Runners like to be in control. We dictate how far, fast, and when to run – even what to train for. But when it comes to weather, it’s the one thing you have the least control of! This means chances are high that you’ll run in heat, rain, and maybe even snow at some point.
Of these, most runners find heat the most challenging. But are there benefits to running in heat, or should you avoid it?
It can be tempting to stay home on those hot days, but in some cases, you might not be able to… And running in heat poses many unique challenges. These include: how fast or slow to run, how to stay hydrated, and how to avoid the potential for heat stroke.
The good news is that running in heat doesn’t have to be dangerous or ruin your run. It can have some benefits, but you also need to take extra precautions to stay safe. Here’s what you need to know!
How Does Heat Affect Your Body?
Your body usually stays at a temperature of 98.6°F, give or take a few degrees. Your brain regulates this temperature pretty strictly, and it’s more important than you might think—many of the body’s processes don’t work properly outside of that very small temperature range.
At high heat levels, your body temperature inches up, which can wreak havoc on many processes. Even if it’s just for a short while, the stress on your body increases significantly, leading to some negative effects.
Sweating is how the body regulates temperature in response to excess heat. When your temperature increases, the brain redirects blood to the skin rather than the muscles.
The veins and capillaries dilate, increasing blood flow to the skin. This triggers the body to respond by producing sweat to cool down as the moisture evaporates against the skin.
However, the more you sweat, the more you dehydrate. If you aren’t staying on top of your hydration, this can quickly get out of hand—your cognitive performance begins to crash if you don’t rehydrate quickly.
As well as excess sweating and the potential for dehydration, your heart has to beat harder to move blood to the skin’s surface.
Despite your heart beating harder, dilating the arteries, veins, and capillaries cause a drop in blood pressure. This can lead to dizziness, feeling weak, or even fainting.
In humid conditions, your heart will work harder, as the excess moisture in the air prevents the sweat from evaporating. This causes it to pool on the skin instead, contributing to the core body temperature increases.
Does Hot Weather Affect Your Running?
The optimal running temperature for top performance sits around 59°F. Research indicates that for every 1.8°F—1°C—the temperature rises above that, runners lose time per mile.
A runner who hits a 6-minute mile or faster can lose a second per mile for each 1.8°F above 59 degrees. Those who run a 7:25 to 10-minute mile can lose 4 to 5 seconds per mile.
Over a 10-mile race, that equates to an extra 10 to 40 minutes, depending on your pace! That’s a significant change to your running performance because of how the heat affects your body.
As your core temperature rises, your rate of perceived exertion (RPE) increases, so you may be running at your usual pace, but it will feel much harder than normal.
The lack of oxygen-rich blood in the muscles leads to higher-than-usual energy expenditure, increased lactate production, and increased fatigue.
Does It Take Long for Your Body to Adjust?
Research suggests that training in the heat for 60 to 90 minutes for two weeks can help your body adapt to hot conditions.
The majority of these adaptations happen in the first week of heat adaptation training, including improved heat dissipation, increased plasma volume, and a lowered heart rate.
However, if you only run in the heat every now and then, it’s unlikely that your body will be able to adjust. You will have to take steps each time to run safely and maintain the same level of performance in the heat.
Research also indicates that heat acclimation isn’t a permanent thing. When training for a week or two in hot conditions, your body will acclimate and you’ll see benefits for a week or two.
Unless you continue to train in the heat, you will slowly lose the adaptations and have to start acclimating again.
Are There Benefits to Running in the Heat?
Running in the heat occasionally isn’t likely to offer any benefits. But actively training in the heat can have numerous benefits that increase your performance. These may include:
Regularly running in the heat can help your body to adapt physiologically to training. You can benefit from these adaptations over time. They may include:
- A lower RPE
- Increase in blood plasma
- Lowered heart rate at regular pace
- Lower salt content in sweat
Other adaptations may increase your fitness levels, making it easier to perform well in both hot and cold conditions. These include:
- Increased cardiac output
- Improved VO2 max
- Higher lactate threshold
Improved Running Economy
With both physiological and fitness gains, your running economy will noticeably improve. This means you’ll eventually be able to run further and for longer, without exerting any more energy than before.
Running at a lowered heart rate also reduces your rate of perceived exertion, which means your runs will start to feel easier and easier.
What Are the Risks of Running in Heat?
As much as there are benefits to running in heat, there are also risks. Knowing the potential risks means you can take steps to reduce the chance of them happening. Here are some of the most common risks when running in the heat.
Heat exhaustion results from the body overheating and can be serious if it’s not treated soon after it begins. Symptoms include:
- Feeling dizzy
- Rapid pulse
If you notice these things happening, recognize the signs of heat exhaustion and treat it before it develops into something more serious!
Heat stroke is extremely serious. It can occur as a result of untreated heat exhaustion when the body reaches the point of being unable to regulate its own temperature.
When the core temperature has risen substantially, the body’s temperature regulation mechanisms fail. The body then can’t get the temperature to come down, leading to the heat damaging the brain and internal organs.
Symptoms of heat stroke include:
- Disorientation or confusion
- Rapid heartbeat
- Hot, dry skin
- An absence of sweating
- Loss of consciousness
Muscle cramps are not as serious as heat stroke or heat exhaustion, but they can be painful and annoying enough to ruin a run!
You may notice that you get more cramps in hot weather. This often occurs when you sweat a lot, as the electrolyte levels in the body become imbalanced by sweating out salt and taking in water without electrolytes.
