35 degrees. 40 degrees. 80% humidity. You still want to run, cycle, compete in your race – or you have to, because the date is set.

Exercising in extreme heat is a different discipline. Physiology changes, risks increase, and strategies must be adapted. What works at 20 degrees Celsius can be dangerous at 40 degrees.

This guide is for anyone who trains or competes in hot climates – whether it's a Mediterranean marathon in the summer, a triathlon in the tropics, or simply training at home during a heat wave.

You will learn how the body reacts to heat, how to prepare, which signs to take seriously, and how to balance performance and safety.

Your body produces heat during exercise. This heat needs to be dissipated – otherwise you'll overheat. At 20 degrees Celsius, this isn't a problem. At 40 degrees Celsius, it's a huge challenge.

Cooling mechanisms: Sweating is the primary mechanism. Sweat evaporates on the skin, providing a cooling effect. This requires dry air – in high humidity, less evaporates, and the cooling mechanism fails. Therefore, hot and humid conditions are more dangerous than hot and dry conditions.

Blood distribution: More blood flows to the skin to dissipate heat. Less blood goes to muscles and organs. The heart rate increases at the same workload – the heart has to pump harder to supply both.

Performance decline: Performance decreases in hot weather. This is not a sign of weakness, but a protective mechanism. The body reduces its output to prevent overheating.

Threshold values: The core temperature should not exceed approximately 40°C (normal: 37°C). Beyond this, heatstroke and organ damage are likely. This limit can be reached during strenuous exercise in hot conditions.

The body can adapt to heat – but it takes time and systematic exposure.

What happens during acclimatization: You sweat earlier and more. Sweat becomes diluted (less salt loss). Blood volume increases. Heart rate decreases at the same level of exertion. The body becomes more efficient at regulating temperature.

Timeframe: 10-14 days for full adaptation. The first few days are the most critical. Initial adjustments are noticeable after 3-5 days.

Protocol: 60-90 minutes of heat exposure daily with moderate activity. Don't go all out right away – start gently and increase gradually. Passive heat (sauna) also helps, but active exposure is more effective.

If you don't have time: Even 5 days will bring measurable improvements. Better than nothing. Sauna or hot baths can be a helpful addition.

Loss of adaptations: The adaptations last for about 2-4 weeks after the end of heat exposure. For a competition: Don't acclimatize too early and then train again in the cooler temperatures.

In hot weather, you sweat more – and lose more fluids and electrolytes. The right strategy is complex.

Fluid loss: At high intensity and in heat: 1-2 liters per hour. More than you can drink without stomach problems. Realistic goal: Drink 500-800ml per hour, the rest after training.

Before training: Hydration begins hours beforehand. Urine should be pale yellow. Don't start drinking at the start.

During training: Drink small amounts regularly. Don't wait until you're thirsty – by then you'll already be dehydrated. During long sessions: Add electrolytes.

Electrolytes: Sodium is the most important. Sweat contains 1-2g of sodium per liter. For prolonged sweating: salt tablets or electrolyte drinks. Hyponatremia (too little sodium in the blood due to excessive water consumption without salt) is a real risk.

After training: Weigh yourself before and after. Drink 1.5 liters of water for every kg of weight lost. Include electrolytes.

Individual sweat rate: Highly variable. Determine by weighing. Some lose twice as much body fluid as others under the same exertion.

External cooling can maintain performance in hot conditions and reduce the risk.

Pre-cooling: Cooling before the start. Ice vest, cold drinks, cold towels. Lowers the starting temperature – you have more of a buffer before overheating. Effective for races under 60 minutes.

Intra-cooling: During exertion. Drink ice water (cools from the inside), use sponges soaked in cold water, pour water over your head, put ice under your hat. For long races: wear ice vests in the transition zone.

Clothing: Light colors reflect sunlight. Lightweight, breathable materials are best. Less is often more – but remember sun protection. A hat or visor protects your head from direct sunlight.

Sunscreen: Waterproof, sports-suitable sunscreen. Sunburn is additionally stressful and impairs sweating.

Use water: rivers, fountains, water stations – run water over the body for cooling. Particularly effective on wrists and neck (large blood vessels close to the surface).

The biggest danger in the heat: maintaining your usual pace. That doesn't work.

Accept a drop in performance: A 5-10% slower pace in high heat is normal and necessary. The same heart rate results in less power output. Don't fight it.

Go by feel and heart rate: not by pace. If your usual pace causes a significantly higher heart rate – slow down. Your body will tell you what's possible.

Conservative start: In the heat, starting too fast is especially dangerous. No reserve power for later. It's better to start conservatively and accelerate at the end (if possible).

Plan breaks: In extreme heat, scheduled breaks can be beneficial. Stop briefly, drink, cool down, then continue. It's better than pushing through and collapsing.

Define stoppage criteria: Decide in advance when you will stop. Certain symptoms, a certain body temperature. Decisions made in the heat of the moment are difficult – protect yourself with pre-defined limits.

