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1766 Views 7 Replies Latest reply: Dec 6, 2007 8:11 PM by RunForFun001
TedAndresen Amateur 247 posts since
Dec 14, 2007
Currently Being Moderated

Dec 20, 2007 10:39 PM

Weight loss per mile in hot versus cold weather?

Do you lose about half a pound per mile whether it’s hot and humid or freezing cold?

Does anyone who weighs themselves before and after and runs in close to freezing temperatures observe the same weight loss per mile?

I weigh myself on a precision scale (+/- 0.1 lbs) just before I begin my morning run and right after I get back and dry off. Now that the wet bulb (WB) temperature has dropped below 60F I’ve been able to compare the weight loss per mile that I experience in cooler weather with my weight loss per mile when the WB is above 68F.

I found something on the Internet that indicated that a person would lose about 350 gm of water through exhalation of water vapor a day. Oddly enough it would take about 2000 Kilocalories to evaporate 350 gm of water. Two thousand is near the average caloric intake of a person per day, so maybe that is the way that the body sheds heat and sweating is just an additive technique that the body uses to shed excess body heat during strenuous exercise.


The calculation in the paragraph is incorrect. It should be about 200, not 2000 kilocalories. So that it not the only mechanism the body used to dissipate its 2000 kilocalories per day. Radiation and evaporation are others.

[http://This message has been edited by TedAndresen (edited Dec-06-2007).|http://This message has been edited by TedAndresen (edited Dec-06-2007).]

  • kudzurunner Rookie 525 posts since
    Dec 6, 2007

    Since I drink water during all my warm weather runs here in Mississippi, I can't be sure of how much water weight I lose.  My record is about five or six pounds158 before run, 152 after runand that was WITH a couple of pints drunk during an 18 miler on a 75 degree day.

    I'm quite sure, anecdotally speaking, that I lose less water weight than that on a 45 degree day.  I say this because I can run up to 15 miles in such temperatures WITHOUT drinking any water during the runmy water is always stowed ahead of time by the side of the roadand without suffering noticeable adverse consequences.  If I tried that on a warm day--well, I have tried it, and I clearly start to notice problems around 9 or 10 miles, which is to say around 80-90 minutes.  HR rises, I slow, I just know that I'm dehydrated.

    Also speaking anecdotally, I've done the before/after weigh-in on cool days and been surprised that I'm only down a pound or two when I've drunk two pints during a 15 miler.

    Hard to work thumbnail calculations, but suppose I said that the difference in expended water between a 75 degree day and a 45 degree day was....3 pounds over 15 miles.  One pound over five miles.  Two-tenths of a pound per mile.  Is that useful?

  • JasonsDrivingForce Rookie 513 posts since
    Sep 30, 2007

    I lost 8 pounds(156-148) last year during the Charlotte Marathon. It was 22 degrees at start time and I naively thought I could get through the whole race on 44 ounces of Gatorade. The problem was that it was so cold I actually had to wear long thermal under wear in addition to my running tights and long sleeve shirt.

    I was sweating a whole more than I realized and it caught up to me at mile 22. I had full lower body cramps and severe dehydration for the next 4 miles(1 hour). I drank about 1 gallon of water in that 1 hour and I still lost those 8 pounds.

    Conversely, I did a 23 mile long run in 30-40 degree weather(Shorts and singlet) and I drank 88 ounces the whole time. I only lost 1 pound the whole time and I completed the 23 mile training run about 10 minutes faster than I completed the 22 miles of the marathon.

    I think it all depends on how well hydrated you are. For me, if I loose more than 3 pounds I know I am getting dehydrated.


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  • angrek Amateur 127 posts since
    Aug 14, 2007


    Originally posted by TedAndresen:

    Does anyone who weighs themselves before and after and runs in close to freezing temperatures observe the same weight loss per mile?


    I live in Tampa and, from my own observations, I sweat a TON more when it's hot and humid here. My shoes this summer were still wet the next day up until the temps started dropping last month. Days when it was 90 and the heat index was triple digits it just poured off me. We're in the mid 60's right now and I'd bet that I sweat maybe half as much if that running at the same perceived exertion level. I'd have to weigh myself to be sure but I know I'm nowhere near at drenched as I am during the hot months.

  • nocknee Rookie 127 posts since
    Dec 14, 2007

    Without consulting my training log, I've observed that my net rate of sweat loss varies by a factor of at least 2.

  • RunForFun001 Pro 626 posts since
    Jan 25, 2007

    Not consitently - but ...

    I have lost up to 12 pounds in Summer on long runs - but more often 6-10 pounds

    In cool fall weather (40-50F) I will only loose 3-6 pounds

    In really cold winter (-15F to 0F) I usually loose 4-8 pounds

    I ran a 16 miler on the TM on Wednesday and lost 8 pounds with drinking 60 ounces of water.

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