Why Heat Was the Big Question at Berlin 2025
When the BMW Berlin Marathon rolled out its start line on a sunny Sunday, the forecast didn’t look friendly for a 42‑kilometre dash. Temperatures nudged the mid‑20s Celsius, and humidity hovered around 70 %. For a city that usually enjoys cool spring weather, runners suddenly faced the kind of heat you’d expect in a summer heat‑wave.
Dr. Matthias Krüll, the marathon’s Medical Director, warned that the body’s cooling system can be overwhelmed when you combine long‑duration effort with warm, moist air. “Sweat evaporates slower in humid conditions, so the core temperature rises faster,” he explained during a press briefing. That set the stage for his four‑point playbook – the “golden rules” that aimed to keep participants from overheating, dehydrating, or cramping out before the finish line.
Dr. Krüll’s Four Golden Rules – Expanded
Below is a deeper look at each rule, with practical tips you can copy for any hot‑weather race.
- Hydration is non‑negotiable. Start loading fluids days before the event. Dr. Krüll suggested sipping water or an electrolyte drink from Friday morning, aiming for at least 2 liters by the evening. On race day, never skip a drinking station – the marathon placed them every 2–3 km, each stocked with both water and a sports drink.
- Choose electrolytes over plain water. Pure water dilutes blood sodium, leading to hyponatremia. The recommended mix is a 4‑to‑6 g sodium solution per liter, or commercially available isotonic sports drinks. If you prefer a DIY option, add a pinch of sea salt and a squeeze of citrus to your water bottle.
- Protect your head and use it to cool down. A lightweight, breathable cap or visor shields you from direct solar radiation. Dr. Krüll also advised runners to pour water over the hat – the wet fabric creates an evaporative cooling effect that can lower skin temperature by up to 2 °C.
- Adjust your goals, not your spirit. In hot weather, aiming for a personal record can be dangerous. Instead, target a steady pace that feels comfortable, even if it means walking a few extra minutes per kilometer. The medical team will be on hand at the finish line, ready to assist anyone who shows signs of heat exhaustion.
These rules aren’t just theoretical. The marathon’s logistics team installed “shower stations” at the 15‑km and 30‑km marks, where volunteers sprayed a fine mist, offering a quick cooldown. Runners reported that a quick splash helped reset their perceived effort level, making the latter half of the race more manageable.
Beyond the basics, the marathon also rolled out a digital heat‑alert system. Participants received push notifications reminding them to drink, check their wrist temperature (if they wore compatible smartwatches), and to use the cooling stations. This tech‑enabled approach blended traditional medical advice with modern gadgets, giving runners real‑time guidance.
While the elite field still chased podium finishes, the overall race narrative was about safety. Men’s winner Sebastian Sawe clocked a world‑leading 2:02:16, and women’s champion Rosemary Wanjiru posted 2:21:05. Their performances proved that with the right preparation, even a warm Berlin can produce fast times.
For the 80,000‑plus amateurs finishing the race, the takeaway was clear: drink often, keep electrolytes handy, shield your head, and respect the heat. By following Dr. Krüll’s simple yet effective rules, participants turned a potentially hazardous day into a celebration of endurance and smart preparation.