5 Warning Signs of Heat Stress & One I Never Ignore

There are 9 symptoms of heat exhaustion according to the CDC but I will focus on a few early warning signs of heat stress that may appear before heat exhaustion occurs.  There is one that I never ignore.

1. Elevated heart rate
2. Headache
3. Dizziness
4. Unusual fatigue
5. Chills (I never ignore this one)

I have dealt with extreme temperatures both at my previous career as a rescue diver but also while bike racing in Northeastern summers which are so hot and humid.  The 5 symptoms listed above are early warning signs that the body is having a difficult time keeping the core temperature steady.  I’ve been in summer road races in 95 degrees with over 60% humidity and pulled out (from the winning breakaway a few times) when I felt chills. Heat stress was already taking hold. If you feel chills in hot weather do not ignore it.  You don’t have long until your life in danger.

CDC’s Warning Signs of Heat-Related Illness

Heat Exhaustion

1. Heavy sweating
2. Cold, pale and clammy skin
3. Fast weak pulse
4. Nausea of vomiting
5. Muscle cramps
6. Tiredness or weakness
7. Dizziness
8. Headache
9. Passing out

Heat Stroke

1. High body temperature (103 degrees)
2. Hot, red, dry or damp skin
3. Fast, strong pulse
4. Headache
5. Dizziness
6. Nausea
7. Confusion
8. Losing consciousness

You can see there is some overlapping but the most important thing to look for are any combination of those listed.  Getting out of the heat and doing anything to cool the body is essential.  Hydration is also key (if person is conscious, of course) in warding off heat-related illness. Dehydration inhibits the body’s ability to cool itself.

A new study from Penn State University set to find out the upper limits of the human body when it comes to heat and humidity.  They took healthy, young men and women, had them swallow a special sensor that measures core temperature, put them in a special environmentally-controlled lab and had them do various activities in different temperature and humidity ratios.

They found that previous guidelines regarding heat and humidity were wrong.  A 2010 study stated that 95 degrees at 100% humidity or 115 degrees at 50% humidity would be the point at which the human body could no longer cool itself.

The Penn State lab study found a much lower critical environmental limit.  88 degrees at 100% humidity or 100 degrees at 60% humidity.  Keep in mind that the test subjects weren’t running or doing anything strenuous.  They were only moving to simulate basic daily activities like cooking or eating.  So, if you’re exerting yourself above that, these critical temp/humidity levels would likely be much lower.

Living in Southern New York, I exercise in high heat and humidity all summer long.  The first hot days are the toughest because the body isn’t acclimated (this takes several weeks of exposure). However, even when I’m acclimated, I pay careful attention to my body and it’s warning signs/symptoms while I’m exercising.  I often have to reduce duration and/or intensity.  Sometimes I’ll even ride my bike indoors in the air-conditioning on really hot and humid days.

After a hot training ride, I’ll have an ice-cold Zenberry smoothie as soon as I walk in the door.  I make it with lots of frozen banana and blueberries to make it thick like ice cream.   This helps to begin cooling the core from the inside-out.  Then I take a cool/cold shower to further reduce my body temp.  I then continue to hydrate the rest of the day/evening.

We often greatly underestimate how much water we really need.  I know this because my smart watch tracks my hydration (I manually add the ounces as I drink) and the algorithm estimates my daily target based on the weather and my activity level.  After long rides I’m often surprised by the recommended fluid intake and struggle to hit the target (sometimes it’s 225-250 ounces!) before my day ends.

To sum things up, do not ignore your body.  Know the warning signs of heat stress and alter your activates when the temps are in the upper 80s with high humidity.

Thank you for reading.