Coach Tip Tuesday: How to Train and Perform Well in the Heat

Summer has arrived in the Northern Hemisphere, which means athletes are starting to feel the effects of the heat.  (Yes, I know the Summer Solstice hasn’t happened yet so it’s not “technically” Summer, but as far as ambient conditions go, it’s Summer in the Northern Hemisphere.)  Every year around this time, I read Post-Workout Notes where athletes are lamenting about how hot it is, how the heat impacted their ability to execute their workout, and how much (some) athletes hate the heat.

I’ll admit it; I always chuckle a little to myself as I read these notes, as many of these same athletes will be lamenting about the cold conditions once Winter has arrived.  While I resist the urge to remind athletes that this is the warmth that they longed so much for in January, I do advise athletes that there are things that they can do to help them train and perform better in hot conditions.  Because yes, it is possible to train and perform well in the heat.

Hydrate, Hydrate, Hydrate

Being sufficiently hydrated is one of the three best things endurance athletes can do for their training and performance.  This is true for so many reasons, and it holds true when the temperature rises.  

A majority of issues that athletes face when training in the heat revolve around the body’s ability to thermoregulate.  Thermoregulation is a process that maintains a steady internal body temperature despite changes in external conditions.  Thermoregulation is therefore an important part of maintaining homeostasis, which is the state of steady internal and chemical conditions maintained by living systems.  In other words, homeostasis is a state of balance among all of the body systems needed for the body to survive and function correctly.

The body needs to keep its core temperature within a few tenths of degrees of its normal (a normal range is 97.7ºF to 99.5ºF).  When Summer rolls around and the ambient temperatures, humidity, and dew point all rise, our core temperature rises alongside them.  In order to try and keep that core temperature in that necessary limited range, the body sends blood toward the skin to off-load the heat that is accumulating in our core.  

Additionally, the body begins to sweat, which sends water outside of the body to the surface of our skin.  Water is an extremely effective heat sink because it can absorb large amounts of heat energy with only a slight increase in temperature to the water itself.  So the heat from inside of our bodies is carried outside of our bodies via water (sweat).  The layer of moisture on the surface of the skin created by sweat cools us as it evaporates.  As the water evaporates and leaves the body, the heat that was contained in that water also is off-loaded from the body.  

Water is the body’s natural coolant.  And since water is the main mechanism the body uses to cool itself, being sufficiently hydrated is critical to being able to properly thermoregulate.  Someone who is dehydrated will never be able to properly and effectively cool themselves.  When you sweat, that water needs to come from somewhere; the body will default to using blood plasma (the watery part of our blood) as the primary source for this water.  However, blood plasma volume drops when we do not maintain sufficient hydration.  The body can only take so much water out of the blood before that becomes unsafe, so when it cannot use blood plasma as its water source, the body will then seek to find that water that it needs for cooling from other sources (such as the organs, muscles, and other soft tissues).

Maintaining good blood plasma volume is just one of the things that being sufficiently hydrated does for us.   If you send your body into a state where it is pulling water from your soft tissues instead of blood plasma, you are at risk for extreme medical conditions such as heat stroke, rhabdomyolysis, and more.  

I think we can all agree that our overall health is more important than athletic performance.  That being said, the impacts of hydration status on athletic performance are profound.   Athletic performance decreases with just a 2% dehydration rate.  How much athletic performance suffers depends on several factors, including the type of workout, the duration of the workout, the intensity of the workout, and how dehydrated the athlete actually is.  However, a 5% dehydration status decreases performance by 30%.  In addition, your subjective and objective ability to tolerate heat decreases dramatically if you are dehydrated.

If you are dehydrated before beginning a workout and you start a workout in a dehydrated state (statistically speaking, you likely are dehydrated since 50% of humans on the planet are not sufficiently hydrated), then your performance during the workout can be reduced by as much as 45%.  Starting a workout properly hydrated gives you a major advantage; while the stress of being in a hot environment alone is enough to cause a 7% decrease in performance, that’s certainly better than a 45% decrease in performance.

Acclimatization is The Way

While you are maintaining a sufficient hydration status, you will also want to consistently expose yourself to hot conditions so you can benefit from a process called acclimatization.  Acclimatization is the process or result of becoming accustomed to a new climate or to new conditions.  Going through the process of acclimatization is the only way that exercising in the heat will ever not feel horrible.  If you don’t expose your body to hot conditions consistently over a period of several weeks, it will never adapt to be able to function well (which translates to you feeling better) in them.

It takes approximately 14-21 days of consistent exposure to hot conditions to adapt to them.  This means that you need to do all of your workouts in hot conditions for at least two consecutive weeks.  Yes, all of your workouts.  Any breaks from hot conditions will at least delay your acclimatization if not reset it entirely.  The bad news is that your workouts in the heat during this 14-21 days window will almost certainly all feel uncomfortable (if not terrible).  

