The American College of Sports Medicine recommends 300–600mg of sodium per hour, or roughly 1.7–2.9g of salt, during prolonged exercise.
While this is a good starting point, the width of that range itself suggests sodium needs aren't a fixed number, but a spectrum. Sweat rate, sweat composition, heat, and how hard you're working all shift where you actually land on it.
There Isn’t a One-Size-Fits-All Approach
Both how much you sweat and how much sodium is in that sweat vary considerably from person to person. Sport, environment, heat acclimation, and individual physiology all shift the numbers, which is why knowing your own body matters more here than an average number.
Depending how intense your training is, sodium losses can range from as little as 600mg per hour up to more than 6,000mg per hour in the same athlete. Having one fixed hourly target might work fine on an easy day, but leave you in a real deficit when you race or push harder than usual.
2 Ways a Standardized Approach Can Go Wrong
Too little fluid or sodium relative to what you're losing can result in dehydration, reduced blood volume, and a harder time regulating your body temperature. Stitches and muscle cramping also get attributed to this sometimes, although actual evidence linking cramping directly to fluid or sodium losses is more contested than the traditional advice suggests.
Too much fluid relative to your losses, especially plain water or a low-sodium drink, and you risk exercise-associated hyponatremia, which is a drop in blood sodium levels that can cause nausea, confusion, and in severe cases seizures or worse. Sodium-containing sports drinks are typically hypotonic and won't reliably prevent this in someone who's simply drinking beyond what they're losing.
The right amount depends on where you actually sit between those two extremes.
What Determines Your Body’s Sodium Needs
There are a few different factors that affect how much sodium you lose:
How much you sweat: More sweat volume generally means more total sodium lost, even before accounting for concentration differences.
How salty your sweat is: Sweat sodium concentration spans a wide range on its own. While low-salty sweaters sit under 30mmol/L, typical sweaters fall between 30–60 mmol/L, and salty sweaters lose 60mmol/L or higher, roughly a fourfold difference in concentration independent of how much they're sweating in the first place.
Heat, humidity, and acclimation: Training and racing in the heat, and how adapted you already are to it, both shift sweat rate and composition.
Exercise intensity: As mentioned earlier, harder efforts don't just increase sweat rate, they can increase sweat sodium concentration too.
None of these are things you can get from a generic chart. The conditions, and the demands of the session are specific to you.
A Practical Way to Figure This Out
You don't need a lab to get a reasonable read on where you sit. Weighing yourself before and after a long session (accounting for fluid intake) gives you a rough sweat rate. Noticing that you finish a hot session with visible white, crusty salt residue on your skin, hat, or kit is a signal that you likely run toward the saltier end of that range. And tracking how you actually feel and perform across different fluid and sodium intakes in training, not just guessing on race day, is how you find out what your body needs.
This is part of why we designed Hydra+ as a real-food carbohydrate and electrolyte drink that you can adjust to your own needs, rather than a single fixed dose assuming everyone loses sodium at the same rate. If you're someone who runs salty, leaning on it more heavily during long sessions makes sense. If you're on the lower end, you likely need less than the default suggests.
Key Takeaways
Sweat rate and sweat sodium concentration both vary enormously between individuals. Differences of four to ten times aren't unusual, even among similarly trained athletes.
Getting it wrong can go in either direction. Too little fluid and sodium relative to your losses risks dehydration; too much fluid relative to your losses, especially low-sodium fluid, risks hyponatremia.
It's fluid volume, not sodium content, that mainly drives hyponatremia risk. Sports drinks with sodium in them won't reliably prevent it if you're simply overdrinking.
A generic "X ml and Y mg of sodium per hour" rule is a reasonable starting point, not a personal prescription. Testing your own sweat rate and salt loss in training is what actually gets you to the right number.
That's all for this week! If you learned something new and are curious to know more, head over to the Blonyx Blog where we keep you up to date on the latest findings from the world of sports science.
Looking for more ways to keep up with Blonyx?
Follow us on Instagram and Facebook for additional sports science information, announcements, exciting giveaways, and more!