Unbalanced electrolytes can lead to involuntary muscle jerks or spasms that can be painful enough to halt your exercise.
Hyponatremia is the more serious consequence of unbalanced electrolyte levels. It’s when the water and sodium levels in the body become skewed, leading to too much water and too little sodium.
Sodium helps to regulate the amount of water in and around the cells. If the sodium levels in the body are skewed, it can lead to a number of unpleasant consequences, including:
- Muscle cramps
Sunburn can happen even if you lather with sunscreen before leaving the house! The more you sweat in the heat, the more the sunscreen washes away, exposing your skin.
Not only can sunburn be extremely painful, but it can also do permanent damage to your skin. Especially if you run in the heat often and get sunburned regularly! It’s important to take extra precautions, like wearing a hat when you’re out in the sun.
Heat rash is an unpleasant condition that occurs when sweat gets trapped in the layers of the skin. It can result in a red, itching rash, most commonly in places where the clothing rubs against the skin.
In most cases, it goes away once the skin has cooled down again. However, you may need a doctor to treat it in severe cases.
When Is It Too Hot to Run?
Unless you’ve done serious training to acclimatize to the heat, running authorities, suggest that you should stay indoors if the temperature is over 98.6°F—37°C. If it’s cooler than that but the humidity is hitting 70 percent or more, you should also avoid running.
Everybody is different, so this is just a general rule. However, given that a runner slows down by one second every mile for every 1.8°F above 59°F, it’s easy to understand how running in 98°F weather is likely to have an adverse effect on your performance.
And when you consider the effect heat has on the body even when it’s not exercising, exerting yourself and raising your body temperature in this kind of heat can be a disaster.
Is It Worse to Run in the Heat or Humidity?
Both heat and humidity can be dangerous if you’re unprepared for them. But while heat can be dangerous as it raises your body temperature, humidity is extra dangerous because it prevents the body from cooling down.
In hot weather, your body temperature rises but it gets offset when sweat production begins. However, the body’s natural cooling mechanism is inhibited when it’s humid.
Humid air already contains a lot of moisture. This means that sweat doesn’t evaporate readily from the skin—instead, it pools on the skin’s surface, preventing heat from being released through the pores.
It also makes it harder to get a deep, oxygen-filled breath in, as the air is so saturated with moisture. You’re more likely to suffer from heat-related problems when it’s humid than just hot.
Should You Fuel Differently to Run in Hot Weather?
Ingesting more carbs can be beneficial in hot weather. You can use energy gels or chews throughout your run, providing a shot of carbs along the way.
These carbs are converted into energy for your muscles to use mid-run. When you’re running in hot weather, the body diverts much of the blood away from the muscles, which means they’re getting less fuel than usual.
Ingesting a few more supplements more often throughout your run can boost your energy. Make sure they’re simple carbs—that digest easily—and have a carb-rich meal before your run to set you up for success.
Tips to Run Safely in Hot Weather
Planning on running in heat? Or just want to be prepared for the future? Here are our best tips for running in hot weather safely.
Take the Time to Adjust
Pushing through the heat is tempting, but taking time is important. Push yourself too hard, and you may accidentally give yourself heat exhaustion. When it’s hot out, reduce your run intensity by 20 to 30 percent and work your way up slowly.
Plan Your Run the Day Before
It’s a great idea to check the weather the day before. If you can see it will be hot or humid, plan in advance. Perhaps you can choose a route with more shade, or one that you know passes by a number of water fountains.
You can also decide on your outfit in advance, so you know you won’t overheat during your run because you’re overdressed.
Start With Easy Runs in the Heat
If you’re spending more time running in the heat, start easy. Working your way up gradually is the way to do it—it lowers your risk of injury.
Monitor Your Pace
On hot days, you’re likely to have to slow down. If you monitor your pace on every run, be prepared for a lower, slower pace on hot days. Don’t aim to hit PBs on hot days—keep your expectations realistic based on the weather.
Hydrate and Restore Your Fluid Balance
Avoiding dehydration is essential in hot weather. Just mild dehydration can reduce your performance and start negatively affecting the body, so stay on top of this.
Aim to drink 10 to 15 ounces about 15 minutes before you run. Then, make sure you take small sips every few minutes. If you start to feel thirsty, you’re already dehydrating!
Add an electrolyte tablet to your water. This will prevent electrolyte imbalance as you sweat if you only replenish with regular water.
Wear the Right Running Gear
Dress for the heat. Choose moisture-wicking fabrics, lightweight materials, and technical fabrics with cooling in mind. A hat is always a good idea, as are sunglasses.
Choose the Best Time of Day to Run
If you can, it’s a good idea to avoid the part of the day when the weather is at its hottest. Get up earlier to run, or run after the sun goes down. This will help you to avoid the most dangerous times.
Run on a Different Surface
Asphalt and concrete absorb a lot more heat than grass and trails. When you run on these surfaces, it can reflect heat back to you. Opting for grass for trails reduces this issue.
Use Water to Cool Yourself
If you have enough water with you or you walk past a fountain or something similar, splash yourself with water to help cool yourself down. As the water evaporates from the skin, it has the same cooling effect as sweat.
Don’t forget the sunscreen! Protect your skin from harmful rays, and you can rest assured knowing that you’re also safe from wrinkles, sun spots, and cancers.