Why does my hydration reading always go up after a long run?

Why does my hydration reading always and I mean always go up after a long run and I am dehydrated. I do not usually carry a drink. Today I lost 2kg during my run but my hydration reading went up. This happens every time and cannot be put down to just error of reading variation. I also observe a direct inverse relationship of body fat to hydration. Just look at your last year's data and flick between hydration and body fat to see if your scale is the same. Shouldn't an increase in body fat correlate with an increase in hydration (body water content) as extra fat is stored along with extra water.

0 3157299 2 months ago

I guess I should have asked is this a fault with my scale or does anyone else have this same issue?

0 luca_roby 2 months ago in reply to 3157299

Possible guess: body water is "the percentage of your weight attributable to fluid in your body and can indicate how hydrated you are". If after a run your weight goes down more than body water does then the hydration percentage might go up even if its absolute value (in kg) decreases,

I hope it makes sense.

Anyway S2 statistics mixing up absolute values in kg (Bone Mass and Skeletal Muscle Mass) and percentages (Body Fat and Body Water) certainly don't help understand the metrics.

0 tobygadd 2 months ago

From the manual: "Garmin recommends waiting two hours before using the device after eating, drinking, exercising, bathing, or visiting a sauna."

So, if your feet or body are wet from sweating or working out, the scale will likely be less accurate. Garmin Index S2 Smart Scale Owners Manual - Tips for Erratic Body Composition Data

That said, many review sites have indicated that impedance body-composition scales like the Index 2 aren't known to be terribly accurate in the best of circumstances. Since I don't have time to wait 2 hours for the most accurate hydration analyses after a workout (at which point I've hopefully had something to eat & drink!), I just use basic weight to determine how much water I've lost from sweating. The scale's weight readings seem to be very accurate, so this works for me.