The good news is that it is possible for your body to adapt to hot conditions, and once it does, you will feel much better when you’re exercising in them.  And you won’t just be feeling better; you will also be performing better in hot conditions.  Studies have shown that heat training is at least as beneficial as altitude training (and may actually be more beneficial than altitude training) for performance not only in extreme environments, but in temperate environments.

If there are cooler days mixed in with warmer days, I recommend going out for your workouts at the warmest time on the cooler day if it’s logistically possible.  Yes, it might feel better or nicer to do your workout in cooler conditions, but the hard truth is that breaking from exposure to hot conditions does reset your adaptations to them.  This also may have the added benefit of training specificity of having you training at the time of day that you will be racing.

I have an amusing story about doing just this in my own training: Several years ago, I was training for IRONMAN 70.3 Augusta, which takes place in late September.  While that time of year is cooler in my home region of Upstate New York, Summer is basically still in full swing in Augusta, Georgia in September.  Thus, I was planning to expect hot conditions on race day.  So whenever possible in my training, I went out to do my workout at the hottest time of the day.  

One memorable morning, I was ten days out from race day and visiting family in Connecticut when I woke up to temperatures of 32ºF.  I decided to delay my planned run until later in the day (when it was forecasted to be in the mid-60s), and I went back to sleep.  My mom woke me up 45 minutes later in a panic, thinking I had overslept and missed my workout window.  She couldn't believe that I - someone who had hated the heat of the Summer as a kid - was intentionally choosing to wait until it was hotter out to do my workout.  In any event, maintaining my acclimatization as best as I could proved to be wise, as temperatures were 105ºF on race day.

In any event, the reason why acclimatization works is that it generates some really important physiological adaptations in the body.  First, total blood volume increases with consistent exposure to the heat.  Very specifically, your plasma and your red blood cell volumes increase.  As we discussed earlier, blood plasma plays a vital role in cooling the body.  Increasing how much of it we have really helps the body keep itself cool when our core temperature rises because it enables the body to improve blood flow to the skin and muscles as well as keep heart rate, skin, and body temperatures lower.  All of this enables you to exert yourself more in terms of time and intensity.  This being said, we can only acquire this adaptation if we are sufficiently and properly hydrated.  Yes, if you do not prioritize hydration, you will not adapt to hot conditions, and exercising will feel uncomfortable or terrible all Summer long.

Second, the composition of your sweat changes as you acclimatize.  This change in composition makes it so you lose fewer electrolytes as you sweat (up to 50% fewer!).  Electrolytes are chemicals that conduct electricity when they are dissolved in water.  In the human body, they regulate nerve and muscle function, hydrate the body, balance blood acidity and composition, and help rebuild damaged tissue.  Losing fewer electrolytes through your sweat allows your body to retain them and to use them for muscle function, which is critical for endurance athletes.

For what it’s worth, while I’ve observed that exposure to hot conditions during workouts definitely helps athletes acclimatize, additional exposure (via being outside for walks, yard work, etc.) to conditions also helps this process.  In some cases, it shortens the acclimatization timeline down closer to the 14-day range.  However, it’s important to note that this exposure should be in addition to heat exposure in workouts, not in lieu of.

Pre-Cooling Techniques for Top Performance

While ensuring that you are sufficiently hydrated and acclimatized are arguably the two best things you can do to prepare yourself to train and/or race in the heat, pre-cooling is an effective technique, especially before a big workout or race.

Pre-Cooling is a strategy that aims to reduce core body temperature before exercise.  By reducing the body’s core temperature before you begin exercising, you increase the margin for metabolic heat production (aka heat that is generated as a result of a workout or exercise).  By increasing this margin, you increase the time it takes to reach the critical limiting core temperature when a given exercise intensity can no longer be maintained.  Basically, pre-cooling allows you to maintain a lower core body temperature for a longer period of time before it rises to the level where you feel fatigued and the need to slow down or stop.

You can pre-cool yourself before a big workout or race by keeping your core body temperature lower in the 24 hours that precedes the workout or race.  Here are some effective pre-cooling techniques:

• Staying in the shade or air conditioning.
• Not getting into saunas.
• Not doing any activities that drive heart rate (and therefore your core temperature) up.
• Submerging yourself in cool water (such as a shower, pool, or bathtub) for 15-20 minutes right before you begin your workout or race.
• Drinking something cold, such as a slushy or otherwise very icy beverage.  (This creates a heat sink, which means you not only store less heat, but you store it more slowly.)
• Using cool towels on your skin to lower your skin temperature by placing them in key areas such as your neck.  (Don’t place actual ice next to your skin; this can constrict your blood vessels and drive your core temperature up (instead of down) before you begin your workout or race.)

