Hydration and short runs

Hydration and short runs

February 16, 2018

The most abundant molecule found in any human body is water.  Water is essential to cells life, body temperature regulations, tissue moistening, organs protection, joints lubrication, waste flushing, minerals dissolution, nutrients transportation, etc.  Water is life!  Water is so important, popular beliefs will sometimes make you believe that one needs to “drink 8 glasses of water a day”.

Muscles at rest typically do not generate much heat.  Running on the other end decuples metabolic reactions and excess heat is almost immediate.  Even at a slow pace, heat is speedily produced, and core temperature regulation is triggered.  Sweat evaporation cools you down and your body starts to lose water.

Losing 1% of your body weight in water means losing about 10% of your physical capacity. Lose 2% of your body weight in water = 20% loss, etc.  Mild dehydration starts at 2%. 10% is considered severe dehydration. 20% is fatal.  Rest assure losing even 5% of your body weight in water is not a fun experience and should be avoided, even for trained runners.

Let’s do some math:

Sweat rates vary greatly.  An average sweat rate of 16 Oz per hour.

16Oz = 1Lb.

The average weight of a human being: is 150Lb.  

1Lb divided by 150Lb = 0.67%

In other words: a typical human running for one hour, under normal conditions, not replenishing water, is expected to lose 0.67% of his/her body weight in water.


This analysis defies popular beliefs.  Running for an hour without any hydration sounds like an ill recommendation!  

In our Kickstarter survey, we found 1 in 5 Casual Runner hauling some type of hydration even during short runs.  The number drops to 1.5 out of 10 with Experienced runners.  In other words, 8.5 experienced runners out of 10 take no hydration on short runs.  Why?  Because the loss of running-induced water has less of a negative impact than the burden of carrying hydration.  Running with hydration is just not as enjoyable as running without.

This information should come with a strong warning: untrained bodies and trained bodies react very differently.  Sweat rates and the effect of dehydration or over-hydration (risk of hyponatremia) are all different. Beginners should first learn to know how their own body reacts before stepping into the unknown.  Be smart, make decisions only based on your own specific situation!


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