Lactate was never the thing making you hurt

A rejected piece of physiology from the last century still governs how many coaches plan sessions and read a burning quadricep.

The burn in the last two hundred metres is not lactic acid eating your legs. Lactate is a fuel. Your heart is happily consuming some of it while you complain about it, and the muscle beside the one that made it may be doing the same.

The old story went like this: oxygen runs short, the muscle switches to an emergency pathway, lactic acid piles up, acidity rises, contraction fails, you slow down. Tidy, dramatic and largely wrong. Lactate production rises with intensity even when oxygen is plentiful. It is not a distress signal. It is what a fast-working muscle does with fuel, and it gets shuttled to other tissue and burned.

The acidity that does accumulate comes from elsewhere in the metabolic accounting, and even that is not the whole story about fatigue, which involves calcium handling inside the fibre, energy supply, and a nervous system that reduces its own output before anything catastrophic happens. Fatigue is a regulated shutdown, not a chemical flood.

Why does this matter beyond pub trivia? Because the wrong model produces wrong sessions. If you believe lactate is poison, you train to avoid producing it, and you build athletes who have never learned to work while it is high. If you understand it as fuel and as a marker, you train the machinery that moves and uses it, which is a different session with a different shape: more work at controlled high intensity, less superstitious avoidance of the burn.

The blood measurement still has value, and I do not want to throw the tool out with the theory. A lactate reading tells you something real about the intensity a body is working at, and tracking it across a season shows whether the aerobic base is improving. But it is an indicator, in the way a temperature gauge indicates an engine. Nobody thinks the gauge is what is heating the car.

The corollary I like least is the cooldown mythology. Athletes jog for twenty minutes to flush lactate that has already cleared on its own within the hour, and skip the parts of recovery that actually influence tomorrow, which are sleep, food and how much load went in yesterday.

The chemistry stopped supporting the story around thirty years ago. The stretching circle at the end of training did not get the message.