Wednesday, June 8, 2011

RUNNING 101 - Running in Heat & Humidity

With the hot weather here, I thought I'd post some information Hydration. The following information was borrowed from Anny Halleran as seen on Knol is a beta application available from Google.


Running in heat and humidity requires a different approach than running in moderate weather conditions. It can and will take a toll on a runner’s body if not adequately prepared. They both can have the same effect on the body, specifically the heart rate. Many people would probably not suspect humidity alone being the cause of a poor performance, but it can be. There are two general areas to consider in preparation for running in heat & humidity: (1) Hydration (2) Heart Rate.  


One of the most critical actions to take to prepare for running in heat and humidity is to ensure hydration.  Many runners think they are drinking enough and the bottom line is they are not. 

Hydration Basics 

  • Hydration begins days before the run.  Drink, drink, drink.
  • Hydration comes in more forms than water.  Drink water, drink soda, drink wine, but drink, drink, drink.
  • Hydration comes in the form of high water content fruits and veggies. Eat lettuce, watermelon, plums. But more importantly, drink, drink, drink.
  • Hydration is critical in 24 hours preceding a run.  Drink, drink, drink.
  • Fluids are best absorbed by the body cold. 40°F is ideal.  Regardless of the temperature of the beverage, drink, drink, drink.
  • Hydration is adequate when urine is clear.

How much fluid is enough? 

There is a simple method to calculate how much fluid is lost during a run. The result equals the amount of fluid to be consumed during a run to avoid becoming dehydrated. Use this method on a typical training run.  
  1. Weigh before a run completely naked.
  2. Track the amount of fluid consumed during the run.
  3. Weigh after the run completely naked. (Weighing clothed will skew results because of the sweat absorbed)
  4. Apply the following formula using the numbers gathered in steps 1-3:  
       Weight post run (#3) – Weight pre run (#1) + Fluid Consumed (#2) = Total Fluid Lost 
5.    Divide ‘Total Fluid Lost’ figure (#4) by the number of miles ran.
6.    Results (#5) are equal to the amount to be consuming per mile to avoid dehydration.  
Below is an example to show the math.  
    Weight Before
    Weight After 138.25 lbs.   
    Weight Lost or Delta 0.25 lbs.   
    Convert to Ounces 4.00 ounces (Delta x 16)
    Liquid Consumed 42.00 ounces   
    Total Loss During Run 46.00 ounces (Delta + Consumed)
    Loss Per Mile 9.20 ounces (Total Loss/Miles Ran)
Given the example above, this runner would most likely benefit from consuming approximately 10 ounces of fluid every mile to avoid dehydration. This figure will vary based on multiple conditions such as weather and training pace.  

What to drink on a run?

A runner has to learn to listen to their body. If water is sloshing around in the stomach, throttle back on the intake because it is not absorbing as fast as it is being consumed. Remember, warm water will not absorb as fast as cold. Always prepare. If running during hot weather, add ice to the fluids being taken on the run. This will allow for better absorption.  
Another point to consider is the stomach’s reaction to different fluids. Some runners prefer Gatorade to water, others can not stomach it.  Literally, it can make them ill and vomiting fluids not only impacts hydration it is physically exhausting and requires energy the body needs to use elsewhere.  Always experiment with fluids during training and be prepared to race with what is required and works on a personal level.  


Here are the statistics of what these two elements can do to impact your running: 
  • Temperatures between 60-75°F will increase heart rate (HR) by 2-4 beats per minute
  • Temperatures between 75-90°F will increase heart rate (HR) up to 10 beats per minute 
  • Humidity levels between 50-90% will increase heart rate (HR) up to 10 beats per minute
When the two elements are experienced together the effect is magnified.  
Let’s look at a typical Tennessee summer day and do the math on a 39 year old woman for an example. [To understand how to calculate your target heart rates, see RUNNING 101 – KNOL 2] You are going for a run outside and the weather is hot and sticky, here’s what it can do to your body… 
    Running HR in Moderate Conditions (60°F/30%):   140 beats per minute * 
    Temperature: 90°F (Add 10 beats/min for heat)     +10 
    Humidity: 70% (Add 10 beats/min for humidity)     +10 
    New HR in Extreme Conditions:                          160 beats per minute 
    * 140 beats/min is 75% of Maximum HR calculation for 39 YO Woman.  
The New HR of 160 beats per minute is approximately 87% of your maximum HR threshold. That percentage is very close to the High Risk Zone or Redline threshold of 90%.  Running at this level can be dangerous.  In this zone maximum physical effort is being exerted. The runner is breathless and the heart is pumping very hard. This level of activity can not sustain for very long without possible serious side effects. This is a sprinting zone, possibly a zone that would be hit during speed work.  It is not a zone intended for running any long period of time.    

Why does this happen? 

One of the body’s core functions is temperature regulation, maintaining an average 98.6°F. In higher temperatures the skin absorbs the heat. To help keep the body in a normal state, the heart's oxygen output is diverted via blood flow to the skin to help dissipate the heat the body is collecting. When oxygen is diverted to another system of the body versus the muscles, a runner has less energy to burn running. If a runner continues to run at the same pace in these conditions, the heart and lungs have to work hard to try to compensate for the needed oxygen for both systems to work.  This results in early exhaustion.  

