Your lactate threshold number means nothing outside the lab that made it

Two testers, two protocols, two sampling delays, and the same athlete walks out with numbers half a minute per kilometre apart.

A runner tells me their threshold is four minutes ten per kilometre. My first question is who tested you. My second is what protocol. If they cannot answer either, the number is decoration.

Blood lactate is a real measurement. What gets built on top of it is a stack of conventions, and the conventions are not shared.

Start with step length. A test using three minute stages and a test using six minute stages will not produce the same curve, because lactate needs time to move from muscle into blood and to reach something like a steady value. Short stages lag. The curve shifts right, the threshold pace looks faster, and the athlete goes home delighted with a number that describes the protocol rather than the athlete. Now change the sampling moment. Drawing at the end of a stage and drawing thirty seconds into the recovery are different measurements of different things, and both are done in practice.

Then there is the definition itself. Some labs use a fixed value, commonly four millimoles. Some use a rise above baseline. Some fit a curve and take a breakpoint, and the fitting method changes where the breakpoint lands. These are not small differences. They can move the reported threshold by enough pace to change how an athlete trains for a whole season.

Add analyser variation, capillary versus venous sampling, whether the athlete ate, whether they did a hard session the day before, glycogen state, even how warm their hands were.

None of this makes testing useless. It makes cross laboratory comparison useless, which is a different claim and the one worth making loudly, because the comparison is exactly what athletes do. They read a number attributed to a professional in a magazine, hold it against their own from a different protocol, and draw a conclusion that is pure noise.

Use the same lab, the same tester, the same protocol, the same time of day, the same pre test week. Then the numbers become a tracking tool, and tracking is where they earn their keep. The absolute value is close to meaningless. The direction of travel across three tests in one season tells you something real.

Anyone quoting a threshold pace without naming the protocol is quoting a rumour.