It’s something you’ve no doubt experienced at some point during the dog days of summer: You head outside for your daily jog or pickleball match, but today it feels impossibly hard. Odds are you can blame the weather.
As the humidity rises, your energy level may drop. But with careful planning and adjustments to your routine, you can still exercise safely and effectively even on the muggiest days.
What is the heat index?
The heat index is a formula created by the National Weather Service. It’s designed to measure the combined impact and feel of the air temperature and the humidity level. For example, if the temperature outside is 96 degrees and the relative humidity is 65%, that equals a dangerously high heat index of 121 degrees.
The formula reveals how much difference high humidity can make in how hot you feel. And that’s true even on days when the air temperature isn’t really that high. On an 85-degree day, humidity hovering around 90% can make the “real-feel” temperature closer to 100 degrees.
Why humidity makes exercise feel harder
When it comes to your body’s ability to stay cool during activity, humidity delivers a double blow. First, that high heat index means you sweat even more than normal. But because of the humidity, that sweat can’t evaporate and cool you down as it’s supposed to.
Sweat is your body’s primary cooling mechanism. Your glands produce more sweat when your body is hot. But it’s the process of the sweat evaporating off your skin that actually helps cool your body temperature down.
When the air around you is humid and already full of moisture, your sweat can’t evaporate as readily. As a result, you feel hotter. And when you feel hotter, exercising feels more difficult.
How to exercise safely in high humidity
When it comes to exercising on a humid day, moderation is key. This isn’t the day to do your longest run or to try to beat your best times in some speed intervals.
Instead, it may be best to dial back the intensity of your workout — especially if your body isn’t acclimated to those conditions. Start slowly, increase gradually and pay attention to how your body is responding.
If you need to do a more intense workout, you might want to seek out an air-conditioned gym.
The importance of staying hydrated in the heat
Because high humidity and high heat index days make you sweat more, your body will lose more fluid. Along with the fluids you’re sweating out, you’re also losing sodium, potassium and other important electrolytes.
Staying hydrated — before, during and after your workout — becomes even more important on sweaty days. Having a few glasses of water a few hours before a workout helps ensure that you’re not starting off dehydrated.
While you exercise, the recommendation is “drink to thirst.” Overdoing fluids can lead to a potentially dangerous condition called hyponatremia. When that happens, your sodium levels get out of balance which can cause symptoms such as:
- Confusion
- Headache
- Muscle cramps
- Nausea or vomiting
- Seizures
Signs of heat exhaustion you shouldn’t ignore
It can be easy to overdo it (and overheat) while exercising on a hot, humid day. Heat exhaustion is the first step on the way to heat stroke, a condition that can be a medical emergency.
If you start experiencing signs of heat exhaustion, it’s important to stop exercising and move to a cooler spot. Signs of heat exhaustion can include:
- Cold, clammy skin
- Dizziness
- Headache
- Nausea
- Rapid heart rate
- Weakness
It is possible to exercise on most days. But when heat and humidity are high, some extra precautions can help keep you safe.
