Wednesday, May 30, 2007

What's Your Rate?

When I race and train I stink up the course... literally. Step by step I'm slinging sweat all over the place. Yeah, I know, we all get wet in the pits when training but did you ever wonder by exactly how much? Being just a leeetle bit inquisitive I decided to do an experiment, with myself as the subject. The question to answer: what's my sweat rate?

Here's what I did:

First, I weighed myself butt nekkid before going for a run. The scale read 75.84 kilograms (167.2 lbs). Then, I ran for one hour at my 10k race pace (high Zone 3 heart rate) and I took a .59 liter (20 oz.) bottle of pure water along. While on the run I downed half of the bottle at 15 minutes and the second half at 45 minutes. said the temperature was 27.22 c (81 f) and the humidity was 61%.

Finally, after the run I undressed and dried myself, including my hair, and weighed in again. This time the scale read 74.93 kilograms (165.4 lbs).

Soooooo, how much water did I leave on the street?
(a) Ending weight = 74.93 kilograms
(b) Starting weight = 75.84 kilograms
(c) Water drank = .59 liters (.59 kilograms)
(d) Urination = 0.00 liters ... Ummm, yeah you gotta measure that too. It's probably easier if you hold it in until after the run and your second weighing... I'm just sayin'.
(e) Time in hours = 1.0
(a - b - c + d) / e = sweat rate
(74.93 - 75.84 - .59 + 0.00) / 1 = -1.50 kilograms (1.5 liters) per one hour.

This means I should drink 1.5 liters (50.72 oz.) per hour under similar conditions.

50.72 ounces per hour? What?? That's over 2 water bottles per hour! Jeeze, what am I, some kind of water buffalo? I have never drank that much during a race or during training. Perhaps here's a piece of the puzzle as why I tend to melt down, like here, in hot conditions, eh?

I'll be doing this experiment again at higher and lower heart rate zones and for both shorter and longer times to see how consistent the data is produced.

So, 'BoomerNation, go ahead and try this little experiment yourself.



Let me know your results.

Stay tuned...


Shelley said...

What if you don't weigh yourself..what if you don't sweat, but perspire..hmmmm...good exercise in calculating your sweat rate though boomer!!

Bigun said...

how long did you wait after your 1 hr run to weigh yourself - you were sweating then too, so you're race per hour would be less if count the time it took to dry off and get to the scale.

I don't know why, but every experiment seems so much more scientific when done in Celcius and the metric system. Great exercise - hey, you identified that no matter what, you are not drinking enough!

Brent Buckner said...

Important as summer looms.

I think some folks are now saying that water liberated from burning glycogen stores contributes to sweat but need not be replaced during an event (as you aren't fixing glycogen during an event).

Andra Sue said...

You know, I've been meaning to do that little experiment for like 2 years. Thanks for the reminder...I expect I am also not drinking enough. Too important during Texas summers not to be diligent about it!!!

Spokane Al said...

I am certainly no expert in much of anything but I do recall reading that we don't need to plan on replacing 100% of the fluids we sweat out and a certain amount of dehydration is natural in an endurance event.

According to the article we should keep that level within certain perameters.

Charles said...

I also have been meaning to measure my rate as well. As mentioned above, you can run a small deficit while racing but remember that the longer you race the more important it is to reduce the deficit. Even a small deficit can add up over an ironman.

ironjenny said...

I've done that exercise and I am a sweater, too. Electrolytes hold more liquids in for ya.
I always carry my own bottle.

Anonymous said...

Sweat Rate = 70 oz per hr.
Sodium loss = 1.2 g per hr.
Learning Na+ loss rate is important also if you are a big sweater. I can dehydrate and still keep high wattage over 4 hrs but not if I get too low on Na+, plus cramping becomes an issue if I bonk on salt. Ryan

Curly Su said...

great equation and experiment, but you have to add a variable for the amount of calories burned...

Siren said...

I'm a ridiculous heavy sweater, so I tried a (much less complex) version of this experiment a while back and was flabbergasted by the results. I don't remember exactly (I'm gonna re-do it when I get back training post-pregnancy) but I remember losing more than 2 pounds in only 30 minutes.

That's about the time I made friends with Nuun.