Running in the Heat: How to Train Smart When It’s 30°C

June, July, August. Your training plan says you should do a tempo run, but it’s 32 degrees outside and the air feels stagnant. You go anyway, because your race in September is drawing near. Ten minutes later, you wonder why everything feels so hard, even though you’re actually running slower than usual.

This isn’t a bad day. This is physiology.

What happens to your body in hot weather

In hot weather, your heart has to do two things at once: supply oxygen to your working muscles and pump blood to your skin so that you can sweat and cool down. That’s an extra strain that simply isn’t there at 15 degrees. The result: your heart rate is higher for exactly the same level of exertion, your muscles receive relatively less oxygen, and you tire more quickly.

What’s more, the evaporative cooler is much less efficient in humid weather. Sweat cools you down through evaporation — but if the air is already saturated with moisture, nothing evaporates. A 2025 study in the Scandinavian Journal of Medicine & Science in Sports showed that the cooling efficiency of sweat drops from 50% to just 16% in high humidity. That is two-thirds less cooling capacity at the same temperature.

Your nervous system reacts to all this by forcing you to slow down. That’s not a weakness. It’s a protective mechanism. Your body won’t allow your core temperature to rise too high, and if you ignore that defence mechanism by trying to maintain your pace at all costs, you risk overheating — and that’s more dangerous than accepting a ‘bad’ training session.

How do you adjust your pace?

This is where most runners make a mistake: they try to maintain their usual pace and don’t understand why it feels so hard. The answer is simple — in the heat, you train by effort, not by pace. Your watch may show a slower split. That’s the idea.

A rule of thumb that works well: add the temperature (°C) to the dew point (°C). That combined figure will give you an idea of how much you need to slow down.

Temperature + dew point (°C)	Temperature adjustment	Status
Under 40	No adjustment required	Fine
40 to 50	0,5% to 1% slower	Comfortable
50 to 55	1% to 2% slower	Hot but okay-ish
55 to 60	2% to 3% slower	Be careful
60 to 65	3% to 4,5% slower	Clearly restrictive
65 to 70	4,5% to 6% slower	Hot weather
Above 70	Running is not recommended	Dangerous

Example: it’s 32°C and the dew point is 22°C. That gives 54. So you need to run 1 to 2 per cent slower. If your normal easy pace is 5:30/km, today you’ll be running at 5:36 to 5:41/km. That feels slow. It is slow, too. But the effort is the same — and that’s what matters.

Train by feel and heart rate, not by pace

This is the most practical advice I give my athletes for the summer: put your GPS pace aside and train by heart rate or how you feel. In hot weather, your heart rate is already higher for the same level of effort. That means that if you stick to your heart rate zones, you’ll automatically run more slowly — exactly as you should.

Research shows that, at the same pace, your heart rate can be 12 to 15 beats per minute higher when the temperature rises from 21°C to 32°C. And when heat and humidity combine, the effect is even greater. If you try to maintain your normal pace in these conditions, you automatically push yourself into a higher intensity zone than you had planned. The quality of your training suffers — and the risk of overexertion increases.

For an easy run: stick to zone 2 based on your heart rate. Accept that this means you’ll have to run much more slowly than usual. For a tempo run: use perceived exertion (a scale of how hard you feel you’re working) rather than pace. A 7 out of 10 feels much harder at 32 degrees than at 15 degrees — and that’s exactly right.

The upside: heat makes you stronger

This is where it gets interesting. Running in the heat doesn’t just feel tough — it’s also a training stimulus in its own right. Your body adapts to the heat, and those adaptations are measurable and valuable.

After 10 to 14 days of regular training in the heat, heat acclimatisation sets in. Here’s what changes:

Your plasma volume is increasing. Heat acclimatisation leads to a 10 to 12 per cent increase in plasma volume. More blood means your heart doesn’t have to work as hard to supply the same amount of oxygen. This effect even carries over into cooler temperatures — so you’ll be faster even when it’s no longer summer.

You start sweating sooner. Once you’ve acclimatised, your sweating system kicks in more quickly and efficiently. Your core temperature stays lower during the same level of exertion, and you can run harder for longer before you overheat.

Your heart rate is slowing down. Cardiovascular adaptations to heat become noticeable after just one week. That same run which pushed your heart rate up to 175 last week might only take it up to 163 after ten days of heat training.

The catch: these adaptations will eventually fade away. After just 1 to 2 weeks without exposure to heat, the benefits start to diminish. So if you go on an altitude training camp in August and then face cooler weather in September, there won’t be much left of them. But if you train consistently throughout the summer — even if progress is slow — you’ll emerge stronger in the autumn than you might think.

Practical tips for summer training

Sooner or later

The best times to train in the summer heat are before 8 am or after 7 pm. At these times, the tarmac is cooler, the sun is lower in the sky and the temperature is noticeably more pleasant. Plan your high-intensity sessions (tempo, intervals) for these times. Midday training sessions are fine for easy runs if you can’t plan it any other way — but expect a higher heart rate and a slower pace.

Drink proactively, not reactively

Thirst is a delayed signal. By the time you feel thirsty during a warm-weather training session, you are already slightly dehydrated. Make sure you’re well hydrated before you start your run (aim for pale yellow urine) and take water with you on runs lasting longer than 45 minutes. In extreme heat or during long runs, consider taking electrolytes, as you lose not only fluid but also sodium through sweat.

Accept the slower times

This is perhaps the hardest part. Your watch shows a pace that you found normal last autumn, but now you can barely keep it up. That has nothing to do with a loss of fitness — it’s all down to thermoregulation. A good summer training session is one where you put in the same level of effort as usual, not the same pace. The difference is crucial.

Protect your head and skin

A cap or running cap with ventilation keeps the sun out of your face and slows down the heating of your head. Sun cream is no luxury on long runs in the sun. Opt for lightweight, light-coloured clothing that wicks away moisture.

Recognise the signs of overheating

Dizziness, nausea, stopping sweating whilst it’s still hot, confusion or a feeling of being ‘disconnected’ — these are warning signs. Stop immediately, find some shade and cool down. Overheating is the only situation where you need to put your pride aside and simply stop.

Training in the summer isn’t much fun. Nobody likes running in the heat. But the runners who keep at it in August — sensibly, adapting to the conditions — are the ones who run their best races in September and October. It’s the effort that counts, not the pace on your screen.