How should I prepare my body for prolonged exposure to heat?

Question

Today I hiked for about 4 hours, and I ended up with sun stroke (terrible headache, trembling etc.). The heat was moderate (about 30°C, 86°F in shade), and the way was half in forest. I had a baseball cap on my head and I drank a lot (about 2.5 liter water). I was not dehydrated, judging from urine amount/color. So in theory, I did what was necessary to prepare myself. However, it seems that my body was overwhelmed in spite of this.

Is there anything I can do to prepare my body for heat? The people on Savanna, for example, are living with much higher temperatures and full day exposure to sun, and I wouldn't handle that in my today's condition. Is this a genetic factor, or it can be trained, for example sauna, intensive exercises or simply exposure to heat?

Answer 1

There are a few things that influence your body's ability to regulate heat. Nutrition, clothing, behavior, and practice are the big ones.

Nutrition is important as far as making sure you're properly hydrated and are replete with electrolytes. It's possible to become dehydrated even while drinking enough water. To fix this, make sure you consume salts such as sodium chloride, potassium chloride, or others you can read about here https://en.wikipedia.org/wiki/Electrolyte#Physiological_importance.

Clothing is important as well, and is easy to do incorrectly if you're unfamiliar with how. You've mentioned you're in a forest, which means you don't have to worry about providing your own shade. Focus on wearing lightweight clothing which allows ventilation. Generally, do not wear cotton. It will absorb several times its weight in water, allowing chafing while preventing your sweat from properly evaporating off your skin. The sweat must evaporate from your skin or a layer of clothing near your skin in order to cool you off; this is called evaporative cooling. Underclothing should also not be cotton, again due to chafing and because your groin is just about the warmest part of your body. Soaked cotton allows much less airflow than soaked wool or synthetics. Wool or wool blend socks are usually best at providing ventilation for your feet to reduce blisters and overheating. The baseball cap you mentioned before is probably also a bad idea, especially if it's cotton. A wide-brimmed hat capable of providing shade while still allowing ventilation is a much better idea. Your head generates a lot of heat, and must be allowed to properly reject it to the atmosphere in order to avoid overheating your brain.

Behavior is a much more simple category for improvements. Stay in shade, move slowly, and move even more slowly if you start to feel hot. Do not hesitate to take a break in the shade. In fact, take a break before you feel like you need to. Don't wipe sweat away unless you must. The sweat must remain on your skin to be effective. If you're producing excess sweat to where you're dripping, it may make sense for comfort reasons to wipe it away, but you wouldn't want to keep, say, a towel with you to clear your brow every few seconds.

Practice is even simpler. Exposing your body to heat while exercising will generally cause you to thermoregulate more effectively. Your body will produce more blood and vasodilate more readily, allowing the blood at the surface of your skin to "donate" larger amounts of heat to the air (if below 38 degrees) or to evaporating sweat (if between 38 and 100 degrees (I really hope you're not going anywhere over 100 degrees)). This is how you see people who live in the tropics or mediterranea go about their day comfortably without sweating like a northerner does.

TL;DR: Wear a wide hat of non-cotton, wear non-cotton shirt/pants/underpants/socks, move slowly, take breaks, drink water, eat salts in moderation, and keep at it.

One controversial piece of advice I'll throw out there that fits with the "practice" paragraph is if you live in a warm place, avoid air conditioning. Or, at least, use in moderation. If you want to get accustomed to 30+ degrees, make sure your AC is set to 25. Just low enough that you don't feel like you're going to die, in other words.

Answer 2

It takes about 2 years to fully get used to heat.

