Sweat Testing 101: What It Actually Tells You — And How to Get Yours Done Properly

Q: Are electrolytes good before a morning workout?

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Q: Can you have too many electrolytes?

{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Yes - over 8 g of sodium per day raises blood pressure in salt-sensitive individuals and stresses the kidneys. During exercise the cap is much higher (3 to 5 g per session is fine for heavy sweaters). Outside of exercise, normal-diet sodium plus 1 to 2 electrolyte drinks per day is the safe range."}]}]}

Q: Should you drink electrolytes every day?

{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Daily electrolytes are unnecessary if your diet contains 2,300 to 5,000 mg of sodium per day (most do, especially with bread, cheese, salty snacks). Add electrolyte drinks on training days, hot days, and post-illness. Daily electrolyte tabs are mostly hype unless you're a heavy salty sweater."}]}]}

Q: When should you take electrolytes - before or after exercise?

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Q: Are electrolyte tablets better than salt tabs?

{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Quality electrolyte tablets deliver sodium plus potassium, magnesium and a small carb dose for absorption. Plain salt tabs deliver sodium only. For most athletes, electrolyte tablets are the better choice. Salt tabs are useful for heavy sweaters who need 1,000+ mg sodium per hour and can't fit it in drink mix alone."}]}]}

Q: How much sodium should athletes consume per hour during exercise?

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Sweat testing is simply the process of measuring how much you sweat and how much sodium is in that sweat, so you can stop guessing and start fuelling to your own numbers.

July 22, 2026 4 min. read

Ella Ransley Sport Science Lead

“The good news is you don't need to piece this together from self-observation alone. At our SIGR Human Performance Lab, a sweat sensor test takes the guesswork out entirely, giving you an actual hydration and sodium target in under two hours.
— Ella, Sport Scientist”

Overview

Knowing both numbers turns "drink when thirsty" into an actual plan: how much fluid to take in per hour, and how much sodium needs to go with it.

If you've ever finished a hot ride covered in white salt streaks while your training partner looks barely damp, you've already seen the core idea behind sweat testing in action: no two athletes lose fluid or sodium the same way. Sweat testing is simply the process of measuring how much you sweat and how much sodium is in that sweat, so you can stop guessing and start fuelling to your own numbers.

The good news is you don't need to piece this together from self-observation alone. At our SIGR Human Performance Lab, a sweat sensor test takes the guesswork out entirely, giving you an actual hydration and sodium target in under two hours.

What Is Sweat Testing?

Sweat testing measures two separate things that get lumped together in most hydration advice:

Sweat rate — how much fluid you lose per hour, typically somewhere between 0.5 and 2.0 litres, occasionally higher in extreme heat or for very heavy sweaters
Sweat sodium concentration — how much sodium is in that fluid, which varies far more dramatically between individuals than most people realise

Knowing both numbers turns "drink when thirsty" into an actual plan: how much fluid to take in per hour, and how much sodium needs to go with it.

The Science: How It's Actually Measured

There are a few recognised ways to test, ranging from lab-grade to DIY:

Whole-body washdown is the reference standard — collecting all sweat runoff during exercise for lab analysis. It's the most accurate method available, but it requires a controlled lab environment, so it's rarely used outside research settings.

Regional absorbent patches are the most practical field method. A small adhesive patch with an absorbent pad is applied to clean, dry skin (usually the forearm or back) around 20–30 minutes into exercise, once sweating has stabilised. The collected sample is then analysed, and a regression equation converts that local reading into a whole-body estimate.

Ion-selective electrodes and conductivity meters allow on-the-spot sodium analysis in the field, though conductivity readings tend to run around 6% higher than lab reference values, so they're best treated as a good estimate rather than an exact figure.

Wearable sweat sensors, like the. Flowbio and HDrop, use microfluidic channels built into a skin-worn device to track sweat rate and sodium loss in real time, syncing to an app so you can build a personal sweat profile across different sessions, temperatures, and intensities without a lab visit.

Pilocarpine iontophoresis is the clinical gold standard for isolating sodium concentration specifically — a mild electrical current stimulates a small patch of skin to produce sweat on demand for precise lab analysis.

What the Numbers Actually Mean

This is where sweat testing gets genuinely useful. Sweat sodium concentration ranges from around 200 mg/L at the low end to over 2,300 mg/L at the high end, with an average around 950 mg/L — roughly a tenfold difference between the lowest and highest sweaters. That variation is largely genetic, coming down to how efficiently your sweat glands reabsorb sodium before it reaches the skin's surface. It doesn't change much with fitness or acclimatisation; once you know your number, it stays fairly constant, similar to knowing your shoe size.

