Heat is the opponent nobody puts on the start list

Racing in humid conditions changes the physiology of an endurance event so completely that comparing times becomes pointless.

A marathon started at six in the morning because it was going to be thirty degrees by nine. Everyone accepted that as sensible. Almost nobody adjusted their expectations of the times, which is where the thinking stops.

Working muscle produces far more heat than movement, and most of that has to leave through skin. To move it there, blood is sent to the surface, which competes directly with the blood the legs want. In humid air, sweat stops evaporating efficiently, so the cooling that the diverted blood was supposed to buy does not arrive, and the athlete keeps paying the price without receiving the service. Heart rate climbs at the same pace. The runner is not weaker. The accounting has changed.

That is why heat mostly eats the back half of a race rather than the front. Core temperature rises gradually, so the first hour can feel deceptively normal, and the athlete who runs to feel rather than to a plan is being lied to by their own sensations.

Acclimation genuinely works, and the mechanism is unglamorous: plasma volume expands, sweating starts earlier and at a lower salt concentration, and the cardiovascular system regains some of the margin it lost. Two weeks of deliberate heat exposure gets most of it. What annoys me is how many federations still treat this as an optional extra for the athletes who happen to train somewhere hot, rather than as a scheduled block for anyone going to a summer championship in a humid city.

Pre-cooling is the other half, and it is undersold. Cold fluid and ice before the start lowers the temperature you begin from, which buys minutes at the end. It looks faintly ridiculous, an athlete in a vest full of ice packs in a call room, and it works better than most supplements anyone is selling.

The part I would change is comparative. Results in these conditions get read against personal bests set on a cool night, and athletes get written off for a performance that was, in context, the best of their careers.

Publish the wet bulb reading next to the winning time. Put it in the graphic. Once you have seen a couple of races with that number attached, you stop asking why nobody ran fast.