Written by Dr. Daniel Shaye
High temperatures and humidity shouldn’t slow you down
Competitive and recreational athletes may exercise to beat the clock, conquer a distance, keep up with their spouse or, quite simply, to experience the joy and freedom of exercise. But fewer people enjoy competing against the ever-climbing summer heat—and adapting your exercise routine to the coming high temperatures is an important step in staying healthy. Runners, walkers and exercisers of all stripes are susceptible to a number of injuries related to the heat and overexertion. These conditions can be nauseating, painful, and even fatal—so respect the heat, and be prepared.
Years ago, I was running intervals (repeats of quick/up-tempo running, interspersed with short walk/jog rest breaks) on a hot, humid and shade-free field. I was young, fit and eager to push my limits. After about 30 minutes of repeats, I received a warning sign: cold chills. I backed off immediately, as “cold” was not an accurate perception of this hazy summer day’s conditions, and this was the first sign that my nervous system was decompensating (overwhelmed, and starting to give up).
It’s important to know your body and listen to its signals. If you do begin to overheat, back off or stop exercising entirely, get to a cool environment as soon as possible, consider icing key areas (such as your head, armpits and thighs), and make sure you’re hydrated.
A main function of sweating is to help the body cool itself through evaporation, but that becomes less effective as a cooling strategy as humidity levels approach 70, 80 or even 90 percent. If it’s too humid outside or your clothing seals in heat, your primary cooling mechanism is out of commission. Before you exercise, don’t just check the temperature—check the humidity, too, so you’re aware of what weather obstacles may lurk ahead.
Did you know that sweat is good for you … and can be trained? Our sweating rates, and even the very content of our sweat, changes as we adapt to heat and humidity. This is a process that can take several weeks: You need to give your body time to adapt, rather than expecting personal bests when your big day falls on a truly exceptional example of summer heat. I’ve found a major problem with modern runners is that we live and work in igloos all summer, yet we expect to handle the heat. Adapting is a long-term process, and it happens even when you’re not exercising. If possible, consider backing off the air conditioning as your race or other event approaches, so your body can acclimate.
Hydration is a critical tool in beating the heat. No matter your event, water is the central, crucial theme to hydration. Other beverages have their pros and cons—and of course, alcoholic beverages are a bad idea—but you should drink water before you run to seek a state of “euhydration,” or full hydration, characterized by clear urine. If you must err, then err on the side of very mildly overdoing your fluid intake such that you need to void just before competition (preferably not during). For lengthy exercise, drinking a standard 500 mL bottle of water per hour is a good bare-bones minimum, but there is no easy formula for rehydration. The best hydration strategy is to learn your sweat rate (volume of fluid per hour), calculated by nude pre- and post- exercise weight. Use that formula to estimate your hydration needs. If you expect to sweat one liter in an hour, then 500 mL will slow your dehydration rate sufficiently to extend your performance. However, you’ll still be losing about a pound per hour in water weight, and will start to crumble over the course of several hours.
FUN FACT: Sweat rates for most humans vary from as low as milliliters per hour, to more than two liters per hour. The great marathoner Alberto Salazar was reported to achieve a world-record exercise sweat rate of 3.7 liters (one gallon, approximately eight pounds) per hour.
If the day is hot and humid, and your core temperature starts to rise, you can hydrate until the cows come home and you’ll still be in trouble—literally cooling the body
is key. “Pre-cooling” is the strategy of treating your body like a cooler: The colder it is inside, the longer it will take to melt. Don’t show up to a race’s starting line already in heat stress. Hiding out in an air-conditioned or shaded environment is an effective pre-event strategy, so long as you remain limber with warmed-up joints, but not a warmed-up core temperature. Literally pouring coolant into your core via consuming a cold beverage may also be effective, but test your body’s response to this in training to avoid cramping on race day.
- 2% and up: That’s a 3.6 pound decrease in body weight for a 180 pound person. This will affect ability to perform, and will tax the body’s systems.
- 3% and up: More severe dehydration will begin to affect both physical and mental performance, increasing the workload on the heart and upping the chances for heat-related illness or injury.
- 5% and up: Flirt with 5% dehydration, and your odds of adverse symptoms approach 100% as your body’s heat compensation and other important systems fail.
