Lactate Threshold, Explained for Runners

Most runners have heard the phrase "threshold pace." It is a real breakpoint in how the body makes energy, and it can be measured in one session on a treadmill.

What is happening in the muscle

At an easy pace, muscle burns mostly fat with some carbohydrate, and the small amount of lactate it makes is cleared as fast as it is produced. As the pace climbs, the muscle leans harder on carbohydrate and lactate production rises. Past a certain point, clearance cannot keep pace with production, and lactate begins to pile up in the blood.

Lactate itself is not the problem. The acid that builds up alongside it is. The body buffers that acid, and buffering releases extra carbon dioxide that has to be breathed out. So breathing rises faster than oxygen use. That shift in breathing is what the test's breath analyzer detects, and it is why these are called ventilatory thresholds.

VT1 is the first breakpoint. Lactate has started to rise above resting levels, but the body is still clearing it. Below VT1 you can run for hours and hold a conversation. VT2 is the second breakpoint. Clearance can no longer match production, breathing turns labored, and the clock starts. A trained runner can hold VT2 pace for roughly 45 minutes to an hour.

Why measuring beats guessing

The common shortcut is a formula: 220 minus age, then percentages of that. The formula misses true max heart rate by 10 beats or more in many people, and it says nothing about where the thresholds fall. Two 45 year olds with the same max heart rate can reach VT2 at very different paces, because threshold reflects training, not age.

Guessing by feel has its own problem. Many runners drift above VT1 on easy days, which leaves them too tired to run hard on hard days. The result is a lot of miles in the middle, where the aerobic gain is modest and the fatigue is high.

How we build zones from it

Our VO2 max test ($249) runs on a treadmill with a mask that measures every breath. Speed and incline step up in stages until the person stops. The sheet gives VO2 max, VT1 heart rate, VT2 heart rate and peak heart rate. We build cardio zones from those thresholds instead of an age formula.

• Below VT1 is where most weekly volume belongs. Easy, conversational, repeatable.
• Between VT1 and VT2 is tempo work. Steady and controlled, a few words at a time.
• Above VT2 is interval territory. Short efforts with real rest between them.

Thresholds move with training, usually before VO2 max does, so a runner on a plan is worth retesting every four to six months to keep the zones honest.

That's why we test it instead of estimating it.

This article is educational and is not medical advice.

Book a VO2 max test at HYBRD Health ($249)