At this year’s Ironman Austria, temperatures were creeping up towards 30ºC — a big jump for any UK-based athlete who's spent the early season training in cool, grey conditions. My wife Beth, and all of the other athletes, had to contend with that reality during their race.

The heat doesn't just feel harder — it is harder. And if you don’t adapt your effort levels on the bike, you risk cooking yourself before you’ve even laced up your running shoes. (TIP:Once you've read this article, check out the two at the bottom of the page with some specific heat training strategies)

Why the Bike Matters Most in Hot Races

It’s tempting to stick to your usual power or heart rate targets on the bike — especially if you've trained by numbers and you're chasing a specific outcome. But your body isn't a machine. In the heat, your heart rate is higher for the same output. You're sweating more. Your body’s working overtime to keep cool, diverting blood away from your muscles and toward the skin. That means less oxygen delivery to the working muscles and a higher perceived effort.

And here's the kicker: if you overdo it on the bike, the run becomes a survival shuffle. Once you're heat-compromised and dehydrated, it's almost impossible to pull things back.

So What Can You Do?

1. Dial it back early.​
Start the bike conservatively — especially in the first 30–60 minutes. Your body is still adjusting to the heat and heart rate lag can be deceptive. Better to be a little under target than a little over.

2. Use heart rate as a ceiling.​
Power is useful, but it doesn’t tell the whole story in hot conditions. Heart rate can act as a safety net — if it’s climbing higher than expected for your target power, that's a red flag. Ease off.

3. Prioritise cooling.​
Cold drinks, ice down the trisuit (if available), soaking your head in aid stations — all help reduce core temperature. A lower core temp = better performance.

4. Rehearse your heat strategy.​
If you’re racing abroad later this summer, simulate heat in training. Overdress. Train indoors without a fan. Or do back-to-back sessions to mimic heat stress. Get your gut, sweat rate and pacing dialled in before race day

And What About the Run?

If you’ve gone too hard on the bike in hot conditions, it’s going to show up on the run — fast. Elevated core temperature, dehydration, and glycogen depletion all come home to roost. You might hit your pace for the first few kilometres, but it won’t last. Once your body is too hot, there’s no easy way back.

Whether you’re stepping off the bike or heading into the second half of a marathon, here’s what heat means for your running performance:

Your Brain Slows You Down to Protect You

Heat stress is not just muscular — it’s neurological. Your brain acts as a governor, reducing muscle recruitment when it detects rising core temperature. That’s why your perceived effort skyrockets, even if your pace drops.

You’re not mentally weak. It’s a protective mechanism.

Pace Targets Can Be Misleading

Just like on the bike, running to pace in the heat can be a trap. That goal marathon or Ironman pace you’ve trained for in 12°C conditions simply won’t translate to 28°C+. Trying to force it is a fast-track to walking, cramping, or even DNFing.

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Strategies for Running in the Heat

1. Switch from Pace to Effort or HR​
Treat your target pace as a ceiling, not a target. Watch heart rate and perceived exertion. Slow down before you feel wrecked. If you’re breathing hard early, back off.

2. Cool the Body, Not Just the Head​
At every aid station: ice, cold water, sponges — use them all. Wet your arms and legs too, not just your head. If ice is available, tuck it into your hat or jersey.

3. Stay Wet​
Keeping your skin wet helps maximise evaporative cooling. It’s the most effective way your body sheds heat, especially if there’s any breeze.

4. Adjust Your Goals (and Your Ego)​
In hot races, survival often is success. Finishing strong beats going out fast and blowing up. Your time might be slower — but so will everyone else’s. Be smart and you’ll pass plenty of people in the final 10K.

Final Thought

Whether you’re racing Ironman, tackling a summer marathon, or heading into a training block during a heatwave — remember: the best performance is one that respects the conditions.

Control the controllables. Manage the heat. Race smart. And you’ll give yourself the best chance to finish strong — instead of crawling home.

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Are you ready to take your training to the next level? Sign up today and train with confidence, strength, and support all the way to the finish line!

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Thanks for being part of the tribe — I’m here to help you stay healthy, strong, and performing at your best. ​ Simon

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Please check out these podcasts and articles

​ PODCAST: Mastering Heat Training Whether you're off to a warm-weather training camp or prepping for a race in hot conditions, heat adaptation can significantly improve your performance. In this week’s podcast, I’m joined by Dr. Lindsey Hunt from Precision Fuel & Hydration to explore practical strategies for training in the heat. We cover lab-based protocols, simple at-home methods, and why something as straightforward as a hot bath could be your secret weapon when it comes to getting heat-ready. Tune in now

ARTICLE: Heat Acclimation for Endurance Athletes: How to Train Smarter in the Heat. Struggling in the heat? With proper acclimation, you can train your body to perform better in hot conditions. Gradual exposure improves temperature regulation, reduces dehydration risk, and enhances endurance. Whether you're racing abroad or training through a summer heatwave, smart heat training helps your body work more efficiently—so you can go further, faster, and safer. Dive in for more tips (3 min read)

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