Running in heat adds a challenge that requires smart adjustments to maintain performance and prevent overheating.
Understanding how heat affects your pace
Temperatures above 18 °C (65 °F) start to reduce endurance running efficiency. The body has to work harder to cool itself, which takes energy away from forward motion. A practical way to estimate the impact on your marathon pace is to add 2 to 3 seconds per kilometre for every 5 °C rise above 12 °C (54 °F).
For example, if the temperature hits 22 °C (72 °F), expect your pace to slow by about 6 to 9 seconds per kilometre compared to ideal cool conditions. This pace tax reflects the extra physical effort your body spends managing heat stress.
Focus on effort, not just pace
Clock pace can be misleading when temperatures climb. Heart rate is a better indicator of how hard you’re working. In the heat, your body pumps blood not only to muscles but also to the skin to dissipate heat. This causes your heart rate to rise even if speed decreases.
Try to maintain your usual race effort level rather than chasing a target pace on your watch. Using heart rate zones or perceived exertion helps avoid burnout and overheating.
Preparing your body: two weeks of heat exposure
Acclimatising to hot conditions is critical for race day success. Start your heat preparation 10 to 14 days before the event. This allows your body to adapt by improving sweat rate, cardiovascular stability, and heat tolerance.
If training outdoors in similar heat isn’t possible, you can simulate the effect indoors. Sauna sessions lasting 25 to 30 minutes after easy runs are effective for heat acclimatisation. Repeat these sessions regularly in the lead-up to your race.
Practical tips for acclimatisation sessions
- Keep exercise intensity low to avoid early fatigue during heat exposure
- Stay hydrated before, during, and after sessions to support your body’s cooling
- Gradually increase heat exposure time each day within comfort limits
- Listen to your body and stop if you feel dizzy or unwell
Adjusting race-day hydration and nutrition
Hydration needs increase in hot weather due to greater sweat loss. Plan your fluid intake according to race length, temperature, and your sweat rate. Overhydration can be harmful, so balance drinking with thirst and avoid excessive water intake.
Electrolytes are important to replace sodium lost through sweat, especially on long runs or races. Use sports drinks or electrolyte tablets as needed.
On race day:
- Start well hydrated but don’t overdo fluids before the start
- Drink small amounts regularly rather than large quantities infrequently
- Use aid stations wisely to avoid slowing too much but get enough fluids
- Practice your hydration plan during training to avoid surprises
Summary: adapt your race plan for heat
Running in hot conditions means accepting a slower pace, focusing on effort over speed, and preparing your body through heat exposure. Adjust hydration and nutrition to support your performance. With these practical steps, you’ll manage the heat calmly and race more comfortably.
Using a system like Racendo can help you track your acclimatisation progress, hydration strategy, and pacing adjustments in one place. This keeps your race preparation organized and stress-free while you focus on reaching your goals.