Your sweat rate tells you approximately how much fluid you’re losing each hour. It does not necessarily mean you need to replace 100% of that amount while running. Your hydration plan should also consider the weather conditions, which vary day to day, run duration and intensity, your individual tolerance, and sodium/electrolyte needs. It is important to repeat the test a few times to get a clearer picture of how much you sweat and need to replace. The idea is to replace sweat as you lose it.
A quick way to help you determine approximately how much fluid you lose while running, is to weigh yourself before your run with no clothes on. Then, run for one hour and keep track of exactly how much fluid you drink during the run. After your run, towel off any sweat and weigh yourself again with no clothes on.
Subtract your post-run weight from your pre-run weight to determine how much weight you lost. Convert that weight to ounces using the estimate that 1 pound equals approximately 16 ounces of fluid. Then, add the amount of fluid you consumed during your run. The total gives you your approximate sweat rate per hour.
Example
For example, if your starting weight is 120 pounds and your ending weight is 118 pounds, you lost 2 pounds. Multiply your pounds lost by 16 ounces equals which would be 32 ounces of fluid lost. If you drank 14 ounces during your run, your estimated sweat rate would be 46 ounces per hour (32 ounces lost + 14 ounces consumed). You can divide this by 4 to tell approximately how much fluid you lose every 15 minutes. In this example, 46 ÷ 4 = 11.5 ounces every 15 minutes.
Starting weight: 120 lb
Ending weight: 118 lb
Weight lost = 2 lb
2 lb × 16 oz = 32 oz
Fluid consumed during the run = 14 oz
32 oz + 14 oz = 46 oz
Estimated sweat rate = 46 oz per hour
Signs of Dehydration
Pay attention to your body and how you feel during and after your run. Dehydration can sneak up on you if you are not intaking enough fluids. There are several symptoms of dehydration that you might not think lack of fluid could be the reason. Some symptoms include:
- Feeling thirsty, which means you’re already dehydrated!
- Fatigue
- Dry eyes and or/dry mouth
- Cramps
- GI distress
- Headache
- Confusion
- Muscle spasms
- The feeling that exercise is much harder than it usually is
- Lethargy
If you experience significant or worsening symptoms, stop exercising and rehydrate appropriately.
