A blood lactate test measures the concentration of lactate in your blood at progressively increasing exercise intensities, revealing the two metabolic thresholds — LT1 and LT2 — that define every meaningful training zone. Unlike FTP testing, which gives you a single estimated power number, lactate testing maps the actual transition points where your aerobic and anaerobic energy systems hand off to each other, producing zone boundaries based on physiology rather than formulas.
Here's the thing nobody tells you about training zones: they're supposed to represent distinct physiological states. Aerobic. Tempo. Threshold. VO2max. Each one a different metabolic environment inside your working muscles. But when you set those zones from a percentage of FTP — 55% for zone 1, 75% for zone 2, 90% for threshold — you're making a mathematical assumption about where your body changes gears.
For some riders, the maths lines up. For a lot of us, it doesn't.
A lactate test shows you where the gears actually shift. And once you've seen that data, you can't go back to guessing.
What a Blood Lactate Test Actually Measures
Your muscles produce lactate constantly, even when you're sitting in a chair reading this. At rest, blood lactate concentration typically sits around 0.8–1.2 mmol/L. Your body produces it, clears it, and everything stays in equilibrium.
When you start exercising and the intensity climbs, lactate production increases. Up to a point, your clearance systems keep pace — lactate is shuttled to the heart, the liver, and other muscle fibres where it's burned as fuel. Blood lactate might creep up slightly, but it stays stable. You could ride at this intensity for hours.
Then you cross a line. A point where production starts to exceed clearance. Lactate begins to accumulate in your blood. That's your first threshold — LT1.
Keep pushing and you hit a second, steeper inflection. Now lactate is accumulating exponentially. Your clearance systems are overwhelmed. This is LT2 — the point beyond which the clock is ticking and you will eventually have to back off.
A blood lactate test captures this entire curve. You ride at progressively harder stages, give a fingertip blood sample at the end of each one, and plot the results. What you get is not a number. It's a shape — and that shape tells you more about your current fitness than any single-number test ever could.
As Faude and colleagues documented in their review of lactate threshold concepts, identifying these two thresholds requires serial blood sampling at defined intensities. There is no shortcut. No estimation from heart rate drift. No proxy from a twenty-minute power test. The blood tells you what the blood tells you.
Lab Testing vs Portable Analysers: Which Path to Take
You have two routes to get this data, and both produce usable results.
Lab testing with a sport scientist is the traditional approach. You book a session at a university exercise physiology lab or a private sports testing facility. A physiologist sets up the protocol, takes the blood samples, and interprets the results. Cost is typically $150–300 per session, depending on location and whether a VO2max test is bundled in.
The advantages are obvious: controlled environment, experienced hands, professional interpretation. Someone who has looked at hundreds of lactate curves can spot nuances — a flat early section suggesting strong aerobic development, a steep late rise suggesting limited anaerobic buffering, an unusually high resting value suggesting incomplete recovery.
The disadvantage is also obvious: you can only do it when you can get to the lab.
Portable analysers put the same measurement in your own hands. The technology is straightforward — a handheld device, single-use test strips, and a lancet for the fingertip prick. You run the protocol on your smart trainer, take your own samples, log the results, and plot the curve.
The main players in the portable space:
- Lactate Pro 2 — The most widely used portable analyser in sport. Small, reliable, requires just 0.3 µL of blood. Costs around $350–400. Strips run roughly $4 each.
- Lactate Plus — Popular in research and coaching. Slightly larger sample volume. Device costs $300–350. Strips around $3–4 each.
- EKF Lactate Scout 4 — Good accuracy, fast reading time. Similar price range to the Lactate Pro 2.
And then there's a different category entirely:
- Moxy Monitor — This doesn't measure blood lactate at all. It measures muscle oxygen saturation (SmO2) using near-infrared light. It's non-invasive — no needles, no blood — and tracks how much oxygen your muscles are extracting in real time. It's useful data, but it's not the same measurement. Don't confuse the two. If you want lactate numbers, you need a lactate analyser.
A word on accuracy. Billat's work on lactate kinetics has shown that the critical factor isn't absolute precision — it's consistency. A portable analyser that reads 0.2 mmol/L differently from a lab analyser but produces the same reading every time you test at the same intensity is perfectly usable for tracking trends. What matters is that you use the same device, the same protocol, and the same conditions each time. That's what makes your curve comparable from one test to the next.
