That Humidity Percentage is Lying To You. Here’s How to Fight Back.
Training in high humidity is brutal. We’ve all been there, it feels like you’re trying to run through soup while breathing through a wet towel. But what if I told you that the humidity percentage you see on your weather app is basically feeding you fake news about how hard your body has to work?
Stick around. I’m about to spill the secrets on why humidity is such a performance-killer and give you the exact strategies I share with my athletes to stay cool, strong, and even get faster when the weather is begging you to quit.
“My Heart Rate is Through the Roof and I Feel Awful!”
As the head coach at Efficient Endurance, my inbox has been flooded with messages from athletes who are getting absolutely demoralised by the humid weather.
They feel sluggish, their heart rate is red-lining even on easy runs, and they’re missing their targets in both training and on race day. It’s a massive confidence-killer. I see athletes who have trained diligently for months feel like all their fitness has just vanished overnight. This post contains the exact same advice I give them, so you can stop fighting the weather and start outsmarting it.
Why Your Body’s A/C Unit Fails
Your body has a brilliant, built-in air conditioning system. When you get hot, your body sends blood to the surface of your skin and you start to sweat. As that sweat evaporates, it takes the heat from your blood with it, and voilà, you cool down. Simple and effective.
Well, until humidity, that unwelcome party guest, crashes the scene.
Humidity is just the amount of water vapour in the air. The more water there is in the air, the less room there is for your sweat to go anywhere. Instead of evaporating and cooling you, it just drips uselessly off your chin, taking none of that performance-sapping heat with it.
Now, here’s the crucial insight that most athletes miss: The percentage on your weather forecast is relative humidity. But what really matters for performance is the dew point, which reflects the total volume of water in the air.
And here’s the kicker: hot air can hold exponentially more water than cold air.
For example, a 32∘C day with 50% humidity feels far more oppressive than a 20∘C day with 90% humidity. Why? Because the hotter air contains a much greater absolute volume of water, making it nearly impossible for your sweat to evaporate and do its job. That lower percentage on the hotter day is lying to you about the thermal stress you’re under.
The Struggle
Let’s relive a moment of shared trauma, shall we? You’re out for a run. It’s hot and humid. You’re sweating buckets, but it’s just plastering your shirt to your skin. Your core temperature starts creeping up. Your body panics and shunts even more blood to your skin in a desperate attempt to cool down.
The problem? That’s blood that’s not going to your hard-working muscles.
To compensate, your heart rate skyrockets to try and pump oxygen everywhere it needs to be. As you become more dehydrated from the ineffective sweating, your blood literally gets thicker. Now your heart has to work even harder to pump that sludge around your body.
You finally stop, check your watch, and see the damage: your pace was 10% slower than you wanted, but your heart rate was 10% higher. You feel completely knackered and defeated.
Your 4-Step Cooling Plan
So, how do we fix this? You don’t need to hide indoors on a treadmill all summer. Here’s your game plan.
Acclimatise Like a Pro Don’t hide from the heat, master it. Training safely in hot conditions is the best long-term solution. In just 7 to 14 days of consistent training (around an hour a day), your body makes incredible adaptations:
- Your blood plasma volume increases (so you have more to go around for both cooling and working muscles).
- You start sweating sooner and sweat more efficiently.
- Your sweat becomes less salty, meaning you lose fewer critical electrolytes. Your body literally learns to be more efficient at cooling itself.
Cheat the System with Pre-Cooling Even if you’re not fully acclimatised, you can trick your body into starting cooler.
- Before you train: My favourite trick is to drink an icy, blended slushie about 30 minutes before heading out. As your body melts the ice, it draws a significant amount of heat from your core. Immersing your feet and hands in cold water or using an ice vest also works wonders.
- During your session: Keep drinking cold fluids to cool your core from the inside out. And don’t be afraid to pour cool water over your head, neck, and arms for instant conductive cooling.
Hydrate Smarter, Not Harder Hydration isn’t about chugging a litre of water right before you start; it’s about what you’ve done over the last 24 hours. Critically, you need sodium. Sodium is the key that unlocks the door, allowing your body to actually absorb and hold onto the water you drink. Without it, you’re just flushing your system without effectively boosting your blood volume. Add an electrolyte tab to your water throughout the day.
Dress for Success This one is simple but often overlooked. Wear lightweight, loose-fitting, and light-coloured technical fabrics. These materials are designed to pull sweat off your skin and onto the fabric’s surface, where it has a better chance of evaporating. That lovely feeling of a cool breeze on the damp fabric isn’t just nice; it’s actively cooling you.
The Coach’s Insight: The Single Biggest Piece of Advice
We’ve covered the physical tactics, but the most important adjustment is mental.
You HAVE to adjust your expectations.
It’s a tough pill to swallow, especially when you’ve paid good money for a race entry. But your body simply cannot perform at the same level in high heat and humidity as it can on a cool, crisp day. It’s physiologically impossible.
So, abandon the pace targets on your watch. They will only lead to frustration. Instead, run by feel. Tune into your Rate of Perceived Effort (RPE). Remember, everyone else is suffering just as much as you are. The difference is, you now have the knowledge and tools to suffer a little less and, as a result, go a lot faster than them. It’s the ultimate example of how to train and race with your head, not just your legs.
Your Key Takeaway
Humidity doesn’t have to ruin your training or your race day. Understand the real reason it’s so hard, acclimatise patiently, and use these cooling and hydration tactics to master the conditions. If you’re ready to apply these principles with a plan tailored specifically to you, see how our remote triathlon coaching can help you unlock your true potential.
