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Sweat & NACL loss during IM

Posted By: KP
Date: Sunday, 21 October 2007, at 5:58 p.m.

From the Director of the Gatorade Sports Science Institute, Chicago Illinois, Bob Murray, PhD, FACSM
(this during the Ironman Medical Conference last week).

Some of us are efficient sweaters -- some are not. Sweat rates ==>

1) low end -- 700ml/hr
2) avg -- 1-2 liters per hour
3) heavy -- up to a gallon an hour!

Losing 2% of our body weight is needed to feel thirst.
However, losing only 1-2% degrades performance (there is a lag).

Over an IM, the avrage body weight loss is 3.5%. Not good.

*** In a 3hr marathon the avg sodium loss is 5g.
*** In an IM, the loss can be as high as 16g of sodium. That is one third of the body's total stores.
I take a minimum of 1000mg per hour and up to 1400mg/hr beginning at the swim start and continuing to the last miles of the run.

CONCLUSION (obvious but often overlooked):

For optimal human performance, we must match loss of H2O and NACL with intake.

coach KP

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