Get tested
Stop guessing.
Go measure it.
Every number I train on came from a test, not a wrist estimate. My watch was 34 seconds per mile wrong about my threshold. I sweat far more sodium than the average runner, and I only found out by paying for it. Here is what each test measures, what it costs, and who to book it with.
1,500
mg sodium per liter, and 40 oz of fluid lost per hour
My result
How much fluid and sodium you lose per hour, so you can replace it
Two runners can lose the same fluid and need four times the sodium. Guessing here is why people cramp, bonk, and finish races in a medical tent.
Typical cost
$0 for the weigh-in version, $150 to $250 for a lab sodium test
Where to get it
Precision Fuel & Hydration →
Advanced Sweat Test, the category standard, plus a free online fuel planner
$150 to $200 in person, planner freeNationwideLevelen →
Mail-in sweat collection kit, results by email
About $150Mail-in kitThe weigh-in protocol →
Scale before, scale after, one hour at race pace. Gets you fluid loss for free
FreeDo it yourself
Clinics and labs
Want to be the one I send runners to?
I am building this into a real directory of labs and clinics I can point athletes toward by name. If you run sweat testing, lactate testing, metabolic carts, or athlete blood panels, tell me about it.
I am a coach, not a doctor. Blood work in particular belongs in a conversation with a physician, and nothing here is medical advice. Prices are typical US ranges as of July 2026 and will vary by provider. No provider on this page pays to be here.