At the start line, a rider pops two salt tablets before the gun's even gone off. He'll take two more at the first feed zone, on schedule, whether he's thirsty or not — because he read once that under-salting is how riders end up in the medical tent. His bottles are always full. He drinks on the hour, every hour, whether he wants to or not, because "staying ahead of it" is the rule he was taught. The tablets feel like the responsible move. Insurance against the thing nobody wants to have happen to them on a hot day.

He's heard the story that justifies the ritual — a friend of a friend who cramped and went down hard on a stage race, and the postmortem around the campfire always lands on the same verdict: not enough salt. Nobody in that story ever asks how much water the guy was actually drinking.

The research on what actually causes that emergency tells a less comfortable story — and it isn't about salt.

Section 01What the data actually says

Hoffman and Stuempfle studied runners at the Western States 161 km ultramarathon, run in genuinely hot conditions, tracking what they ate, drank, and supplemented against their blood chemistry at the finish (Hoffman & Stuempfle, 2015). Sodium supplement use was close to universal in this field: 93.9% of runners used sodium supplements during the race (Hoffman & Stuempfle, 2015).

And here's the finding that should reframe how you think about the tablets in your jersey pocket: sodium supplement use did not distinguish the runners who finished hyponatremic from the runners who finished with normal blood sodium (Hoffman & Stuempfle, 2015). The people who got into trouble weren't the ones who skipped their tablets. Almost everyone was taking them, hyponatremic and normonatremic finishers alike.

What did track with finishing blood sodium, according to the authors, was body weight change over the race — not how much sodium a runner had taken in (Hoffman & Stuempfle, 2015). Runners who finished heavier, or who lost the least body weight, tended to finish with the lowest blood sodium; runners who lost more weight — the expected direction for a long hot effort — did not. The pattern points away from the runners who were most dehydrated and toward the ones holding on to more fluid than their bodies were actually losing. The authors' own summary of it: low sodium intake "has minimal responsibility for development of hyponatremia," while overhydration is "the primary characteristic" of the runners who ended up there (Hoffman & Stuempfle, 2015).

Section 02Why salt doesn't fix a dilution problem

Blood sodium concentration is a ratio, not a fixed quantity: total sodium in your bloodstream divided by total water in your bloodstream. You can develop low blood sodium in exactly two ways — losing too much sodium, or gaining too much water relative to the sodium you have. Sports nutrition marketing has spent two decades treating the first pathway as the whole story. The data above says the second pathway is doing most of the damage in the field.

Here's why a salt tablet doesn't reliably intervene on that second pathway. A tablet you swallow has to be absorbed from your gut before it changes anything in your bloodstream — it doesn't act instantly, and the amount involved is small relative to the roughly 92 grams of sodium already circulating in a typical adult's body fluids. If you are actively drinking in more water than you are losing through sweat and urine, you are diluting that existing pool faster than a tablet or two can meaningfully top it back up. The tablet is trying to solve a concentration problem by adding a small amount of the wrong side of the ratio, while the larger side of the ratio keeps climbing.

Under normal circumstances your kidneys are extremely good at holding this ratio steady — adjusting how much sodium and water you excrete, hour to hour, to keep blood sodium in a tight range regardless of exactly what you eat or drink. That regulation has real limits, though, and prolonged, hard exercise pushes right up against them: sweat losses climb, gut absorption of anything you're taking in slows, and if fluid intake keeps outpacing what the kidneys can process, the ratio drifts before regulation can catch back up. Salt sitting in your jersey pocket doesn't change how fast that regulation works. Matching your intake to your actual losses does.

Section 03What to actually do about it

1. Drink to thirst

   For the large majority of rides, thirst is a well-calibrated signal. Riding to a fixed hourly bottle count "just in case" is the behaviour most associated with the runners who finished worst off in this dataset.
2. Use finish-line weight as your own check

   A modest weight loss at the end of a long, hot effort is normal and expected. Finishing heavier than you started, or barely lighter, is the actual warning sign — not your tablet count.
3. Reserve deliberate sodium replacement for the real edge cases

   Long, hot, high-sweat-rate efforts, and riders with a personal history of cramping, are where individualised sodium planning earns its place. It is not a default for every bidon on every ride.
4. Don't swing the other way into under-drinking

   This isn't a case for restricting fluids. It's a case for matching intake to what your body is actually asking for, rather than a fixed schedule set by fear.
5. Know the difference between a pacing plan and an emergency

   Confusion, severe nausea, or collapse during or after a long effort is a medical situation, not a hydration debate — treat it as one, immediately, regardless of what anyone's fuel plan says.

Section 04Where riders get this wrong

The most common misread is hearing "sodium supplementation didn't prevent hyponatremia" and concluding sodium doesn't matter at all. That's not what the data shows. Sodium losses are real, sweat rates vary enormously between riders, and genuinely long, hot, high-output efforts can still benefit from deliberate, individualised sodium planning. What the research actually undercuts is the specific belief that a fixed tablet schedule is protective by itself, independent of how much you're drinking.

The second misread is treating this as permission to under-drink out of fear of the alternative. The data doesn't argue for restricting fluids — it argues for drinking in proportion to what you're actually losing, using thirst and finish-line weight as your checks, rather than defaulting to a fixed volume "to be safe."

The third misread is applying a 161 km ultramarathon finding, at pace and duration extremes, directly to a two-hour club ride without adjustment. The mechanism generalises — fluid balance drives blood sodium, not tablet count — but the stakes scale with effort duration and heat. A short weekday ride and a multi-hour race in summer heat are not the same risk profile, even if the underlying physiology is identical; use the principle here, not a one-size number, and scale your attention to the conditions in front of you.

The fourth misread is assuming this only applies to ultra-distance events. The physiology doesn't have a distance cutoff — a four-hour gran fondo in heat, or a long gravel day with limited feed stops, sits closer to the ultramarathon end of this spectrum than to a quick club loop, and deserves the same drink-to-thirst thinking rather than the fixed-schedule habit most riders default to.

Section 05Applying it with HELIOS

HELIOS can't test your blood sodium mid-ride — nothing wearable can, and nothing in the THRIVE app claims to. What it can do is give you an honest picture of the two things that actually matter here: how long and how hard you rode, and how your body came back from it. The ring's recovery and readiness numbers the next morning reflect how the whole ride landed on your system — heat, duration, and fluid handling included — feeding back into how Marco adjusts the plan for what comes next.

The practical shift this research asks for isn't a new sensor. It's using your own finish-line weight and how you actually feel — not a fixed bottle count decided the night before — as the signal that tells you whether your hydration strategy for a long, hot ride is actually working. That's a more honest check than a schedule set in advance, because heat, pace, and your own sweat rate change every single time you're out, and no plan written the day before a ride can account for any of that in real time.

Section 06Bottom line

In this field study, sodium supplementation did not distinguish the runners who finished hyponatremic from the ones who didn't — 93.9% of the field was taking sodium supplements, hyponatremic and normonatremic finishers alike. What did distinguish them was body weight change: lower finishing blood sodium tracked toward runners who gained weight or lost the least of it, not toward the ones who were most dehydrated. The tablets in your pocket are not doing nothing, but they are not the lever that matters most. How much you actually drink, relative to how much you're losing, is.