Heat is a pace you didn’t choose.
It’s 11 in the morning, you’re 30 km into a race you’ve trained months for, and the valley has stopped moving air. Your heart rate is ten beats higher than it should be for this pace. You haven’t sped up. The day has. If you hold the pace you planned in the cool of the morning, you’ll pay for it in the afternoon, and the bill in heat is steep.
Summer is here, and with it the big South African mountain races. Heat decides more of those days than fitness does, so here is how we think about it, how we train for it, and what to do when it goes wrong.
Why the same pace costs more
When you run, most of the energy you burn comes out as heat. On a cool day that heat leaves easily. On a hot day your body has to work to get rid of it: it sends more blood to the skin to shed heat and makes you sweat to cool it. That blood isn’t going to your legs, and the sweat is fluid you lose from your blood volume. Your heart makes up the difference by beating faster.
That’s why the honest answer to “what pace should I run in the heat?” is “slower than you want to”. The effort is the same as it always was. The speed it buys you is lower. Run to effort and breathing, not to the pace on your watch, and accept that a hot day is a slower day for everyone on the course.
The runners who do well in the heat aren’t the ones who suffer best. They’re the ones who slowed down first.
Heat is trainable
Your body adapts to heat, and it does it fairly quickly. With regular, controlled exposure over about ten days to two weeks, most runners start sweating earlier and more, lose less salt in that sweat, carry more blood plasma, and run with a lower heart rate and body temperature at the same effort. The adaptation also fades if you stop, so it belongs in the last few weeks before a hot race, not three months out.
A few ways to do it safely:
- Run easy in the warmer part of the day two or three times a week, rather than always at dawn. Easy means easy: heat is the stress, so the pace comes down.
- Dress warmer than the day needs on a short easy run if you live somewhere cool. It’s not glamorous, and it works.
- Keep your hard sessions cool. Heat and intensity together just make a hard session worse. Get the quality done when it’s cool, and use easy running for heat exposure.
If you’re training somewhere cool for a race somewhere hot, this matters even more. Up here in Hogsback the mornings are often misty and cool, which is lovely for training and no preparation at all for a hot valley in the afternoon.
Know what you lose
Everyone sweats at a different rate, and the spread is wide. Many runners lose somewhere between half a litre and a litre and a half an hour, and some lose more. Generic advice like “drink 500 ml an hour” is right for some runners and badly wrong for others, in both directions. Drinking far more than you lose is its own danger.
So measure it. The test is simple: weigh yourself, run for an hour at an easy-to-steady effort without drinking, weigh yourself again. The weight you lost is close to the sweat you lost. Do it on a warm day and on a cool day, and you have two numbers to plan with. It’s one of the field tests in Sigwren, and the result goes straight into your race-day fuelling and drinking plan.
Salt matters too. Nausea, a sloshing stomach and the feeling that water is going in but nothing is happening can all be signs your electrolytes are low. Carry electrolyte drinks or tablets you’ve used in training, and a small sachet of salt for emergencies.
Keep the heat off you
- Use water on the outside as well as the inside. Splash your head, neck and torso at every chance, and soak your cap or buff. If the course crosses a river and you have time, use it.
- Dress for the sun. A light cap or brimmed hat, a neck flap, sun sleeves and proper sunscreen, especially at altitude, where the sun is stronger than it feels.
- Breathe slowly. When you’re hot and anxious, breathing runs ahead of the effort, and you start working hard to breathe without getting much for it. A long, smooth exhale settles the breath and the nervous system with it. We wrote about why in The Physiology of Calm.
When it goes wrong
Heat exhaustion usually comes on gradually: heavy sweating, weakness, headache, light-headedness, nausea, cramps. It’s your body telling you it can’t keep up. Slow down, get into shade, cool off and take fluid and salt.
Heatstroke is different, and it’s a medical emergency. The warning signs are:
- confusion, disorientation or behaving out of character;
- hot skin that has stopped sweating;
- shivering, goosebumps or feeling cold in the heat, a sign that temperature control has failed;
- collapse, severe cramping or seizures.
If you see this in yourself or another runner, stop. Get into shade, or make shade with your emergency blanket. Start cooling immediately with water on the torso, head and neck, ice or a slushy if there is any, and fanning. Get medical help as fast as possible. Heatstroke can kill, and fast cooling is what saves people.
How we plan for it
Heat isn’t an afterthought in how we plan a race. In Sigwren, heat is one of the factors that goes into what each stretch of a course will cost you, alongside the gradient, the ground underfoot, altitude and darkness. A section you’ll reach at midday on an exposed slope is planned slower than the same ground at dawn, and your pacing and fuelling plan on your watch reflects that. In training, sessions are adjusted ahead of a heatwave so the session still does its job.
None of that takes away your judgement on the day. It just means you start the race with a plan that already expects the heat, instead of finding out about it at 11 o’clock in the valley.
Racing somewhere hot this summer? If you’d like a coach to help you plan for the heat, book a free discovery call. It’s 30 minutes, and there’s no obligation. Or see our coaching plans.