The Step Test Protocol: How a Lactate Test Actually Works
Whether you're in a lab or on your turbo trainer at home, the protocol follows the same structure. It's called a step test — or a graded exercise test — and it goes like this.
Warm-up. Ten minutes of easy spinning. Nothing structured. Get the legs moving, get the blood flowing. This isn't part of the test; it's preparation.
Starting power. The first test stage begins at a power output well below your aerobic threshold. For most trained amateur cyclists, that's somewhere around 100–130 watts. If you're not sure, start lower. Starting too high means you miss the early, flat part of the curve — and that flat section is important.
Stage duration. Each stage lasts 3–5 minutes. Three minutes is the minimum to reach a physiological steady state at each intensity. Five minutes gives a more stable reading, particularly at higher intensities where lactate kinetics are slower to settle. Most protocols use 4-minute stages as a sensible middle ground.
Power increments. At the end of each stage, power increases by 20–30 watts. Smaller increments (20W) give you more data points and a more detailed curve. Larger increments (30W) keep the test shorter but sacrifice resolution. For a first test, 25-watt steps are a good default.
Blood sampling. In the final 30 seconds of each stage, you take a blood sample. This is a fingertip prick — a small lancet, a drop of blood onto a test strip, and a reading in 15 seconds. The technique matters: clean hands, dry skin, use the second drop of blood (the first can be diluted by interstitial fluid), and get the sample onto the strip quickly.
Heart rate and RPE. Record both at each stage. Heart rate gives you an additional data stream to cross-reference. RPE (rate of perceived exertion on a 6–20 or 1–10 scale) gives you a subjective anchor that's surprisingly useful when comparing tests over time.
Termination. The test continues until one of three things happens: blood lactate exceeds 8 mmol/L, you can no longer maintain the target power, or you've completed the planned number of stages. For most riders, 8–12 stages covers the full range from easy spinning to well above threshold.
The whole test takes 40–60 minutes including warm-up. You'll use 8–12 test strips. And at the end, you'll have a dataset that looks something like this:
| Stage | Power (W) | Lactate (mmol/L) | Heart Rate (bpm) | RPE | |-------|-----------|-------------------|-------------------|-----| | 1 | 120 | 1.0 | 112 | 8 | | 2 | 145 | 1.1 | 121 | 9 | | 3 | 170 | 1.2 | 130 | 10 | | 4 | 195 | 1.4 | 138 | 11 | | 5 | 220 | 1.8 | 147 | 13 | | 6 | 245 | 2.4 | 155 | 14 | | 7 | 270 | 3.2 | 163 | 16 | | 8 | 295 | 4.8 | 172 | 17 | | 9 | 320 | 6.5 | 179 | 19 | | 10 | 345 | 8.9 | 185 | 20 |
That's your raw data. Now you need to read it.
Interpreting the Curve: LT1, LT2, and Everything Between
Plot lactate (vertical axis) against power (horizontal axis). You're looking for two inflection points — two places where the curve changes behaviour.
LT1 — The First Lactate Threshold. This is the point where lactate first rises meaningfully above your resting baseline. In the sample data above, lactate sits flat around 1.0–1.2 mmol/L for the first three stages, then starts to creep up at stage 4 and lifts more clearly at stage 5. LT1 sits somewhere around 195–220 watts in this example.
Physiologically, LT1 marks the upper boundary of genuine aerobic riding. Below this point, your body clears lactate as fast as it produces it. Production and clearance are in balance. You are riding in a metabolically sustainable state — true zone 2.
LT1 typically shows up at a blood lactate concentration of 1.5–2.0 mmol/L, though this varies between individuals. The wattage matters more than the concentration.
LT2 — The Second Lactate Threshold. This is where the curve steepens sharply. In the sample data, there's a clear acceleration between stages 7 and 8 — lactate jumps from 3.2 to 4.8 mmol/L. LT2 sits around 280–295 watts.
LT2 represents the point where lactate accumulation outpaces clearance. Ride above this intensity and you're on borrowed time. This correlates closely — though not perfectly — with your functional threshold power. LT2 typically occurs at 3.5–5.0 mmol/L.
