Night GPS running watch for Beginner Runner (at Wet/Rainy Conditions)

[Daniel]

Hi @Henry,

Thanks for the update!

@Henry

The Garmin Connect dashboard actually has nice features to control the GPS mode intensity and the display brightness, and turn off certain features if desired. Quite handy.

I’m glad you found this! Yes, they can be dimmed or even disabled if you want.

@Henry

So looking at this, I would believe that I switched to multi-band between 1AM and 2AM, when the pace variance curve stopped increasing. It still decreased slowly likely because of the GPS mode transition — it takes a few minutes to stabilise. And I would guess that at around 3:30 the wind picked up and made the GPS accuracy improve quite quickly.

Interesting findings! I am surprised, however, that the GPS pace variance really didn’t decrease much at all until around 3:30 AM. However, it makes sense if there are only tiny breaks in the tree canopy.

@Henry

Anyway, maybe the timestamps and hypothesis are not right and it’s difficult to know now, but I was impressed to see how quickly the GPS pace variance increased (and likely it was 16% higher due to altitude), and how it can potentially have affected so often our training data quality in the past.

I know how hard it is to balance outdoor GPS accuracy and conditions (like tree canopy), but this is the reason I almost always run with multi-band GPS enabled now (even if just for the key segments). I’ve found that decreasing the pace variance from > 0.5 min/km to less than 0.1 has vastly improved my training data quality. However, this isn’t always possible if you’re running in heavy tree cover due to battery drain concerns. My wife has also noticed a massive difference in training load accuracy (and pace consistency) so now she will also insist we always have multi-band GPS enabled during quality sessions.

@Henry

I found also quite interesting to observe the expected heart rate pattern here. In the controlled flat environment, the heart rate readings stabilised over time until reaching a plateau in the middle of the run. And likely when the GPS mode was switched (fresh signal coming in), we also observe the heart rate becoming more stable. I believe the multi-band GPS mode was more accurate than the GPS+GLONASS, leading to such behaviour.

I would love to hear more about this once you receive the outdoor GPS reference device, as I wonder how accurate (or inaccurate) GPS tracking is where you train. Based on how this graph is inverse to the GPS variance graph, I believe your conclusion that the multi-band mode is more accurate is spot on.

I think this is where having a reference GPS device will really help you. It makes it much clearer to know when switching to multi-band mode is a benefit or detriment.

@Henry

This for me was the most intriguing behaviour… I have not yet read about training load other than it’s a relative metric. But I was not expecting it to positively correlate with the GPS pace variance in that way, and I would like to hear your thoughts on this

This is particularly interesting. You are right in that GPS errors can influence training load calculations from Garmin watches, however, pace variance should not greatly impact optical heart rate readings (which the Elevate v4 is). Also, the GPS chipset should not be impacted much at all unless the GPS variance is very high. In fact, from what I’ve read, the Airoha AG3335M should have little to no sensitivity to pace errors, and the Elevate v4 should not be significantly influenced by GPS accuracy. As such, I would say that you do actually have a GPS calibration issue in that specific running zone.

It sounds like you’re already very aware of the relative nature of GPS accuracy metrics, but this post explains the Garmin GPS accuracy scale in more detail:

GPS Running Watches for Heart Rate

Luckily, on Garmin watches you can change the GPS baseline calibration period to multi-band mode (look under ‘activity settings’), meaning it is far more useful than a chipset that adjusts every 24 hours.

One thing to consider here is that runners exhale trace amounts of body heat and moisture. While a very small amount, they can accumulate over a long run, and this could explain the training load increase if no other accuracy issues are present. While the increase would be relatively small (I would think), it may be that your usual GPS accuracy levels are so good that even a small increase in pace variance shows up. To test this, I would try running the route (without any tree cover) and completely open the GPS mode to multi-band so there is no environmental restriction. Does the training load still increase? If so, there is another accuracy source that you might want to look into — if there is nothing obvious, I would guess it is GPS calibration drift.

@Henry

And regarding the training load I’m still puzzled… this run I observed the same behaviour. Then I tried to switch to GPS-only mode during the run in the morning, but training load stayed quite high regardless. Only solution was to indeed switch to multi-band mode, then it stabilised rapidly.

Does your GPS watch have a Stryd footpod as backup? If not, it won’t stabilise training load during GPS outages, only during clear-sky sections.

@Henry

Another experiment I tried was during the day to just run on the flat open route again, but this time without any tree cover. But the training load didn’t increase then. I’m not sure whether it could be potentially impacted by the GPS pace variance itself, or even by some other route-specific factor…

I only just read this now, but I think what I mentioned above may be the case. Runners can generate heat and motion artefacts. For example, wrist movement and skin contact artefacts occur during running and this could build up enough to trigger the Elevate v4 HR sensor inaccuracies if there is no GPS stabilisation. Since you’ve already tried the open route experiment, I think this is likely the reason for your increasing training load during tree-covered routes.

These are all really interesting findings. Thanks so much for sharing!