Staying safe this summer: How to avoid heat stress whilst exercising

An article about body awareness, timing, fluidity – and why you should learn to listen to your body’s subtler signals.

There’s that one moment in summer when everything seems to slow down. The light lies heavy over the landscape, the air shimmers, and even the wind seems sleepier than usual. Anyone wishing to exercise in this atmosphere needs to know what they’re doing. Because heat isn’t an opponent, but it is a factor – one that should be taken seriously.

What exactly is heat stress?

Heat stress refers to the strain placed on the body by high outdoor temperatures, particularly when combined with physical exertion. When you move, your body produces heat. Normally, this is counteracted by sweating and increased blood flow to the skin. However, if the outside temperature rises sharply – particularly above 30 °C – and is accompanied by high humidity, this cooling system reaches its limits. The result: dehydration, circulatory problems, difficulty concentrating – and, in the worst case, heatstroke.

The body is not a fridge – it is a finely regulated system

Something that is often underestimated: the physiological response to heat doesn’t just start with sweating. Even with a moderate rise in temperature, your blood volume changes, your cardiovascular system has to work harder, and blood flow to your muscles can be restricted. All of this costs energy – energy that you’ll then be lacking whilst exercising. That’s why it’s important to remember: anyone training outdoors in summer needs not only determination, but also knowledge.

Strategy 1: Train at the right time

The best time of day for exercise in summer is early in the morning – between 6 am and 9 am. The air is still cool, UV levels are low and ozone levels are manageable. If you can’t exercise in the morning, it’s better to switch to the late evening. Between 11 am and 5 pm, intense outdoor exercise is a no-go – unless you’re looking to take a risk.

Pro tip: On hot days, opt for indoor training or a run in the woods – the difference in perceived temperature can be huge.

Strategy 2: Drinking is not a ‘nice-to-have’

Fluid loss through sweating can range from 0.5 to 2 litres per hour, depending on the sport. Even a fluid deficit of just 2 per cent of body weight can significantly reduce performance. However, if you only drink when you feel thirsty, you’re drinking too late.

What really matters:

Before training: 300–500 ml of water or diluted juice, about 30 minutes beforehand.
During training (lasting 45 minutes or more): drink small amounts every 15–20 minutes.
After training: Mineral water, sparkling water with juice or a recovery drink containing electrolytes.

And very importantly:

If you lose a lot through sweat, you lose not only water but also electrolytes – primarily sodium, potassium and magnesium. These must be replenished – through isotonic drinks, natural sources such as coconut water, diluted fruit juices or isotonic electrolyte powders.

Strategy 3: Protecting your skin means respecting the sun

UV rays are not only harmful to the skin, but they also weaken the immune system – and, if the body is overtaxed, can lead to sunstroke or heat exhaustion. Therefore:

Apply sun cream, with an SPF of at least 30, which is waterproof and sweat-resistant.
Wear functional clothing with UV protection (especially on long rides).
Headwear with a peak or visor – not only protects against sunburn, but also keeps the head cooler.
Sunglasses with UV protection – because your retina and cornea are more sensitive than you might think.

Strategy 4: Listen to your body – before it cries out

Most symptoms of overheating develop gradually. Typical early warning signs:

Dizziness
Nausea
Muscle cramps
Heart palpitations
A dry mouth despite sweating
A feeling of ‘inner restlessness’ or irritation

Anyone who carries on in this state is taking a big risk – not only of a drop in performance, but also of medical complications.

Rule of thumb: If you feel that ‘things aren’t going well today’, then perhaps you’re right. Your body isn’t trying to harm you – it’s trying to protect you.

Respect is the wisest training partner

Summer means energy, movement, freedom – but also responsibility. When you train outdoors, you’re not competing against nature, but with it. That means: strategy rather than defiance. Hydration rather than bravado. And above all: honesty with yourself. You don’t always have to go faster, further or harder. Sometimes the smartest thing you can do is to stop a bit earlier – or start a bit later.

Because summer belongs to you. But only if you enjoy it sensibly.