Carbs, Fluid & Sodium: Building Your Ultrarunning Fueling Plan

Yeah, it's a really good question, Cliff.

I think a lot of the principles are actually very similar.

Uh, in terms of the actual numbers of intake, say, carbs, fluid, and sodium, they differ definitely from pros to amateurs, for example.

The actual processes of how we make the strategy and individualize it is very similar when I'm chatting to a top-level pro athlete, uh, and an amateur just on a customer call, for example.

Can you walk me through what a sweat test actually measures and what that means for an athlete's hydration plan?

Yeah, absolutely.

So our at-rest sweat test measures sweat sodium concentration, so it's a 30-minute test.

An athlete just kind of sits there.

There's two main parts to the test.

We induce someone to start sweating, and then we collect that sweat, and we analyze it, and what that tells us is their sweat sodium concentration.

So that can be a huge range, anywhere from 400 all the way up to 2,000 milligrams per liter.

Um, and ultimately, you get your sweat sodium concentration, and that'll help you determine the relative sodium concentration that you might aim for while you're racing.

So, uh, for example, take an athlete, say, Rachel Entwistle.

She's quite salty.

She loses just over 1,500 milligrams per liter, and therefore, in her drinks and her intake over a race, she's aiming for about 1,500 milligrams per liter as a concentration to match her sweat sodium concentration.

And is there a field method for athletes who can't get tested in the lab?

There's definitely some signs and, say, symptoms of being a salty sweater.

You'd know whether you're on the higher end, I'd say.

A lot of people get marks on their kit, especially if it's black.

You get the kind of stinging in your eyes.

It tastes very salty.

Um, is a good kind of indicators that you're on the top of that range.

We fit people into buckets based on their sweat sodium concentration, so you could be, like, small, moderate, high, very high, um, and then kind of give recommendations based off that.

I think if you can't get a sweat test, a good place to start is down the middle.

So the average sweat sodium concentration is 950 milligrams per liter, so you might start around 1,000, which is about how much I lose, actually, and then there's a little bit of trial and error and adjusting from there, and then ultimately, hopefully, you'll be able to get a sweat test and determine your exact sweat sodium concentration.