Gnarly Hydration Test
Gnarly Hydration Test

Gnarly Hydration Test

The sweat test

Step 1

Get in your birthday suit (strip naked) → urinate → weigh yourself before running.

Step 2

Run (clothed*) for one hour and try to match the pace and conditions** of race day.

Step 3

Take note of how many ounces of fluid you drink in that hour.

Photo: Tim Behuniak of Gnarly athletes Trevor Fuchs and Erin Storck running in the Wasatch at sunset.

Step 4

Return → strip naked → remove sweat with your Grizzly Bear towel → weigh yourself.

Step 5

Grab a calculator or someone that knows math.

Step 6

Subtract post-run weight from pre-run weight and convert that weight into ounces

(16 ounces in 1 pound).

Photo: Luke Webster of Gnarly athlete Mike McKnight making up a Gnarly Hydrate mix.

Step 7

Add the ounces of fluid you consumed while running.

Step 8

Press enter on your calculator.

Step 9

This is the number of fluid ounces/hour you should consume while running.

Step 10

Divide that number by three and consume that amount every 20 minutes of running.

Photo: Dave Burleson

Gnarly Jeff’s Hydration Test

Jeff is a man beast weighing 193 lbs. When he’s naked, he’s 190 lbs. even. (Three lbs. of clothes ain’t bad for a bachelor.) This 190 is his pre-run dry weight; his nude post-urination weight. When Jeff runs for an hour at race pace, he consumes four ounces of water. After running, Jeff strips down naked while no one is watching, dries off his sweat (show Grizzly Bear towel), and weighs himself on a man scale. Come to find out, Jeff’s post-run weight it 189 lbs.


Using his Ti-83 calculator (way more processing power than you need for this experiment), Jeff subtracts 189 from 190 and gets 1 lbs. Converting a pound into ounces would be 16 oz. Jeff then adds the 4 oz. that he drank to the 16 oz. that he lost, equaling 20 oz. What Jeff learned from this hydration test is that he needs to be drinking 20 oz. of fluid every hour he runs. This could be consumed at a rate of 10 oz. every 30 minutes, or 6-7 oz. every 20 minutes.

All this math has Jeff feeling super confident so he’s going to call his mother and tell her the good news while we tell you more. Running with proper hydration is essential to the success of your body and your races. Even if you think you’re getting enough fluid while running, we recommend that you do this test (because the results may surprise you). Furthermore, skimping on hydration can cause muscle cramping and fatigue, nausea and headaches, and it can damage your internal organs preventing you from improving your performance.


So go ahead, don’t be shy, get naked, go pee, weigh yourself, go running*, and see if you’re drinking enough fluid. We can only hope that everyone will use this Hydration Test. It’s easy, insightful, and essential to race improvement.

We also recommend doing this test again as your performance changes and as your environment changes. As you become stronger and run faster, you will find that you consume more fluid. And as you run in different environments (at different altitudes and temperatures), you will find that your hydration needs fluctuate with these changes. Be conscious of these changes so you don’t under-hydrate or over-hydrate when it comes time to warm up those muscles and run.

check out this gnarly product to help you manage hydration

Gnarly Hydrate

Jeff’s Hydration Test at a Glance

The old Jeff

Jeff’s Pre-run Weight: 190 

Jeff’s Post-run Weight: 189

Jeff’s Mid-run Fluid Consumption: 4 ounces

Math skillz

190 lbs. – 189 lbs. = 1 lbs = 16 oz.

16 ounces were lost and 4 ounces were consumed.

Jeff needs to be drinking 20 total ounces/hour.

The new Jeff

Jeff now drinks 20 ounces of fluid each hour he runs.

Jeff’s New Pre-run Weight: 190

Jeff’s Post-run Weight: 190

 Jeff’s Fluid Consumption While Running: 20 ounces.

Big J's consumption intervals

Ten (10) ounces every 30 minutes.

Forty (40) oz. bottle in two hours. 

*Our research shows that running naked can relieve stress but we recommend you wear clothes if you’re going to run in public.

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