• A ball cap is not good. Get a vented brim hat. The old straw hats are very good, they absorb moisture, and cool by evaporation. The woven reed cone Asian style hats are good.
• Wear light colors. Cotton wicks moisture away to help cool. Tropical wool is the best there is. I recommend a 60% cotton 40% wool mix.
• Wear sandles, not socks.
• Eat a banana with a little salt on it.
• Wear loose fitting cloths, where you can out and about.
• Dip or soak your hat in water, for extra evaporation. Take some cloth with you if water is close, so you can soak it and wrap it around your wrists. Old cotton sock tops are good for this. Keep them wet to damp, it pulls the heat out of your blood.

From the tropics here.

Answer 3

I go to Arizona and hike around the desert pretty much every summer. One thing I've noticed that makes a difference is to immerse yourself in the heat. Don't try to avoid it; embrace it.

I have experienced up to 121 °F (49 °C), that I know of. While that certainly felt hot, the limiting factor for walking around was how much liquid I was willing to carry, not being out in the heat. However, at that point I had been outside for a few days.

Try to avoid artificially cooled places. Sometimes you have to get supplies and go into air conditioned stores. A few minutes doesn't make much difference, although even then you notice the heat more when you get out than when you went in. However, absolutely don't sleep in a air conditioned space. That deprives your body of getting used to the heat.

Stay hydrated and think about electrolytes. The first thing I do when I get to AZ is to get a large tub of Gatorade powder. After that, I make it a rule that I only drink diluted Gatorade. That, together with salts in what I eat seems to work well enough, at least for me.

The first year I went to the desert in summer, I took plenty of water on a hike but hadn't considered electrolytes. After probably about 7 miles I got sick enough to throw up and lie down for a while where there was a little shade. It was the longest 1½ miles back to the car I've ever experienced. After that, I stuck with diluted Gatorade and haven't had a problem since. That was about 15 years ago.

Answer 4

I lived in a city where temperatures didn't rise above 31°C until I was 18 year old, and then moved to another where summer easily gets above 42°C (real feel can reach 54°C). I'm a climber, and I do climb in those temperatures.

I can only advise you based on my experience.

When I got here I was constantly passing out in the street/bus. I have Polish inheritance so my genetics is not the best to endure this sort of climate. Even nowadays, almost 10 years after I've moved, I still get light headed and stressed sometimes; but what really changed the game for me was something that might look stupid (and maybe is) and, actually, might also be just a placebo, but it helped me greatly: a sauna. A year after moving I decided I had to get myself used to the heat and started going to the sauna twice a week, as if I were in some kind of training. You cannot believe the consequences.

Regarding clothes: get yourself dressed such that most of your body is covered from the sun, but the fabric lets the air circle around your body.

I also learned, with that weird sauna training, that a huge part of "heat sickness" is psychologic. I couldn't stay 15min inside, but when I started meditating in the sauna I became able to stand the heat almost for an hour.

Just my $.02.

Answer 5

As a native Floridian I can tell you dealing with the heat takes a lot more awareness then dealing with the cold. Cold is easy compared to heat. Mostly because cold effects can be felt, while heat can’t (in general).

So in Florida it can get well over 37 C in the sun, and it’s humid. It's normally around 35 C to 38 C, Humidity is generally in the 80s - 90s, some times over 100% but that's rare. High 90s is pretty common.

The point is this. It's hot, and dealing with heat takes a lot of practice. So let's talk about what you should and should not do.

• Drink a lot. 2.5 litres is not enough. Not even close. It doesn't matter that your pee was clear. You should be drinking closer to 10 litres. This can take a lot of practice. 2 litres is enough to be sitting around. I drink 2 litres a day to sit inside with the air conditioner. I plan on 5 gallons a day when camping and 3 gallons when hiking.

• Pee ALOT. Obviously with all that water flowing through you it's got to have some where to go. If you’re not peeing every couple of hours you need to up your water intake.

• Under no circumstances should you get thirsty. If you get thirsty then you need to stop, seek shade, and rest. Thirst is the first sign of dehydration, but in the heat, it's very easy to miss or ignore and the second sign means heat stroke is just around the corner.

