Heat Training: Everything You Need To Know, Including Benefits and Safety Tips

As soon as temperatures hit the high 80s, many outdoor fitness enthusiasts scurry indoors and trade asphalt for treadmills. We can’t blame them. Every person’s idea of perfect outside conditions varies, but they likely involve low humidity and cool temperatures.

Just because we can’t have spring weather all the time doesn’t mean we can’t take advantage of the heat and achieve our fitness goals. That's what heat training is all about if done safely.

What Is Heat Training?

Heat training is using heat to boost your exercise performance and overall health. The idea is that exercising in a hot climate or heated environment may ramp up the demands of your workout and trigger a series of adaptations in your body that improve your endurance.

If your outside conditions are not particularly hot, there are a few ways to add heat to an exercise session. These include:

• Using a sauna
• Working out in heated water
• Wearing multiple layers of clothing
• Using an athletic chamber, a room that enables you to raise the heat and humidity to specific levels

It's important to note that researchers have debated the benefits of heat training, particularly for individuals who are not elite athletes. Researchers note that for some people and in some settings, the benefits of heat training may be modest or absent.

Here's what you need to know about what heat training can do for your body and how to go about it safely.

Benefits of Heat Training

Heat training has been demonstrated in various studies to improve aerobic exercise performance, which means exercises such as running, cycling, rowing, etc. Researchers say heat training triggers a series of physiological adaptations that can boost your performance.

Boosts Hemoglobin

If you’re an elite athlete, the most notable benefit of heat training is an increased production of hemoglobin—the key protein in your red blood cells that carries oxygen to your body’s major organs and tissues. This has a direct effect on your overall endurance.

One 2020 study found that training for five hours a week for five weeks in 100-degree heat boosted the hemoglobin levels in male elite cyclists by 4-5%, boosting overall oxygen intake.

“By increasing your hemoglobin concentration, you’re enhancing the oxygen-carrying capacity of your blood, and you’re improving upon that potential weak link for the endurance athlete,” Robert Mazzeo, PhD, associate professor of Integrative Physiology at the University of Colorado Boulder, told Health.

Keep in mind, though this study was done on elite athletes. For recreational athletes, it’s not likely the limiting factor in your performance is your max cardiac output and oxygen delivery systems, so the hemoglobin benefit isn’t expected to be dramatic.

Increases Plasma Volume

After just a few days of heat training, you could experience a boost of almost 20% of plasma volume in your veins (plasma is essentially the liquid portion of blood).

An increase in plasma volume may make athletes better at thermoregulation, or the body's ability to maintain a certain body temperature. In the simplest of terms, by getting acclimated to heat, your body gets better at sweating and cooling itself down.

When you're training, you want a certain amount of blood and oxygen to go to your muscles. If you're training in the heat, you have to divert some of that blood flow to the skin to cool you down and help your body maintain its core temperature, which causes plasma production to go into overdrive.

Essentially, "increasing your plasma buy-in helps you thermoregulate by helping the blood go into the skin, keeping it as cool as possible, given the disruption in its homeostasis," said Dr. Mazzeo.

The benefits of increased plasma volume go beyond helping your body stay cool, too. More plasma in your body means more blood can be sent to cool your skin without compromising the supply of oxygen being carried to your muscles, allowing you to last longer, even when you take your workouts back inside.

"Increases in plasma volume from heat acclimatization may lead to better endurance and longer lactate threshold when returning to cooler or normal training temperatures," Roger Adams, PhD, ACE-CPT and owner of eatrightfitness in Oklahoma, told Health.

The way higher plasma levels directly affect endurance is still debated. Still, most scientists agree that extra plasma dilutes the concentration of red blood cells in your blood, which in turn triggers the production of more hemoglobin-rich red blood cells, making it easier for your muscle to obtain oxygen.

Potential Risks of Heat Training

Heat training does come with risks. Exercising in a high-temperature environment can sometimes result in heat-related illness.

Inability of the Body To Cool Itself Off

You can get sick in high temperatures if your body has a hard time adjusting to the heat and cooling you off. If the humidity is high, sweat won’t evaporate as quickly, so your body cannot cool itself during scorching weather.

There are also many factors that can play a role in whether a person can cool off enough in very hot weather, including:

• Age
• Obesity
• Fever
• Dehydration
• Heart disease
• Mental illness
• Poor circulation
• Sunburn
• Prescription drug use
• Alcohol use

Of note, individuals at the highest risk of heat-related illness include:

• Adults 65 and older
• Children younger than 2
• People with chronic diseases or mental illness

The most common heat-related illnesses include heat stroke, heat exhaustion, heat cramps, sunburn, and heat rash. These illnesses are outlined below:

Heat Stroke

The symptoms of heat stroke include:

• High body temperature (103°F or higher)
• Hot, red, dry, or damp skin
• Fast, strong pulse
• Headache
• Dizziness
• Nausea
• Confusion
• Losing consciousness (passing out)

Heat Exhaustion

The symptoms of heat exhaustion include:

• Heavy sweating
• Cold, pale, and clammy skin
• Fast, weak pulse
• Nausea or vomiting
• Muscle cramps
• Tiredness or weakness
• Dizziness
• Headache
• Fainting (passing out)

Heat Cramps

Heat cramps symptoms include:

• Heavy sweating during intense exercise
• Muscle pain or spasms

Sunburn

Sunburn symptoms include:

• Painful, red, and warm skin
• Blisters on the skin
  

Heat Rash

Heat rash symptoms include:

• Red clusters of small blisters that look like pimples on the skin (usually on the neck, chest, groin, or in elbow creases)
  

Who Should Avoid or Limit Heat Training?

