When I actually need electrolytes (it turns out it's not every run)

When I first wrote about why I built this site, I said I end most workouts with a headache that goes away when I dose electrolytes properly. I’ve been running that as a blanket rule ever since: every run gets a bottle, every bottle gets the full mix.

This past month I decided to actually test it instead of assuming it. So I started running some days with my usual mix and some days with nothing but plain water, and paid attention to how I felt. Not just during the run, but the rest of the day and the next morning too.

The answer turned out to be more specific than “I always need them.”

The setup

Nothing fancy. Over about four weeks I alternated. Some runs got a bottle dosed off the calculator, some runs got plain water at the same volume. I didn’t blind it, I can taste the salt, so this isn’t a clean study. It’s just me paying honest attention.

I split the runs into two rough buckets:

• Short: under about 10K, 30–60 minutes, mostly easy.
• Long: 10K and up, the runs where I’m out there over an hour and into my actual training volume.

I wasn’t tracking a stopwatch reaction. I was tracking the dumb, real signals: did I get a headache, did I feel flat, how were my legs and my head that evening and the next day.

Short runs: I genuinely couldn’t tell

This is the part that surprised me. On the short runs, electrolytes or no electrolytes, I felt the same.

Same during the run. Same that afternoon. Same the next morning. No headache either way. No sluggishness either way. If you’d asked me to guess afterward which bottle I’d been drinking, I’d have been flipping a coin.

So the blanket rule I’d been running was wrong, at least on the short end. For an easy 5 or 6K, plain water did the job and the mix wasn’t buying me anything I could feel. That’s a little humbling to admit after building a whole calculator, but the salt rim on a 40-minute run just isn’t a big enough loss for my body to care.

Long runs: the difference shows up later

The long runs were a different story, and the difference didn’t show up where I expected it.

During the 10K+ runs on plain water, I mostly felt fine in the moment. The trouble came after. The afternoons I’d feel flat and sluggish, like I was moving through syrup, and a few times I picked up a dull headache a couple hours after I’d stopped. The next morning I’d still feel a step behind. On the long runs where I’d actually dosed the mix, none of that. Normal afternoon, normal evening, normal next day.

That lag is the thing I want to remember. It wasn’t a mid-run bonk that screamed “drink salt.” It was a slow, hours-later tax that I’d probably have blamed on a bad night’s sleep or a long day if I weren’t specifically watching for it.

It lines up with the original headache I built this thing around. I just had the trigger slightly wrong. It’s not “any run.” It’s the long ones, and the bill comes due after I’m already home.

What I’m changing

So I’m adjusting my own protocol. Electrolytes on the long runs, plain water on the short ones.

Concretely, that means anything 10K or over gets a bottle dosed off the calculator, same as before. Anything under that, an easy 5 or 6K on a normal day, I’ll just carry water. It cuts down the powder I’m using, the bottles I’m washing, and the salt I’m choking down on runs that don’t need it.

A couple of honest caveats, because this is an n=1 over one month:

• This is my body, my sweat rate (I land in the heavy-to-very-heavy bucket, see the sweat rate test), and this month’s weather. As it gets hotter through summer, I’d bet the line where “short” starts to matter creeps down. A 6K in July heat is not the same loss as a 6K in June.
• “10K” is a stand-in for “over an hour and into real volume,” not a magic number. The duration and the heat probably matter more than the distance itself.
• I haven’t tested where exactly the threshold sits. Somewhere between my short bucket and my long bucket is the real line, and I don’t know if it’s 7K or 9K yet.

I’ll keep watching it, especially as the temperature climbs. If the threshold moves, I’ll write it down here. For now the rule is simpler than the one I started with: short and easy gets water, long gets the mix.

If you’ve run your own version of this test and found a different line, I’d like to hear where yours sits.