, this isn't just for competitive athletes. From advanced beginner to ambitious triathlete: as soon as you want to make targeted progress, you get more out of every session by working in the right zones. For anyone coming back from an injury, it's also a safe way to dose the load.

What a test actually involves

Here's how a session usually goes:

1. Beforehand you arrive rested, fed and hydrated, with a fixed routine so your results stay comparable over time.
2. You start with an easy warm-up of fifteen minutes.
3. Then come the stages: a few minutes at a fixed intensity, followed by a prick for a drop of blood, after which the intensity steps up. This repeats through a handful of stages.
4. It gets progressively harder and ends at a near-maximal effort or when your lactate climbs steeply.
5. Afterwards the tester draws your curve, determines your two thresholds, and hands you your personal zones in pace, heart rate and power, with training advice to match your goal.

Measuring is progressing

At HYTX the lactate test is the starting point of every coaching relationship, not a one-off measurement that disappears in a drawer. We translate your zones into your concrete schedule and match the load to your goal race and your life. As you get fitter, we retest, so your zones grow with you.

That scientific foundation runs through all our disciplines, whether you're working with a running coach or building towards a triathlon with a triathlon coach in Antwerp. Training on feel gets you part of the way. But if you truly want to make targeted progress, you stop guessing and start measuring.