What Happens To Your Body When You Exercise In The Heat
As soon as you throw your body into the heat and begin to exercise, you create a need to circulate blood out to the skin for cooling, and this both draws blood away from working muscles and also lowers the amount of blood your heart can pump with each beat. Since evaporative cooling from sweat is the primary mode of heat reduction during exercise, this redistribution of blood to the extremities is combined with a loss of fluid and blood volume via sweat, which places additional demand on an already stressed heart.
As blood pressure and cardiac output fall from this drop in blood volume, temperature elevation accelerates, performance is impaired as the body reaches a critical core temperature, and neuromuscular drive and metabolic function subsequently begin to plummet.
In other words, the “wheels fall off”.
So what can you do about? Can you do anything about it? You bet.
Not only can you condition your body to maintain a higher blood volume, increased sweat rate, decreased salt in the sweat produced, increased salt store availability, decreased fatigue rate of sweat glands and more rapid onset of sweating, but you can also keep your body’s core temperature cooler during exercise in the heat.
And in this article, you’re going to learn how to be a mad scientist, hack yourself to handle the heat, and throw every possible wrench at your body to keep it from blowing up when the pressure cooker is on.
5 Tips For Exercising In The Heat
1. Body Cooling Gear
Let’s begin with the heat-hacking fashion you can wear: body-cooling sleeves, vests, gloves, grips, and a well-vented helmet. Now please do not confuse this with so-called “cold thermogenesis” gear, which is highly effective for fat loss and conversion of white adipose tissue into brown fat (and could theoretically be used as a “pre-cooling” strategy for hot exercise) but is bulky and not practical for donning during an exercise session.
The science behind body cooling gear is that it blocks solar radiation and increases sweat evaporation by increasing the surface area of the skin. In addition, many of the items of clothing, including arm and leg sleeves, contain Xylitol, a natural sugar-alcohol that produces a cooling sensation when wet. A 2017 study at the University of Colorado found that evaporative cooling fabrics increased energy efficiency and output in cyclists performing a 60-minute lactate threshold test Some good brands to try for arm, torso and leg cooling sleeves include Zoot, CEP, Craft, Desoto, New Balance, and perhaps most notably 37.5 Technologies, which has created gear to reduce humidity next to skin to maximize evaporative cooling using fibers infused with volcanic sand and activated carbon (made from coconut shells).
Several studies show that a light-weight body cooling vest could possibly get you even better results: in one study, after nearly 40 minutes of warming up in the heat, participants wearing a body cooling vest ran an average of nearly 13 seconds faster in a 5K, with heart rate 11 beats per minute lower. You can read up on additional body cooling research here. Since a vest covers an even greater surface area than the sleeves, this could be a better option or an addition to the sleeves. You can easily find multiple versions of cooling vests, including some that are very light and appropriate for racing, on Amazon.
But just in case sleeves and a vest aren’t enough for you, back in 2004 two Stanford biologists developed a special grip that maximizes heat transfer through the palms. The palm is a point where a large amount of heat radiation occurs, and blood vessels in the palm surface bring heated blood from the core to be dissipated at the extremities. If the palm is cooled, the cold blood from the palm is brought back to the core to assist with heat management. While the Stanford “Core Control” device is too bulky to effectively carry in a race (ESPN did an interesting write-up on a version of it here), by freezing an ice pack and securing it to the hand, you can achieve a similar effect by holding something cold during exercise, and several companies have developed cooling grips that fit just this purpose (although they’re admittedly hard to find these days, and a frozen ice pack that you grip in your hand could work just as well). A vest will still extract over three times as much heat as a palm-cooling device, but the latter is more portable and affordable.
If you’re planning on breaking out cooling gear for a long hot event like a marathon or Ironman, consider the logistical implications – your gear should be kept as cold as possible until you use it, and the grips and vest will only maintain cooling for up to a couple of hours. This means that you might wear sleeves on the bike, then add in the vest and grip from a cooler in your transition bag.
No discussion of gear would be complete without addressing helmet ventilation for you cyclists out there. Balancing aerodynamics and cooling in an aero helmet is a technological barrier that TT helmet manufacturers must overcome since vents, holes or any other gap in the smooth surface of a helmet can significantly increase drag. You can choose a well-vented aero helmet, such as the Specialized TT2, or if you’re a triathlete, simply wear a road helmet if you’re willing to sacrifice aerodynamics (interestingly, the well-vented road helmets will cool the head better than if you didn’t wear a helmet at all).
