3 Mistakes You’re Making with LT1: Fix Your Zone 2 Training!

Lactate threshold one, or LT1, is arguably the most important marker to determine your Zone 2 endurance training. Here the three things you likely get wrong about LT1. Number one. LT1 is determined as the first increase in lactate concentration. That refers to a test where you increase the load or speed in an incremental or stepwise manner, and you plot the lactate concentration on the y-axis and the power or speed on the x-axis. Now the question is, what determines, or how do you define, the first increase in lactate concentration?

First, is it an increase above the resting value, or is it an increase above the minimum value? And so, what is the first increase? Is it 0.01 mmol, 0.1 mmol, 0.5 mmol? What is it? Well, matter of fact, it depends on the actual testing device that you're using. Likely a handheld lactate meter has an error of measurement, so for example, if the error of measurement in your lactate meter is 0.5 mmol, then you could actually not determine an increase smaller than 0.5 as a real increase in lactate concentration.

So you would have to take this into account. Error number two: step duration, or duration of an increment. As mentioned, LT1, lactate threshold one, is defined as the first increase in lactate concentration, and therefore it is linked to the testing protocol. Now it's a matter of fact that short step durations, shown here as a blue lactate profile curve, result in not as low lactate concentration. So the decrease in lactate at low intensity will be not as pronounced, and then the rise, the increase, the exponential part in lactate comes later, meaning at a higher speed or power output, and is not as steep.

In contrast, longer step durations can result in, or they likely result in, a more pronounced decrease in lactate concentration at the lower intensities, and then a steeper, so earlier and steeper, increase of lactate at the higher speeds or power. Now obviously you can see that this changes whatever you define as the first increase. It changes the power, speed, at which it happened. So LT1 is highly dependent on the test protocol. The other error that most people got wrong is the assumption that LT1 actually is the same as maximum fat combustion rate, or maximum fat oxidation rate, which science tells us it is not.

Okay? First, as mentioned, it depends on the test protocol. Second, the maximum fat combustion happens individually, depending on the metabolic profile of your athlete, at different intensities, and is not related to the first increase in lactate concentration. Another thing that most people get wrong is the assumption that you need a lactate meter, that you need to do a lactate profile test, to actually determine LT1. That's not true. You can calculate lactate concentration curves for any duration using the Power Performance Decoder of INSCYD, and therefore get a lactate profile also if you're actually not doing a lactate test.

So with that you can determine LT1 for any athlete not coming into a lab, just doing remote testing using a power meter or a GPS device like the GPS running watch.