Know Your Sweat Rate, and Finish Your Races Strong

Normally we focus on our sweat rate during those hotter months, but it is something you need to keep in mind when you’re running in the Antarctic Marathon as much as at Badwater.
Knowing your sweat rate can be the key to avoiding some of the most debilitating and indeed deadly conditions you can experience when running Ultramarathon distances, such as dehydration or Hyponatremia. Keep in mind that when you sweat you are losing electrolytes as well as fluid.
Measuring your sweat rate is fairly simple; basically weigh yourself before and after an event. Add the weight of anything you consume during the run to the difference, and you will have the weight of fluid that you have lost as sweat during the run (assuming you didn’t pee, bleed or vomit!). The volume of fluid you lose is equal to 1 litre per kilo of weight lost. Then just adjust for the time you were running to give you your rate (so if you lost 1.5litres in 2 hours, your sweat rate is 750ml per hour).
This figure is not definitive for you as it will vary dependent upon conditions, both physiological and environmental. The most noteworthy of these are temperature and humidity. Your body sweats as a means of cooling your body, and is most effective when the sweat evaporates from the surface of the skin, rather than dripping off or being absorbed into clothing. 
Obviously you can’t do much about the environmental conditions, other than trying to run in the shade or out of the wind (and these actions can make a significant difference to your sweat rate, especially when you’re running for 4hours plus). Where you do have control is on your clothing choices and the key considerations should be on the type of material, colour and how closely it fits.
So it is important to calculate your sweat rate under a variety of conditions, and to log these so that you can understand how your body will react during races. When you have an appreciation of your sweat rate you can plan your race strategy more effectively and hopefully get you to the finish feel sharp and strong.
Happy Running!
Andy
"My advice is that you should use your brains more and train less."  - Yiannis Kouros
Training 21-10-2010 (Hill repeats on trails)
Training 23-10-2010 (28.4km Hill trail)
Training 24-10-2010 (32.1km Trail)
Training 26-10-2010 (Hill repeats on trails)
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