Pacing in Heat and Humidity

In tropical climates, heat and humidity are the biggest outside factors on race day. Races in such climates often start very early (for example, a 03:00 start for the full marathon) to avoid the worst of the heat, but humidity is high from the start and temperatures rise after sunrise – exactly when runners reach the hardest part of the race.

How heat affects pacing#

• At the same pace, heart rate and perceived effort gradually rise in hot and humid conditions. A pace that felt easy in the first hour can feel hard in the third.
• Runners lose more fluid and salt through sweat, and many slow down in the final part of the race.
• This is one of the main reasons for the conservative start in every strategy plan: energy saved early is energy available when it is hottest.
• It is also why pacers need a sufficient pacing buffer. A pacer who is close to their own limit will suffer more from the heat than the runners they are pacing.

Preparation in training#

• Run several training sessions at the same time of day as the race, so that you know how your body responds to early-morning conditions.
• Practise your drinking and electrolyte routine in training; never try anything new on race day.
• Notice how your heart rate and effort drift at target pace during longer sessions, so that it does not surprise you on race day.

Race day#

• Drink well and include electrolytes the day before the race; arrive well hydrated.
• Wear light, breathable clothing; late finishers should consider a cap and sunscreen.
• Do not change the pace plan on your own because of the weather. If conditions require an adjustment, the pacer coordinator will communicate it to all teams.
• Watch your runners closely.