Pacing the run when it gets hot mid-race

The reality

The Hub's Fueling planner builds a plan against the forecast conditions you entered at planning time. Conditions on the day can be worse: temperature 5C hotter than forecast, humidity higher, sun stronger. The run is where heat costs the most: it is the leg with the highest metabolic heat production per minute.

Pace adjustment for heat

A reasonable rule of thumb (Daniels and others):

• 18C or cooler: no pace adjustment.
• 18 to 22C: 1 to 2 percent slower than target pace.
• 22 to 26C: 3 to 5 percent slower.
• 26 to 30C: 6 to 10 percent slower.
• 30C+: 10 percent or more, plus accept that DNF risk rises sharply.

A 4:30 / km target at 28C becomes 4:48 to 4:54 / km. That is not "going easy"; that is going at the pace your body can actually sustain in those conditions.

Hydration shift

In hot conditions, fluid loss can easily double from moderate-temperature baseline. The Fueling planner projection will undershoot if conditions diverge:

• Per hour fluid target +30 to +50 percent for race-day temperature 5 to 8 C above your planning baseline.
• Sodium per hour +25 to +40 percent for the same shift. Heat acclimation lowers sweat sodium but the absolute total sodium loss still goes up because sweat rate goes up.

Cooling tactics

• Ice in hat, ice in trisuit at every aid station.
• Sponges down the front of the trisuit if available.
• Cold water on the head, not just down the throat.
• Run in the shade of any tree, building, or aid station awning that the course passes.

Cooling matters more than the marginal extra fluid. A brief moment of skin cooling buys minutes of pace.

When to walk

Walking through an aid station from km 5 onward in a hot run is not slow. It lets you drink, ice, and recover HR without losing more than 20 to 30 seconds per aid. The alternative (skipping aids to "save time") leads to overheating and a full-on bonk that costs minutes per km.

Red flags

If during the run any of these appear, slow down or stop:

• Goosebumps in heat (sign of impending heatstroke).
• No sweating despite high exertion.
• Disorientation.
• Severe muscle cramps.

The day's race is over the moment safety is at risk. Walk in, medical tent if needed, DNF if needed. See DNF / DNS handling.

What to do after

Refile a race recap noting weather notes and any pace / fueling adjustments you made. Future race plans for similar conditions improve from those notes.

See also: Fueling planner, Sweat rate test, Race plan reading.