You have a hydration strategy. Everyone does. Drink X ounces per hour. Take a salt tab every 45 minutes. Use this electrolyte mix because a podcast recommended it.
The problem is that none of those numbers are based on your body.
Sweat sodium concentration varies enormously between individuals — from as low as 200 mg/L to over 2,000 mg/L. That is a ten-fold difference. Two athletes doing the same workout in the same conditions can lose radically different amounts of sodium per hour. One might need 300 mg of sodium replacement per hour. The other might need 1,500 mg. Generic hydration advice treats them the same, and at least one of them will pay for it on race day.
This is not a minor performance detail. It is a physiological variable that determines whether you cramp, bonk, or finish strong.
Why Sodium Matters More Than Water
Most hydration advice focuses on fluid volume: how many ounces per hour, how much weight you should lose during exercise, when to drink versus when to wait. Volume matters. But sodium is the variable that most athletes get wrong, because they have no way to measure it without testing.
Sodium is the primary electrolyte lost in sweat. It plays a central role in maintaining plasma volume, nerve signal transmission, and muscle contraction. When sodium levels drop too low relative to fluid intake, you get hyponatremia — a potentially dangerous condition where blood sodium concentration falls below normal range. Symptoms include nausea, confusion, headache, and in severe cases, seizure.
On the other end, athletes who lose large amounts of sodium but only replace water end up diluting their blood further. They feel terrible despite drinking plenty. The issue was never hydration volume. It was sodium.
Cramping is another common signal. While the science on cramping is still evolving — with neuromuscular fatigue playing a role — there is strong evidence that sodium depletion is a significant contributor, particularly in prolonged exercise in the heat. Athletes who know their sodium loss rate can stay ahead of it. Athletes who guess are rolling the dice.
What Sweat Testing Actually Measures
A sweat test measures two things:
Sweat sodium concentration (mg/L): How much sodium is in each liter of sweat you produce. This is largely genetic and does not change much with training, heat acclimation, or diet. It is your number — and without testing, you have no way to know it.
Total sweat rate (L/hr): How much total fluid you lose per hour under specific exercise conditions. Unlike sodium concentration, sweat rate does change with intensity, temperature, humidity, and fitness level. This is why testing under different conditions or in different disciplines has value.
Together, these two measurements let you calculate your total sodium loss per hour — the number that actually drives your hydration and fueling strategy.
For example: an athlete with a sweat sodium concentration of 900 mg/L and a sweat rate of 1.5 L/hr loses 1,350 mg of sodium per hour. That is a very different fueling protocol than someone with a concentration of 400 mg/L and a rate of 1.0 L/hr, who loses only 400 mg per hour.
Same workout. Same conditions. Three times the sodium loss. No generic plan accounts for that.
How We Do It at Plus10
At Plus10, sweat testing is done in-house during a controlled exercise session, using the professional version of the Nix sweat biosensor. Here is how it works:
- You book your session. We send pre-test instructions covering hydration and food for the 24 hours before.
- We fit the sensor. A single-use Nix sweat patch goes on your arm with the Nix pod clipped on. No needles, no blood draws.
- You exercise under controlled conditions. This is typically a 45 to 60 minute session on a treadmill or bike, at the intensity you want answers for. Once you are sweating steadily, the sensor reads your sweat continuously.
- Your data is processed on the Nix Pro platform. It reports your sweat volume (sweat rate), your sweat sodium concentration and your sodium loss per hour.
- You get your results the same day. No samples to mail and no waiting on a lab.
- We build your hydration plan. We walk through your numbers and turn them into a detailed plan: how much to drink and how much sodium to take per hour, in training and on race day.
We also offer a double test option for athletes who want data across two disciplines (bike and run, since sweat response can differ by sport) or two conditions (moderate temperature versus heat, or easy pace versus race pace). Two data points give you a more complete picture and let you build condition-specific plans.
Who Should Get Tested
Sweat testing is most valuable for athletes who:
Train or race in Texas heat. High temperatures amplify sweat rate and sodium loss. If you are training outdoors in DFW from May through October, you are losing more than you think.
Do long-course endurance events. Marathons, ultras, Ironman, century rides — anything over 2 hours where cumulative sodium loss becomes a performance-limiting factor.
Experience cramping. Persistent muscle cramping during or after exercise, especially in the heat, is a signal worth investigating. Your sodium concentration may be higher than average.
Have GI issues during long efforts. Nausea, bloating, and stomach distress during exercise can be caused by osmolality imbalances — often driven by too little sodium relative to fluid intake.
Want to optimize, not guess. If you already test your VO2 Max, track your lactate thresholds, and monitor your body composition with DEXA, sweat testing is the next logical data point. It completes the picture.
Pricing
Sweat testing at Plus10 is priced as a flat fee; bundle discounts and Progress Track rebates do not apply.
Single test: $125. One discipline, one condition set. Includes the Nix Pro sweat analysis and your detailed hydration plan.
Double test: $200. Two disciplines or two condition sets. Includes the Nix Pro analysis of both sessions and a hydration plan for each.
Stop Guessing
You would not train without knowing your heart rate zones. You would not race without knowing your pace targets. So why would you fuel without knowing your sodium loss rate?
Sweat testing removes the guesswork from the one variable that derails more race days than any other. Your sweat is as individual as your fingerprint. Now you can measure it.
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Ready to know your numbers? Book a sweat test at plus10life.com/our-pricing-2 or call us directly.
Questions? Reach us at info@plus10life.com or (817) 527-8020.
Plus10 Longevity & Performance Center | 400 Gerault Rd, Flower Mound, TX 75028