Running In Humidity, The Performance Drain + Dew Point Explained

At Marathon Handbook we often get runners coming to us via our Facebook community saying things like “It’s so humid, I’m finding it too difficult to run.”

Weather stress is real and summer running can get rough.

But high temperatures arent always the biggest culprit, often it is the high humidity and dew point.

Both of these can have a huge impact on your perceived effort, your heart rate, and your running pace.

In this article, we are going to dissect humidity running, dew point running, and take a look at:

  • What humidity and dew point are,
  • What running in high humidity does to your body,
  • What personal factors affect the way we cope with humidity,
  • Tips for running in humidity.

Ready?

Let’s go!

running in humidity dew point running

What is humidity and how can it be deceptive?

The issue with using humidity as a metric is that it is inconsistent and often, what we interpret as ‘high humidity’ isn’t always so.

Let’s break this down.

For example, if it is 90°F (32°C) outside at 60% humidity it will feel pretty humid outside.

However, the humidity isn’t actually that high, it’s relatively moderate. What is high though is the temperature.

The humidity % is a measure of how saturated the air is with water; 100% humidity means the air is carrying as much water as it can.

When the temperature is hotter, it is easily misinterpreted as high humidity.

Humidity in isolation isn’t useful. It only means anything in the context of temperature.

Even 100% humidity isn’t always uncomfortable!

Take these two mock days as examples.

Temp (°F)Temp (°C)Humidity (%)How it feels
Day 15716100crisp and pleasant
Day 27725100humid and muggy

See how humid it feels drastically varies depending on the temperature, even though both days have 100% humidity.

This is because humidity is actually relative humidity. Humidity tells you how much moisture is in the air relative to how much the air can hold.

And the higher the temperature, the more moisture the air can hold.

This is why, if you really want to know how humid it will feel outside before heading out for a run, you need a graph with both the humidity and the temperature on it, accompanied by a description of how each combination will feel.

Sounds complicated right?

It can take a minute to wrap your noggin around.

This is where the dew point comes in.

running in humidity dew point running

Dew point running- what is dew point?

Unlike humidity, which is relative, dew point is an absolute measure. Knowing the dew point, you will know exactly how going for a run will feel ‘humidity wise’.

The dew point is the temperature below which water droplets condensate, and due forms.

You might be familiar with dew point in reference to when water droplets form on grass and flowers in the morning.

But did you know that the same thing happens with humans?

And it’s a more reliable measure than humidity. The higher the dew point, the more water droplets (or sweat) form on our skin.

Dew point running-how does it feel?

Marathon Handbook asked Excercise Physiologist Todd Buckingham, PhD from Mary Free Bed Sports Rehabilitation Performance Lab to break down how running dew point feels. Here’s what he told us.

“Dew points 60-64°F (15.5-18.3°C) are when things become slightly uncomfortable and humid with a “sticky” feeling.

When the dew point reaches 70°F (21°C), that’s when things become very uncomfortable, and the humidity feels oppressive.

When the dew point reaches extreme temperatures, it is imperative to slow your pace goals by 5% or more (decrease your pace with an increase in dew point).”

running in humidity dew point running

If you’re a more visual learner and trying to wrap your head around this, take a look at this graph by Alex Tran.

running in humidity dew point running

Obviously though, everyone has their own comfort threshold and the best humidity for running really depends on the person.

What can be useful to do is to take a mental note of which percentage of dew point you are personally comfortable with. Therefore, when you check the dew point, you know what you’re in for.

High dew point running is tough, but why?

What does running in high humidity do to your body?

Seeing as we are now on the same page, from now on, when I write ‘humidity’ I’m referring to ‘dew point’!

So, what does running in high humidity do to your body?

Essentially, a high dew point means that your sweat simply won’t evaporate from your skin, as the air is already saturated with moisture.

When sweat evaporates, it takes your body heat with it, cooling you down.

This means that when the humidity is high, you aren’t able to reduce your body heat.

running in humidity dew point running

This means that your body will just keep sweating!

As you sweat on overdrive, you will be more at risk of dehydration and when you’re dehydrated, your body goes into survival mode.

This means that your body prioritizes keeping your essential organs ticking, so very little blood will go to your digestive tract, potentially making you feel nauseous.

