It’s 35°C (95°F). Your training plan calls for intervals or a long endurance session. And you’re wondering: “Should I go anyway? Postpone it? Skip it altogether?”
You’re not alone. Every summer, thousands of recreational athletes ask themselves the same question, torn between the fear of losing fitness and the fear of ending up exhausted—or worse, in the emergency room. And every summer, hospitals treat people who pushed themselves just a little too far.
The good news? You can absolutely exercise in hot weather—provided you adapt your training intelligently. The goal isn’t to stop training altogether, nor to pretend the heat doesn’t matter. In this article, we’ll explain how to adjust your outdoor workouts, when it’s smarter to move indoors, and most importantly, how to recognize the warning signs you should never ignore.
Why Heat Changes Everything for Your Body?
When you run or ride in 30°C (86°F) instead of 18°C (64°F), it’s not just “less comfortable.” Your body has to perform two demanding tasks at the same time:
- Exercise: producing energy to keep you moving.
- Thermoregulation: dissipating the heat your body generates to prevent overheating.
And the hotter it gets, the more energy your body has to dedicate to cooling itself.
In practical terms:
- Your heart rate increases by 5 to 10 beats per minute at the same effort level.
- You may lose 1 to 2 litres of sweat per hour, compared with roughly 0.5 to 1 litre in moderate conditions.
- Performance typically drops by 5 to 20% once temperatures exceed 25°C (77°F).
- The risk of heat exhaustion and heat stroke rises sharply above 32–35°C (90–95°F), especially in direct sunlight.
Trying to maintain your usual pace or power output at 35°C simply isn’t realistic. Your body is using a significant portion of its energy just to stay cool. That’s physiology—not a lack of mental toughness.
How to Adapt Your Outdoor Training?
If you still want to train outdoors, follow these essential guidelines.
Choose the Right Time of Day
Timing makes all the difference.
- Before 9 a.m. or after 7–8 p.m.: temperatures are lower and the sun is much less intense.
- Avoid training between noon and 5 p.m., even for short sessions. This is the hottest and most dangerous part of the day.
Summer often requires changing your usual routine. If you’re unsure whether mornings or evenings suit you best, read our article The Best Time to Exercise: Morning or Evening? to find the schedule that fits your lifestyle while maintaining training consistency.
Pick the Right Environment
Where you train matters just as much as when.
- Forests and shaded trails are far preferable to exposed roads.
- Coastal routes or lakesides benefit from cooling breezes.
- Avoid riding or running on sun-baked asphalt, which can reach surface temperatures of 50 to 60°C (122 to 140°F) and radiates additional heat back towards you.
Hydrate More Than Ever
In hot weather, your hydration needs increase dramatically.
- Before training: drink 400–500 ml during the two hours beforehand.
- During training: aim for 500–900 ml per hour, compared with 400–600 ml in cooler conditions.
- After training: replace approximately 150% of the weight you’ve lost (weigh yourself before and after your workout if possible).
Most importantly, replace electrolytes during sessions lasting longer than one hour in hot weather. Salt tablets, electrolyte drinks or sports beverages help replace sodium lost through sweating. Drinking large amounts of plain water without replacing sodium can lead to hyponatremia, which is potentially more dangerous than mild dehydration.
Dress for the Heat
Your clothing can make a significant difference.
- Wear light-coloured clothing, as black absorbs more heat.
- Choose technical, moisture-wicking fabrics instead of cotton.
- Wear a cap or damp bandana, along with sunglasses.
- Apply sunscreen—sunburn increases physical stress and fatigue.
Reduce Your Training Intensity (The Coach’s Rule)
This is probably the adjustment most recreational athletes forget to make. When temperatures rise, your target intensity should come down.
Here’s how:
- Reduce your target pace or power by 5 to 10% during your first hot-weather sessions.
- Increase recovery time between interval efforts.
- Pay more attention to heart rate than pace or power. In hot conditions, heart rate provides a much more accurate picture of your actual physiological load.
- During long endurance sessions, think in terms of heart rate zones, not finishing times.
Heat Acclimation: Your Body Adapts in 7 to 14 Days
The good news is that your body learns surprisingly quickly. If you gradually expose yourself to warmer conditions—for example by completing easy sessions in 25–28°C (77–82°F) weather over one to two weeks—your body begins to adapt.
You’ll experience several physiological improvements:
- Increased blood plasma volume.