• Electrolytes are a mixed bag. You need some extra because you’re going to sweat out salt and potassium, but too much is a bad thing as well. This will take some practice. My best advice is to listen to your body. If you feel weak or tired when you don't think you should, then you should eat salty foods (pretzels are good, more later). If you’re getting cramps or "Charlie horses" then it's time to eat some bananas. If everything is ok, then maybe just let it ride a bit, but remember by the time you feel these things it's already too late. Sadly, I know of no magical way to tell.

• Do sweat. Don't wipe it off, don't clean it off, DO NOT USE ANTIPERSPIRANT. Sweat, Sweat, Sweat, Sweat, Sweat. Let your cloths get soaked, be nasty, sticky, and gross. Sweat. It’s basically your best defence against heat. Letting the sweat stay on your skin lets the salt "soak back in" a bit. Washing your self off, or pouring water over your head essentially rinses all that nice, awesome, salt away.

• Wear a "breathing" hat. Straw is awesome. But some synthetics can be great too. Stay away from anything that "wicks sweat away". Other great options are rags, towels, handkerchiefs, and anything cotton. Your baseball cap, not a great selection as it would hold in the heat more then let it out (usually, there are exceptions).

• Eat chocolate and salt. Pretzels are good. My favorite are Pretzel sticks and M&Ms. The sugar is a nice little boost, the chocolate contains great things that will help your body, the bread has a lot of "long term" energy, and the salt will help with electrolytes.

• Look to fruit for flavor. Especially dry fruits, like raisins. They have sugar too, and well help with other bathroom needs. You want a dry fruit because the wet ones will just be a disaster in the heat. Raisins, dried bananas, dried apricots, dried oranges, are really hard to "ruin" with heat. An apple, orange, pomegranate, won't last 10 minutes after you break the skin.

• When it's time for lunch. MEAT!!! Red meat contains a lot of things your body has now spent. Fish is ok too but much harder to keep fresh. That said portions should be smaller than normal, a 16 Oz. steak might just literally kill ya. But a 4-6oz steak, laughable at a dinner table at home, is perfect. You want your energy to come from breads and fruits (and chocolate) not from meat. But your body will need the meat to rebuild a bit.

• Avoid synthetic foods. They may have lots of cards per pound, but they are harder to digest. You want nice easy to digest foods. Foods that are harder to digest (like the fruit) should be used sparingly. 1 Oz of Raisins to 1 pound of M&Ms and pretzels. Remember it's going to take energy and effort to digest foods and that will heat you up.

• Rest often. Especially if you’re not accustom to the heat. Walk for 25 mins and rest for 5. You should never feel tired. If your feeling tired rest longer. Even if it means walking for 5 and resting for 25, that's ok.

• As to clothes, it's a bit counter intuitive. Wear Pants and a short sieve shirt. The pants, actually help keep you cool. Make sure the pants are cotton and not something else. Jeans are a really good start. It may "feel" warmer, but it will be more regulated. Avoid sweat pants, track pants, and pants that are a blend of fabrics, and shorts. It may seem your cooler in shorts, but you won't really be. Legs are not that good at sweating.

• Keep your shirt on. A lot of people want to take their shirt off when hot. Don't do that. You care more about regulating heat then staying cool.

• Ware a cotton T-Shirt. Cotton breaths. Silk would do ok too, but that's not very durable. Cotton is king in the heat. Stay away from blends

• You want all your cloths to be "loose". Not Grandma's moo-moo loose, but loose. You want air to flow through them nicely. You do not want any tight cloths (except socks and you want those really tight).

• Socks should be super tight. Not cutting off circulation but as tight as you can wear them comfortably. If you’re sweating and they move around, you’re in for a problem. You want them tight so they can soak through with sweat and still be tight.

