Running (and racing) in high temperatures means more than hydrating properly. Here’s a summertime survival guide.
By John Hanc THURSDAY, JULY 14, 2011, 12:00 AM
Stop! My brain screamed.
It was 9 o’clock in the morning and almost 90 degrees. Instead of sitting with my feet up in a breezy breakfast nook, I was exhausted on mile eight of the Hottest Half in Dallas. Raising my legs required every single recruitable muscle fiber. Moving my arms felt like swinging sandbags. Even breathing was tiring, each exhale laboriously propelled from the wheezing bellows inside me.
I didn’t know it, but with 5.1 miles to go, my core temperature had risen to a 10th of a degree shy of possible heatstroke. I ignored my brain’s urgent demand and kept running.
You may unsubscribe at any time.
I hate the heat. It makes me grouchy, uncomfortable, and sluggish. As a runner, I live for cool spring mornings and the snap of crisp, autumnal air. But loathe heat or love it, you can’t mess around with it.
“Heat can kill you,” says William O. Roberts, M.D., medical director for the Medtronic Twin Cities Marathon in St. Paul, Minnesota. “That’s why we have to be so careful with it, especially runners.”
Running in sauna-like conditions can throw your internal equilibrium seriously out of whack. The body normally cools itself by moving blood—which is mostly water—to sweat glands in the skin, says Douglas Casa, Ph.D., A.T.C., COO of the University of Connecticut’s Korey Stringer Institute. The glands create sweat droplets that carry heat to the surface of the skin, where it evaporates.
“The droplets of sweat are like little containers for the heat,” Casa says. When you continue to run, your organs and working muscles compete for a limited blood supply, which compromises this cooling system. Humidity compounds the problem, by hindering the evaporation of sweat, making it harder to cool yourself. And runners performing intense exercise in hot weather tend to become dehydrated, says Casa. “With less water in the body, you have less blood plasma volume—the liquid portion of your blood—to serve all your needs.”
Once your body temperature climbs to 104 degrees, you’re in the heatstroke danger zone. Continued hard running at this temperature can overwhelm your cardiovascular system. Hit 105 degrees for 30 minutes or more and your body may start to cook from the inside out. The hyperthermia can weaken the heart, cause the kidneys and the liver to shut down, and cause cell damage. Exertional heatstroke has arrived.
A complicating factor for runners is that everyone reacts to heat differently. For example, average at-rest body temperature is 98.6 degrees; normal while running in the heat is 101 to just below 103. Some people who hit 103 will feel fatigued and light-headed, while others will feel fine. Same with 104 degrees. At this point, your body may be generating more heat than it can dissipate, and you may feel like death—or feel nothing at all. “The symptoms are the key,” says Casa. “If you feel poorly—light-headed, nauseous, extremely fatigued, have cramps or a headache—those are big-time warning signs to back off the pace.” Perhaps the most important symptom, he says, is when everything seems harder than it normally does. “That’s a sign to ease up and slow down. Your body is now locked in an internal battle, trying desperately to keep itself cool while you are forcing it to keep working.”
Ultimately, says Roberts, there’s only one surefire way to prevent heat distress on a hot day: “Go lie in a hammock.”
But as a runner living on Long Island, avoiding the heat just isn’t an option. I did wonder, though—could I learn to tolerate it better? To test myself, I signed up for the sweatiest race I could find—the Hottest Half, a half-marathon held in Dallas in mid-August, where average temps hover in the mid 80s, with 50 to 60 percent humidity. Then I called on Roberts, Casa, and Matt Ganio, Ph.D., a researcher at the Institute for Exercise and Environmental Medicine at University of Texas-Southwestern, to see if they could teach me the finer points of sticky summer racing and make it a little less awful.
Three things, they said, could optimize my performance in Texas: acclimatization, getting my body used to exercising in the heat; proper hydration, which stocks blood-plasma stores and replaces fluid lost through sweat; and precooling, which involves deliberately lowering core body temperature within 30 to 60 minutes of the starting gun.
Acclimatization meant gradually training my body to run in the weather conditions I would face on race day—starting off with short, slow runs in the coolest part of the day, and working up to running at race pace in Dallas-esque temperatures. The acclimatization process fortifies your body against the heat by prompting several important physiological adaptations: your sweat rate increases, which helps cool you more effectively; your blood volume increases, which makes more fluid available as sweat; and your body starts to utilize sodium more efficiently, which helps maintain fluid balance in and around your cells. It takes about seven to 10 days to acclimatize. Since last July in New York was like living in an oven, I’d gotten a head start. “That’s good,” said Casa when I told him. “If this was February and you said you wanted to run a half-marathon where it was 100 degrees, I’d say the best thing to do is start measuring you for a casket.”
