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Heat Related Illnesses and Running

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Question: What happens to your body when the heat gets to be too much?

When I first started to research this topic, I thought it was going to be fairly cut and dry.  Define the heat related illness, describe the symptoms, and discuss the treatment.  That is how it was going until I started to read Dr. Timothy Noakes and his much more scientific explanation of what happens to the body when running in the heat.  My world of heat cramps and heat exhaustion as I knew it, quickly got turned upside down.  Completely. 

Conventional Wisdom

First, let me describe what we commonly hear about heat related illnesses.  There are three degrees of heat related illnesses: heat cramps, heat exhaustion, and heatstroke. Heat cramps can easily be treated while heatstroke is much more serious and life threatening.

The actual cause of heat cramps is unknown, but it is widely believed that they are caused by electrolyte deficiencies.  In the heat you sweat more and therefore, you lose more sodium, potassium, and magnesium.  The athlete is dehydrated.  Heat cramps are muscle spasms that can be painful, involuntary, brief, and intermittent.  Fortunately, they can be treated easily by slowing down and replacing fluids.

Heat exhaustion is a little more serious than heat cramps.  With heat exhaustion the body temperature can rise above 100.4 degrees Fahrenheit, and the person may experience dizziness, vomiting, weakness, headaches, goosebumps, and profuse sweating.  If an athlete suffers from heat exhaustion, he/she can be treated at home by elevating the feet and drinking an electrolyte drink.  As long as the individual can maintain proper hydration, there is no need to go to the hospital.

Heatstroke is the most serious heat related illness.  The symptoms are similar to those of heat exhaustion however, they can progress to affecting the central nervous system.  If someone is suffering from a heatstroke, they may be disorientated, have an unsteady gait, experience loss of consciousness or seizures.  Other symptoms include cessation of sweating, rapid or shallow breathing, a rapid heartbeat, and elevated or lowered blood pressure.  A heatstroke is considered very serious and should be treated so.  Get out of the heat, begin cooling the body with damp sheets/blankets, and seek medical attention ASAP.

That is what we commonly hear and what is predominantly out there on the running websites and blogs.  But what does the science community have to say?

Unconventional Wisdom

I always find it interesting that during the earlier years of marathoning, there were no aid stations, athletes didn’t have a handheld, and they would even brag about how far they were able to run without having a drink.  I think that this quote from Dr. Noakes sums up how the expectations of marathoning have changed:

When I began running marathons in 1972, there were no medical tents at the end of races. What was more likely was that runners would have to present a medical clearance indicating that they were fit to start the race.  Once you started, you were essentially on you own.  At that time, heatstroke was the only serious heat illness that was recognized.

Dr. Noakes takes a very scientific approach to discussing heat related illnesses.  Whereas we commonly hear that dehydration is the cause of heat cramps and heat exhaustion, he has a very different hypothesis.  As I attempt to explain this, please remember that I am a Spanish teacher and NOT a science teacher…

Apparently, there are no studies that actually prove dehydration causes heat cramps or heat exhaustion.  There are, however, studies that show there are no differences in “serum electrolyte concentrations” and plasma volume between runners who developed cramps during a marathon and those who did not.  In other words, muscle cramps are not caused by an electrolyte imbalance.  The more scientific and modern hypothesis suggests that instead of dehydration, muscle cramps are the “result of alterations in spinal neural reflex activity by fatigue in susceptible people.”  I’m not exactly sure what that is saying, I just know that, according to some scientists, dehydration does not equal heat cramps.  Heat cramps come from being tired.

So what about heat exhaustion?

Dr. Noakes groups heat exhaustion and heat syncope together, which means the athlete collapses during or after exercising in the heat.   He suggests that heat exhaustion is not a true heat disorder caused by a rise in core body temperature during exercise.  Instead, when an athlete collapses, it is caused by a drop in blood pressure that comes with the cessation of exercise.

Let me try to explain (all information is from The Lore of Running):

Studies have shown that rectal temperatures are not abnormally elevated in people with heat exhaustion or exercise-associated collapse.  Meaning their body temperatures are within normal range and similar to those other athletes who did not collapse.  Also, (and I find this to be quite interesting), 85% of those athletes who collapse (which would be defined as heat syncope), do so after they have stopped exercising.  If they had been suffering from heat exhaustion, they would have collapsed during exercise, not after.  It is instead the stopping of exercise, which leads to a drop in blood pressure, that causes the athlete to collapse.  Not heat exhaustion (or dehydration).

In summary, “… there is no evidence to suggest that dehydration of the levels present in endurance athletes exercising under more moderate environmental conditions poses any major health risks or that it even predisposes to heatstroke.”   So why do we often hear so much about dehydration being the cause of heat related illnesses?

As someone who has run a 24 hour relay event in 100 degrees, seen people collapse, and experienced one of the hottest Boston marathons ever, it’s crazy for me to think of heat cramps and heat exhaustion as Dr. Noakes explains them.  Did dehydration play a much smaller role in my DNF than I originally thought?  I have no idea but I find the other explanations of these heat illnesses to be very compelling.  I plan to do a little experimenting with hydration come June and July, but would be interested to hear what you all have to say about this alternate hypothesis.  Thoughts?

Happy Trails and Happy Running,


Lindsay getting ready for Boston 2012

At least I stuck to my motto

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