The gap between LT1 and LT2 is itself informative. In the example, that's a range of roughly 75 watts. A narrow gap suggests the rider's aerobic system is relatively underdeveloped — there isn't much room between "easy and sustainable" and "threshold and failing." A wide gap suggests strong aerobic development with a large trainable zone between comfortable endurance and threshold work.
The curve shape matters as much as the threshold numbers. A curve that rises gently and then steepens late is the hallmark of a well-developed aerobic engine — the rider can push to relatively high power outputs before lactate begins to climb steeply. A curve that rises early and steeply suggests the opposite: the aerobic base isn't clearing lactate efficiently, and the rider is leaking into anaerobic metabolism at lower intensities than they should be.
Here's where it gets really interesting. When you retest after a training block, the question isn't just "did my thresholds move?" It's "did the shape of the curve change?" A rightward shift — the entire curve sliding to the right, meaning you're producing the same lactate at higher power outputs — is the clearest sign that your aerobic system has improved. Your body is doing more work before it starts to struggle.
Setting All Five Training Zones from Lactate Data
This is the practical payoff. Once you have LT1 and LT2 identified, you can set every training zone with physiological precision instead of percentages.
Zone 1 — Active Recovery. Below 85% of LT1 power. In the example above, that's below roughly 170 watts. Blood lactate stays at or near resting levels. This is properly easy — easier than most people ride when they think they're going easy.
Zone 2 — Endurance / Aerobic Base. 85% of LT1 up to LT1 itself. In the example, roughly 170–210 watts. Lactate is stable and below 2 mmol/L. This is the zone where you build mitochondrial density and fat oxidation capacity. The zone most amateurs ride above because their FTP-based zone 2 is set too high.
Zone 3 — Tempo. LT1 to roughly 85% of LT2 power. In the example, 210–250 watts. Lactate is rising but manageable — you're above the aerobic threshold but not yet approaching the anaerobic one. This is the grey zone that gets a bad reputation, though it has legitimate training applications for sustained power work.
Zone 4 — Threshold. 85% of LT2 up to LT2. In the example, 250–290 watts. Lactate is approaching the steep part of the curve. You can sustain efforts here for 20–60 minutes depending on fitness. This is where FTP-based zones often overlap — but with lactate data, you know exactly where threshold sits rather than estimating.
Zone 5 — VO2max and Above. Above LT2. In the example, above 290 watts. Lactate is accumulating rapidly. Efforts here are measured in minutes, not hours. Short, hard intervals to push maximal aerobic power.
The key difference from percentage-based zones: the boundaries are where your body puts them, not where a formula predicts they should be. For some riders, LT1 sits at 68% of FTP. For others, it's at 78%. That's a meaningful difference — ten watts or more — and it's the difference between riding in genuine zone 2 and drifting into the grey zone on every endurance ride.
When and How Often to Retest
The lactate curve is not fixed. It responds to training. That's precisely why it's useful — it doesn't just tell you where you are, it tells you whether your training is working.
During a structured training block: retest every 8–12 weeks. This is enough time for meaningful physiological adaptation to show up in the data. Testing more frequently than every six weeks is mostly noise — the changes are too small to distinguish from day-to-day variation.
At the transition between training phases: a test at the end of base, another at the end of build, and one pre-season gives you three data points across a macro-cycle. That's a story you can read.
Consistency in testing conditions is non-negotiable. Same time of day. Same warm-up. Same fuelling state — ideally fed, with the same pre-test meal. Same hydration. Same analyser, same brand of strips. If you test fasted one time and fed the next, you're comparing apples and bicycles.
What you're looking for between tests:
- Rightward shift of the whole curve — you're producing the same lactate concentrations at higher powers. This is the sign that aerobic training is working. Your mitochondria are clearing lactate more efficiently.
- LT1 moving right — your aerobic threshold has increased. Zone 2 now covers a wider power range. This is the primary target of a base training phase.
- LT2 moving right — your anaerobic threshold has increased. You can sustain higher power before lactate goes exponential. This is the target of a build phase.
- The gap between LT1 and LT2 widening — your trainable range is expanding. There's more room to do tempo and sweet spot work without crossing into threshold.
- Curve shape flattening — the early stages stay flatter for longer before rising. This is a sign of improved aerobic efficiency across the board.