In order to know how to hydrate properly on race day, I needed to take a sweat test to help Casa determine how much fluid I needed to drink to replace what I lost through sweat. Replacing fluids helps maintain your cooling system—falling short causes that system to break down. For the reading to be accurate, I had to mimic race day by running at goal pace for an hour in Texas-like temps. So I weighed myself before a 71-degree (75 percent humidity) run along Jones Beach—164.5 pounds. Eight sweaty miles later, I weighed 162.8. From those figures, Casa calculated that I lost about a liter of sweat. To remain hydrated throughout the Hottest Half, I had to suck down one liter of fluid per hour—and practice doing so throughout my acclimatization—and I’d be fine!
So I thought.
I emerged from the Dallas-Fort Worth International Airport at 4 p.m. and stepped into an industrial-strength clothes dryer. It was 102 degrees—the 15th day in a row of triple-digit temperatures. The forecast called for more of the same the next day. Race day.
What had I gotten myself into?
At my hotel, I whipped out Casa’s final-hours, hot-race preparation checklist. First up: Eat salty food with dinner. Sodium not only makes you thirsty (so you drink more), it helps your body retain fluid—and the final 24 hours before a race is a critical period to hydrate. I went to a nearby Japanese restaurant, ordered two bowls of miso soup, a plate full of sushi rolls, and started checking off to-do #2:
Drink 600 milliliters (about 20 ounces) of water three hours before bed. While I had been hydrating as I normally do all day, filling the tank like this would help boost my blood-plasma flow and improve my body’s ability to cool itself the following day. By the time I returned to my room, I urgently needed to attend to point three: Check for light-colored urine. If it was darker than the color of straw, my instructions were to drink an additional 300 milliliters, or 10 ounces. (Drinking to the point of colorless urine can cause hyponatremia, a condition where blood-sodium levels dip to life-threatening low levels.)
The temperature of my room was comfortably cool and I had eight hours to sleep, which aligned well with item four: Sleep in air conditioning. Although the mechanism remains unclear, getting sufficient sleep appears to enhance heat tolerance, says Casa. And an air-conditioned room offers a better venue for decent shut-eye than one entombed by heat.
Just before hitting the sack, I checked off another box: Swallow the thermometer. The CorTemp Core Body Temperature Monitoring System was an encapsulated, mini-thermometer about the size of a large vitamin. Ganio—who lives in Dallas—planned to take my temperature at two-mile increments during the race to see if our hydration and precooling measures (which would start the next morning) were working. Taking it before bed gave it time to reach my small intestine, where the reading is most accurate (it would pass through me in 24 hours).
As I fell sleep, I imagined the thermometer navigating its way, Fantastic Voyage-like into my bloodstream to set up camp for its transmission duties the next day.
At 5 a.m. I got back to my list. Drink 300 milliliters. This additional fluid would top off my tank. Next up: Eat more salt. I polished off an extra-salt bagel, a banana, and coffee. At 6 a.m., Ganio, a handsome, unflappable 30-year-old, arrived to whisk me off to the local 7-Eleven. It was time for the precooling portion of my checklist. Precooling is the process of deliberately lowering core-body temperature 30 to 60 minutes before exercising in the heat. For me, that process started with: Drink a Slurpee one hour prior to start. In 2010, researchers from New Zealand found that runners who drank an icy, sweet drink ran 10 minutes longer on a treadmill in a heated room than runners who drank syrup-flavored cold water. The “ice slurries” lowered their core temps, which may have allowed them to run longer before their bodies overheated. In short, they were better precooled.
I dispensed a Big Gulp’s worth of cola-flavored Slurpee and started slurpeeing.
Once we arrived at White Rock Lake, Ganio weighed me on a portable scale, strapped on a heart-rate monitor, and sent me off for a urine check. When I returned with a vial of my pee, Ganio held it up to a color chart. I cringed watching my piddle undergo public inspection. “Pale yellow,” he announced. “You’re going into this race well hydrated.”
He then held up the black CorTemp Monitoring System receiver—about the size of an iPhone but thicker—to my body. Beep. I looked down at my chest. That little gizmo was in there transmitting!
