[ SWEAT ]■
Know what you lose.
How much you sweat and how much sodium you lose doing it. We weigh you, patch you, and send you out onto the LA River trail for a real run in real conditions. Then we build your hydration plan from what came out. Treadmill or bike are also options. $199, or part of the Baseline for $349.
What you get
Your sweat rate in liters per hour.
Your sweat sodium concentration and total sodium lost per hour.
Where you fall: low, moderate or high sweater, and salty or not.
A hydration plan: how much to drink and how much sodium to take per hour, for training and race day.
Product picks that match your numbers, so you’re not guessing at the aid station.
Why it matters
Your electrolyte mix is a guess. Electrolyte products range from a few hundred to over 1,000 mg of sodium per serving. Your sweat might hold anywhere from about 230 mg to over 2,000 mg of sodium per liter, and athletes lose 0.5 to 2+ liters an hour (Baker, 2017). One product can't be right for everyone. For some people it's half what they need, and for others it's triple.
Too little sodium.
Dehydration: salty sweaters who replace fluid without enough sodium hold onto less of what they drink. Losing more than 2% of body weight measurably hurts endurance performance (Sawka et al., 2007).
Cramping: in one study of football players, the ones who cramped lost about twice as much sodium in their sweat as the ones who didn't (Stofan et al., 2005).
Fading late: heavier legs, a higher heart rate and a slower pace in the back half of a race.
Cramps aren't only about sodium, though. Fatigue and pacing play a big role too, so loading up on salt won't fix every cramp. Knowing your losses rules sodium in or out.
Too much sodium. More isn't better.
On race day: heavy dosing can cause stomach problems, bloating and extreme thirst.
Every day: the average American already eats about 3,400 mg of sodium a day before any electrolyte drink (CDC). A 1,000 mg stick at your desk on a rest day adds to a total that's already high. If you have high blood pressure, talk to your doctor before supplementing.
Too much water. The most dangerous mistake is drinking more than you sweat. At the 2002 Boston Marathon, 13% of finishers tested had low blood sodium, some critically. The biggest warning sign was finishing heavier than they started, and finishers slower than 4 hours were most at risk (Almond et al., 2005). Plain water or a low-sodium drink makes it worse (Hew-Butler et al., 2015).
The fix: know your numbers. We measure your sweat rate and sodium loss and turn them into a plan: how much to drink, how much sodium to take, and which products fit. You stop guessing at the aid station and stop buying electrolytes you don't need.Who it’s for
Marathoners, ultrarunners, triathletes and cyclists. Anyone who cramps, fades late, finishes caked in salt, or feels sloshy on long efforts. Anyone racing in heat.
How to prep
Eat and drink like a normal training day. Wear what you race in. Plan for a steady 45 to 60 minute run.
FAQ
Does it change over time? Yes. Heat, fitness and acclimation all shift it. Recheck before a big race with the Race Week Dial-In ($79).
Can I do it with the Active Metabolic Test? Yes. That’s the Baseline: both in one visit for $349.
The research
Almond CSD, et al. Hyponatremia among Runners in the Boston Marathon. NEJM, 2005.