In the hot 70.3 World Championships event in Vegas, I successfully used both a body cooling vest and a palm cooling deviceto keep my body temperature feeling significantly lower during the half-marathon. However, this doesn’t work for some competitions, especially triathlons. For example, despite being frozen and placed in a foldable cooler during the Ironman Hawaii bag check-in at 5 pm on Friday, by the time I accessed my cooling devices at my 1 pm start of the marathon on Saturday, they were only slightly cool, offered no advantage over ice water dousing, and I opted to leave them behind during the Ironman Hawaii. So if you plan on using these type of heat-hacks during a race, ensure that you can have access to your gear on race morning, and also pack a cooler with ice.
2. Heat Acclimation
Now that your warm-weather fashion is set, it’s time to address heat acclimation hacks. Gradual exposure to repetitive exercise and non-exercise heat stress will produce beneficial physiological adaptations, including improved heat transfer from core to skin, more efficient cardiovascular function, decreased heart rate, skin and body temperature during hot exercise, increased blood volume and less electrolyte loss via kidney filtration.
For cold-weather and Northern climate athletes, preparation for a hot race should begin with frequent exposure to simulated heat, since opportunities to train in the racing environments are not available. For these athletes, there are two options: passive acclimation and active acclimation:
Passive acclimation involves sitting or standing in a dry heat sauna, an infrared sauna or a steam room to simulate heat and induces the same cardiovascular and sweat changes without the recovery implications or discomfort that accompany exercise in the heat. Sweat evaporation and cooling efficiency appear to occur most favorably with hot-wet conditions (steam rooms), but both methods will achieve favorable results.
Positive adaptations can occur with as few as 10 days of passive acclimation, but for optimum results, begin passive acclimation 4-8 weeks prior to the race, beginning with 10-15 minutes and gradually working up to 45-50 minute sessions every 1-3 days.
Active acclimation, or exercise in the heat, is crucial for experiencing the physiological and psychological responses to hot weather racing and can be accomplished via hot yoga, calisthenics, treadmill or cycling sessions in a dry heat sauna, or in a small room with a heater or humidifier under a stationary bike or treadmill. You can use a steady-state exercise protocol, and if you begin to get too hot to exercise comfortably, you’ll still get results if you stop exercising, or remove the heat, allow the body to cool, and then progress back into the routine when you are ready (this is called “controlled hyperthermia”).
During active acclimation, the elevation of both core and skin temperature is necessary for complete heat adaptation, but wearing too many extra layers of clothing during these sessions could actually be detrimental. Clothing is semi-permeable to water, so the climate developed under your clothing creates a water vapor pressure that prevents sweat evaporation and rapidly elevates discomfort and dehydration.
Full benefits of active acclimation can take 45 to 60 minutes of moderate-intensity exercise in the heat for 7-10 consecutive days, or four to five times a week for two to three weeks.
For these same cold-weather athletes, arriving early to a hot weather competition is highly recommended (similar to high altitude events), but initial exposure to a hot-humid environment can result in lethargy, sleep disturbances, loss of appetite, dehydration, greater discomfort of training, and reduced training capacity. After 7-10 days, these responses diminish, assuming the athlete isn’t spending the majority of time in an air-conditioned car or home (for this reason, it is recommended to turn the A/C off for full acclimation, aside from at night while one is sleeping). You can lose the positive benefits of heat acclimation in as few as 7 days, so it’s important to continue to engage in heat exposure until close to any hot competition.
For three weeks prior to 70.3 World Championships in Vegas, I supplemented my relatively cool Spokane, Washington training by sitting in a dry heat sauna for 20-40 minutes, 3-4 times per week. I repeated this protocol for three weeks prior to Ironman Hawaii, but primarily used a steam room instead, to simulate the more humid environment. Compared to previous races without sauna or steam room preparation, my mental and physical heat tolerance seemed (subjectively) significantly higher.
Water and hydration are of course the ultimate heat-acclimation hacks. Not only does your blood require water to maintain volume, but water can be used to cool the skin and body. Let’s begin with pre-race water immersion.
One study found that torso immersion of elite cyclists in a cold water bath for up to 30 minutes improved subsequent power on the bike, and another study found 5 minutes of cold water immersion to increase power during a heat time trial, and finally, if a cold tub is not available, a combination of a cool air fan and a cooling vest can significantly improve cycling endurance in hot conditions. You can read up more on the research behind hacking your hot sessions (or any exercise session, really) with pre-cooling in a fantastic guest post by Brad Kearns here.
It’s way easier than you may think to have your own cold tub setup at home. Read my article, “The Ultimate Guide To DIY Cold Thermogenesis: The Cold Tub Secrets Of Some Of The Top Biohackers On The Planet & How To Make Your Own Cold Tub Setup.” for detailed instructions on making your own cold tub using an old chest freezer.
