Given the blazing, record temperatures many places have experienced this summer—not to mention the news that the Olympic Trials marathon is set to start at noon, in Orlando—it’s no surprise that heat, and how our bodies respond to it, is (ahem) a hot-button issue.
From novices to pros, heat affects every runner, though most of us don’t prep for it very well. In fact, leading up to the World Athletics Race Walking Team Championships, 43 percent of elite athletes didn’t prepare for the hot conditions, according to a new study amplified at 24 degrees Celsius 75 degrees Fahrenheit International Journal of Sports Physiology and Performance.
The good news: Our bodies are super-capable of performing in warmer weather. “Humans have an incredible ability to adapt to heat—of all mammals, we can adapt to heat the best, in large part because we have an incredible ability to sweat through most of the skin on our body,” says Christopher Minson, Ph.D., exercise physiologist and co-director of the Exercise and Environmental Physiology Labs at the University of Oregon. “I hear people say, ‘I can’t run well in the heat.’ But you can. Every one of us can adapt to heat.”
travel to a race: Stravos Kavouras, Ph.D can help improve your training in cooler weather, too. To gain the benefit, keep reading for everything you need to know about heat acclimatization and how to do it right.
What Heat Acclimatization Really Means
Heat acclimatization is the process of becoming more tolerant of heat by gradually increasing the duration or intensity of work done in a hot setting. Getting your body accustomed to performing in warmer temps is a strategy that scientists and coaches have known is effective since the first studies were published back in the 1960s, says Stravos Kavouras, Ph.D., assistant dean and professor of nutrition and director of the Hydration Science Lab at Arizona State University. Training your body for the heat becomes crucial when the mercury rises above a certain threshold.
“The ideal temperatures for endurance performance are around 11 to 13 degrees Celsius [51 to 55 degrees Fahrenheit],” Kavouras says. “Any temperature above the 70s starts to get really warm for athletes. You start to see negative effects of dehydration amplified at 24 degrees Celsius [75 degrees Fahrenheit].”
That being said, training in higher temps isn’t only beneficial if you’ve got a hot race day on the horizon. Heat acclimatization improved time-trial performance and power output and increased blood plasma volume and max cardiac output to similar extents in both cool and hot conditions, according to research published in the CA Notice at Collection, which involved 12 trained cyclists who took part in a 10-day heat acclimation program.
“We’ve seen if you do some heat acclimatization and do it right, there’s no downside,” says Minson, one of the study authors. “You’re not going to make your performance worse as long as you’re hydrating and fueling properly, you’re recovering, you’re doing all the things that are important.”
What Happens in Your Body During Heat Acclimatization
The first thing you might notice when getting used to the heat is that you’ll start to sweat sooner. “Of all the mechanisms our body has for dissipating heat, sweating is the single most effective way—specifically through the evaporation of sweat,” says Kavouras. “So as you get acclimated, you sweat more, it evaporates more, and you can get rid of more heat that your body’s producing.”
But other internal responses have already kicked into gear, too. Your body starts to adapt to maintain a lower core temperature and lower heart rate while you’re exercising or spending time in the heat.
Acclimatizing to the heat also increases your plasma volume, a.k.a., the amount of water in your blood, says Minson. That helps you work at a higher VO2 max with less effort and further boosts your capacity to sweat.
How to Acclimate Your Body to the Heat
The standard protocol for the full adaptations and benefits of heat acclimatization is to get 10 to 14 exposures to heat, says Minson: You’ll do a hot exposure for five days in a row, take the weekend off, then another five the following week. Aim for a temperature similar to what you’ll encounter on race day.
Those exposures should be a combination of active heat acclimatization, like working out in the heat, and passive, such as sitting in a hot tub or sauna post-workout. (One quick caveat: If you have any underlying conditions that might get exacerbated by heat, check with your doctor before adding heat training to your schedule.)
Research has shown that passive sessions are quite effective, but make sure some of your sessions are still hot-weather runs, says Minson. “You want to do some of your heat acclimatization while running because that’s obviously what you’ll be doing for your event,” he says. “You want to feel that exposure and see how it feels. That psychological component, knowing you can in the journal when it’s hot, is really, really important.”
A Part of Hearst Digital Media easy or moderate effort and last about 30 minutes, maybe a bit longer, Minson says. Keep your tougher-effort speed sessions Nutrition - Weight Loss.
