Tuesday, September 14, 2010

10k and Rehydration

Today's workout:

Distance:  10k (6.2 miles)
Time:  53:45 (8:41/mile)
Music of choice: Sara Bareilles - Live at The Fillmore
BPM: 150

Today I started keeping tabs on another aspect of my training in order to better understand how to rehydrate and refuel my body.  Up to this point, in my previous triathlons I've simply taken water during the bike and swim, but I'm sure if I get to the point of marathons or more intense triathlon racing, I'll value knowing how to best fuel my own body.

What I'm doing is determining my sweat rate, the rate at which my body expels liquid in order to maintain body temperature.  First question I'm sure is "how do you do that?"  Well, I weigh myself before and after my workout and take the difference to be the amount of sweat I expelled in the given time frame.  Of course, you have to consider any liquids you drank during the workout and keep tabs on the temperature, your level of exertion, etc.  But overall, it gives me an idea of how much liquid my body needs per hour to maintain a certain hydration level.

As an example, this is my calculation:
- Weight before running = 164 lbs
- Weight after running = 160 lbs
- No. of kilograms in a pound = 0.453 kg/lb
- Density of water (sweat) = 1 kg/L
- Amount of water intake = 0.0 L
- Time out exercising =  53:45 = 0.896 h

[ ( [ (164lbs - 160lbs) * 0.453 kg/lb ] / 1 kg/L ) + 0.0 L] / 0.896 h = 2 L/h

Therefore today, at a temperature of 77 degrees, my body had a 2 liters/hour sweat rate.  That means that in order to keep my body hydrated at today's workout level, I need to drink 2 liters of water every hour.  Crazy!!

It's a good thing I already am in the habit of drinking lots of water throughout the day.


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