heat challenge

Springtime Heat Challenges: Strategies for Exercising on Isolated Hot Days

By Jason Koop,
Head Coach of CTS Ultrarunning

It feels a little strange to write about how to handle the heat when it’s still April. But, as I scrolled through my athletes’ comments on TrainingPeaks over the weekend, it’s obvious that athletes are contending with short term bouts of warmer conditions. This initial challenge, when actual temperatures are not that intimidating (say, 75° F), but represent a big temperature shift (like +10° to +20°) catches athletes off guard every season. Athletes head out the door with too little fluid and hammer up the same climbs at the same intensity. Somewhere in the middle of the run the heat catches up with them, they overheat and run out of fluids, setting off a cascade of heat related performance implications.

The challenge

Because hot weather days at this time of year appear and disappear so quickly, it leaves little time for athletes to physiologically adjust to the heat. When we use heat stress interventions like a sauna or hot water bath to prepare athletes for races in hot weather environments, those protocols last for ~5-10 days, which is a relatively short timeframe for anything related to endurance sport adaptations. That timeframe is important, as it represents just enough time for the body to improve and not so much that it causes undue stress. However, even though those heat stress adaptations kick in quickly, they still take days, not hours in order to make a meaningful impact.

One of the challenges a one-off hot weather day presents is that your body does not have enough time to make the necessary adjustments in order to cope with the heat. One way your body copes with chronic heat is to expand plasma volume. Plasma volume expansion happens on the order of 1-3 days after chronic heat exposure. Another way your body cools down is by sweating. Even this mechanism takes several days to adapt once exposed to heat. The point is, when you have isolated temperature increases, your body literally cannot respond fast enough to produce any meaningful coping mechanism. So, you are left with other options for handling the heat.

heat acclimation effects

Figure 1- Adapted from Périard, Racinais, and Sawka 2015. Illustration: Abby Hall


Schedule adjustments

The obvious way to work around the detrimental effect of heat on purposeful run workouts (interval training) is to train during cooler periods of the day. Many runners shift to morning or evening runs instead of performing interval workouts in the mid-day heat. Athletes who cannot make that schedule change may consider performing mid-day interval workouts indoors on a treadmill in an air-conditioned space.

This is typically when athletes push back and say something like, “If I have to race in the heat, then I need to train hard in the heat, too!” Remember, the efficacy of interval workouts is based on the quality of your efforts. Develop fitness in the best environment to do so; exercise in a hot environment to minimize how much of that fitness the heat strips away. Additionally, you will have plenty of time closer to your race to use a specific heat acclimation protocol.

To balance the needs of purposeful training and heat acclimation I recommend performing endurance runs in hot environments, as opposed to interval workouts. These training sessions will not be as detrimentally affected by heat because the intensity is lower, and the exposure to heat will aid in acclimatization. For most athletes who live in regions that experience hot summer days and are preparing for events with similarly hot daytime temperatures, additional heat training protocols may not be necessary. If you are preparing for extreme heat (Badwater 135) or live in Alaska, you might benefit from engaging in proactive heat training strategies.

Hydration Monitoring

Although your body might not have the chance to physiologically adapt to sporadic warmer days, you can start off on the right foot and ensure you are properly hydrated before you begin your workout.

The WUT protocol (Cheuvront and Sawka, 2005) is an easy way to assess your day-to-day hydration status. When you wake up, assess your level of thirst. Then observe the color of your urine. After you have urinated, weigh yourself without clothing.

Your morning urine should be light in color or relatively clear. The tipping point for the WUT assessment is if your urine is approximately the color of apple juice or darker. Be aware, however, that clear urine does not necessarily mean you’re in the clear (bad pun intended). If you guzzled a full bottle of water before bed, your morning urine may be light in color because you consumed so much water in a short period of time. Ideally you also need to evaluate the color of your urine stream, not the diluted urine in the toilet. Your weight should remain relatively constant from day to day, varying about 1%. Even if you are gradually losing weight as part of a weight management goal, the changes from one day to the next won’t vary more than 1%.

When only one of three indices is abnormal, your hydration status is likely good. When two of the three indices are abnormal, you are likely dehydrated. And when all three indices are abnormal you are very likely dehydrated. Starting your day with a better hydration status means you are optimally prepared for a better and more productive training session or competition.

