Running in the Heat

Many of you have a fall marathon or ultra coming up.  As we know from history, race day in September or October may be unpleasantly warm. I’d like to share with you an  expanded version of a Dr. Mark’s Desk piece that I initially wrote after this year’s Boston Marathon on racing a marathon in the heat. “An Evolutionary, Scientific, and Experiential Approach to Marathon Strategy” was published in the summer 2012 edition of the American Medical Athletic Association Journal. I’ll be speaking again at the AMAA conference at the Marine Corps Marathon.

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An Evolutionary, Scientific, and Experiential Approach to Marathon Strategy

Sir Roger Bannister once said, “Experiments in the laboratory are not of much practical value to athletes.” Reality during a race often trumps observational testing. For distance runners, this is especially true, since race conditions such as heat or humidity can often make a mockery of weeks, if not months of sustained training. No one likes to DNF. Even worse, no one wants to end up in the medical tent.

With the hot temperatures putting a distinctive stamp on the 2012 Boston Marathon, runners needed to employ common sense in order to have a safe race. The Boston race committee made the wise decision of putting personal responsibility in the decision of the runner. Forty-eight hours before the race, emails went out to all participants alerting that the race would occur in the “red zone” ,offered deferments for the following year, and encouraged all but the fittest runners to participate. “This is the year for experiencing, not racing the Boston Marathon” was the message.

Even more prudently, the race committee also issued the statement “Good hydration is important, but overhydration is dangerous.” In other words, drinking too much water is not only unhealthy, but potentially fatal.
Heat was also the foe at three warm Midwest marathons this spring. The Green Bay Marathon halted mid run, the Madison Marathon canceled, and the Med City Marathon went on with caution. The three races did not have the message of “drink to thirst.” Green Bay’s message was “stay well hydrated” with 22 aid stations (1).

Winning times for men and women were over nine minutes slower than 2011. Consistent pacing ruled the day and attempts to surge in the men’s race showed the limits of thermoregulation. The sun is a powerful brake through radiant heat. With shade temps in the mid to high 80s, the road temp in the sun was likely 10 to15 degrees warmer (2). Even though temperatures in Beijing Olympics were just as warm, it was cloudy and Sammy Wanjiru ran a 2:06. According to numbers compiled by race officials, nearly 2,100 cramping and weary runners were treated in the three air-conditioned medical tents stationed along the course and at the finish line. Over 150 runners were sent to hospitals, though none fortunately were in life-threatening conditions. Even many of the elite frontrunners were DNF. Last year’s record-breaking winner Geoffrey Mutai dropped out after 18 miles with stomach cramps.

I played it safe and finished nine minutes slower than last year’s time, yet came away with fourth in my age group (45-49) and moved up a bit in place. More importantly, I avoided the medical tent by following good racing practices. I wasn’t here to see how fast I could run, but to enjoy myself and soak up the terrific vibes of the race.

In the preceding days before the race good karma was passed on to me over a coffee with 1984 women’s winner Lorraine Moeller and 1976 winner Jack Fultz. The 1976 race started in near 100-degree heat and was known as “Run for the Hoses” as spectators used garden hoses to cool runners down. It should be noted that even then it was the “Run for the Hoses,” neither the Gatorade nor water stations. Common practice in 1976 was not to drink beyond thirst.

Lorraine Moller shared her pre-race cooling strategy before the Barcelona Olympics where she won bronze. Her manager found a local home where the team could take cold showers before the race while competitors waited at the start in the heat. Later, Deena Kastor and Meb Kezflezighi would use higher tech cooling vests before their Olympic medal performances. I did the low-tech cooling by relaxing at a family friend’s house in Hopkinton and pouring an ice cold bottle on my head before the start.

I didn’t drink very much during the marathon, maybe 12 to16 ounces of water, but repeatedly cooled down by pouring water over my head and body. The primary cooling is evaporative and thankfully the humidity was low enough for this to happen. In April the body has not yet fully developed the sweat mechanisms. Too often, runners mistakenly think that drinking a copious amount of water will lower the body’s core temperature; however, over drinking won’t cool you down.