- Earlier and more efficient sweating.
- Reduced sodium loss through sweat.
Once you’re heat-acclimated, workouts that initially felt overwhelming become much more manageable. It’s very similar to altitude training: the first few days are challenging, but your body gradually adapts and becomes more efficient.
When to Move Your Training Indoors?
There comes a point when insisting on training outdoors is no longer a sign of determination—it’s simply unsafe.
Here are the situations where I always recommend moving your workout indoors:
- Above 32–33°C (90–91°F) for high-intensity sessions (intervals, threshold workouts or VO₂ max training).
- Above 35°C (95°F), even for endurance rides or runs.
- During an official heatwave warning.
- If you’ve recently experienced dizziness or heat-related discomfort while exercising.
- If you’re returning from a break or your fitness level isn’t yet at its best.
Training indoors isn’t “giving up.” It’s choosing to keep making progress in conditions where your body can focus on training instead of spending up to 30% of its energy trying to stay cool.
To learn more, check out our article Indoor Training and Fans: How Better Cooling Improves Your Performance, an essential read if you want to train seriously indoors during the summer.
Kinomap: Your Best Ally During a Heatwave
This is where Kinomap really comes into its own. Whether you’re riding on a smart trainer or running on a treadmill, you can maintain the full quality of your training—intervals, long endurance sessions and threshold workouts—without exposing yourself to unnecessary health risks.
With Kinomap, you can:
- Place a powerful fan in front of you (essential—it makes a huge difference).
- Open your windows early in the morning to let cooler air circulate.
- Choose refreshing routes through Norwegian fjords, snow-covered Alpine passes, Iceland or Patagonia. The psychological effect is real: cooler landscapes often make the effort feel easier.
- Monitor your heart rate and power output without the additional physiological stress caused by extreme outdoor temperatures.
If you’re short on time, 30 to 45-minute workouts are ideal during the summer. For inspiration, read our article No Time to Exercise? Five 30-Minute Workouts on Kinomap to Stay Fit.
Above all, keep using that fan. A room at 28°C (82°F) without airflow can quickly feel hotter than an early morning outdoor ride. Air conditioning certainly helps, but moving air is what really improves sweat evaporation and keeps your body cool.
Warning Signs You Should Never Ignore
Heat stroke is a medical emergency. Recognizing its symptoms can save your life—or someone else’s.
Stop exercising immediately if you experience any of the following:
- You suddenly stop sweating even though you should be.
- Your skin becomes hot, dry and flushed instead of damp.
- Dizziness, nausea or vomiting.
- A severe, persistent headache.
- Confusion, disorientation or difficulty speaking.
- Chills despite temperatures around 35°C (95°F)—a paradoxical but very serious warning sign.
If these symptoms occur: stop exercising immediately, move into the shade or a cool place, cool your skin and the back of your neck with water, drink fluids. Don’t hesitate to call your local emergency services if symptoms don’t improve quickly. Heat stroke can become life-threatening within minutes.
Common Mistakes to Avoid
- Sticking rigidly to your training plan regardless of the weather. Missing one interval session is far better than ending up in hospital.
- Underestimating hydration. By the time you feel thirsty, you’re often already dehydrated. Drink before thirst sets in.
- Forgetting electrolytes. During workouts lasting longer than one hour in hot weather, water alone isn’t enough.
- Training at your usual time even though it’s the hottest part of the day.
- Ignoring warning signs and telling yourself, “It’ll pass.” It usually doesn’t—it gets worse.
Conclusion
Exercising in hot weather isn’t about toughness. It’s about training intelligently. Adjust your schedule, reduce your intensity, improve your hydration strategy and don’t hesitate to move your workouts indoors once temperatures exceed safe limits.
During a heatwave, your goal isn’t necessarily to improve your fitness. Your priority is to maintain your training safely without losing momentum—or risking your health. One week of smart, well-managed workouts is far more valuable than suffering heat stroke and being forced to stop training for two weeks. Smart athletes don’t fight the weather. They adapt to it.
By Fanny Marre
Cycling, running and triathlon coach
fannymarre99@gmail.com
See previous coaching articles:
STAY ACTIVE DURING YOUR HOLIDAYS: SIMPLE WAY TO KEEP FIT
INCREASE YOUR CYCLING POWER : 5 EFFECTIVE WORKOUTS
HOW TO IMPROVE YOUR RACE: NUTRITION, PACING, TIPS