Once you’re finished immersing yourself, you should ensure that you are pre-loading with water before your event. A practical way to do this is to drink 15-20 ounces of water 2 hours before you go to bed at night, then another 15-20 ounces of water as soon as you wake. Continue to drink 15-20 ounces of water for every hour leading up to the hard workout, competition or race, tapering off water consumption about 30 minutes before the race begins. This form of hyperhydration can be potentially be enhanced through the use of glycerol, a binding agent that allows you to retain extra water, but this practice can be dangerous if you overload with water, which is why until recently glycerol was actually banned by the World Anti Doping Association (WADA).
While it may not seem like a sexy, new hack, you’ll definitely want to continue to drink ample amounts of water during your hot weather event. The American College of Sports Medicine recommends 20-40 ounces of water per hour, but Tim Noakes, hydration expert and physiologist, says that performance is optimized when athletes drink according to thirst and that drinking more or less can impair performance, and produce fluid accumulation in the legs. Based on these recommendations, when you get thirsty during a hot event, you should consume 4-8 ounces of water.
The colder the water you’re drinking the better, since cool fluids leave the stomach more quickly than room-temperature or body-temperature fluids. Finally, there is some evidence to suggest that electrolyte-containing fluids will result in a greater amount of hydration compared to plain water.
Contrary to popular belief, there may not actually be a need for increased electrolyte intake as a heat hack. Research shows that high sodium intake during exercise may actually increase sodium loss, and the body’s natural stores of sodium may be much higher than the 10 grams frequently cited by electrolyte manufacturers. Therefore, taking in “extra” electrolytes because the weather is hot may simply cause you to sweat or urinate those additional salt. Based on this, it may not be necessary to exceed 2-3g of electrolytes on race or competition day. Ideally, supplementation should contain sodium, chloride, potassium, magnesium, and manganese, from capsules, tablets, powder, or pre-mixed liquids (remember that most gels also contain 80-300mg of electrolytes).
The importance of water “immersion” will continue into the race. Your perception of heat will heavily influence your perceived rate of exertion, and while ice, ice sponges and cold water on the back of the neck, inside the front of your clothing, or down the legs will not significantly reduce core temperature, these cold water-dousing methods can significantly decrease perceived heat.
Finally, water consumed in the form of ice slushies can lower physiological strain and core temperature. To make your own slushies, you can fill a water bottle with crushed ice or grab cups of ice from an aid station during a race, then chomp down, chew and swallow as you go.
When it comes to hacking the heat, there is an important supplement consideration (that often flies under the radar) based on the propensity of the gut to become more permeable during exercise in the heat. This can cause diarrhea as the body attempts to avoid toxins from gut organisms entering the bloodstream, where they can lead to heatstroke and organ damage.
Enter colostrum, a nutrition supplement extracted from the milk of mother cows and goats, that has been found to reduce gut leakiness by up to 80 percent during maximum aerobic running. Supplementation with colostrum should be initiated at least 2 weeks prior to hot weather competition, and you should be warned that colostrum may increase growth factor levels above that considered acceptable by the WADA. However, small doses for a couple of weeks going into a competition can significantly reduce gastric permeability and stomach distress in hot weather. To learn more about colostrum, how it works, and brands I use, go listen to my podcast with the Renegade Pharmacist.
The final heat-hacking element to consider is sunscreen. Most oil-based sunscreens will limit cooling capability due to the creation of a non-porous structure on the skin’s surface, but a sunscreen made with specific components that create a porous polymer can allow the skin to breathe, and enhance cooling. One “safe” non-toxic brand I was able to find on Amazon is Christina Moss, a porous sunscreen that allows the skin to breathe and leaves no feeling of clammy skin. I was able to exercise for multiple hours in the midday sun with no significant sunburn marks. It is completely free of parabens, synthetic chemical fragrance, retinyl palmitate, PABA, oxybenzone, propylene glycol, SLS, SLES and phthalates (it’s also gluten free but I’m not sure that’s too important unless you plan on smearing it on your gluten-free bagel).
While no single heat-hack listed above will produce any shocking or magical surges in performance, the collective result of their combined effect has influenced my ability to compete in significantly high-temperature races such as Ironman Hawaii and endurance competition in hot locations like Thailand, Florida, and Japan with relatively low heat discomfort and a notably faster recovery. Using these devices may seem like a logistical annoyance, but especially for cold climate athletes with limited ability to prepare the body for hot conditions, I would consider the use of these tips for exercising in the heat a crucial addition to the competition and recovery toolbox. I trust these hot weather hacks will help to make your hot exercise sessions or heat-based competitions just a bit more manageable.
How about you?
Have you discovered good ways to stay cool when you’re working out in a frying pan?
By: Ben Greenfield
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