Although it was my 19th time running Boston, like many in this year’s race I was totally overwhelmed by the generosity and kindness of spectators who lined the streets with water and hoses for cooling. These weren’t official volunteers. They were family, kids, and students, all eager to help runners in the heat. Better yet, because the water was coming from peoples’ homes, it was cold– much colder than the aid stations. I’d douse myself with the water from these impromptu aid stations and find a new burst of energy.

The science of cooling and how we evolved.

Here are some take away messages based on the science of cooling and how we evolved. Historically the best performers end the race in what many would clinically call “dehydration” and with a core temperature above baseline (3,4). But they are not ill, just appropriately warm and tired and in need of some recovery. Dr. Tim Noakes, in his books “Challenging Beliefs” and “Waterlogged,” dissects the faulty science connecting hydration and heat illness and many of the myths of “dehydration”. Ingrained human behavior of “I am hot and must drink more” is slowly being replaced with “I am thirsty, so I should drink.” We evolved to run for hours in the sun without an aid station every mile (5).

Conventional wisdom, mostly in America, is that the body will somehow fry if we lose fluid. ACSM guidelines (1996) stated that “individuals should be encouraged to consume the maximal amount of fluids during exercise that can be tolerated without gastrointestinal discomfort up to a rate equal to that lost from sweating” (6). In 2007, the 2nd EAH Consensus Conference shifted the thinking: “…the goal should be to expect to lose up to two percent of body weight and never to gain weight during exercise” (7).

Dr. Noakes questions any relationship between levels of dehydration, body temperature elevations in the safe range (<40C), reduced cardiac output, and important adverse events. “Dehydration” (used quotes as this is a non clinical term with no real definition) is normal and humans “developed favorable biological adaptations that permit prolonged running in the heat” (3,4,6,8). Heat stroke occurs more frequently in shorter events when the body’s engine is on high. Heat stroke can also occur in cool temperatures under conditions of the high heat production of intense exercise. Body temperature exchange is a balance of metabolic heat production and the exchange with the environment (9).

We are designed to run (albeit maybe not race) in the heat and are the best warm weather runners on the planet. Understanding this helps our cooling strategy and pacing. Running on two feet reduces our surface area to the sun and gets us off the hot surface of the ground. As we get warmer, more blood is diverted to the skin for cooling, thus a pace reduction is needed. We have an innate sense of fatigue and warmth and our brain will shut off motor units at about 40 degrees Celsius. Be self-aware and do not override this. Modern day persistence hunters will run two to six hours at paces of 4-10km/hr with very little water. If they needed to stop for water they’d have to give up the chase. Our lack of fur and smooth skin facilitate the sweating. We run with relatively small muscles and long springs of our tendons, an efficient stride that benefits us in the heat (3,4).

Here are a few modern day strategies which complement our evolutionary human properties.

• Pre-cool as best you can to allow for more thermal load (10). An ice cold towel at the start, an electrolyte popsicle, a cold bottle to pour and carry, finding shade, and not “warming up” can all be applied.

• Keep the body wet for evaporative cooling. Grab water and pour on the large body surface areas. Sunscreen can bead the sweat and fluid and it just rolls off you so use this sparingly to prevent burn in key areas only.

• Radiant heat transfer from the sun is huge. We all feel this. So find the shade even if running a bit more distance. (My GPS read 26.6 as I ran along the right side of the road, instead of the tangents, to grab water for dousing as well as a little tree shade.)

• Run clear of the pack. Heat load can increase with tight group running so run solo and get some air around you. This is easier for the faster runner in a less crowded pack.

• Drink when you are thirsty and know your body. Apply the “sip and carry” method. Do not drink to replace every ounce lost. You will lose fluid. The glycogen and associated stored water can be four pounds. That is why we have a post-race party. We are designed to do this safely as long as we replace later at a meal (3,4).

