June 30, 2008

Sweat Rate

I think I've finally figured out a reasonable strategy for fluid and electrolyte replacement!

Lately I've been anal retentive about documenting my pre and post run weight, fluid intake, electrolyte intake, etc. As it turns out, I've only been drinking about half of what I should be, which can be a BIG contributor to muscle cramping. I've been somewhat reluctant to gulp down lots of fluids because: a) fear of hyponatremia, especially being a salty sweater, b) I don't want an upset/sloshing stomach while running, c) I never needed that much fluid during road runs, d) most of the peer reviewed literature suggests that it's best to be a little dehydrated than overhydrated, and e) I don't want to be pissing like a race horse during a trail run.

Last weekend at Afton, I calculated my sweat rate to be 2.25 lbs/hour, meaning I need to drink 36 oz of fluid/hour to maintain my body weight (I only drank 32 oz for the 2 hours I was out there - less than half of what I should have). I also took 1 S cap/hour and didn't have any problems with cramping or hand swelling.

Today at Hyland, my sweat rate was 2.1 lbs/hour, meaning I need to drink 33-34 oz fluid to maintain (I drank 16 oz/hr + 1 S cap). Pretty close to what I'd expect compared to Afton, especially since Hyland is easier terrain to run on.

Game plan for Saturday at Afton = 36 oz HEED/hour + 1 S cap/hour, which works out to about 400 mg Na/hour (recommended range is 200-500 mg Na/hr) and 21 mg K/hour (recommended range is 20-50 mg K/hr).

If I cramp up this time, it will most likely be because of muscle fatigue due to deconditioning rather than dehydration or electrolyte imbalance. And the cramping will most likely take place in the grass that is taller than I am on the snowshoe loop. I hope I don't get lost.... ;)


Wayne said...

That snowshoe loop is sounding like quite the wild place... it'll be the first place to look if people don't show up at the finish line as expected! :)

Runnin-from-the-Law said...

Good luck this weekend Kel!

SteveQ said...

I couldn't believe I was up to 40 oz. per hour last week. I'm hoping it was making up for a sort of chronic dehydration. I expect to be dehydrated during the race Saturday and make it up afterward; at Trail Mix I had a total of maybe 35-40 oz in 4 hours.

It's the 50 miler in three weeks where I'll drink all I can get.

phillip said...

I don't think I've read anyone stating it better about not wanting to stop in the woods during the race.
Race horses are probably now rejoicing. . . .

The information of the sweat rate was also helpful.

Looks like Saturday's Afton will be a good preliminary test for the Voyageur heat wave, too.

Phillip Gary Smith