The three energy systems do not take turns

The textbook diagram of one fuel handing over to the next is a teaching aid that has quietly become a coaching error.

Every introductory physiology class draws the same picture. A short bar for the phosphate system, a medium bar for glycolysis, a long bar for aerobic metabolism, arranged like relay legs. Ten seconds, then two minutes, then everything after.

It is a useful cartoon. It is also wrong in the way that matters, because all three run at once, from the first step, and what changes across a race is only the proportion each contributes. Your aerobic system is working during a 60 metre dash. It contributes very little to that dash, but it is not asleep waiting for its shift.

Why care? Because the relay picture produces relay training. Sprinters decide aerobic work is irrelevant to them and drop it entirely. Distance runners decide sprint mechanics belong to somebody else. Both lose something.

The sprinter case is the one I find most obviously mishandled. A championship 100 metres is not one race, it is three or four efforts inside two days, with heats, semi-final and final, plus warm-ups that are themselves substantial work. What determines whether the fourth effort matches the first is largely how fast the athlete restores phosphate stores and clears the by-products of the previous one, and that restoration is an aerobic process. An athlete with no aerobic base runs a brilliant heat and a flat final, and everyone says he peaked wrong or got nervous.

The distance case runs the other way. A five thousand metre race is decided in the last lap by an anaerobic effort layered on top of an already exhausted system, and an athlete who has never trained above threshold has no top gear to reach for. Being aerobically superb and unable to change pace is a recognisable way to finish fourth.

The counterargument is that specialisation exists for a reason, and it does. There is limited training time and adaptations do compete with each other. Nobody should turn a sprinter into a tempo runner. But the choice is not between purity and dilution, it is about deciding which supporting quality is being neglected because a diagram implied it would not be needed until later.

Treat the systems as three taps, all open, with the handles moved by the demand of the moment. Train the tap you will actually need to open. Then look at your programme and ask which of the three you have never touched, and why that felt safe.