• This brings us to cooling off. **DON'T COOL OFF* Stay out of the swimming hole, don't pour water over your head, don't run a fan (these are horrible and will cause issues), DO NOT COOL OFF. Once you are cool then swim. Going from very hot to cool will cause a shock to your system. It can even cause heart attacks, stokes, and other really nasty things. Don't do it. Sit, relax and let yourself cool down naturally. Think of yourself like glass. You can't go from one extreme to the other, you need to cool and warm up in between.

• Finally, make sure your drinking water is warm. Cold drinking water when you’re hot can make you very sick. The drinking water should be the same temp as it would be if you just left it sitting out in the shade. Heck even hot water would be better than cold.

• Bonus, just cause it needs mentioning some times. Don't drink booze for at least 2 days before and after something like this. Not even beer. It adds extra strain and won't cool your off or heat you up. (It might actually cool you off a little bit, but it's not worth it).

Based on your story I would say you were dehydrated (the headache) and had an electrolyte issue (the shakes). You did not have heat stroke. If you did you would not be writing this now. Even mild heat stoke requires weeks of recovery time. You would have had seizures (not just shakes), probably passed out, confusion, vomiting, and in some cases coma. A heat stroke means your core body temp was over 104 F / 40 C. It's nasty and if you were alone, may have (probably would have) resulted in death.

I would lose the baseball cap in favour of a straw cap, drink a lot more (OSHA recommends a litre an hour for outdoor workers), and then do something about your food. You didn't mention what you ate, but a homemade mix of dried bananas, pretzel sticks and M&M while hiking is amazing, Fish before (with lots of carb heavy foods) and Red meat after (with only a few extra carbs) works really well for a single day.

For reference https://www.osha.gov/SLTC/heatillness/heat_index/protective_high.html

Answer 6

As there are already a lot of good answers, I thought I'd just tackle the one bit I haven't seen addressed.

tldr: Drinking water and passing water can help remove excess heat in itself, disregarding the effects of sweat evaporation and benefits of avoiding dehydration.

Start drinking more before you plan to go out (12-24hrs), if you start fully hydrated then you start at the right place and that's less water to carry. If you think about how much energy it takes to heat up water, just the act of passing it through your body is going to remove heat.

I have no scientific evidence, but from personal experience it seems to be more important to steadily cycle water through me (camel backs are really handy as you can constantly drink little sips).

So all the time I'm drinking I'm bringing on cold and when urinating I'm releasing liquid warmer than when it went in. So this is less about hydration levels and more about heat removal.

Obviously I'm completely ignoring any heat the body might produce to counter act this process but seeing as you are hot to begin with, it works with homeostasis. As others have mentioned if you get headaches/stomach pain eat something and have some salt, don't drink large amounts of water in one go or you could end up with water poisoning, again camel backs are super handy. If you have to stop to drink, it discourages drinking and encourages large gulps when you do.

The Pseudo science

Since I had nothing to back me up other than experience, have some pseudo science:

The specific heat capacity of water is really high (4.186 J/(g °C)) So say you drink 1 litre of water (~1kg) at 20 degrees and lets say it is all heated to body temperature (~37.5) and then leaves your body via urine/sweat/breath.

Energy to heat that water =

4.186(J/(g °C)) * 1000(g) * (37.5-20)(°C) =73255(J)

Assuming the human body has a specific heat capacity of 3.8 (3.6-3.9) now what effect has that on a 50kg human body?

=-73255 (J) [as heat] / (3.8 (J/(g °C)) * 50000(g))

= -0.386 °C (decrease in body temperature)

From these rough calculations you can see you'll see a bigger benefit from this type of heat loss if:

• The water is colder
• More water is drunk
• The body temperature is higher
• The body mass is lower
• The body's specific heat capacity is lower, NOT saying you should try to influence this, it might as well be a constant but it's an interesting point as tissue types must differ so would benefit some body types differently even at the same mass.

One last thing, it might be psychological but if I have not drank much I find I can get colder/hotter more quickly maybe because I have lowered my body's specific heat capacity by not having enough water in me ;)