Heat-related illnesses develop across a spectrum. Recognize and act early.

Heat cramps: Painful muscle cramps, often in the calves or abdomen. Cause: Electrolyte loss and dehydration. Treatment: Rest, stretching, salt and fluids. Early warning sign.

Heat exhaustion: Profuse sweating, weakness, nausea, headache, dizziness, pale, clammy skin. Body temperature elevated but below 40°C. Treatment: Stop immediately, cool down, drink fluids, seek shade. Improvement with cooling within 30-60 minutes.

Heatstroke: Medical emergency. Body temperature above 40°C (104°F). Confusion, altered mental status, dry, hot skin (sweating may stop), rapid pulse. Treatment: Call emergency services, cool immediately and aggressively (ice water if possible), elevate legs. Without treatment: organ failure, death.

Be aware of the transitions: The transition from exhaustion to heatstroke is gradual. If confusion or altered consciousness occurs: Act immediately.

Tropical climates combine heat with high humidity – the most difficult combination.

Humidity as a killer: At 90% humidity, sweating hardly works anymore. The sweat runs off instead of evaporating. The cooling effect is minimal. WBGT (Wet Bulb Globe Temperature) is a better indicator than temperature alone.

Timing is even more critical: Early morning hours are often the only acceptable time. Midday may be impossible. Some people train at night under artificial light.

Indoor alternative: In extreme tropical heat, air-conditioned indoor training may be the only option. A treadmill or stationary bike is better than risking heatstroke.

Longer acclimatization: Full adaptation to tropical conditions may take 14 days or more. The combination of heat and humidity is a major adjustment.

Minimal clothing: In tropical humidity, more exposed skin can be better – more surface area for evaporation. Sunscreen is then more important.

Observe local athletes: They have adapted and know the conditions. Observe when and how they train.

Diet also needs to be adapted to hot conditions.

Before training: Lighter meals. Fat is digested slowly and produces more heat. Prefer carbohydrates and moderate protein.

During long training sessions: Carbohydrates remain important. Liquid calories (sports drinks, gels with water) are often better tolerated than solid food in hot weather.

Salty snacks – chips, pretzels, broth – can help replenish lost sodium, especially during very long workouts or when you sweat a lot.

After training: Cool food can be more appealing. Smoothies, yogurt, fruit. Don't forget electrolytes.

Loss of appetite: Appetite is often reduced in hot weather. Nevertheless, eat – the body needs energy for cooling and regeneration.

Avoid alcohol: It further dehydrates, impairs temperature regulation, and worsens sleep. Especially problematic in hot weather.

At what temperature should I stop training outdoors?

No fixed limit – depends on humidity, wind, acclimatization, and the individual. Temperatures above 35°C with high humidity become critical. WBGT above 28°C: caution is advised for most. WBGT above 32°C: only for acclimatized individuals and with extreme caution.

How long does heat acclimatization take?

10-14 days for full adaptation. First noticeable effects after 3-5 days. Protocol: 60-90 minutes of moderate activity daily in the heat. If less time is available: Even 5 days will bring measurable benefits.

Should I consume more salt?

For long workouts in the heat: Yes. Sweat contains sodium. For workouts longer than 60-90 minutes: electrolyte drinks or salt tablets. Don't overdo it – but don't drink only water in the heat either.

Why do I feel so slow in the heat?

Normal. More blood goes to the skin (for cooling), less to the muscles. The heart has to work harder. Same heart rate = less power output. Accept it and adjust your pace.

Is pre-cooling really effective?

Yes, especially for shorter, intense workouts (under 60 minutes). An ice vest, cold drinks, and cold towels before starting will lower your baseline temperature. You'll have more of a buffer before overheating.

How can I tell the difference between heatstroke and heat exhaustion?

Heat exhaustion: Profuse sweating, nausea, headache, but mental clarity. Heatstroke: Confusion, disorientation, altered consciousness, often dry, hot skin. Heatstroke is an emergency – cool down immediately and call emergency services.

Can I get used to extreme heat?

Up to a certain point, yes. Acclimatization significantly improves tolerance. But absolute limits remain – intense exercise is dangerous for everyone at WBGT above 35°C.

What's the best thing to drink in hot weather?

Water plus electrolytes for longer sessions. Sports drinks (6-8% carbohydrates) for activities over 60 minutes. Cold drinks are absorbed faster and cool you down from the inside.

How does heat affect my heart rate?

In hot weather, your heart rate will be higher at the same workload (cardiovascular drift). An increase of 10-20 beats per minute at the same pace is normal. Train according to your heart rate, not your usual pace.

Should I cancel my race if there's a heat warning?

Weigh the options: Health takes precedence over results. In extreme conditions and without acclimatization: Possibly. If you do start: Conservative pace, clear criteria for dropping out. A race isn't worth risking heatstroke.