WUT graphic

Figure 2- Adapted from Cheuvront and Sawka 2005.Illustration- Abby Hall


Hydrate Before Exercise

When your day-to-day hydration status is good, you have a better chance of having a great workout or event performance. The next step is to consume 16-20 ounces (a regular sized hydration flask water bottle is typically about 16 ounces) of cold fluid (water or electrolyte-rich sports drink) in the hour prior to exercising in the heat.

This pre-workout bottle spares the fluid you’re carrying. Although it’s a good idea to consume fluids early in workouts, in the real world a lot of athletes wait at least 20 minutes before drinking. Runners carrying bottles automatically start rationing fluid to make it last longer. Consuming a bottle before you leave gets water on board, so to speak, for this early period of your workout.

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What about hyper-hydration or pre-load hydration products?

Hydration products marketed as hyper-hydrators are designed to increase the amount of water your body stores, and they do so by supplying a huge amount of sodium. The idea is that by starting hot-weather exercise with greater body water, you have a bigger reservoir of fluid that can absorb heat from working muscles, move it to the skin, and dissipate it as sweat. As a result, your core temperature doesn’t start rising as early, and rises more slowly during the first hour of exercise. However, these products are not recommended for everyday use. They contain extremely large amounts of sodium (3.5 grams/liter, or 1700mg/500ml bottle). You don’t need these drinks for short or moderate-intensity workouts. They are purpose-specific drinks designed for athletes training or competing in extreme conditions or for athletes who consistently struggle with significant weight loss (5+%) during exercise, are always craving salt, and finish workouts crusty with salt on their skin and clothing. If you consume them when you don’t need them, the high sodium content can lead to nausea. When might you use one? Perhaps before a long and/or very intense workout in hot conditions, or before a race in abnormally hot weather. As always, try it in training before utilizing it in competition.

Use Pre-Cooling Strategies

While it would be great if you could schedule all of your interval training in cooler environments, that’s not always practical. If you know you are going to be working hard in a hot environment, you can consider some pre-cooling strategies. Starting with lower core and skin temperatures increases your heat storage capacity (you store heat internally even when you sweat), meaning you can accumulate more heat in your body before reaching a temperature that hinders performance. Pre-cooling will not prevent you from reaching high skin or core temperatures during a long or strenuous workout, but it will give you more time to perform high-quality work before elevated core temperature hurts your performance.

Lots of pre-cooling methods have been studied, and most are effective but impractical. You can immerse your body in cold water or take a prolonged cold shower, but those are inconvenient. Cold air exposure (much colder than normal air conditioning) can be effective, but it requires a long time to work. From a practical standpoint, here’s what works:

Cover your torso with cold, wet towels.

The key is to cool a relatively large portion of the body, which is why ice vests or wet towels will do more good than cooling just your hands, arms, or neck.

Ice sock around your neck.

If wrapping in cold towels is not an option, consider a sock filled with ice. Because this will result in a soaked shirt, this is often used outside during a warmup rather than indoors before leaving for your run. As such it is both pre-cooling and during-workout cooling (for a little while, at least).

Drink an ice slurry drink (Slurpee time!).

Before exercise an ice slurry drink is a great choice. During exercise, research suggests cold water is better than an ice slurry because the ice slurry can signal temperature sensors in the stomach to reduce sweat response and skin blood flow, potentially causing you to store more heat (not what you want).

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Getting the Best Bang for your Buck

It’s impractical for most athletes to do everything mentioned above before going out to train in hot weather. It’s best to keep it simple by choosing a few of the modalities mentioned above that you can achieve easily and consistently. Particularly when warmer weather days sneak up on you, you can use some of these simple strategies as short term coping mechanisms to get the most out of your workouts.


Cheuvront, Samuel N., and Michael N. Sawka. 2005. “SSE# 97: Hydration Assessment of Athletes.” Sports Science Exchange 18 (2): 1–12.

Périard, J. D., S. Racinais, and M. N. Sawka. 2015. “Adaptations and Mechanisms of Human Heat Acclimation: Applications for Competitive Athletes and Sports.” Scandinavian Journal of Medicine & Science in Sports 25: 20–38. doi:10.1111/sms.12408.



Comments 1

  1. It’s hard to relate to this article this week as we’re getting several inches of snow here in CO and the high is in the 40s… I’ll read this article in 2 months!

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