If VO2 max is the number everyone has heard of, lactate threshold is the one that arguably matters more for most athletes and lactate testing is the process that actually tells you where yours sits. It gets less airtime than its flashier counterpart, partly because it's harder to explain in a single sentence, and partly because the word "lactate" still carries the ghost of an old misconception most coaches wish would quietly disappear.

Here's a clear-eyed look at what lactate testing actually involves, what it reveals about your physiology, and what you should, and shouldn't, expect it to tell you.

What Lactate actually Is

First, the misconception worth clearing up: lactate is not the villain it was once made out to be. For decades, lactic acid was blamed for the burning sensation in your muscles during hard efforts and the soreness that follows. That story turns out to be largely wrong.

Lactate is a byproduct of carbohydrate metabolism, your body produces it constantly, even at rest. At low intensities, your body clears it about as fast as it makes it, and blood lactate levels stay low. As exercise intensity increases, production begins to outpace clearance, and lactate starts to accumulate in the blood. The point at which this accumulation begins to accelerate meaningfully is what we're interested in.

That point is your lactate threshold, and finding it precisely is what lactate testing is designed to do.

What a Lactate test actually involves

A lactate test is a staged exercise protocol, typically conducted on a treadmill, bike ergometer, or rowing machine. You work through a series of incremental efforts, usually three to eight minutes at each stage, starting at a comfortable pace and increasing gradually.

At the end of each stage, a small blood sample is taken, usually from a fingertip or earlobe. The sample is analysed immediately using a portable lactate analyser, which returns a blood lactate concentration in millimoles per litre (mmol/L). Heart rate is recorded throughout, and in a well-run test, power output or pace data is captured at each stage too.

Plot those data points, lactate concentration against intensity, and you get a curve. The shape of that curve, and where it inflects, is the whole point.

What the curve tells you

At low intensities, blood lactate typically sits between 1 and 2 mmol/L and stays relatively flat. As intensity increases, it begins to rise gradually. Then, at a certain point, it starts rising more steeply, the curve bends upward.

There are two reference points practitioners commonly identify within that curve:

LT1 (the aerobic threshold) is the intensity at which lactate first begins to rise meaningfully above baseline. Below this point, you're working almost entirely aerobically, and you could sustain the effort for a very long time. This is the foundation of easy training and one reason why a lot of that training should feel genuinely easy.

LT2 (the anaerobic threshold) is the intensity at which lactate accumulation begins to accelerate sharply. Above this point, your body can no longer clear lactate as fast as it produces it, and fatigue will accumulate progressively. This roughly corresponds to what most athletes feel as their "comfortably hard" ceiling, the pace or power they can sustain for roughly an hour at maximum effort.

The gap between these two points, and how high an intensity you can sustain before LT2, is one of the most practically useful things you can learn about your physiology.

Does Lactate Threshold Predict Performance?

More reliably than VO2 max, in many cases.

While VO2 max describes the size of your aerobic engine, lactate threshold describes how much of that engine you can actually deploy during a race. An athlete who can sustain 90% of their VO2 max before hitting LT2 will generally outperform one with a higher VO2 max who runs into trouble at 75%,  even if the second athlete has more raw ceiling to theoretically work within.

This is the reason elite marathon runners can hold extraordinary paces for two hours or more: it's not just that their VO2 max is high, it's that their lactate threshold sits at a very high percentage of it. For most recreational athletes, raising LT2, either as an absolute intensity or as a proportion of VO2 max, is where the most meaningful performance gains live.

Can you improve your lactate threshold?

Yes, and in many ways it's more trainable than VO2 max.

The primary driver of lactate threshold improvement is volume, specifically, consistent aerobic work that develops the mitochondrial density and capillary network needed for more efficient lactate clearance. This is one of the physiological arguments for keeping most of your training genuinely easy: it builds the infrastructure your body needs to handle harder work better.

Threshold-specific sessions, sustained efforts at or just below LT2, often called tempo runs or sweet spot rides, also directly improve the intensity you can sustain before accumulation accelerates. And high-intensity interval work pushes the ceiling higher, which can in turn shift threshold upward over time.

The good news for more experienced athletes is that lactate threshold often continues to respond to training even when VO2 max has largely plateaued. It's one of the reasons that athletes in their thirties and forties, who are training intelligently, can still meaningfully improve their race performances.

What lactate testing won't tell you

A lactate test gives you a snapshot of your physiology at a single point in time, under specific test conditions. It doesn't tell you how you'll respond to a race that starts too fast, a hot day, or three hours of glycogen depletion. Threshold values also shift with fatigue, illness, and changes in training load, so a result from six months ago may not reflect where you are today.

There's also some variability in testing protocols, the stage length, the starting intensity, and even the timing of the blood draw can affect the curve you produce. Consistency of method matters enormously if you want to use repeat tests to track progress meaningfully.

And, as with all physiological metrics, a number in isolation only tells part of the story. Lactate data becomes genuinely powerful when it's interpreted alongside VO2 max, running economy or cycling efficiency, and an honest picture of training history and recovery.

So, should everyday athletes bother?

For a recreational athlete training for a local 10k or their first half marathon, a formal lactate test probably isn't essential, though it can still be illuminating. The training practices that improve lactate threshold (aerobic base, structured threshold work, consistency) are worth doing regardless of whether you've measured it precisely.

Where lactate testing earns its place is for athletes who are serious about performance and want to stop guessing. Knowing exactly where your thresholds sit means your easy days can be truly easy, your threshold sessions can be properly calibrated, and your race pacing can be built on something more reliable than feel. It removes the most common and costly training error in endurance sport, working too hard on the days that are meant to build your base, and not hard enough when real quality is called for.

Combined with VO2 max testing and sweat analysis, lactate profiling gives you a genuinely complete picture of what's happening physiologically and turns training from an educated guess into an informed plan.