Two riders post the same VO2max and the same body weight. One holds 280 watts for an hour. The other cracks at 250. VLamax is the metric coaches blame, and it might explain the gap, but it’s far shakier than most sales pages admit.
Here’s the honest version: VLamax is a computed number, not a direct reading, and it has real error bars. Use it as a lens, not a verdict.
What VLamax Is and How It’s Measured
VLamax (maximal lactate accumulation rate) is how fast lactate builds in your blood during a flat-out 15-second sprint. Your VO2max is the most oxygen your body can use per minute. Your FTP (Functional Threshold Power) is the highest power you can hold for about an hour without blowing up.
The lab test is simple. You sprint for 15 seconds. A tech compares blood lactate before and after.
VLamax = (peak lactate - resting lactate) / (15 s - alactic time)
The “alactic time” is the first few seconds fueled by stored phosphocreatine, which makes no lactate. Researchers usually assume 3.5 seconds. In short: you divide the lactate rise by the time glycolysis was actually working.
Trained cyclists score about 0.5 to 0.7 mmol/L/s. One study of 50 cyclists averaged 0.54. Another of 30 averaged 0.64 to 0.67. Reviews report 0.2 to 1.0 across all groups.
One catch matters. This is lactate piling up in your blood, not a direct count of glycolytic flux. It’s a stand-in. That’s why the best papers call it model-derived.
How Reliable Is VLamax Compared With VO2max?
Not very, compared with VO2max. Sprint peak power repeated almost perfectly (ICC 0.986). The lactate part is the noisy part.
In a 30-rider study, the test-to-test error (CV, the average swing between repeat tests) was 18.6%. Peak power swung only 4.7%. A 2026 review of 11 studies found errors from 4.6% to 26.4%, with a pooled score of 0.84. Running tests held up better than cycling tests.
Translation: your VLamax can move a lot between two identical tests, just from noise.
How VLamax and VO2max Set Your FTP
Think of a bathtub. The faucet is glycolysis, which makes lactate fast. The drain is your aerobic system, which clears it. VLamax sets how wide the faucet opens. VO2max sets how big the drain is.
At a steady effort, the water level holds. That’s your maximal lactate steady state, close to FTP. Push harder and the faucet outruns the drain. The tub overflows. That’s the moment you blow up.
So the Mader model says a bigger faucet lowers your steady-state power. A bigger drain raises it. Same drain, wider faucet, lower threshold. That’s the 280 versus 250 puzzle.
Here’s the catch. Researchers used VLamax, VO2max and body mass to predict steady-state power in 13 active men. The average matched the lab (282 W versus 277 W). Individual errors ran from about minus 39 to plus 29 watts. For one rider, that’s a coin flip on a 280 W FTP.
The model also assumes your glycolysis rises on a fixed schedule with effort. Training changes that. Treat the output as an estimate.
Models explain. They don’t replace your power file.
Can You Train VLamax Up or Down?
Popular advice says sprints raise it and Zone 2 lowers it. The one randomized trial I found says otherwise. Participants did 4 to 6 all-out 30-second sprints, three times a week. Within two weeks, their VLamax dropped by 0.08 mmol/L/s. Then it plateaued. A second group rode 60 minutes at an easy lactate level of 1.5 to 2.5 mmol/L. Their VLamax didn’t move.
Treat that carefully. Ten people per group is tiny. Individual results varied widely. After six weeks, the groups didn’t differ significantly in VLamax, VO2max or calculated steady-state power. It’s a warning against confident claims, not a new rule.
So what should you do with it? Don’t pick workouts to chase a VLamax target. Pick them to improve what you can see: sprint power, threshold power and how well your heart rate holds on long rides. Those numbers move, and your files show it.
Even the experts aren’t settled. Wackerhage, Seiler and colleagues note that no accepted measure of maximal glycolysis exists. They propose a new one, called vLapeak. Other researchers say it looks promising but needs long-term studies. In plain words: the field is still arguing about what to measure.
What about fat burning? Mader-style software claims a higher VLamax suppresses fat oxidation and lowers your best fat-burning power. I found no peer-reviewed study that measured both. Treat it as a model hypothesis. For the base-building side, see how Zone 2 builds the aerobic base.
Who Should Care About VLamax
| Event | Model-based lean | Why |
|---|---|---|
| Criterium, track | Higher VLamax can help | Repeated surges and sprints |
| Time trial, Ironman bike | Lower VLamax tends to help | Steady, sustained power |
| Olympic or 70.3 | Middle ground | Mix of surges and steady work |
| Running (5K to marathon) | Weak link | Added just 4.4% explained variance in a 5000 m model of 44 athletes |
These leans come from the model, not from trials. Treat the table as a starting guess.
If you race crits, sprint power is your weapon, and you can already see it in a power file. If you race a 70.3 or an Ironman, the question is different. Can you hold steady power for hours without your heart rate creeping up? That’s a drift question, not a sprint question.
Runners get the weakest case. Researcher Quittmann noted that cycling findings don’t transfer cleanly to running. In his 5000 m work, VLamax was linked to finishing kick and pacing. It still explained only 4.4% extra variance. In short: for a runner, it’s a small piece of the puzzle.
An elite-cyclist study (n=11) found VLamax tracked 15-second sprint power closely. The authors argued it adds little beyond the sprint power itself. That’s a fair point. You can see your sprint without a needle.
A Case Study: Dan’s Two Numbers
Take a triathlete I’ll call Dan, 41, training for a 70.3. This is a fictional example. His best 5-second power is 980 W and his FTP is 250 W, a ratio of 3.9. His 3-hour rides show a drift ratio, the change in heart-rate-to-power efficiency between first and second half, of 9%.
He wants a lab number. Instead, he reads what his own files already say. A high sprint-to-threshold ratio plus heavy drift suggests a punchy engine that fades on long steady efforts. So he drops two sprint sessions and adds a long steady ride each week.
Twelve weeks later his sprint holds at 940 W, FTP reaches 262 W, and drift falls to 4%. Nothing here proves a VLamax change. The practical result still shows up in the file.
Using Your Own Data Without a Lab
You don’t need blood to act on the idea. Compare your short peak power with your threshold power. Watch how your heart rate drifts on long steady rides. Our deep dive on aerobic decoupling shows how to read it.
AthleteOS uses your historical power and heart rate data to place your training zones, then tracks your drift ratio on long efforts. It doesn’t measure or compute VLamax. If you’re weighing the lab-based tools that do model it, we compared them in the VLamax block tool comparison. To get zones that reflect how you actually perform, start a free trial of AthleteOS.
Your file already knows your engine. Read it.