This summer, the hot weather in WI has seemed especially relentless. Between the high temperatures and humidity, even everyday activities can feel more challenging. I got some foreshadowing first hand of this warm summer that was to come while training for a half marathon in May.
How Weather Reality Check
I completed a half marathon in May, and I started training for it back in February. At the time, I actually thought the timing was perfect. Since my training would gradually carry me from winter into spring, I assumed I would naturally acclimate to warmer temperatures. If race day happened to be warm (which, on Memorial Day weekend in Wisconsin, you truly never know), I figured I’d be ready.
Throughout my entire training cycle, I only had one long run where the temperature climbed above 60 degrees. It was only in the mid-60s, but the humidity was incredibly high. I was excited to finally wear my new running shorts and leave the cold-weather gear behind. Instead, that run completely humbled me.
By mile four of my 10-mile run, I had already finished all of my water and electrolytes. My head was pounding. My legs felt heavy. Every mile seemed harder than it should have been, and my pace slowed dramatically.
I knew the hot weather was playing a role, but it was still frustrating. I felt weak, and with only four weeks until race day, I started worrying that if the half marathon was warm, all of my training would go out the window.
A Simple Question Changed My Perspective
For this race, I worked with a nutritionist to make sure I was fueling appropriately throughout training. When I checked in after that difficult run, I explained how discouraged I felt. Before asking about my training or nutrition, she asked one simple question:
“What were the weather conditions?”
After I told her it was my first run in over 60 degree weather since the previous fall, she made it all make sense.
She said it’s completely normal for runners to slow down in hot weather. In fact, once temperatures climb above roughly 60°F, many runners naturally see their pace slow by around a minute per mile depending on the temperature, humidity, and individual athlete.
I knew that warmer temperatures caused increase energy expenditure and therefore increased effort. But above 60 degrees? I always considered that ideal running weather. It turns out our bodies begin working much harder than we realize long before temperatures feel “hot.”
How Hot Weather Affects Athletic Performance
When you exercise, your muscles generate heat. To prevent overheating, your body redirects more blood toward your skin so you can cool yourself through sweating.
While that’s great for temperature regulation, it also means:
- Less blood is available to deliver oxygen to your working muscles.
- Your heart has to work harder to pump blood throughout your body.
- Sweat causes you to lose both fluids and important electrolytes.
- Your core temperature rises more quickly.
- You fatigue sooner, even if you’re running at your normal pace.
Add humidity and things get even harder. Normally, sweat evaporates from your skin to cool you down. However, when the air is already full of moisture, sweat can’t evaporate as efficiently. Instead of cooling you, it simply drips off your body while your core temperature continues to rise. This is why a humid 70-degree day can often feel much harder than a dry 80-degree day.
Signs the How Weather Is Catching Up to You
Everyone responds differently to hot weather, but common signs include:
- A much higher heart rate than usual
- Slower pace despite the same effort
- Heavy legs
- Headache
- Dizziness
- Feeling unusually fatigued
- Chills or goosebumps despite being hot
- Excessive thirst
If you experience dizziness, confusion, or stop sweating altogether, it’s important to stop exercising immediately and cool down, as these can be signs of heat-related illness.
How to Improve Performance in Hot Weather
The good news is that your body can adapt. But it takes some important steps and planning.
1. Give Yourself Time to Acclimate
Heat acclimation doesn’t happen overnight. Most runners need about 7–14 days of regular exposure before their bodies become noticeably more efficient at exercising in hot weather. In my situation, it was 1 day. My previous long run was about 20 degrees cooler! It makes sense that I feel the way I did.
As you acclimate, your body begins to:
- Sweat sooner.
- Produce more sweat for better cooling.
- Conserve sodium more efficiently.
- Maintain a lower heart rate at the same effort.
- Better regulate body temperature.
If your goal race is expected to be warm, it is best to include some training in similar conditions if at all possible.
2. Prioritize Hydration
Hydration starts long before your run. Drink fluids consistently throughout the day instead of trying to “catch up” right before heading out the door. Or worse..after the dehydration has happened!
For longer runs, especially those lasting more than an hour, consider replacing electrolytes in addition to water. Sodium, in particular, plays a key role in maintaining fluid balance and helping muscles function properly. Everyone’s sweat rate is different, so it may take some trial and error to determine how much fluid you personally need.
For me, my nutritionist recommended doubling the electrolytes I had planned on!
Need a creative way to add in electrolytes? Check out Summit’s fun take on homemade electrolyte drinks!
3. Adjust Your Expectations
This was probably the hardest lesson for me. Sometimes, slowing down is actually the smartest thing you can do. Instead of chasing a specific pace, run by effort or heart rate during hot weather. Your body is already working harder, even if your watch says you’re moving slower. A slower pace on a hot day doesn’t mean you’re losing fitness. It simply means you’re adapting to more demanding conditions.
4. Plan for Hot Weather Ahead of Time
If you know it’s going to be hot:
- Train early in the morning or later in the evening.
- Choose shaded routes whenever possible.
- Carry water or plan refill stops.
- Wear light-colored, moisture-wicking clothing.
- Consider shortening or modifying your workout if conditions become unsafe.
Being flexible with your training is often a sign of smart training, not weak training.
Lessons Learned
In the end, race day was actually cool, and the weather wasn’t a factor at all. Still, I’m grateful that difficult training run happened.
It taught me that hot weather changes more than just how comfortable a run feels, it actually changes how your body performs. It also reminded me that a slower pace isn’t always a sign that your fitness is slipping. Sometimes your body is simply working overtime to keep you safe.
The next time you head out for a run and wonder why everything feels harder than usual, take a quick look at the temperature and humidity before judging your performance. Your body may be working much harder than your watch can tell you.