Sunday, June 27, 2010

Sweat! Let's talk about sweat.

Got out this morning in what I called "Marshmallow Fumidity" it was so humid. No sun could penetrate this thick cloud of yuckiness. This was good, though! I wanted these conditions (75 degrees, 81% humidity) because this was the morning to test out how much I sweat in these conditions. I ran 6.67 miles in exactly 1 hour for a 9 min/mile flat pace, which is my base.

Here is the formula that I learned when I wrote my Beating the Heat, My Plan post. I didn't eat or drink anything during the run and didn't use the bathroom after or before the measurements. What is lost is purely through sweat, tears, and thermal energy.

Starting Weight 154.5
Finishing Weight 151
Total Loss 3.5
Calories Burned 667 (I burn roughly 100/mile)
Calories in Weight 0.2
Total Sweat Loss 3.3
Sweat in ounces 52.8
Ounces lost per mile 8
1 Liter of liquid 33.8 Ounces
My loss in Liters 1.56

Isn't this convenient!!! So had I known my sweat rate, and if I had a race today in these conditions, I would need to drink 1 cup of liquid per mile to keep my body @ a constant hydrated level, roughly. Fortunately NYRR races in the summer have water stations @ every mile.

But it all makes sense now! I was doing just that (drinking ~8 oz every mile) in New Orleans in April and ran a 1:56:xx Half Marathon in my second Half Ironman, which I still consider a VERY successful run.

What you sweat out of your pours is not just stinky H2O. You are also losing electrolytes (sodium & potassium). I had salt stains on my tri suit yesterday from the 3 hour ride in the heat. How much sodium was that and notice that I used both salt and sodium in the same sentence? Salt and sodium are two different things that both share sodium. Salt is sodium chloride, sodium is just sodium. Its not like you have table salt running through your veins. Table salt is just a crystalized form of sodium with about 100 other minerals involved, primarily chloride.

According to all of the articles on the trustworthy inter-webz, a normal average person can sweat out ~1000mg of sodium per liter of sweat lost. So for me, @ ~1.5 liters of sweat lost per hour while running, I could be losing ~1,500mg of sodium. Other than feeling tired and thirsty, I noticed no muscle cramping, but then again I was only out there for an hour. Tack on another hour, and I'd prolly bonk from lack of nutrition before the lack of electrolytes got me. I have never had an issue with cramping (knock on wood) and for the Half Ironman distance, I have raced them both hot and cool, and have never had issues other than not consuming enough calories.

I guess what I am going to take from this test is that I now know how much I need to drink per mile on the run in hot conditions to stay hydrated and to keep my core cool(er). I remember hearing a pro triathlete talk about how he keeps his core temp down on the run in the heat, and that is through the ingestion of cool liquids. Yes, dumping water over your head helps, but its only a temporary solution. Ever see them handing out ice @ aid stations? Call that your best friend and chomp that stuff down and wait a few mins. I did this down in New Orleans and I kept coming back to life over and over again.


  1. I can barely keep up on these posts! Love the high geek factor to these sweat rate posts.

    I'll have to try and calculate my sweat rate this week. I can't imagine having to consume 8 ounces of water every mile though. It seems like at some point my stomach would feel incredibly sloshy.

    PS: Maybe if you HTFU and stopped crying during the run, you would lose less fluid during the workout! haha :)

  2. oh ZING!!! hahahahahahaha!.....that was a good one.......

    I forgot about the sloshy effect.....buyer beware?

  3. Used the simplified nutrition method on the bike it!!! and goin with it for the rest of the summer. Also used your tip to eat every 30 minutes instead of the 60mins I was previously doing. Thanks.

    I've had to toss a couple of run hats due to the salt stain factor! Do you use some sort of salt tabs or replacement? Today I used the Nuun electrolyte tablets for the first time they worked well.


  4. Like the new layout Jon ... clean and easy to read!

  5. LOVE the new layout!

    Wow, that is pretty interesting stuff - but I am afraid of the sloshy effect too.

  6. Nice numbers...aren't sure exactly what they mean, but they look pretty!

  7. This is great. I was thinking about your last post on this wen I was out on the bike today. I had to pee when I left, but b/c of my sweating and despite drinking almost 42 oz of water, I never had the urge to go....sweating out your pee..try it, ha!

    I also can't imagine 8oz of fluid per would definitely be sloshing in my tummy.

  8. I used to get the sweat stains up until last year and sometimes the dehydration stomach cramping when it got really bad. Then, i found the powerade zero added a NUUN tab to it and just like that, no more sweat salt stains and no more stomach cramps. Now if i could get someone to follow me while i run and hand me ice cold water and cups of ice every mile, i'll be rockin it!


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