by Jeff Sankoff M.D. (a.k.a. the Tri-Doc)

It has been a record setting summer with respect to high temperatures across the northern hemisphere. In Europe and North America, triple digits have been the norm, forest fires have raged unabated and ocean temperatures have hit levels previously thought unimaginable.

Through it all, endurance athletes have continued to train and race albeit under the continued threat of heat stress and illness. In order to succeed in our training and not succumb to the increasing threats posed by the warming climate, we need to understand how our bodies produce and eliminate heat. With this knowledge, we can then better appreciate some of the novel strategies and products out there that can help us stay cool in the face of higher temperatures.

When considering the balance between heat production and elimination in the human body I find it helpful to consider an automotive parallel. A car engine burns gasoline to propel the vehicle forward, but the combustion of fuel produces a huge amount of heat as well. Similarly, our muscles and the mitochondria within them also burn fuel but instead of gasoline, our cells use carbohydrates. Doing so results in muscle contraction allowing for locomotion but there is again a significant amount of heat generated as well.

A car engine utilizes a pump that circulates engine coolant through hoses in the engine block. That coolant removes thermal energy as it moves to the radiator where it transfers that heat energy to air passing over it. Once cooled down, the liquid recirculates back into the engine block to begin the process anew.

In the body, the pump takes the form of the heart, the coolant is the blood, the radiator is the skin and the hoses are the blood vessels. Diseases affecting any of these tissues or organs can significantly impair heat dissipation and that’s one more reason why it is important to stay fit in the face of climate change!

Even under the best possible conditions, our bodies’ capacity to eliminate heat can be overwhelmed in different circumstances. If we overexert, we can overwhelm those mechanisms designed to regulate our internal temperatures and if environmental conditions are extreme as we have seen this summer, that too can play a role. Higher ambient temperatures and humidity both decrease the efficiency of our cooling systems and make exercise more dangerous.

There are a few options for athletes who wish to continue to train even when temperatures are high; they can do so indoors in climate-controlled gyms, they can exert themselves at much lower effort levels to decrease the level of internal heat production or they can employ novel means of cooling informed by some of the latest science.

Broadly speaking, newer, novel cooling methods leverage the body’s existing cooling mechanisms and simply enhance them. The most efficient means of cooling is evaporative whereby sweat evaporates from the skin and in doing so removes with it large quantities of thermal energy.

Gustavo Cadena is an engineer from Mexico. Cadena was looking for a way to help people stay cooler and thinks that he found it with the Omius headband that he developed. “The Omius amplifies the surface area of the skin by five times.” Cadena told me. “It is made of light, thermally conductive graphite that has been treated to make it absorb water so that it enhances evaporative cooling from the forehead.”

Cadena told me that the Omius has not been shown to meaningfully decrease core temperature in athletes who are exerting themselves in the heat. However, there seems to be important local effects including on the brain where different hormonal responses may be at play fooling the mind in to believing the body is cooler than it is allowing for improved performance.

One of the important ways that the Omius works is by taking advantage of an arteriovenous anastomosis in the forehead. This is one of several places in the body where high flows of blood can be found because there is a rich network of blood vessels close to the surface and arteries and veins are in close proximity to one another. Consequently, surface temperature closely mirrors core temperature and cooling at this location could have an outsized impact on reducing total body heat load.

Another arteriovenous anastomosis can be found in the hand where the palmar arch carries a large amount of blood from the brachial artery to the brachial veins. Researchers have looked at various methods of cooling at this location and have found that it can be very impactful.

Some research has found that wearing ice gloves does not improve the ability to perform strength exercises in hot conditions, but other studies have shown that cooling gloves can mitigate the rise in core temperature and improve exercise ability in hot environments.[i]

Another arteriovenous anastomosis is internal, surrounding the esophagus. Cooling of this area can be accomplished by ingesting a slurry of ice and water that is a useful strategy both for cooling and for hydration. This cooling adjunct was used extensively during the very hot Tokyo Olympics to great effect.[ii]

I spoke with Canadian Olympic and now professional triathlete Matthew Sharpe who told me “Before and during races we had access to pretty much unlimited slushies. When ice is broken down there is more surface area to cool internally, and I found that these worked really well along with the ice vests that we had access to before each event.”

Pre-cooling prior to beginning training or a race with an ice vest as Sharpe described is a very useful way to ensure that you do not begin your event in an overheated state. Another valuable strategy and one that Sharpe referenced was the concept of adaptation. “Pre-race adaptation is key. Either by being immersed in the environment of the event as early as possible or artificially through heat chamber, hot tub or sauna protocol.” Sharpe said.

Most of us can’t justify the expense of an Omius headband, ice vest or travel to a hot environment for a couple of weeks before our event in the heat so what can we do to stay cool if we find ourselves traveling to a destination that has extreme heat and/or humidity for training or racing?

First and foremost, heat adaptation is a valuable and worthwhile effort. If you cannot go to the race location early enough, spending a half an hour a day in a sauna for two or three weeks before you leave has been shown to confer many of the physiologic adaptations that will pay off as improved heat tolerance on the day of your event.

Second, stay hydrated and increase electrolyte intake. In hotter environments you will sweat far more and it is important to keep pace with fluid and electrolyte losses by increasing intake.

Third, use your body’s anatomy and physiology to help cool you the most efficiently. On the bike, douse yourself with water at each aid station. That water will evaporate as you ride and cool your core down quite dramatically.

On the run wear a hat and pour ice water over it at aid stations. Take some ice cubes in your hand to carry and allow it to melt as you run. Pour more ice in to your shorts. The groin is another area where heat transfer can occur and result in significant core cooling. Crushing ice in your mouth and then swallowing the bits will act as a slurry that can also help with internal cooling. All of this takes some time but with practice it need not take that much more time than you would otherwise take just grabbing a cup of water or a gel. Furthermore, taking that little extra time in the aid station to do this could just result in your staying cooler than your competition and allow you to keep the pace higher when they are overheating and having to slow down.

However you do it, be sure to be mindful of the signs and symptoms of overheating. If you stop sweating, begin to feel lightheaded or feel confused then chances are you need to stop exerting yourself immediately and seek aid. Better to survive to race another day than try to push through and succumb.

Train hard, train healthy.

[i] Park J, Kim J. Effects of cooling glove on the human body’s recovery after exercise and improvement of exercise ability. Technol Heal Care. 2023;31(S1):259-269. doi:10.3233/THC-236022

McMahon G, Kennedy R. The Effects of Palm Cooling on Physiological and Metabolic Responses, Exercise Performance, and Total Volume During High-Intensity Bench Press Exercise in Resistance-Trained Men. J Strength Cond Res. July 2023. doi:10.1519/JSC.0000000000004530

Iwata R, Kawamura T, Okabe F, Fujita Z. Effects of Palm Cooling on Thermoregulatory-Related and Subjective Indicators During Exercise in a Hot Environment. doi:10.2139/SSRN.4357741

[ii] Taylor L, Carter S, Stellingwerff T. Cooling at Tokyo 2020: The why and how for endurance and team sport athletes. Br J Sports Med. 2020;54(21):1243-1245. doi:10.1136/bjsports-2020-102638