Body Battery and Morning Coffee

Any number of factors could be causing the stress results to record high (and therefore drain your body battery) even when you're still.

For example - did you do extremely strenuous exercise the day before? If so then perhaps your heart/body are still in recovery mode causing the watch to record high stress levels.

Or it might be the case that your resting heart rate is relatively high, which would make it more difficult for the heart rate monitor to distinguish between high and low heart rate variability which is what the watch uses to determine stress levels. Coffee could certainly raise your resting heart rate, but there doesn't appear to be much if any effect on HRV so that probably isn't the cause of your body battery issues.

Personally I've found body battery to be occasionally confounding (like giving me almost no recharge after a full 8 hour sleep) but even on these occasions it hasn't been too far off where I've actually been in terms of physical performance. Almost scary actually. In the aforementioned scenario where a full (and at the time I felt restorative) sleep led me to think I could tackle a big workout saw me fade extremely quickly during it. Another day where I had a disrupted and seemingly poor sleep the BB told me I was still good to go and against my better judgement I did a workout and powered through it. Your mile may vary obviously but I've found it a useful if somewhat confusing metric.

Garmin actually specifically has said that caffeine does not affect body battery in any substantial way.

Stress is measured not by heartrate BPM, but rather by HR variability. I think what that means is that when you are stressed, your HR is irregular, and when you are not stressed your HR is more consistent. It is not directly correlated with how high your HR is. You can just as easily be experiencing stress (variable HR) while sleeping or sitting on the couch, as you can when you're out running.

If you're resting and your HR is relatively consistent, your body battery will go up. If you're resting but you're stressed (your HR is more variable), your body battery goes down.

HRV is the other way round - low variability is a sign of stress and high variability is a good sign. Hence why if you have a higher resting heart rate it might be harder for the sensors to get a good HRV read and flag high stress levels.

I can't explain it very well (and I'm not a medical professional) but Firstbeat (whom Garmin license IP from for their HR related metrics) have a page on HRV which explains it well.

https://www.firstbeat.com/en/blog/what-is-heart-rate-variability-hrv/

carl.andersson said:

HRV is the other way round - low variability is a sign of stress and high variability is a good sign. Hence why if you have a higher resting heart rate it might be harder for the sensors to get a good HRV read and flag high stress levels.

It is a very interesting topic and Body Battery obviously works very well (at least for me). I just checked one of my recent runs and I have a standard deviation over 5 minutes periods of 28 ms which is quite a lot for and average of 390 ms between beats. Personally I feel very relaxed while running, even though I know I'm thinking  about a lot of things I have no clue about what when I'm back home :-)

Try to do similar recording while sitting or laying down. You'll see how the variability goes up when you do nothing and are relaxed. I would think that during an activity everything is a bit more complicated.

Also what matters is the difference between HR when you breathe in vs out. When you are relaxed the difference is large. That is where most of the HRV comes from.

For me it also correlates with resting HR .. whn that is low, HRV is rathe higher and thus the stress level is very low.

Marbuel said:

For me it also correlates with resting HR .. whn that is low, HRV is rathe higher and thus the stress level is very low.

Agreed - so for a while ago back in Februrary I wore a Fenix 6 Pro and a Forerunner 245. The Fenix 6 Pro was and still is inaccurate for resting heart rate for me (usually 5 to 8 BPM higher than a belt). The Forerunner 245 was belt-accurate. So I always saw lower body battery on the Fenix 6 Pro than the 245 which I put down the the F6 Pro being 'off' when resting.

try my watch face/widget and app, all them has live stress so you can observe how coffee/alcohol/others influence on stress

apps.garmin.com/.../apps

your HR is irregular, and when you are not stressed your HR is more consistent. It is not directly correlated with how high your HR is. You can just as easily be experiencing stress (variable HR) cup while sleeping or sitting on the couch, as you can when you're out running.

It’s the other way around. HR is regular when stressed and irregular when relaxed.