Five is the Floor — Sympolymathesy, by Chris Krycho

Assumed audience: People who wear or are interested in fitness tracking devices of various sorts.

I wear my Garmin Forerunner 255 most days, and thus have the opportunity to observe its Body Battery “measurement” behavior over time. If you haven’t seen it, the Body Battery is notionally a measure of how much energy you have left in the day. It operates on a notional scale from 1 to 100, with 1 being “none” and 100 being “full”.

I do not find this useful in practice, because, being a normal human being and not a machine that needs gauges to track its fuel level, I can feel how much energy I have left for my day. I can also tell how well I slept and whether it reenergized me effectively. I may not be able to tell HRV numbers without a device, but even that can be hilariously misleading at times.¹

I do watch the Body Battery reading out of curiosity, though — just to see how it interprets different things going on in my life.

I have hypothesized for a while, and was able to get some strong empirical evidence this week, that it literally never lets the value go below 5. On July 4, for example, it claimed that I started my day at 56 and that it had hit 5 by 6:30pm. After which I proceeded to take my family over to see fireworks, and Garmin thought I was experiencing high, ongoing stress… but the number did not budge. It just sat at 5.

I can guess why this made this choice. People who are less in tune with their own bodies might freak out if it got down to 1 or, heaven forfend, 0!

Screenshot of the Garmin Connect app’s Timeline for July 4, with a black line representing the Body Battery level, orange and bars behind it representing stress and rest throughout the day, and a green circle showing where the Body Battery line goes flat for many hours at the end of the day, even while estimated stress remains high. — The body battery that can never run out

This is one more reason to trust your body over your metrics. The data can be useful, but it is only a tool, and it is always secondary to what you actually feel when you pay attention to your body and how it works. The measurement wasn’t just wrong in showing that my “battery” was flat for that period; it was also wrong in measuring “stress” for that period!

Happily, these days I take what a device tells me with a mountain of salt.

Notes

Say: when you’re taking a prescribed muscle relaxant at night to prevent your back and leg from clenching up in response to an irritated nerve in your lower spine. Just for example, no particular reason at all that would come to mind. «ahem» ↩︎