Nutrition & Weight Loss

Effects of Dehydration

Effects of Dehydration

We’ve all heard how important it is to stay hydrated, instead, let’s look at what happens to our body when we lose fluids while training. A number of factors can speed up the rate of water loss including hot and cold temperatures, high humidity, altitude, caffeine, excess body weight, restrictive clothing, illness, and prolonged exercise.  

Marathoners, and other non-endurance athletes like football, soccer, and basketball players can lose several quarts of water during an event lasting longer than one hour, so fluid intake is critical for optimal performance. A one quart loss in sweat raises your heart rate by eight beats per minute, which places stress on the cardiovascular system, increases core temperature, impedes the body’s cooling system, and affects all metabolic pathways. This loss causes the blood in your circulatory system to get thicker, making it harder for the heart to pump, and reducing your ability to regulate body heat. A slight loss of water can have physical, mental, and emotional consequences with a mere two percent loss in water weight. What seems like an insignificant number, this can compromise your judgement by as much as twenty-five percent.

So how much water do we need? First of all, thirst should not be an indicator.  At this point you may already be about a quart low on fluids. The best rule of thumb is to gauge your fluid intake by your fluid output. In other words, the frequency of urination, relieving yourself about every 1-2 hours is ideal. It should also be clear, not yellow.

Here’s a look at hydration guidelines from the American College of Sports Medicine – before, during, and after an event:

Daily – So many variables to consider, try to follow the fluid loss/intake rule.
Pre-Event – 18 to 24 ounces 2 hours prior, and 15 to 20 ounces 20 minutes before.
During Event – 6 to 9 ounces every 20 minutes.  During intense exercise lasting longer than one hour it is recommended to ingest carbohydrates at a rate of 30-60 grams per hour.

Post Event – 18 to 24 ounces (with a carbohydrate/electrolyte replacement)


Boone A Ebel

Specialist in Performance Nutrition


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This post was written by:

- who has written 8 posts on Trail Running Club.

After graduating from Western Illinois University in 2004, Boone furthered his career in the health & fitness industry and owns a training and coaching business in Arizona. A lifetime runner and outdoor enthusiast, Boone enjoys competing in endurance events on both road and trails. When he is not training clients, odds are you can find him on the trail somewhere around the Southwest.

Since 2009, Boone has 33 Top Ten finishes including: -1st Overall 2014 San Pedro Park 10K -3rd Overall 2014 San Luis Obispo Marathon -4th Overall 2014 Oakland Marathon -2nd Overall 2013 Tucson Half Marathon -1st Overall 2013 Pass Mountain 12K (CR) -3rd Overall 2013 Canyon de Chelly 55K -4th Overall 2013 Santa Rosa Marathon -7th Overall 2013 Phoenix Marathon -2nd Overall 2013 Desert Classic Marathon -1st Overall 2013 Rose Bowl 10K -2nd Overall 2012 Mesquite Canyon Trail 50K -4th Overall 2012 Lost Dutchman Marathon -2nd Overall 2012 XTERRA McDowell Mountain 15 mile run -6th Overall 2011 Zane Grey Highline Trail 50 Mile Endurance Run -4th Overall 2011 Old Pueblo 50 Mile Endurance Run -1st Overall 2010 Sedona 50K -1st Overall 2010 Flagstaff 50K

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