On the first day of NFL training camp in 2001, Korey Stringer — a 335 lb right tackle for the Minnesota Vikings — left practice with heat casualty symptoms. The next day he collapsed on the field and was taken to a hospital where his core temperature was 108.8 degrees Fahrenheit. He was dead 12 hours later.

It’s easy for hot and humid weather to sneak up on an athlete, especially when they are trying to be tough and “gut it out” through a workout. While the worst case scenario is death, it’s more likely that training in the heat and humidity will decrease training performance. We can recover from one sub-par training session, but habitually having a decreased performance throughout the summer due to the heat is unacceptable.

Some of you may train or play outside during the summer, and some of you stay in the gym. Despite staying inside in the air conditioning, some gyms will still have a higher average temperature in the summer, and you’ll still be exposed to the elements during the rest of your day. Either way, understanding how your body responds to heat stress will help you prepare to train effectively.

How Heat Effects the Body

There are four ways the body dissipates heat: radiation, evaporation, conduction, and convection. When the air temperature rises, the only method that retains effectiveness is evaporation via sweat, and that’s assuming the humidity is low enough to allow evaporation to occur. When the god forsaken humidity is high, evaporation is less effective regardless of temperature, so the body will continue to sweat if the other methods are not effectively cooling. A combination of increased core temperature and increased sweating is the primary reason performance decreases in warm environments.

When the core temperature rises, the body undergoes changes in order to reduce the temperature. This normally happens during exercise; in fact, the muscles’ energy systems are more efficient with slight increases in temperature, but significant increases above 104 degrees Fahrenheit can be detrimental. Blood vessels will dilate to move as much blood to the surface of the skin to allow heat to radiate or conduct out. Since blood is being diverted to the skin, cardiac output increases (via increasing heart rate and contractility) to simultaneously pump blood to the skin and muscles, and the trade off is a decreased blood flow to the organs. Sweat glands excrete fluid that comes from blood plasma and contains electrolytes.

Sweating is of particular concern for us as mild dehydration can noticeably reduce performance. It’s not difficult to lose more than 1 liter of sweat in an hour per square meter of body surface. For a 165 lb child-like male adult, that could be 1.5 to 2.0 L of sweat or 2.5 to 3.2% of body weight in an hour. Technically that’s enough to put them in mild to medium levels of shock. Losing these levels of fluids means the entire body doesn’t work as efficiently at that moment and through the recovery process…and we aren’t even considering the stress from the training itself.

Some of you may be reading this thinking, “This doesn’t apply to me, I’m just a lifter.” Well, the more you sweat, the higher your core temperature, and the more disruption to your homeostasis, the less effective your actual set is. More importantly you can’t rest as well between sets and subsequently between workouts. If you sweat your ass off because it’s 80 degrees in the gym instead of 70, you now have the additional systemic stress of losing fluid volume, and this can add up over time to effect your overall progress.

Adding more systemic stress to an already stressful training program means you aren’t recovering and making as much progress as you could be. If you’re gonna spend five, ten, or fifteen hours in the gym a week, then you should be doing everything outside of the gym to make sure you aren’t wasting your time. Preparing for the heat and staying hydrated is vital to not waste your god damn time.

How to Prepare

The best way to prepare for the heat is to acclimate to the environment. Doing some relatively lower intensity activity (i.e. not as hard as what you normally do) in the environment you’re adapting to for one or two weeks will acclimate you. We’re already in the middle of the summer, so it’s likely you went through this process by default. For example, if you train in your garage, you would have steadily experienced the slowly rising temperatures from winter time. The result is that the body is able to maintain a lower core temperature and keep a lower heart rate, but sweating rates will increase for adapted trainees.

I point this out because when your body is more efficient, you sweat more. Yet this also means you’ll need a higher awareness of hydration to prevent the issues associated with dehydration. Other than acclimating to the heat and humidity, the best way to prepare to is to consistently hydrate and eat well.

By the time you are thirsty, the dehydration process has already occurred. Studies show that when people merely drink when they are thirsty, it takes 24 to 48 hours to fully rehydrate. And that’s assuming they aren’t exposed to heat, humidity, or exercise again in that time frame. For a 200 pound man who isn’t training or exposed to the elements, he’ll need to drink almost 2 liters of water (and I already accounted for 30% of water that comes from food). If you’re training hard, especially in the heat and humidity, you’ll need even more.

Hydration is not merely a day-to-day concept; it’s a persistent continuum. If you were slightly dehydrated yesterday, and you don’t hydrate today, it compounds on itself. I know someone who was working outside in the heat all week, trained in the gym each day, and then they lost consciousness during a Friday dinner due to chronic dehydration.

Electrolyte levels in blood are relevant to hydration, but if you are consistently eating quality meals, this shouldn’t be a problem unless you are strenuously training for a long time in the heat. If you were doing that, you could use some rehydration products with water (they typically include sodium, chloride, potassium, and a little bit of glucose). Typically commercial drinks like Gatorade or Powerade aren’t ideal because they have so much glucose that it increases the osmolarity in your small intestine which actually draws fluid out of the interstitial space into the intestines, further dehydrating you, but that’s a digression, sir.

I typically recommend solely drinking water throughout the day (after coffee, of course). Yes, you can get water from drinking shit like soda, but unnecessary sugar, phosphorous, or chemicals are not what you drink if you actually care about things like performance, building muscle, or decreasing body fat.

Worst Case Scenario

Some of you will find yourself in the heat for work (fire fighters, soldiers, cops, etc.), play (hiking, water sports, motor sports), or training, so it’ll be good to review heat injuries. Keep in mind that if you have not gone through an acclimation process, then you are more susceptible to these conditions. Furthermore, anyone is susceptible to them if they do too much, too long, on too hot a day.

Heat Cramps — These aren’t very serious, yet they are an indication you are not hydrated well and likely have low sodium. It’s a misconception that potassium and bananas will prevent these. Cease activity if you can and hydrate with salt accordingly.

Heat Exhaustion — This isn’t just feeling tired in the heat, this is the beginning of a downward spiral of the body shutting down. It occurs when the thermoregulatory and cardiovascular system can’t keep up with the demands of the increased temperature and cardiac output shift. If you feel dizzy, extreme fatigue, headache, nausea/vomiting, or you lose consciousness, then cease the activity and hydrate as discussed above. IV fluids would be ideal, and so would external cooling. Get into a cool environment with a fan, get someone to spritz water on you, and get some ice or cool packs under your arms and in your groin for a few minutes.

Heat Stroke — This is life-threatening. If this is happening to you, you won’t really be able to help yourself, so teach others what to look for. The same symptoms from heat exhaustion will occur, but the two that should jump out are the cessation of sweating and altered mental status (i.e. disorientation). All of those cooling measures above should happen immediately. This is what people die from on a regular basis, and it isn’t when the temperature is 95 degrees with 90% humidity; most heat casualties occur when it’s a balmy 85 degrees because people don’t expect it.

Wrap Up

While this article doesn’t have helicopter penises and “fuck yous” to hipsters, my aim is to a) prevent any unnecessary heat injuries, b) emphasize the importance of hydration all the time, but especially in the summer months, and c) give you something easy to do to efficiently train and recover to get stronger, faster, and conditioned. If you’re outside every day, then you need to drink much more water than you think you need to. Even if your job and gym are inside, you’ll still be exposed to the heat throughout the day, so take care of hydration now before it becomes a problem.