Females Struggle with the Heat More Than Men

While all athletes - regardless of gender - can certainly train and perform well in the heat, females do have a bit of a rougher road ahead of them due to our physiology.  Women sweat less than men, and our sweat is more diluted.  In addition, we have fewer sweat glands per square inch on our bodies.  In order to begin sweating, a female’s core temperature has to rise to a higher number/threshold than a male’s does because women vasodilate first and sweat second.  (Vasodilation is when the blood vessels in the body widen, allowing blood to flow through them and to lower blood pressure.)  All of this means that women start sweating later after they begin a workout than men do.

Over the course of a female’s menstrual cycle, changes in estrogen and progesterone cause women to respond to heat losses from the body differently depending on which phase of their menstrual cycle that they’re in.  In the high-hormone phase (days 15-28 in an average cycle) of the menstrual cycle, women are less sensitive to the heat because their skin temperatures and blood flow are lower in that phase.  Conversely, women have a harder time tolerating heat in the low-hormone phase of their cycle (days 1-14 in an average cycle) when their temperatures are higher.

Finally, where a woman is in her lifecycle impacts how she will tolerate heat.  Menstruating females tolerate heat differently than women who are in perimenopause.  Women who are in menopause tolerate heat differently than menstruating or perimenopausal women.  Once a woman is through menopause, her body is permanently changed in terms of how she tolerates heat (and it’s not for the better).  Fortunately for endurance athletes, endurance exercise has been shown to offset and improve some of the hormonal changes that women experience in menopause.  This means that endurance training itself can help perimenopausal, menopausal, and post-menopausal women tolerate heat better not just in workouts, but in their everyday lives.

Manage Performance Expectations When Training and Racing in the Heat

When it’s hot, you need to manage your expectations of what you will be able to do performance-wise during a workout.  Hot days are not the days to have an ego and chase times or pace-based goals just because you want to feel good about yourself.   Remember: Even if you are sufficiently hydrated and acclimatized when you begin a workout, being in hot conditions will decrease your performance automatically by 7%.  You are not and will not be able to achieve the same performances in hot conditions that you can in temperate conditions, and don't make the mistake of thinking that you are the exception to that. 

If you are training with time-based (pace-based) targets, you may need to adjust the pace targets and goals.  It may be wise to adjust to using heart rate as your gauge for the workout; ensuring that your heart rate doesn’t rise to levels where it’s impossible for you to keep moving is important in hot conditions.  (This is actually the strategy I personally deployed at the aforementioned IRONMAN 70.3 Augusta.)

Rating of Perceived Exertion (RPE) is always a viable and effective strategy to deploy in hot conditions (or in any conditions, really).  If you take the time to develop your self-awareness, to learn RPE, and to have a true understanding of how you feel and what is sustainable for you, you will be able to take that skill with you and deploy it in any condition, temperate or extreme.

Be honest with yourself about what the ambient conditions are, and adjust the workout or race strategy itself as-needed so you can still challenge yourself and be successful.  Perhaps you would benefit from incorporating regular walk intervals into your run from the beginning of the run.  Maybe you need extended rest intervals in a bike workout in order to allow your heart rate to recover and your core temperature to come down a bit.  If the water is warm and you’re swimming, you need to be especially mindful of your effort level and not make the rookie mistake of going too hard.  Though you can’t feel it because you are in water, you do sweat while swimming.  Since you’re expelling water (sweat) into water that is surrounding you while you’re swimming, you don’t get the benefit of evaporation, which is what cools you.  As a result, you can overheat more quickly in water.  (This effect is why wetsuits are banned in triathlons when the water temperature is over a certain temperature.)

The Bottom Line

Hot days are not something to dread when it comes to your workouts and races.  Embrace the challenge that they bring and confront them by hydrating well, consistently exposing yourself to hot conditions so you can acclimate to them, and modify your workout or race strategy as needed to be appropriate for what conditions you are actually facing.  If you do these things, you will discover that it is very possible to train and perform well even on the hottest days. 

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Sources:

Sims, Stacy. ROAR: Match Your Food and Fitness to Your Unique Female Physiology for Optimum Performance, Great Health, and a Strong Body for Life. Rodale, 2016.

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Jeukendrup, Asker. Sport Nutrition, Second Edition. 

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Ferreira-Pêgo, C, et al. “Total fluid intake and its determinants: cross-sectional surveys among adults in 13 countries worldwide”. Eur J Nutr . 2015 Jun;54 Suppl 2(Suppl 2):35-43.

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Saunders, Philo, et al. “Special Environments: Altitude and Heat”. Int J Sport Nutr Exerc Metab . 2019 Mar 1;29(2):210-219.

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Lorenzo, Santiago. “Heat acclimation improves exercise performance”. J Appl Physiol (1985). 2010 Oct; 109(4): 1140–1147.