This also means the "salty sweater" experience is real and measurable: at higher sweat rates, sodium secretion increases faster than the glands' capacity to reabsorb it, so heavy sweaters in the heat lose disproportionately more sodium, not just more fluid.

Why This Matters for Your Fuelling Strategy

Once you have both numbers, the maths is simple: sweat rate × sodium concentration = hourly sodium loss. Someone sweating 1L/hour at 1,200mg/L is losing roughly 1,200mg of sodium an hour — more than double what a generic single-strength electrolyte drink typically provides.

This matters most in exactly the conditions where fuelling tends to go wrong: long, hot events with high fluid intake. Under-replacing sodium in these conditions is linked to cramping in some athletes and, in more extreme cases, dilutional hyponatremia, where drinking plenty of fluid without enough sodium actually lowers blood sodium levels. Over-replacing isn't typically dangerous but can mean unnecessary gut load or wasted product. Either way, generic advice can't account for a tenfold individual range — which is exactly why a fixed-strength approach works for some athletes and clearly doesn't for others.

Should You Get Tested? A Quick Self-Check

Before booking, it's worth checking whether you're showing the signs of a heavier sodium loser — it's a good indicator of how useful a test is likely to be for you:

Visible white salt marks on your kit or skin after training
Sweat that tastes noticeably salty
Lightheadedness or dizziness after long sessions
A history of cramping in longer or hotter efforts
Consistently underperforming in the heat relative to cooler conditions
Strong cravings for salty food after training

Ticking several of these is a strong signal that a generic electrolyte strategy is probably costing you performance — and that it's worth getting your actual numbers rather than continuing to guess.

How to Get Tested: The SIGR Human Performance Lab

Rather than relying on self-observation or a DIY patch, you can get a proper sweat sensor test done at our SIGR Human Performance Lab.

What the sweat sensor test measures: your individual sweat rate and sodium excretion during a real exercise effort, giving you precise, personal hydration targets — how many ml/hour to drink and how much sodium to take in alongside it — rather than a population average.

What you get afterwards: a detailed personal report within 48 hours, including your hydration targets (ml/hour and sodium guidance) so you can build your fuelling strategy around real numbers rather than estimates — the exact figures this article has been building toward.

Full pre-test instructions are emailed once you book, so there's nothing complicated to prepare beyond turning up ready to train.

The Takeaway

Sweat testing won't change how hard a session feels, but it takes the guesswork out of one of the few parts of performance nutrition that's genuinely different for everyone. If you're fuelling long or hot efforts on a one-size-fits-all sodium strategy, it's worth finding out your real numbers — and the SIGR Human Performance Lab is the most direct way to get them.

FAQ's

Are electrolytes good before a morning workout?

Yes for sessions over 60 minutes or in heat. 500 mg of sodium in 500 ml of water 30 to 60 minutes pre-session covers overnight fluid losses and primes sweat-sodium replacement. Skip if the session is short and easy - water alone is enough.

Can you have too many electrolytes?

Yes - over 8 g of sodium per day raises blood pressure in salt-sensitive individuals and stresses the kidneys. During exercise the cap is much higher (3 to 5 g per session is fine for heavy sweaters). Outside of exercise, normal-diet sodium plus 1 to 2 electrolyte drinks per day is the safe range.

Should you drink electrolytes every day?

Daily electrolytes are unnecessary if your diet contains 2,300 to 5,000 mg of sodium per day (most do, especially with bread, cheese, salty snacks). Add electrolyte drinks on training days, hot days, and post-illness. Daily electrolyte tabs are mostly hype unless you're a heavy salty sweater.

When should you take electrolytes - before or after exercise?

Both, plus during. Pre: 500 to 1,000 mg of sodium in the 60 minutes before sessions over 90 minutes. During: 300 to 700 mg per hour for sessions over 60 minutes. Post: replace 1.5 L of fluid + 1.5 g sodium for every 1 kg of body weight lost.

Are electrolyte tablets better than salt tabs?

Quality electrolyte tablets deliver sodium plus potassium, magnesium and a small carb dose for absorption. Plain salt tabs deliver sodium only. For most athletes, electrolyte tablets are the better choice. Salt tabs are useful for heavy sweaters who need 1,000+ mg sodium per hour and can't fit it in drink mix alone.

How much sodium should athletes consume per hour during exercise?

Standard guidance: 300 to 700 mg of sodium per hour for sessions over 60 minutes. Salty sweaters: 700 to 1,500 mg/h. Hot conditions or all-day events: up to 1,500 mg/h. Pre-load with 500 mg in the hour before sessions over 90 minutes for early protection.