“Perfect,” Ganio said. “99.1.” (Normal, considering the 80-degree heat.)
We were now down to the final box on my checklist: Put on cooling vest 30 minutes before start. The Arctic Heat vest uses special gels to lower skin, and therefore core, temperature. “The goal for all of the precooling measures,” said Ganio, as he helped me with the vest, “is to lower your core body temperature. If you start at a lower temperature, you’ll have more room to go up.”
All these precooling measures necessarily came within an hour of my 7:30 a.m. start time. Had I done them any farther out, my natural activity would have slightly raised my core temp and offset any chilling effect. That’s also why I didn’t warm up. “Walking in the shade is okay,” Casa said. “But I wouldn’t recommend jogging as a warmup for distance races in hot weather.”
Minutes from the start, the mercury read 85 degrees, while my internal temp read 99—roughly a degree or so lower than I might have been without the Slurpee and vest, according to Ganio. He slipped off the vest just before the gun went off. “Good luck!” he said.
I took off at sub-seven-minute pace. Three months earlier, I’d run a half in 1:30, and I hoped to finish in 1:35. Generally, coaches recommend that you add 10 to 15 percent to your time when racing in the heat; which meant nine to 13 minutes for me. Five sounded better.
Roberts had warned me against this. “Running slower means you generate less heat,” he said. “I’d focus on hydrating properly and finishing the race feeling okay. I wouldn’t worry about your time.”
Alas, in races, I always do.
At mile two, Ganio bounded out to record my temperature. It was 101.5.
“How you feeling?”
“Great!” I said.
It was true. I felt like I’d just stepped out of a pool on a hot day: warm on the outside, cool on the inside.
After the three-mile mark, the 10-K runners peeled off for their turnaround. Can’t take the heat, eh? I thought. We real runners are going 13.1.
I continued to feel fresh—and cocky—through mile five. Then I cracked. The discomfort of exertional heat stress can be sudden or gradual—for me, it was like a 1,400-pound longhorn fell on my back.
Ganio could tell immediately when he dashed out for another reading at mile six. “How you feeling?” he asked.
“Fine,” I snapped.
Crabbiness is another sign of heat distress. Everything felt harder, just like Casa had said. Ganio’s receiver showed my temperature had shot up a full degree in two miles. By mile eight, my insides sizzled at 103.9 degrees, and my heart raced at 188 beats per minute. I had pushed my body beyond what it considered tolerable, and the self-preservationist side of my brain was begging me to stop, while the Type-A side threatened to beat me up if I did. I was Texas toast.
I considered dropping out. Instead, I walked through the next water station and downed two cups of fluid. From there, I walked at every station and drank a cup each of water and sports drink. By mile 10, my temperature had dropped .3 degrees and the feeling had gone from nearly unbearable to just miserable.
I crossed the finish line in 1:40, exhausted and disgusted with my own hubris. I fought the heat, and the heat won.
Immediately, Ganio guided me to the scale he’d set up. I had lost nearly four pounds. “That’s a 2.3 percent body-mass loss—anything more than two percent will affect your running,” he said. Being that dehydrated elevates core temperature, decreases sweat rate, increases muscle fatigue, and strains the cardiovascular system—perfect ingredients for a crappy run. “So despite our hydration plan, you still became moderately dehydrated.”
With an air temp of up to 90 degrees and humidity at nearly 60 percent, this had been the hottest of the Hottest Halves. My sweat rate in Dallas was likely higher than it was running at Jones Beach. Between gulps of Gatorade, I pointed out that the precooling measures seemed to last until mile six. Maybe I would have been better off with the 10-K? “That might be one lesson,” Ganio said.
Casa pointed out a few more. “Your pace could have been slower,” he said.
“You should have taken two cups at each water stop from the beginning. Had you done that, you might have felt better in the second half of the race.”
I left Dallas feeling like a major hot-weather flop. To make matters worse, New York was mired in another weeks-long stretch of enervating heat and humidity. I still hated it. But I kept running and fiddling with what I had learned. Six weeks after the Hottest Half, I entered the Great Cow Harbor 10-K on Long Island. I adhered to most of my prerace hydration and precooling checklist (minus the edible thermometer and the trunk-chilling vest). I planned on grabbing two cups at every water station.
