Marathon Race-Day Heat Strategy: Pacing, Cooling and Fuelling When It's Hot

Reset Your Pacing Plan Before the Gun

The single biggest race-day mistake in heat is starting at your goal pace and hoping to hang on. Large-scale marathon weather studies show finishing times slow by roughly 0.3% for every 1°C the dew point sits above the optimum, and the slowdown is steepest above a dew point of about 18°C. Build that into your plan before you start, not after you've blown up at mile 16:

• Dew point 15–18°C: aim 3–5% slower than your dry-weather goal pace.
• Dew point 18–21°C: aim 5–8% slower, and treat the race as an effort-based run rather than a pace-based one.
• Dew point >21°C: run entirely by heart rate or perceived effort — a fixed pace target will only tempt you to go out too hard.

Splitting the first 5K noticeably slower than "normal" isn't giving up time — in heat, it's the time you'd otherwise lose to walking later.

An Aid-Station Cooling and Fuelling Plan

Treat every aid station as two separate jobs — cooling and fuelling — rather than one grab-and-go stop.

Cooling: dousing vs drinking

Pouring water over your head and neck lowers skin temperature and eases the sensation of heat, but it doesn't rehydrate you — our guide on why marathon runners pour water on their heads covers the evidence behind this in more detail, including when it helps and when it's mostly psychological. On race day, use it as a genuine two-part routine at hot-weather aid stations: one cup over the head and back of the neck for cooling, a separate cup actually drunk for hydration. Don't let the dousing cup substitute for the drinking cup.

Fuelling: don't let heat wreck your gut

Heat diverts blood flow away from the gut towards the skin for cooling, which is part of why gels and sports drinks that sat fine in training can suddenly cause stomach trouble on a hot race day. Slightly diluting sports drink, taking gels with extra water rather than alone, and not increasing your usual carb intake just because it's hot all reduce that risk.

Adjust Your Electrolyte Plan for the Day

Sweat rate and sodium loss both climb in the heat, so a fuelling plan built around a cool training run can under-deliver on race day. Our electrolytes-per-hour guide covers how to work out your own targets — on a genuinely hot race day, that usually means shifting towards the upper end of your normal range rather than adding an arbitrary extra dose. Test any change in a training run first; race day is not the place to try a new electrolyte strategy for the first time.

Recognise the Warning Signs Before They Become a DNF

Dizziness, confusion, goosebumps despite the heat, or a sudden stop in sweating are not "push through it" signals — they're the same early warning signs covered in our heat exhaustion guide, and on a hot race day they're far more likely to show up. Walking through an aid station to cool down and reset is a pacing decision, not a failure; continuing to push through genuine heat-illness symptoms is how a bad patch turns into a medical tent visit.

Pre-Race Checklist for a Hot Marathon

• Light-coloured, breathable kit you've already raced or long-run tested — race day is not the day for new gear.
• Sunscreen applied before the start, reapplied at a drop-bag point if the race is long enough.
• A cap or visor, and sunglasses if the course is exposed.
• A realistic, effort-based pacing plan written down (or set on your watch) before the gun, not decided mile-by-mile in the moment.
• A clear idea of where the course's water and aid stations actually are, so you're not caught out between them.

Frequently Asked Questions

Should I still try for a personal best in a hot marathon?

Be honest with yourself before the start. If conditions are genuinely hot, chasing a PB pace plan usually ends in a much slower finish than running to effort from the gun. Many experienced runners quietly switch their "A goal" to a "B goal" the morning of a hot race — that's a smart adjustment, not a failure.

Is it better to start slower than planned or risk it and adjust later?

Start slower. The pace you lose in the first few kilometres by being cautious is almost always smaller than the time lost walking or stopping later if you go out too hard in heat.

What if the race doesn't have enough water stations for how hot it is?

Carry your own fluids if the course allows it, and don't be afraid to adjust your goal significantly or drop to a run-walk strategy. Finishing safely matters more than any single race-day number.