PUBLISHED 08/31/2006
The Test
1) Weigh yourself nude right before a run.
2) Run at race pace for one hour, keeping track of how much you drink (in ounces) during the run.
3) After the run, strip down, towel off any sweat, and weigh yourself nude again.
4) Subtract your weight from your prerun weight and convert to ounces. Then add to that number however many ounces of liquid you consumed on your run. (For example, if you lost a pound and drank 16 ounces of fluid, your total fluid loss is 32 ounces.)
5) To determine how much you should be drinking about every 15 minutes, divide your hourly fluid loss by 4 (in the above example it would be 8 ounces).
6) Because the test only determines your sweat losses for the environmental conditions you run in that day, you should retest on another day when conditions are different to see how your sweat rate is affected. You should also redo the test during different seasons, in different environments (such as higher or lower altitudes), and as you become faster, since pace also affects your sweat rate.
