The four hundred is not the endurance event people call it

A single lap of the track is run almost entirely without oxygen, which is why the last hundred metres looks like a different sport.

There is a persistent idea that a lap of the track sits somewhere between sprinting and middle distance, a sort of compromise event where you sprint a bit and then hang on aerobically. That is not what is happening physiologically, and getting it wrong is why so many athletes train the event badly.

For roughly the first forty seconds of maximal effort, most of the energy comes from stored phosphates and from breaking down glucose without oxygen. The aerobic system contributes, and its contribution rises through the race, but it never becomes the main supplier at this distance. What limits the runner is not running out of fuel. It is the accumulation of the by-products of producing that fuel quickly, which is why the last eighty metres look like a man wading through setting concrete rather than a man who is tired in any ordinary sense.

That distinction matters because it dictates training. If you believe the event is part endurance, you spend the winter building an aerobic base and running long repetitions at a pace nobody races at. Some of that is useful, mostly for recovering between sessions. But the specific adaptation the event needs is tolerance: the ability to keep recruiting muscle fibres and keep coordinating a sprinting action while the chemistry inside the muscle turns hostile. You only get that by putting yourself in that state repeatedly, which is brutal, which is why it gets avoided.

The second consequence is tactical and it is the one coaches argue about. Because the anaerobic supply is finite and largely front-loaded, the fastest way around a lap is to run the first two hundred hard and lose less than everyone else in the second, not to run even splits. Even pacing works in events where the aerobic system is the main supplier. Here it leaves capacity unused.

The risk, obviously, is going out too hard and tying up at two eighty, which is the most public failure in athletics and looks like a lack of discipline. It usually is not. It is a bet placed correctly that did not pay.

I would rather watch an athlete misjudge that bet than watch one run a tidy, conservative lap and finish fourth having felt fine at the line.