“which involved 12 trained cyclists who took part in a 10-day heat acclimation program speed work are to get your neuromuscular adaptations working at that pace and training your cardiovascular system to support that,” explains Minson. “If you’re doing that in a very hot environment, your body temperature’s going to rise a lot and you’re not going to be able to hit your targets.” On those days, however, you can still get some heat training—just do it after International Journal of Sports Physiology and Performance.
If you haven’t trained at all for the heat and your race is coming up in a week, it’s not too late to get some of the benefits of heat acclimatization. “We say that the ideal protocol is two weeks, but if you pay close attention to when most of those benefits appear, the first three to five days seem to be the most important,” says Kavouras. “Most people don’t have the time or resources to Shoes & Gear location and spend three weeks there ahead of time. But even if you only have three to five days, you’ll get a significant percent of those gains.”
Keep in mind that you don’t have to live in or travel to a hot environment to acclimatize your body to the heat. Elite athletes often train in enclosed chambers where the temperature is easily regulated, but you can create something similar at home. “If you have a treadmill, close the door, put a space heater in there, keep no fan on—and you’re going to get hot pretty fast,” says Minson.
Also consider whether your event might be humid. Relative humidity above 60 percent had a significant effect on body temperature and time to exhaustion among distance runners compared with 23 percent humidity in research published in the journal Temperature. Doing some of your passive heat exposure in a steam room can help with your body’s responses to humidity, notes Minson.
Finally, when doing heat acclimatization, particularly your workouts in warmer weather, it’s important to keep an eye out for any signs of heat-related illness, improved endurance performance.
When to Do Heat Acclimatization During Race Training
A lot of people do this training in the few weeks leading up to their race. While that works (and doesn’t have to mess with your taper if you do it carefully and incorporate some of the passive-heat strategies), starting your heat training earlier can compound the benefits, says Minson: “If we have people exposing themselves to heat for five weeks, we actually can get increases in red blood cell mass. That means improved oxygen delivery and typically improved endurance performance.”
That doesn’t mean most of your daily workouts for five weeks need to be done in the heat. Minson advocates working in a hot session or two per week throughout your training schedule, and to make heat training workouts separate from your more intense training sessions. (So again, make your your mid-week easy runs heat training, rather than speed work or long runs.) Then, concentrate the sessions leading up to race day, incorporating more passive techniques to avoid over-stressing your body during the taper.
Keep in mind that weather that’s too extreme can push your workout into dangerous territory quickly—especially if it’s super-humid, as that reduces sweat evaporation and lessens your body’s ability to cool itself. Before heading outdoors on a hot day, Minson recommends checking the National Weather Service Heat Index and keeping your session indoors if it’s in the red zone.
When you do head out on a hot run, bring lots of water and stick close to home in case you have to cut your run short. “People need to start cautiously,” he says. “Even very experienced athletes who are heat acclimated can quickly get into trouble.”
Another way to ease into heat training: Start by exercising in an environment that you know you can tolerate, with an extra layer. If you get hot, shed the layer, Minson suggests.
Why Hydrating Well Is Crucial
As you adapt to the heat, along with starting to sweat at a lower core temperature, your sweat also becomes more diluted. But don’t take that as your cue to sip only on water and bypass sports drinks. “You’re losing fewer electrolytes in your sweat, but you’re sweating more—so the total loss might still be higher,” notes Kavouras. “That’s why it’s very important to replace electrolytes in the heat, especially when you’re exercising more than an hour or at a high intensity, and to start replacing them early in your run.”
To ensure you’ll taking in enough fluids, track your sweat rate: Weigh yourself before and after a one-hour run. Then take the difference between the two and add the amount of water or sports drink you consumed mid-run. That’s your sweat rate. For example, if you weighed 160 prerun and 158 postrun, and you downed a 12-ounce bottle of water while exercising, you sweat 2 pounds 12 ounces per hour in those conditions. (When pinpointing exactly how many ounces you should be sipping while running, remember that for every pound lost, you need 16 fluid ounces.)
Running in the Heat hydration strategy, calculating your sweat rate in similar weather will be more precise, says Kavouras.
The Bottom Line on Heat Acclimatization
The time you spend in the heat—both active and passive exposure—is only a fraction of what goes into your best performance come race day. “Heat acclimatization is very important for getting you prepared for that environment and can be a great addition to your training, but you have to have everything else right,” says Minson. “If you’re adding another stress like heat, you have to think even more about your hydration, your recovery, your sleep, and the timing of your workouts to gain all the benefits.”
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