Heat Kills: How to Survive Your Marathon!

By Dr. Jon Hooper, Medical Director, Tamarack Ottawa Race Weekend

Ok, the title is a bit dramatic, but this is coming from a guy who has treated thousands of runners with various heat related illness. If not prepared, a hot day can make your marathon day miserable, slow, and potentially make you ill.

Race weekend is at the end of May: the weather can be cool or it can be very hot. You have been training in the cold and even a moderate temperature on race day may affect you.

If you are like every other runner out there you are reading this and saying “it won’t be me who gets sick.” I can’t tell you the number of times I have heard that. If the illness thing doesn’t worry you maybe the fact that overheating will affect your performance will.

The basic principle behind heat illness is that you are producing more heat than your body can get rid of.

The harder you run, the more heat you make (“picking up the pace” significantly during a race will obviously generate more heat than a slower training pace). The bigger you are, the more heat you make (hence guys are usually more at risk).

There are limited ways your body can get rid of heat:

  1. Radiating heat to the environment – This obviously will not work well if the temperature is high as there is less of a gradient between you and the environment. What you wear will also make a difference. Clothes can keep the heat in; hence loose, light coloured, breathable clothes are best. A visor will help keep the sun off our face.
  2. Sweating – When sweat evaporates off your skin you lose heat. Sweating is less effective if the environment is hot or humid. Sweating is impaired if you become dehydrated. The more dehydrated you are the less effective your body is at losing heat. The message here is clearly don’t become dehydrated (more on this below). Having said that it is very possible to overheat despite adequate hydration.

We are all different in our abilities to lose heat. Some bodies are well adapted to losing heat, and others are not. However with training we can all get better. There are all sorts of training plans out there, without getting into all the specifics I would highly recommend that in your training you do spend some time running at race pace (to help your body adapt).

This next bit is key!

One of the issues with spring marathons is that you may have spent countless hours training but at a much cooler temperature (and less humidity) than Race Day brings. Acclimatization is one of the body’s best defenses against overheating!

It takes 10 to 14 days to fully acclimatize to new temperature and humidity. That is fine if Mother Nature co-operates and provides Race day conditions for a few weeks before, but don’t bet on that. One option is to assume it will be hotter on Race Day than during your training, so in your last few weeks of training overdress a bit. Obviously you don’t want to overdo it and become ill in training but you can gradually change what you wear so that you are a bit uncomfortable (remember you will need to increase your fluid intake so as not to become dehydrated). Yes it is gross coming home in sweaty clothes, but it is worse to have a terrible race day.


During the Race

Pouring water over your head and body can be an effective way of cooling. Grab a glass of water at every aid station and pour it on yourself (every aid station). And don’t forget some to drink as well. Use sponges if available. If you have family and friends along the course watching, get them to bring ice cold water/sports drinks that you can pour over yourself or drink (if you plan on winning the race this may disqualify you). If it is hot at the start then drink cold fluids prior to the start. Bring some ice-cold water that you can pour on yourself just prior to starting.

If you know it is going to be hot (or hotter than you are used to) then don’t wait until you feel hot (too late): prevent it by using all these suggestions. If the thought of getting sick/dying doesn’t worry you consider the following – athletic performance decreases as you get hotter, you will finish faster (and healthier) with an ounce of prevention.


Other Factors

There are a number of medications that can predispose one to overheating, if you are on a prescription medicine ask your doctor if it puts you at risk. Some non-prescription drugs can also affect heat loss, with cold medications containing some of the common culprits (ephedrine is one common offender).

Having a cold will also affect your ability to control your temperature. If you have a cold or are just getting over one on Race Day then you may want to adjust your goals for that day.

Some athletes take anti-inflammatories  (NSAIDS like Advil, Naprosyn, Motrin, Celebrex) pre-race to prevent aches and pains. These do not put you at increased risk for heat illness but they can make it worse if you do get it (same goes for acetaminophen (Tylenol).


What do I do if it is smoking hot on race day?

Hot and humid weather increases the chances of dehydration, heat illness, and visiting the medical tent (not good). Taking precautions can make your day much more pleasant.

  • this is not the day to try for a PB, relax, enjoy the race
  • you will need to increase your fluid intake
  • when passing a water station you can always take one cup to drink and pour another over your head to cool down
  • dress appropriately (light weight, light colored clothes, use a visor)

If you do not feel well during or after the race please seek medical attention.

Read Part 2 of this article: Why the Big Fuss Over Hydration?

Dr. Jon Hooper is the Medical Director of the Ottawa Race Weekend and an Intensive Care Physician at Ottawa’s Civic Hospital.