- Hyponatremia (fluid overload): Occurs when endurance athletes actually gain weight during prolonged exercise in the heat, because of over-hydrating. This is the opposite of dehydration, and can be just as dangerous although it is a rare condition. Technically this condition is a depletion of salt, but the literature suggests it’s more a problem with over-hydration than with sweating away too much salt.
- Exertional heatstroke: Defined by a rectal temperature greater than 104°F, accompanied by signs of organ system failure and, most often, central nervous system dysfunction (confusion, loss of consciousness). Typically occurs in hot, humid conditions, but can occur in cool conditions with intense or prolonged exercise.
- Heat exhaustion: As with heatstroke, heat exhaustion can occur in cool conditions with intense or prolonged exercise. In fact, heat exhaustion commonly does not involve elevated body temperature, but instead is a result of fatigue, dehydration, electrolyte depletion, and/or nervous system failure.
- Heat cramps/exercise-related muscle cramps: Painful dysfunctions of muscle that may result in “knots” and inability to exercise. As in heat exhaustion, core body temperature may not be elevated.
Other factors that may affect your response to heat include medications and your age, as children and seniors have challenges others do not. And here’s something you may not know: Sleep deprivation may correlate with heat injury and heat-related fatality. If you’re sleep-deprived, consider alternatives to high-intensity exercise in the heat and humidity. This might be a good day for the treadmill, running through the shady woods instead of the asphalt road, swimming in the pool or taking time off.
Finally, if your big day arrives and the weather is blazing hot, scale back your expectations. I know, this is hard for competitors, but it’s a proven fact that heat and humidity negatively impact endurance performance. Console yourself with the fact that like a big hill or strong wind, weather affects everyone. View heat and humidity as competitors or obstacles to be negotiated with and respected. Though running and other endurance endeavors are typically gentler than football or rugby, heat and humidity are the brutal exceptions that can hit you and your loved ones harder than any pro tackle. Respect them, learn to adapt to them, and even learn to “live to fight another day.”
I look forward to seeing you on the roads and trails. Happy running!
Race Calendars:
WILLIAMSBURG / HAMPTON ROADS
JULY 4
Yorktown Independence Day 8K
York High School
8 a.m.
happypaceraces.com
JULY 13
Triskaidekaphobia 5K Run/Walk
Clara Byrd Baker Elementary School
7 p.m.
wjcc.k12.va.us
AUGUST 4
TCYorktown CG Day 5K Run
Coast Guard Training Center, Yorktown
8:30 a.m.
active.com
AUGUST 7
Tom Ray Memorial Predict Your Time 5-Miler
Newport News Park Bikeway
6:30 p.m.
peninsulatrackclub.com
AUGUST 11
The Vineyards of Williamsburg 5K
The Vineyards Clubhouse
7 p.m.
5K.cdr.org
AUGUST 14
Lake Matoaka 4.3 Mile Trail Challenge
Zable Stadium, College of W&M
6:30 p.m.
rickplatt1@juno.com
AUGUST 18
Smart Smiles 5K
Mariners’ Museum
8 a.m.
1milburn@bagclub.com
AUGUST 21
Swamp Bridge 5K
Newport News Park
6:30 p.m.
peninsulatrackclub.com
AUGUST 25
2012 Coastal Edge ECSC 8K
Virginia Beach Oceanfront
8 a.m.
surfecsc.com/compete
RICHMOND
July 4
Brandermill 7.4
Clover Hill High School,
Midlothian
8 a.m.
brandermillrace@gmail.com
July 4
Patriots 5K
Robious Landing Park
8:30 a.m.
raceit.com
July 14
Project Athena Richmond
Relay Marathon
Brown’s Island
7 a.m.
projectathena.org
July 21
Christmas In July 5K
Great Meadow, The Plains
8 a.m.
warrentonfauquierjaycees.com
July 22
Rocketts Landing
Triathlon & Duathlon
Rocketts Landing
7 a.m.
richmondmultisports.com
July 28
Pony Pasture 5K
Pony Pasture Park
7:30 a.m.
raceit.com
August 9
Moonlight 4Miler
Virginia Farm Bureau
7 p.m.
raceit.com
August 19
Pink Power Triathlon
Midlothian Family YMCA
All day
richmondmultisports.com
August 25
Patrick Henry Half Marathon
Randolph Macon College
7 a.m.
sportsbackers.org