Individuals who are at risk for heat-related illnesses or may be affected by higher temperatures should choose other active options beyond heat training. However, in terms of exercise in general, the following individuals should be very aware of how heat can affect them.

Older Adults

Older adults can have issues adjusting to sudden temperature changes. They are also more likely to have chronic medical conditions or take prescription medications that can affect how their body:

• Responds to heat
• Controls its temperature
• Controls its ability to sweat

However, tolerance to heat may vary among older individuals based on their aerobic fitness level. People who are active at intensity levels associated with their fitness level may have less heat vulnerability.

People with Chronic Medical Conditions

For individuals with chronic medical conditions, too much exposure to hotter temperatures might:

• Increase the risk of a condition getting worse
• Increase the risk of death for people with multiple different conditions
• Impair judgment or behavioral crisis events for people with mental health issues or Alzheimer's disease

Those with chronic medical conditions may be less likely to realize that there has been a change in temperature. As a result, they also may unable to respond to that change. The medications that these individuals take can also worsen extreme heat effects.

Some people may have conditions that lead them to be immunocompromised (have a weakened immune system). This immune system status can result in potential extreme heat-induced reactions.

Pregnant Individuals

People who are pregnant can become dehydrated easily in extreme heat, and it takes more work for their bodies to cool down. Their core temperatures can rise, which may lead to pregnancy complications (e.g., birth defects).

However, research has suggested that the following activities, for a limited time, may be appropriate for those who are pregnant:

• 35 minutes of exercise or less, at 80 to 90% of maximum heart rate in conditions of 25 degrees Celsius (77 degrees Fahrenheit) and 45% humidity
• 45 minutes of water immersion exercise or less, in water that is 33.4 degrees Celsius (92.12 degrees Fahrenheit) or less

These exercise suggestions were associated with core temperatures that would not be harmful during pregnancy.

No matter the individual, however, it's best to consult a healthcare provider before doing exercise regimens, especially those related to high temperatures.

How To Work Out in the Heat Safely

Heat training is no joke, and it's not something to be taken lightly—primarily because it's just not your body's go-to for training purposes.

Prepare and Train Properly

You shouldn't start training in 90-degree weather daily without much preparation. Dr. Adams said it takes about 10-15 days for your body to acclimate to the heat, so make sure that you:

• Take it slow
• Follow a program
• Be smart about the time of day you choose to get outside

It's also wise to consider the risks of hot summer weather—heat stroke, sunburn, and dehydration, to name a few—which makes it even more important to focus on safe heat and exercise practices.

Choose the Time of Day for Your Workout Carefully

The timing of your workouts matter. “Heat, plus humidity, plus direct sunlight is a triple-threat combination, so keep that in mind, and try to schedule your workouts accordingly,” Chris Ryan, CSCS, NSCA-certified personal trainer on NBC’s Strong, told Health. “Do the harder portions earlier in the day and lighter portions in the hotter parts of the day.”

The fitter you are, the better your body can tolerate exercise in the heat. If you’re starting to heat train for the first time in the dead of summer, do a shorter and slower-that-normal workout. You want to make sure you don’t go too fast trying to match your spring pace or intensity right when you’re starting out. On each subsequent hot day, go a little farther and a little faster.

Stay Hydrated

It's also in your best interest to stay properly hydrated, said Ryan. And you have to start even before you hit the pavement. "It starts 24-48 hours before a hot workout or competition. Electrolytes are key to ingest every hour of activity, as well as moderate salt intake."

Dr. Adams has his athletes weigh themselves before and after they train, and then for every pound they have lost, they need to consume two cups of water. “I have my athletes consume 16 ounces or more of water or hydration solution right before training and then keep consuming around four ounces every 20 minutes or so,” said Dr. Adams.

Wear Appropriate Clothing

Of course, there's also the element of proper clothing. “Proper clothing that allows the sweat to wick off is a plus, as clothing that traps heat and sweat may increase your chances of heat-related issues and lessen your body’s ability to cool off effectively," said Dr. Adams. Naturally, don’t forget to apply sunscreen regularly with at least SPF 30 to protect from damaging sun rays.

A Quick Review

So while you may not willingly choose to run a few miles outside in the middle of summer under typical circumstances, heat training may up your performance—just make sure to do it slowly and safely and to listen to your body even more when out under the hot sun.