What is Lactate?
Lactate often gets a bad reputation. It's frequently blamed for that burning feeling in your legs during a hard effort, but the reality is more nuanced.
Lactate is a by-product of your body breaking down carbohydrates for energy. It's produced constantly, even at rest.
At easy paces, your body creates lactate slowly and clears it just as fast so it never builds up. The process is smooth and efficient. As you run faster, your muscles need energy more quickly than your aerobic system alone can provide. Your body starts producing lactate at a faster rate, and this is where the balance starts to shift.
What is Lactate Threshold?
Your lactate threshold is the tipping point: the pace at which lactate begins to accumulate in your bloodstream faster than your body can clear it. Below this point, you're in balance. Your body is producing lactate and recycling it efficiently. You can maintain the effort for a long time.
Above this point, lactate starts to pile up. That build-up disrupts your muscles' ability to contract efficiently, leading to the familiar heavy, burning sensation that forces you to slow down or stop.
Think of it like a bath with a drain. Easy running = water trickling in slowly, drain keeps up. Hard running above threshold = water pouring in faster than the drain can handle. The bath overflows. Your lactate threshold is essentially the highest intensity you can sustain for a prolonged period before that overflow begins.
How is it Different from VO₂ Max?
These two terms are often used interchangeably, but they measure different things.
VO₂ max is the maximum amount of oxygen your body can use during exercise. It reflects your aerobic ceiling – your absolute top-end capacity.
Lactate threshold reflects how close to that ceiling you can sustainably run. Two runners can have the same VO₂ max, but the one with a higher lactate threshold will race faster over longer distances because they can operate at a higher percentage of their capacity without fatiguing.
Why Does it Matter for Running Performance?
Your lactate threshold has a direct impact on how fast you can run, for how long, across almost every race distance.
Half marathon and marathon: Your threshold pace sits close to half marathon race pace, and just above marathon pace. Raising it means you can hold a faster pace throughout the race without accumulating the fatigue that causes you to fade in the final miles.
10K: You'll spend much of a 10K at or just above your threshold. A higher threshold means you can push harder before the wheels come off.
5K: Even at 5K, where you're working above threshold for most of the race, a higher threshold gives you a stronger base to work from, and makes the effort feel more manageable.
In short: raise your lactate threshold, and you become a faster, more efficient runner across every distance.
How Do You Know You're at Threshold?
You don't need a lab test to recognise threshold effort. Here are the real-world cues:
Breathing: Noticeably harder than easy running, but rhythmic and controlled, not gasping. You could speak in short sentences, not comfortably hold a conversation.
Effort: Hard, but not all-out. Somewhere between "this is challenging" and "I couldn't hold this much longer." Around a 7-8 out of 10.
Legs: Some fatigue accumulating, but manageable. Not the burning, heavy sensation of going too hard – yet.
Sustainability: You could hold this pace for roughly 40-60 minutes if you had to. Not much longer.
If you feel like you're on the edge of unravelling, your legs are seizing up, and your breathing is ragged, you've likely crossed above your threshold into anaerobic territory.
How Does Lactate Threshold Change With Training?
This is the good news: your lactate threshold is highly trainable.
When you consistently run sessions that target threshold intensity, your body adapts in several ways:
Your muscles become more efficient at clearing and recycling lactate
Your mitochondria (the energy-producing units in your cells) increase in number and efficiency
Your cardiovascular system gets better at delivering oxygen to working muscles
Your body learns to rely more on fat as a fuel source at higher intensities, sparing carbohydrates
Over weeks and months of structured training, you'll find that paces which once felt hard become manageable, and your threshold pace itself will shift faster. That's the adaptation working.
Progress won't feel dramatic week to week. But if you look back after 8-12 weeks of consistent training, the paces in your Runna plan will reflect how much your threshold has moved.
How Does Runna Train Your Lactate Threshold?
Runna targets your lactate threshold through two key session types that appear regularly in your plan:
Interval sessions break the work into shorter, harder efforts at or around your threshold pace, with walking recovery between reps. The structure lets you accumulate more time at threshold than you could do continuously, which drives strong physiological adaptation.
Tempo runs keep you at a sustained, controlled effort just below threshold, building your ability to hold a strong pace for longer and improving lactate clearance over extended efforts.
Both session types are working towards the same goal, raising the point at which your body tips from aerobic to anaerobic, just via slightly different routes.
The Bottom Line
Lactate threshold isn't just a technical term coaches throw around, it's one of the most important physiological factors determining how fast you can race. Raise it, and almost everything else in your running improves: your race times, your ability to hold pace late in a run, and your overall endurance.
Every interval session and tempo run in your Runna plan is doing exactly that – progressively pushing your threshold higher, so that the pace that once felt hard eventually starts to feel controlled.