Race day was 72 degrees and a stifling 84 percent humidity. On the notoriously hilly course, runners wilted all around me, but I felt…strong. On the last mile, I threw down the hammer. Maybe I can break 42 minutes. This time, my brain had no argument. Go! it commanded. Go! And I went—right to the finish in 41:26.
I was elated. The Hottest Half hadn’t been a total loss—I was acclimatized, hydrated, and precooled enough to finally beat the heat.
Now when it gets really hot, I use what I learned. In training, I back off the pace or cut back on the miles. I opt for shorter races. And on those days that feel a lot like mid-August in Dallas, I’ll go for a jog—then climb into that hammock.
Adjust your workouts according to the conditions
High heat (85+ degrees) + low humidity (under 30%)
Blood sent to skin to assist with cooling decreases blood supply to working muscles.
Reduce run by 20 percent, says Joe Puleo, coauthor of Running Anatomy.
High heat (85+) + high humidity (over 60%)
Raises core temp, reduces blood volume; humidity interferes with evaporation of sweat.
“Stick to easy runs or use the treadmill,” says Puleo.
High humidity (over 60%)
Decreases effectiveness of cooling system by hampering evaporation of sweat.
For runs of an hour or less, drop your pace by 30 seconds per mile. For runs over an hour, scale back by 60 seconds.
Heat from ground radiating upward
Hot surfaces alter microclimate around runner, making it hotter.
Run on dirt. “Trails absorb less radiant heat than pavement or a track,” says Doug Casa, Ph.D.
How much you sweat tells you how much to drink
Proper hydration requires replacing fluids—on the run—that you lose through sweat. Figure out your sweat rate so you know just how many liquid ounces you need.
1] Weigh yourself naked (with an empty bladder) before your run.
2] Run at or close to your race pace for one hour and keep track of how much you drink (in fluid ounces) during that time.
3] Weigh yourself naked after your run.
4] Subtract your postrun weight from your prerun weight.
5] Convert the difference into ounces (multiply by 16).
6] Add to that number the amount of fluid ounces you consumed. For example, if you lost one pound (16 ounces) and drank 16 ounces of fluid, your total fluid loss equals 32 ounces.
7] Divide your hourly fluid loss by four to determine how much to drink every 15 minutes. In the example above, you would need to drink eight ounces every quarter-hour.
New technology helps runners survive the dog days of summer
1 COLD TO THE CORE
After being submerged and placed in the freezer for two hours, the Arctic Heat Cooling Vest can stay cold for up to two hours. $220 arcticheatusa.com
2 REFLECT THE RAYS
Coldblack running shirt blocks up to 80 percent of heat absorption from sun. Find it on Trail Blazer Tee Coldblack. $50 runningroom.com
3 CAP IT OFF
IceFil’s fabrication absorbs and disperses heat—not just sweat. Find it in Zoot Sports Ultra IceFil Cap. $30 zootsports.com
Don’t Cook Yourself
How to recognize when you’re overdoing it
The best thing about heat illness is that it’s preventable. “You simply have to pay attention to how your body feels,” says Douglas Casa, Ph.D., A.T.C. “If things feel strange, back off.” Here’s what happens if you push it too far—and how to bring yourself back.
HEAT CRAMPS: Painful muscle contractions that occur during or after intense exercise
The Cause: Muscle fatigue, water and sodium loss
The Symptoms: Dehydration, cramps, fatigue
The Treatment: Massage, rehydrate
HEAT EXHAUSTION: Inability to continue exercise due to overwhelmed cardiovascular system, depleted energy
The Cause: Exercising in hot or humid environments, dehydration
The Symptoms: Include fatigue, irritability, nausea
The Treatment: Move to shade, elevate legs, apply ice bags, rehydrate
HEAT SYNCOPE: Fainting episode that occurs in high temps, typically during initial days of heat exposure
The Cause: Coming to a standstill immediately after activity, or standing suddenly or for long periods causes blood to pool in legs
The Symptoms: Dizziness, tunnel vision, pale skin, weakness, decreased pulse rate
The Treatment: Move to shaded area, elevate legs, rehydrate
EXERTIONAL HEATSTROKE: Potentially fatal condition characterized by a core temp of 105° F
The Cause: Includes vigorous exercise in a hot environment for more than one hour, poor fitness
The Symptoms: Include hyperventilation, disorientation, dizziness, vomiting
The Treatment: Full immersion for 30 minutes in cold (35 to 59° F) water