Marathon Training Update: Major Dehydration Problem

dehydrationLast Saturday (9/15) I was tired from a long week and lacking sleep and after a good 8 miles, I had to alternate walking and running the last 4.  But after good short runs last week on Tuesday and Thursday, I set off this past Saturday morning on another 12 mile long run with the hopes of doing the whole 12 miles without stopping to walk and hopefully in about 120 minutes.  Everything seemed to be going according to plan through the first 8 miles again and then things headed downhill.

Shocked by the Scale
Mile 9 was really tough and a short way into mile 10 I had to stop and walk.  I started running again after a minute or so but couldn’t finish the 10th mile without walking again.  From that point on it was about half walking and half running.  I finished the 12 miles in 139 minutes and was pretty disappointed.

When I got home, I decided to do something I hadn’t done before – I weighed myself before drinking anything.  Now I didn’t weigh myself before I left, but when I stepped on the scale I was shocked to see my weight 8 pounds less than average.  That’s right – I lost about 8 pounds during that 12 mile run!

I weigh about 160, so, we’re talking about 5% of my body weight.  Yikes!  No wonder I had trouble at the end of it.

Hydration Details
It’s not as if I didn’t drink anything beforehand or along the way.  I had an 8 oz glass of water, an 8 oz cup of coffee, and cereal with milk about an hour before the run.  Then I had another 4-6 ounces of water before I left.  During the run I stopped at 3 water fountains – the first at 5.5 miles, the second at 8 miles, and the third at 10.5 miles.  There’s no way to know how much water I consumed at each stop, but I would guess 4-6 ounces.

Looking back I can definitely see that I did not consuming enough fluids.  If you consider the water and coffee I drank a hour before was probably gone from my system before I left, that means I consumed between 16 and 24 ounces during the 12 mile run.  I live in the Tampa, FL area and it was a pretty comfortable morning (at least for our standards).  I ran from 6 AM until shortly after 8 and it was probably around 75 degrees with a slight breeze.

Confusing and Conflicting Recommendations
I’ve done quite a bit of searching online and it’s hard to find anyone who will give even a ballpark figure of how much fluid per distance or time is needed.  Where I have found recommendations they’ve included a huge range, like 5-12 ounces of fluid every 15-20 minutes, which if you do the math for a 2 hour training run could work out anywhere from 30 ounces to 96 ounces.  For a 4.5 hour marathon could be about a half gallon to almost 2 gallons.

That seems to be because running conditions vary greatly (heat and humidity), individual sweat rates vary greatly, and there are concerns both about dehydration and hyponatremia (caused by drinking too much).  In fact, many sports medicine doctors refuse to give any specific hydration recommendations at all and simply say the best rule is “Drink when you’re thirsty.”

If you do the math on the amount of fluid I lost Saturday… 8 pounds x 16 ounces per pound = 128 ounces + 20 ounce (est) consumed = 148 ounces.  Divide that by 12 miles and I would have to consume 12.7 ounces of fluids per mile to stay fully hydrated.  That sounds crazy! 

Then I come across this 2005 NY Times article which says, “This year, for the first time, the participant handbook for runners in the Nov. 6 New York City Marathon tells them how much to drink – no more than eight ounces of water every 20 minutes.”

Let’s go back to the chalk board… 8 ounces every 20 minutes… if I’m running 10 minute miles is 4 ounces per mile.  So, the NYC marathon says no more than 4 ounces per mile, but my body seems to be saying I need 3 times that.

What’s the Solution?
The first thing I need to do is start weighing myself before and after each run, so I know exactly how much weight I’m losing.  The second thing I’m going to do is try drinking more immediately before the run.  The third thing I’m going to is go back to running 3 mile loops around my house so I can set drinks out in my driveway.  This will allow me to drink at regular intervals, to drink Gatorade rather than water, and to know exactly how much I’m drinking.

Any thoughts?


  1. Live Intentionally » Blog Archive » Marathon Training Update: First Half Marathon - October 1, 2007

    […] Marathon Training Update: Major Dehydration Problem […]

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