Heat is the training load nobody logs

Squads count kilometres and jump contacts obsessively, then treat a thirty-degree afternoon as weather rather than work.

A tempo session in cool conditions and the same tempo session in humid heat are not the same session. Everybody accepts that in conversation and almost nobody records it. The log says eight by four hundred at a given pace. The physiology says one of those was substantially harder, produced more cardiovascular drift, drew down more glycogen and left the athlete needing another day.

Heat load is a real training stress with a delayed cost, and it hides from every monitoring system in common use because those systems count external work. Distance run. Contacts made. Weight lifted. All of it environment-blind.

The internal measures ought to catch it, and they partly do. Heart rate runs higher for the same pace, which is why coaches who watch heart rate in the summer often think their athletes have lost fitness in June and found it again in September. They have not. They were pushing blood to the skin. But heart rate at a given pace is a lagging and crude proxy, it is confounded by hydration and sleep, and it tells you the session was hard without telling you how much recovery it will take back.

My view is that heat deserves the same status as altitude in a plan, and it does not get it. Nobody would send a squad to two thousand metres for a fortnight without adjusting expectations for the first ten days. Plenty of squads will train through a heatwave at unchanged intensity and then wonder why the following block feels flat.

There is an upside worth being greedy about. Repeated heat exposure produces adaptations that are useful in cool conditions too: plasma volume expands, sweating starts earlier, the cardiovascular cost of a given pace falls. That is a genuine training effect available for free to anybody who happens to live somewhere warm, and it is being harvested accidentally rather than planned.

Which is the actual complaint. Not that heat is dangerous, though it can be. That it is a dose, and doses should be prescribed rather than suffered.

Write the temperature and humidity in the log next to the splits. Do it for a season. You will find at least one block where the athlete was not overtrained and was simply hot.