Sweat Test

Today was warm (88F) and on the dry side for here (40% humidity), so I decided to do a sweat-test run around lunch time. I ran to Giant and back which is just under 5 miles. I tried to stay within the heart rate parameters of my online Coach. It took me 20 minutes to get there, 30 minutes to get back (I had to stop and let my heart rate and EPOC level drop because I was trying to stay within these guides, or I would have done it 20 minutes each way).

I got my hair wet and weighed myself before my run - 173.5 pounds.

After the run, I toweled off the excess perspiration and weighed myself - 167 pounds.

I didn't eat or drink anything between the two, so that 6.5 pounds difference is almost all perspiration. If water is 8.35 pounds per gallon, and perspiration is almost all water, then my hourly sweat rate is about one gallon per hour.

Today felt a lot like my most recent marathon, Seattle. I felt dry from the get-go. Maybe I just lost a ton of water in Seattle, and that was why I didn't feel well? Makes sense.

To replenish my internal body water supply under these conditions, I need to absorb about one quart of water every 15 minutes. That is a lot of water to drink. And it isn't just drink it, but absorb it from my stomach/intestines into my blood stream.

Typcially people don't lose much electrolyte in their perspiration. But at rates this high, I am losing a lot of electrolyte. I haven't figured that one out exactly, yet. Sodium, potassium, chloride, calcium, and magnesium I think are the big five.

So to be successful at the Philadelphia 24-hour run, all I have to do is make myself drink a quart of liquid each 15 minutes. People are going to get out of my way in the race when they hear me sloshing along behind them.