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Monday, May 31, 2010

Heat management or how to race when it's hot out.

It's getting hot out. Based on the theory of Global warming, it's getting hotter. So whatcha gonna do? Ok, maybe you can deny Global warming, but you can't deny the summer heat that is about to take place here in Mid-America. I'm talking 90s (Fahrenheit) and an occasional trip into the 100s (32 to 37+ degrees Celsius).  There are several helpful tips to maximize your racing performance during high temperatures and they all involve heat management techniques listed below. 

Train in Race-Day Conditions

The first and possibly one of the most important tips is to train/exercise in the high temperatures that you expect to encounter on race day.  The goal is heat acclimatization,  and this will improve your ability to tolerate higher temps, feel more comfortable, and most importantly be able to race better. A large portion of adaptation can occur within 3-4 days, but total effects are realized in 10-14 days.

Some really cool stuff happens in your body during this period. My personal favorite is plasma volume expansion resulting from increased plasma proteins and increased sodium chloride retention, ranges from +3 to +27%, and is accompanied by a 15-25% decrease in heart rate (Armstrong 1998). Cool stuff huh?

Here's why plasma volume expansion is my favorite effect of training in the heat:  after a sudden exposure to a large and sustained temperature gain during a racing weekend, two or three days later, I found that I had gained 5-6 pounds. The reason for this was a physiological adaptation to heat (or that 5 pound burrito from Chipolte's).  This weight gain comes from water weight in the form of increased plasma volume, which will be used for increased sweat production for cooling purposes.  Weight watchers take note:  plasma volume is a healthy weight gain; performance effects are diminished as dehydration occurs (Cheung and McLellan 1998).  

 The Multiple Reasons for Proper Hydration

My second tip is as important if not more and is just a little bit obvious: WATER! It's by far the biggest performance enhancer out there (and it's totally legal!!!).  Our body's are largely composed of water, about 50-60% of our total mass, and water plays critical roles in cooling, blood circulation, respiration, and digestion, among many other processes.   Your body knows that water is extremely effective at keeping you cool, which is why you sweat.  It's your body's natural cooling mechanism to maintain a homeostasis.   But as you perspire, you have to replenish the loss of water and electrolytes.  It's important to note that the thirst response is slow compared to the speed that dehydration can occur while exercising in high temperatures, and therefore it is best to drink before becoming "thirsty"  In addition, you can help out your body by using the evaporative properties of water the same way your body does. 

There is a ton of research to describe all the different aspects of this topic, but for pithiness I have gleaned the following rules regarding proper hydration: Drink H20 until your urine is no longer dark yellow, but instead is lightly colored. Do not drink so much that you are peeing a lot and your urine is water clear (Water intoxication is caused when sodium levels drop below 135 mmol/L when athletes consume large amounts of fluid without electrolyte additives). For short criteriums (less than 1 hour) I think you can get away with 2 bottles of plain iced water (along with a normal healthy diet). For road races I strongly encourage a electrolyte to powder such as "Hammer Endurolytes Powder", or "Nuun",  to reduce cramping and some energy foods such as "GU" (I consume 2/hr). Drink one bottle every 30-45 minutes if possible.

But as I mentioned above, water on your skin and clothing can be more effective than sweating alone.  Spray water on your head, back and thighs. Pre-race pre-wet your jersey, shorts and hair (not groin area or shoes because of risk of rash and wet shoes are heavy rotating objects).  When combined with your circulatory system, the external water will produce a heat exchange, just as it does when it evaporates through perspiration.  Additionally, it's valuable to note that occasionally flushing salt deposits from clothing and skin with fresh water facilitates evaporation by effectively lowering of vapor pressure the surface fluids there (this would have greater importance for long events where salts can build up from evaporation).

Consider starting with some frozen water as well.  For criteriums, put ice packs in zip locks or frozen water bottles or frozen sponges in your jersey pockets.  Socks, nylon stockings or jersey pockets full of ice can be helpful as well, stuffed in jersey pockets and hung around the neck or stuffed in the helmet vents during extreme temperatures.  If you use the ziplock bag, dump the melted water down you head/back if possible.   It's nice if your frozen water can do "double duty" - that is - provide cooling and later a drinking supply (in the heat, ice will melt rather quickly).