If your curve hasn't shifted after 12 weeks of training, that's data too. It might mean your training zones were wrong (which is exactly the problem lactate testing solves). It might mean you need more volume, or different intensity distribution, or better recovery. But at least you know — instead of guessing for another three months.
Portable Analyser Buying Guide: What to Actually Spend Your Money On
If you're going to self-test, here's the practical breakdown.
The device itself is a one-time cost. The strips are the ongoing cost. This is the economics of lactate testing, and it's worth understanding before you commit.
A Lactate Pro 2 costs around $350–400. The strips come in boxes of 25 and cost roughly $90–100 per box — about $3.50–4.00 per strip. A single step test uses 8–12 strips. So each self-administered test costs $30–50 in consumables.
Compare that to $150–300 per lab visit. If you test four times a year — which is a reasonable frequency for a structured training programme — the portable analyser pays for itself within the first year.
What to buy:
- Lactate Pro 2 — smallest sample volume (0.3 µL), fastest reading time (15 seconds), most widely used in elite sport. This is what I'd recommend for most self-testers. The strips can be hard to source in some countries, so check availability before buying.
- Lactate Plus — solid build, reliable, slightly larger but very accurate. Good choice if Lactate Pro strips aren't readily available in your region.
- EKF Lactate Scout 4 — competitive on accuracy and strip cost. Worth considering if the price is right where you are.
What to buy alongside it:
- A box of 25 strips to start (gives you two full tests plus spares for technique practice).
- Lancets — single-use, spring-loaded. They're cheap. Buy a box of 100.
- Alcohol swabs for cleaning the finger before sampling.
- A logbook or spreadsheet template for recording results.
Technique tips that matter:
Wash your hands before testing. Any sugar residue on your skin — from a gel, from food, from a sports drink — will contaminate the sample and give a falsely high reading. Dry your hands thoroughly. Prick the side of the fingertip, not the pad — it's less painful and bleeds more freely. Wipe away the first drop of blood with a clean tissue. Apply the second drop to the strip. This second-drop technique is standard practice in exercise physiology labs and eliminates interstitial fluid contamination.
Rotate fingers between stages. You'll be pricking ten times in an hour. Spreading the pricks across multiple fingers keeps any single fingertip from becoming too sore to give a clean sample.
What Lactate Testing Won't Tell You
Let me be straight about the limitations, because this test isn't a crystal ball.
Lactate testing doesn't tell you your VO2max. It doesn't tell you your anaerobic capacity. It doesn't measure fat oxidation rates (though it gives indirect clues). It doesn't tell you whether you'll win on Sunday.
It tells you where two specific metabolic transitions happen and how your body responds to increasing intensity. That's a lot. But it's not everything.
Combining a lactate step test with a VO2max test — which most labs can run simultaneously — gives you a much more detailed picture. Adding a substrate oxidation analysis (measuring expired gases to see how much fat and carbohydrate you're burning at each stage) is even better. But those tests require lab equipment. The lactate test is the one you can do at home, repeatedly, for the cost of a few test strips.
The other limitation is interpretation. A lab physiologist has context. They've seen hundreds of curves. They know what a stressed curve looks like versus a well-rested one, what dehydration does to readings, what poor sampling technique produces. If you're self-testing for the first time, consider booking one lab test first to establish a baseline and learn the protocol, then self-test going forward.
The Practical Bottom Line
FTP testing gives you a number. Lactate testing gives you a map.
That number — your FTP — is a useful training reference. Nobody is saying throw it away. But it's one coordinate on a map that has at least two landmarks you need to know about: LT1 and LT2. And the only way to find those landmarks is to measure them.
For a masters cyclist investing serious time in structured training — and let's be honest, if you're reading this far into an article about lactate kinetics, that's you — the $350 investment in a portable analyser and a quarterly testing habit gives you something that no amount of twenty-minute FTP testing provides. It gives you the actual physiological data that your training zones should be built on.
You'll ride easier on easy days. Harder on hard days. And you'll stop wasting time in the grey zone that makes you tired without making you faster.
That's fixable. And now you know how.
If you want to talk through your lactate test results with riders who've been through it — or argue about whether 4-minute stages are better than 3-minute stages (they are) — the Roadman Cycling community on Skool is where that conversation happens. We get into the detail.