You are also more prone to side stitches when you overheat, particularly if your breathing becomes shallow and uneven.

Another horrid side effect of overheating is that it impairs your ability to assess your own body temperature.

You might experience cold flushes, or simply have no idea how hot or cold you are, this makes it very difficult to address your needs.

4 factors that affect how you cope with running in humidity

High dew point running isn’t a one size fits all scenario, many factors come into play to influence how your body copes with these conditions.

running in humidity dew point running

1. Your body size.

The more weight which you carry on your body, the more heat that your body generates. The more heat that your body naturally generates, the easier it is to overheat, and the harder it is to cool down.

This is because fat has a lower thermal conductivity than lean tissue. This means that fat serves as a barrier to heat loss and influences thermoregulatory abilities.

For this reason, being a leaner runner in extreme humidity certainly has its advantages.

2. Your age.

According to studies, as you age, your body becomes less able to thermoregulate.

Ageing-related changes to your sweat glands decrease your ability to sweat, and reduce your body’s overall ability to cool itself down effectively.

3. The content of your sweat.

The content of your sweat is individualised. Some runners have higher concentrations of electrolytes, such as sodium or chloride, in their sweat than others.

Runners that lose more electrolytes in their sweat increase their risk of cramps if they don’t take in enough electrolytes.

running in humidity dew point running

4. What you have acclimatized to.

Where you live plays a role in how you deal with high dew point running. According to this study, it can take as little as seven days for the body to begin to acclimate to humidity and lower its core body temperature.

But the general advice for athletes who travel to more humid climates to compete is to arrive 10-14 days before race day to acclimatise.

Runners who live and train in areas with a higher dew point will have naturally better acclimatised to the conditions and their best humidity for running may vary drastically from yours.

How to cope with running in high dew point

A high dew point doesn’t need to knock you off your training. You can train through it using the following 5 techniques.

  • Plan your route to be through shaded areas. Think through the woods, or down narrow streets.
  • Wear technical, sweat-wicking running clothes. This will mean that your clothes won’t stick cling to your skin as much.
  • Wear a running hat soaked in cold water or filled with ice. This will keep you cool for obvious reasons, it feels great!
running in humidity dew point running
  • Drink more fluids per hour. You will inevitably sweat more. Stay safe and hydrated!
  • Adjust your pacing targets. It is good to be mentally prepared for your slower pace. Just remember you’re not getting worse at running, it’s just the weather!

The benefits of running in humidity

Although it may seem like running in humidity is a constant uphill battle with little reward, training in these tough environments can actually benefit your running game in the long run.

Marathon Handbook spoke to Alyson Sheppard MS, Exercise Physiologist and Sports Performance Coach at Optimize Performance about the benefits of running in uncomfortably high humidity and dew point. She told us that;

“Yes, it is harder to breathe, harder to keep your specific pace, but listening to your body and building your aerobic base will grant you MORE room to grow with pacing and mileage once the weather cools down”

running in humidity dew point running

She told us that the key to reaping these running rewards lies in ones ability to keep their heart rate down;

When you keep track of your heart rate and slow your pace down to allow your body to work efficiently, it may feel like wasted mileage, but what you’re actually doing is building a solid aerobic base.

The moment the weather cools down, your body doesn’t have to use energy for cooling itself as much as it did prior, it can use the energy to get oxygen to the working muscles allowing for increases in pace at the same heart rate.”

So maybe next time, instead of saying to yourself that it’s too hot to run, with these training benefits in mind, you might just lace up your shoes and get out there.

How to find out the dew point

As with pretty much anything, there’s an app for that!

Here are a couple that you can choose from;

  • WeatherBug This app is free and was awarded best weather app of the year in 2019. It also has the largest weather network of any app, so it’s likely to cover your location!
  • Weather UndergroundThis app is alos free. Here, you’ll be able to find dew point for most major cities worldwide. It updates real time and It’s pretty good.

Still after more hot weather content?

Check out this Summer Running Guide for tips and tricks on how to stay cool.

Maria Andrews

Maria Andrews

Maria Andrews is a runner, cyclist, and adventure lover. After recently finishing her Modern Languages degree and her first ultramarathon, she spends her time running around and exploring Europe’s mountains.

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