Why Is Heat Dangerous During Exercise?
During exercise, muscles generate heat — up to 75% of the energy used is converted into heat. At high ambient temperatures, it is harder for the body to cool down, and body temperature can rise to dangerous levels (above 40°C), causing heat stroke — a life-threatening condition.
Risk factors:
- High temperature + high humidity — sweat does not evaporate, the body does not cool down
- Dehydration — even a 2% loss of body weight in fluids reduces thermoregulation
- Intense exertion — the more intensely you exercise, the more heat you generate
- Certain medications — diuretics, antihistamines, antidepressants
🌡️ Spectrum of Heat-Related Conditions
| Condition | Symptoms | Body Temp. | Actions | Risk |
|---|---|---|---|---|
| Heat cramps | Painful muscle spasms (calves, abdomen) | Normal | Rest in the shade, electrolyte drink, stretching | Low |
| Heat exhaustion | Profuse sweating, weakness, dizziness, nausea | Up to 39°C | Stop exercise immediately, shade, cold compresses, fluids | Medium |
| Heat stroke | Body temp. >40°C, dry skin (does not sweat!), confusion, loss of consciousness | >40°C | 🚨 URGENT MEDICAL HELP 112. Ice bath, cold compresses. | FATAL |
💧 Hydration Strategy in Heat
⏰ Before Training
Drink 500–600 ml of water or an isotonic drink 2–3 hours before. The last 200–300 ml — 20 min before the start. Urine should be light yellow.
🏃 During Training
150–350 ml every 15–20 minutes. If the workout >60 min — isotonic drink with electrolytes (sodium, potassium). Do not drink too much plain water — hyponatremia can occur!
🔄 After Training
Weigh yourself before and after. For every kilogram lost, drink 1.2–1.5 l of fluids. Choose an electrolyte drink rather than plain water.
⚡ Electrolyte Balance
With sweat, the body loses: 900–1300 mg sodium/l, 150–250 mg potassium/l, 10–30 mg magnesium/l. When exercising in the heat for more than an hour, it is ESSENTIAL to replenish not only water but also electrolytes.
📊 WBGT Index — When Is It Safe to Exercise Outdoors?
WBGT (Wet Bulb Globe Temperature) — this is a heat stress index that takes into account temperature, humidity, wind and solar radiation. It is a much more accurate indicator than air temperature alone.
| WBGT | Risk Level | Recommendations |
|---|---|---|
| <18°C | Low | Safe to exercise without restrictions. |
| 18–23°C | Medium | Monitor hydration. Take short breaks. |
| 23–28°C | High | For beginners — reduce intensity. Breaks every 15 min in the shade. |
| 28–30°C | Very High | Postpone competitions. Limit training to 45 min. Hydration is mandatory. |
| >30°C | Extreme | Do not exercise outdoors. Move training to the morning/evening or to air-conditioned indoor spaces. |
🔄 Acclimatization Protocol
The body needs 10–14 days to adapt to heat. During this time, sweating efficiency increases, heart rate during physical exertion decreases, and electrolyte conservation improves.
| Day | Duration | Intensity | Notes |
|---|---|---|---|
| 1–3 | 15–30 min | 50–60% max | Light workload — start of adaptation |
| 4–6 | 30–45 min | 60–70% max | Duration can be increased, not intensity |
| 7–10 | 45–60 min | 70–80% max | Gradually increase intensity |
| 11–14 | 60–90 min | 80–90% max | Full adaptation. Normal training is possible. |
🧊 Practical Tips for Sport in Heat
💧 Practical Tips: Hydration Test
How to Know If You Are Adequately Hydrated?
1. Urine Color Test: Light yellow (straw-colored) — good. Dark yellow/amber — dehydrated. Completely clear — too much water (risk of hyponatremia).
2. Weight Test: Weigh yourself before and after training. Weight difference = lost fluids. E.g.: -1.5 kg = need to drink ~1.8 l fluids (1.2× weight difference).
3. Thirst Test: Thirst is already a late sign of dehydration. Do not wait until you are thirsty! Drink regularly — every 15–20 min, 150–250 ml.
Homemade Isotonic Drink:
500 ml water + 250 ml orange juice + 1/4 tsp salt. Mix. Provides carbohydrates, sodium, and potassium — an excellent alternative to expensive sports drinks.
🛒 Recommended Supplements
🔗 Related Tools
📋 Heat Stroke First Aid Protocol
What to Do If Heat Stroke Is Suspected:
- Call 112 immediately — heat stroke is a life-threatening condition
- Move the affected person to shade or an air-conditioned room
- Actively Cool: ice packs on the neck, armpits, and groin; cold water; a fan
- Do not give anything to drink if the affected person is confused or unconscious — they may choke
- Monitor breathing and pulse until medical help arrives