Electrolyte sachets: who actually needs one

What the guidance actually says

The American College of Sports Medicine's position on exercise and fluid replacement sets the goal plainly: avoid losing more than about 2% of body mass in water during exercise, and avoid large swings in electrolyte balance. It adds that sweat rates and sweat sodium concentration vary considerably between people, so replacement should be individualised rather than prescribed. And it notes that drinks with electrolytes and carbohydrate beat plain water under certain circumstances — long, hot, sweaty ones — rather than in general.

Read that back and the shape of the advice is clear. It is a protocol for people losing a lot of sweat, and the quantity to replace is the quantity you lost. Nothing in it describes a baseline deficiency that a healthy person on a normal diet needs to top up every morning.

The 2% rule is the useful number

For a 75 kg person, 2% is 1.5 kg — about a litre and a half of sweat. A 45-minute indoor session at a moderate pace does not usually get near it. A long ride in summer, a hot yoga class, a match in August or a day of manual work outdoors does. That is the honest dividing line, and it is a much better guide than a sachet subscription: if the session was not long enough or hot enough to cost you around a kilo, water and your next meal cover it.

Weigh yourself, once, and stop guessing

The single most useful thing in this whole subject takes one session to do. Weigh yourself before and after a hard hour, with minimal clothing, and subtract. The difference is roughly the fluid you lost. Do it for the kind of session you actually do, in the season you actually do it, and you will know your own sweat rate rather than a number from a marketing page — which is exactly what the position stand means by individualised.

Where dehydration does show up in your data

Hypohydration is one of the things that genuinely moves the overnight numbers. Studies on hydration status after exercise find HRV falls and heart rate rises when you are down on fluid — the same direction as a hard session, an illness or a late drink, which is precisely the problem: your ring cannot tell you why the night looked expensive.

That is worth knowing in both directions. If you trained hot and did not replace properly, the raised resting heart rate that night is partly a hydration signal rather than pure training cost, and reading it as overtraining will have you backing off for the wrong reason. If you replaced sensibly and the night still reads high, hydration is off the list.

The part the trend gets backwards

The sachets are sold as prevention, taken on days with no meaningful sweat loss, which is the one situation the guidance does not cover. Sodium is not stored for later use in any way that makes a Tuesday morning dose useful on Saturday's long run. If you like the taste and it gets you drinking water, that is a real if modest benefit. It is just not the mechanism on the label.

One caveat that is not medical advice: a gram of sodium a day matters to some people. If you have been told to watch your salt for blood pressure, heart failure or kidney reasons, an electrolyte habit is a conversation for your clinician, not a wellness default.

Testing it on yourself

Pick the sessions where you actually sweat hard, replace deliberately after them, and mark that stretch as a period rather than tagging each day. Then compare the nights that followed against your own baseline — overnight resting heart rate and HRV first, since those are what hydration moves. Vitra computes that on your own machine against your own history, which is the only comparison that means anything for a variable this individual.

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