What about humidity?

Studies in Japan on ambient humidity result in the same effect because humidity prevents the body’s sweat from evaporating. Sweating is the body's method of keeping cool. When it is not functioning properly again the blood flow is diverted to the skin. This study shows that hot, humid environment at sea level is as much incapacitating as is hypoxia at high altitude. [Ref. Journal of Applied Physics, Vol. 40, Issue 2, 206-210] 


Most runners understand the impact of running at high altitudes and compensate their training, runs and races to prepare for it.  Many overlook the impact of heat and humidity, especially humidity. Then there are others unaware of the impact heart rate can have on results because there is no indication of a problem. Whether or not a runner is experiencing any negative side effects is irrelevant, because understanding and training to heart rate has the potential to improve overall performance.  
There are several heart rate monitors on the market right now for this specific reason. They track a variety of things: heart rate, calories, mileage, timer, interval timer, etc.  The basics needed for an HRM to be effective are heart rate and interval timer. Adding more or fewer features is a matter of personal preference. 

What are the training methods?

There are two basic methods to managing heart rate during a run.  What is important to note is that methodology is all about trial and error. What works for one runner will not for another. Finding what works at a personal level is the key to successful training to heart rate.   
One method is to reduce pace. It’s very straight forward, clear and simple.  If a runner is hitting an 8 minutes mile, reduce it to a 10 minute mile and monitor heart rate. If that is not enough, reduce it to a 12 minute mile and monitor heart rate. There are many examples to follow, such as the ones listed in Jeff Galloway’s training plan, which can be found at  He suggests adding 30 seconds per mile slower for each 5 degrees of temperature increase above 60°F. This same logic would apply to humidity.   
The other method is for runners who use a run/walk/run method of training and/or racing. This method reduces the interval of run/walk.  For example, if a runner’s current interval is 4:1, or 4 minutes running and 1 minute walking, then the object is to reduce the run interval. It could be reduced to 3.5:1 or even 3:1. The concept is the same as reducing the pace. The walk interval allows the heart to recover resulting in a lower heart rate during the run intervals.   

How does running slower impact overall performance?

Oddly enough, training to heart rate and running slower can actually improve overall performance and give better results on race day. This is the basic concept: Maximizing the development of the Aerobic system is done by exercising at/or below the Aerobic Threshold. In essence, running at a lower heart rate threshold (60-70% of maximum HR) will in increase the threshold tolerance for pace, time and distance. Over time this will improve overall performance in all three areas.  The results are a faster 5k or the hitting a new PR for distance (i.e. same pace taking a runner 10k instead of 5k).    
Training to heart rate is essentially training to exercise the capacity for faster runs, longer runs or both. Bill Wainright has an excellent article explaining all of the physiological details on this at  
Listed below are some important items to know and actions to take when running in heat and humidity.  


  • Chills
  • Light-headedness
  • Dizziness
  • Confusion 


  • Stop running immediately
  • Seek shade
  • Sit down
  • Drink fluids
  • Call for help (stop a stranger if necessary to help in taking these actions)
Editorial Commentary: In regards to this KNOL, I run to keep my heart rate in the 160's, the lower the better.  During my walk periods I focus on relaxing and breathing to reduce my heart rate to the 130's.  As I deal with hills, humidity, heat, etc. I have to watch my heart rate because it will increase rapidly.  While it's ok run at a higher rate, it does not allow me to stretch my system and improve over time.  So I have actually had to take my intervals down to 3:1.  
In general, running is a passion for me. I learned a lot by running with The Leukemia & Lymphoma Society’s Team in Training (TNT). I started running in March 2008 with zero experience. I ran my first 5k in less than 4 wks. Then I trained with TNT for the Nike Women’s Half Marathon in San Francisco to take place November 2008. I ran in honor of my grandfather who was fighting lymphoma. As I began my training, I learned many lessons hard and fast. I share these lessons on my blog at You can read about my progress and other running lessons there.  
Training is for preparation.  It is to stretch our systems - cardiovascular, muscular and mental - to prepare us for future runs.  There are a lot of methodologies to training and ways to go about preparing your body for a half marathon or marathon or even an ironman triathlon. The most important thing to know is that you have to find what works best for you.  It's no one else's race but yours. Only you know how to prepare your body and mind the best. The only wrong decision you can make when it comes to training for a run is to not do it! So get out there!  KEEP MOVING FORWARD!!! 
Medical Disclaimer:  Posted information is not medical opinion. It is all based on personal experience and research. Seek the advice of a physician before beginning any physical exercise program. If you are experiencing any of the symptoms discussed, please speak with a medically licensed professional.

1 comment:

Karen77 said...

Thanks for this great post, Steve. Here in Chicago we have experienced record highs this week in the high 90's with full humidity. It's been a very difficult week for a lot of us runners as our bodies are not acclimated to the heat yet. It helps to know a lot of this!