• Pace with common sense and turn the watch off. The winners were over 7% slower, and many elites dropped out or were well over 10% off their usual times. Slower runners will have an even higher percent difference. Anticipate at least a 2% difference for every five degrees over 12 degrees Celcius (11).

• Dress white and light and test your shoes and socks when wet. (I do not use socks and run daily in light minimalist shoes so, fortunately, this was not an issue for me.)

• Know your electrolytes if you are going to be running, sweating, and replacing fluids for over four hours. Electrolytes will help maintain better fluid balance. You can drink extra sports beverages to get your electrolytes or you can use electrolyte tablets, gels, or powdered mixes.

• Acclimatize, if you can, at your home location if warm conditions are predicted. Simply overdress relative to being cool and comfortable on training runs. All successful Olympic performances in runners who are native to cooler climates involved several weeks of preparation for warmth. In 7 to14 days of acclimatization, one can increase plasma volume, decrease heart rate during exercise, decrease sodium concentrations in sweat, increase sweat rate, and increase cutaneous vasodilation (12).

• Do not run in the heat if you are poorly conditioned, have existing medical problems, are taking prescription medications which affect heat regulation, use dietary supplements (especially stimulants), or have a history of heat illness.

I’d like to give a massive thanks to the thousands of spectators, volunteers, race organizing team, and the medical team for preventing heat-related disasters. The Boston Marathon is a special event and is supported by surrounding towns and cities like no other event in the world.

 REFERENCES

• Ferstle, J. The long, hot spring. Road Race Management News. May 2012.

• Martin D. Strategies for optimising marathon performance in the heat. Sports Med. 2007; 37(4-5):324-327.

• Noakes TD. Challenging Beliefs. Cape Town SA: Zebra Press, 2012.

• Noakes TD. Waterlogged. Champaign, IL: Human Kinetics Publishing, 2012.

• Bramble DM, Lieberman DE. Endurance running and the evolution of Homo. Nature. 2004; 432:345-352.

• Noakes TD. Hydration in the marathon using thirst to gauge safe fluid replacement. Sports Med. 2007; 37(4-5):463-466.

• Hew-Butler T, et al. Statement of the second international exercise-associated hyponatremia consensus development conference. Clin J Sport Med. 2008; 18:111–121.

• Noakes TD. Reduced peripheral resistance and other factors in marathon collapse. Sports Med. 2007; 37(4-5):382-385.

• Kenefick RW, Cheuvront SN, Sawka MN. Thermoregulatory function during the marathon. Sports Med. 2007; 37(4-5):312-315.

• Quod MJ, Martin DT, Laursen PB. Cooling athletes before competition in the heat: comparison of techniques and practical considerations. Sports Med. 2006; 36(8):671-682.

• Montain SJ, Ely MR, Cheuvront SN. Marathon performance in thermally stressing conditions. Sports Med. 2007; 37(4-5): 320-323.

• Wendt D, van Loon LJC, van Marken Lichtenbelt WD. Thermoregulation during exercise in the heat: strategies for maintaining health and performance. Sports Med. 2007; 37(8): 669-682.

 

Additional References:

• O’Connor PJ. Monitoring and titrating symptoms: a science-based approach to using your brain to optimise marathon running performance. Sports Med. 2007; 37(4-5):408-411.

• Abbiss CR, Laursen PB. Describing and understanding pacing strategies during athletic competition. Sports Med. 2008; 38(3):239-252.

• Roberts WO. Exertional heat stroke in the marathon. Sports Med. 2007; 37(4-5):440-443.

• Cheuvront SN, Montain SJ, Sawka MN. Fluid replacement and performance during the marathon. Sports Med. 2007; 37(4-5):353-357.

• Coris EE, Ramirez AM, Van Durme DJ. Heat illness in athletes: the dangerous combination of heat, humidity and exercise. Sports Med. 2004; 34(1):9-16.