This is what a sweat test actually tells you.
One athlete’s finished report, in full — the patch reading, the correction applied to it, and the race-day sodium plan that falls out of it. Read it before you spend anything.
You're a heavy sodium sweater — targeted electrolyte replacement is especially important for you, particularly in the heat.
Read the whole thing — free.
You’ve seen the headline number. The part that matters is how it was arrived at, and that’s the part still below the fold.
- The forearm reading and the whole-body correction, with the published equation worked out on the page
- The sweat rate derived line by line from the weigh-in — before, after, and fluid drunk
- The hour-by-hour race-day fluid and sodium plan, dialable to your own event
- A brand-free table matching that target to what you already carry
Five sections, and the working shown for each.
A report you cannot check is a report you have to take on faith. This one is built to be argued with — which is why the inputs sit next to every number.
The raw reading, then the correction
A forearm patch reads saltier than the body as a whole. The report shows the raw number, the published regression applied to it, and the whole-body figure that comes out — with the equation and citation on the page, not asserted.
Sweat rate from a scale, not a model
Body mass before, body mass after, and everything drunk in between. Worked line by line, because concentration alone says nothing about volume — and it is volume that turns a salty result into a large hourly loss.
Milligrams of sodium per hour
The one number you actually fuel against, and the only one that translates into a plan. Everything above exists to arrive at it honestly.
An hour-by-hour race-day plan
Fluid and sodium per hour for the race length, intensity and heat you pick. Dial it to your own event and watch the targets move.
A brand-free fuel table
What that target means in bottles, packs, capsules and tablets — by format and sodium density, so you can check your own labels against it. We do not sell a mix and are not paid to point you at one.
The things worth being skeptical about.
Is this a funnel into your own electrolyte product?
No — there is no house mix, and no affiliate deal behind the recommendations. The fuel table in the report is deliberately brand-free: it lists formats and sodium densities so you can hold your own labels up against it. Selling a mix is exactly the incentive that makes other people’s test results hard to trust.
Why not just use a population average?
Because the spread is roughly tenfold. Sweat sodium runs from about 200 to 2,000 mg/L between athletes, so an average can miss your real losses by more than 1,000 mg an hour — which is the difference between a plan that works and one that quietly fails in the last hour.
How is this different from the at-rest patch tests?
Those stimulate sweat chemically while you sit still. This measures the sweat you actually produce during a workout you were doing anyway, in the heat and at the intensity you race in — and it takes the workout’s own data as context rather than ignoring it.
How accurate is it, honestly?
The forearm-to-whole-body regression explains about 70% of the variation between athletes (R² ≈ 0.70), which puts a band of roughly ±300 mg/L around your number. That band is printed in the report rather than hidden. It is a strong estimate to aim with, not a physical constant — and it beats a population average by a wide margin.
What do I actually have to do?
Wear a patch during a long, hot workout you had already planned, weigh yourself before and after, and mail the patch back in the prepaid envelope. The report lands in your account. The kit is $129 with shipping both ways included.
Read the report, then decide.
It takes about four minutes and costs an email address. The kit is there afterwards if the method holds up.