The reason for wetting your clothing is that water is 25 times more conductive than air, and as the water evaporates from your clothing/skin, the captured heat is removed with the water.  (cooling towers efficiently cool large buildings using these principles).   As an illustration of the effectiveness of evaporative cooling, consider the results from the following simple test done with canteens covered with water soaked fabric covering versus canteens with dry fabric covers with only 3 hours of temperature exposure:
Starting Water Temperature (both containers): 74 degrees F
Air Temperature: Varied; between 98 and 101 degrees F
Ground Temperature (in direct sunlight): 119 degrees
Water in Plain Canteen after three Hours in Sun: 117 degrees
Water in Canteen with wet cover, hung in sun but in breeze: 75 degrees
Evaporative cooling produced a 42 Fahrenheit degree difference in the interior water temperatures (23.4 degrees Celsius difference)! 

Now imagine that the water inside the canteen is your blood and vital organs.  You can further increase the rate of evaporation by riding your bicycle because you will create air currents that constantly lower the vapor pressure at the immediate surface area of the water.  Wind plus water equals cooling.   Pre-wetting your clothing can temporarily save  (or extend) body fluids and can increase your stay-time to exhaustion during a heat stress event.   Water has some amazing properties for heat management.  For example:  water temperatures below 70 (21.1C) degrees can actually remove body temperature faster than the body can produce it.   Air cooling doesn't compare to the cooling effects of water.  While being exposed to 50 (10 C) degree air temperature isn't generally dangerous;  being immersed in 50 (10 C) degree water can quickly become life threatening. Such are the effects and power of water via conduction and evaporation.  Therefore keeping your tight fitting clothing wet can produce a huge cooling effect (with lower levels of humidity).  A loose flapping jersey will not transfer heat from your body nearly as effectively as a wet skin suit.   

Another trick is to consume an ice slurry before racing. This reduces your core temperature and as a result increases your body's heat capacity and (most importantly) performance during high temperatures. 



Some other heat management tricks:
  • Wear as little clothing as possible during racing or to wear light colored clothing that is designed    to be breathable and wick moisture away from the body. Again, adding water to the clothing will significantly increase the cooling through both conduction and evaporation.   I personally don't wear gloves, but if you do wear them, wet them.  Generally, I recommend not wearing large sunglasses or ANY if the conditions permit (they block heat transfer and evaporative cooling).  An exception may be when the face is exposed to direct sunshine (they can reduce radiant temperature in this case).    If at all possible, try to avoid warming up on a trainer.  Stay in the shade or  air-conditioning prior to racing and warming up.  Consider a very short warm up (again wet your clothing), then drink the ice slurry. 

Click this link for greater information on thermoregulation, the body's basic responses to heat and humidity, fluid loss, clothing for exercise in the heat, and heat acclimation.  It's a pdf article written by Matt Richardson, and Stephen Cheung, entitled The Basics of Thermoregulation.

Some additional information:  A person should cease exercise if they begin experiencing heat exhaustion symptoms.  Symptoms include:  fatigue or weakness, nausea, headache, dizziness and can lead to worsening and additional symptoms.  Generally, once a person has experienced a heat injury their body is more susceptible to heat injury again.  (Perhaps this is the body's response to rising core body temperature to prevent it from overheating again by  making exercise unbearable).

Although training in heat is necessary for adapting to heat, there must be limits and restrictions.  I can not quantify this level (variables include environmental temp., humidity, physical work load, cooling techniques used, subjects level of adaptation to heat environments).    High humidity combined with temperatures exceeding  >90 degrees Fahrenheit (32.2C), and rigorous physical activity can be potentially dangerous.  Duration and intensity of exercise should be shortened with higher heat index numbers (temperature/humidity rating).  .  I have read, believe, and even have written an in depth article that shows that high intensity of training can trump duration of training alone for athletic improvement or maintenance.  Shorter intense workouts can reduce the total exposure amounts to heat stress which can lead to heat injuries.   With higher temperatures and humidity it can also be helpful to split up a workout to a heavier exercise load (intensity and duration) in the cool of the morning, and a light short workout (or exposure event) in the high heat environment in the mid to late afternoon.
 


Remember, cooler heads prevail...... literally!  Stay wet my friends!




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5 comments:

  1. You have the best blog posts of anyone on the internet. And I read tons of blogs.

    ReplyDelete
  2. Thank you for writing these, and sharing them, and sharing them again later :) You may have heard this already, but you should write a book!

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