Trail running is a sport of human vs. nature. As much as we like to romantically think that trail running is all about moving with the land and blissfully frolicking through the wild (which it is to some extent!), it's also a battle of us against the elements. There's the visible hazards we have to overcome: hills, sticks, roots, mud, and bears; but then there are the not as visible barriers. Those hazards that sneak up on us throughout the run and can turn a day of frolicking in the wild to a slogfest. One of the greatest of these invisible hazards is heat.
Body temperature management while running is crucial in endurance events. Marathon and ultra marathon trail runners should pay special attention to heat management strategies. As stated in "Heat Stress and Thermal Strain Challenges in Running" from the Journal of Orthopedic and Sports Medicine:
As environmental heat stress (modulated or augmented by air temperature, humidity, wind speed, and solar radiation) and intensity and duration of a training run or race increase, metabolic heat production, the parallel need for heat transfer from the body to maintain thermal equilibrium, the consequent increase in blood flow to the skin, and the concomitant sweating response are progressively and proportionally amplified.
The longer your runs, and/or the hotter the weather the more important heat management and hydration becomes to bodily function. This post will not dive into hydration needs, or heat training (using saunas, extra layers, etc. to get used to warm weather), rather we'll outline a few things you can do during your run to keep your core temperature down.
The biggest thing you can do is regulate your pace. This is true at all temperature ranges, but even more important on warm days. Give the hot weather the respect it deserves and back off the pace initially. As stated above, the intensity of your run has a an effect on your ability to transfer adequate heat "from the body to maintain thermal equilibrium." If you're running harder than the temperatures allow you'll start shutting down, just like a car that exceeds the red line for too long. Coach Jack Daniels of the Run S.M.A.R.T project created a calculator that can include the effect of heat on pacing, and can help you adjust goals for race day depending on the temperature.
There are a few tricks, though, that can keep you from needing to slow down as much to regulate the heat. Wear a breathable hat, and sunglasses to shade your face. Wear sunscreen. The sunburn prevention also serves as a buffer layer to slow rising body temperatures. If you're in a race or running a trail that has creek crossings you can soak your hat at aid stations or in the water. Arm sun-sleeves can also work and, when kept wet, especially help with heat transfer through temperature sensitive forearms.
Use ice externally and internally! Externally you can put ice in a bandana around your neck, hidden under your hat, tucked in your sports bra, or slipped inside your arm sleeves. Keeping your skin cool is a fantastic way to keep that heat equilibrium in your favor. Internally, studies have shown that ingesting an ice slurry is better for keeping your core temperature down when compared to just cold water. The conclusion taken from a paper by Siegel et al., out of the Edith Cowan University states:
Compared with cold water, ice slurry ingestion lowered preexercise rectal temperature,increased submaximal endurance running time in the heat, and allowed rectal temperature to become higher at exhaustion. As such, ice slurry ingestion may be an effective and practical precooling maneuver for athletes competing in hot environments.
Now, you're unlikely to be testing your rectal temperature at the conclusion of a run, but rectal temperature in a lab setting is the most accurate way to measure core body temperature. Functionally it's not likely that you crew at your next race is going to have gas station ICEE's on hand (maybe they will if they are rock stars), but the big takeaway from this study is that you can use an ice slurry as a precooling method. So before you head out the door, or head to the start line, drink that smoothie. It will buy you some extra time on those hot days.
Keeping up with hydration is also important. That same article from the Journal of Orthopedic and Sports Medicine asserts that a "body-water deficit can have a measurable negative effect on cardiovascular and thermal strain, exercise-heat tolerance, performance, and safety." As promised, we are not diving into recommended hydration levels, we'll save that for another post and recommend you consult with a dietician about your hydration needs, but we will say that proper hydration with the appropriate electrolytes is crucial to keeping performance normal in warmer weather.
With summer coming on and many trail races seeing hotter temperatures than ever before, please respect the heat as you venture out for your next run or race. That way you can frolic more and slugfest less! If you have questions about heat, or heat training, let us know and we can recommend more resources or point you to experts.
-Bergeson, Michael. "Heat Stress and Thermal Strain Challenges in Running," Journal of Orthopedic and Sports Medicine. September 2014. Volume 44, 10: 831-838.
-Siegel, et al., "Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in the Heat," American College of Sports Medicine, 2010.