Heat Acclimation working principle

6795703 said:

What are the principles under the hood?

What Is Heat and Altitude Performance Acclimation? | Garmin Customer Support

trux said:

...please especially note that it is the temperature your watch shows on the Weather widget in the moment of the start of the activity that decides about the acclimation.

Thanks, next time I'll check it before going outside. 

trux said:

So if the temperature on the widget is wrong (and that's often the case in some locations), then you may have problems to get the right acclimation data. And yes, I know, it is really stupid.

At least it could be double checked during Connect App sync (Activity upload).

6795703 said:

At least it could be double checked during Connect App sync (Activity upload).

There is no postprocessing. In Garmin's environment, practically all data processing happens in real-time on the device. That's the reason they use the weather data at the start of the activity. Though, they could at least re-read the actual temperature every 15 minutes, since that's being pulled by the widget anyway (as long as there is Internet available). And that's not the case, unless it changed since the last time I looked at it. 

That answers my question. I started at 6:30 am (daylight, but not too hot) - I was still going at 2pm (hot, direct sun, no shade).
So obviously the lack of heat acclimation was because I started when it was still cool :-)

Looks like the "old way" of having a supplementary notebook to log stuff still has some uses.

For me heat acclimation is an "optional extra" anyway. Yeah, 30 Celcius can be a real thing in an event. 40 Celcius starts triggering national heatwave records
[btw, I live in England].
For me, it is mostly about the amount of water I need to carry, rather than prepping for any specific mid-Summer "hot" event.
[I like to do activities "unsupported" where possible, and with a modest number of large "refuel and reload stops" when not - being in my late 50s, I am never going to set any World Records anyway!]

PedalPusher said:

That answers my question. I started at 6:30 am (daylight, but not too hot) - I was still going at 2pm (hot, direct sun, no shade).
So obviously the lack of heat acclimation was because I started when it was still cool :-)

An available workaround is splitting the activity into several parts (stopping, saving it, and starting a new one when it gets warm enough). If necessary, you can merge the activities later using the FIT File Tools. Possibly, using the Pause & Resume Later could work too, hence without splitting the activity into several pieces, but I am not sure about it - you would have to test it.

trux said:

There is no postprocessing.

I always thought that there is some kind of postprocessing, because sometimes the Primary Benefit is changed after Garmin Connect sync. For example after finishing the activity the watch summary page shows VO2 Max and after sync it is changed to Threshold.

Anyway, checking Weather synced status before going for a run really helped to get proper heat acclimation.

I've never did this, and used to have heat acclimation in summer. I guess it is related to that recent reports don't have temperature "section" at all. I checked it and 10.10 was the last version which had this kind of data:

6795703 said:

I guess it is related to that recent reports don't have temperature "section" at all.

They do, but you have to enable the Temperature recording option in the settings of each respective activity profile, since by default it is turned off at most sports (except of at OW Swim, and perhaps at a few others). However, that's not the Weather Widget Temperature used for the Heat Acclimation. It is the temperature measured by the internal sensor (hence rarely showing the ambient temperature, except if kept in away from the body, or when used in water). The internal thermometer cannot be used for the acclimation.

6795703 said:

Anyway, checking Weather synced status before going for a run really helped to get proper heat acclimation.

But not today, though I synced again before the run. I don't get it.

I noticed that sometimes, even shortly (30-45 minutes) after a sync, the weather widget indicates that phone connection is required. It possible, that after I left the flat, the weather widget went to "sync needed" state and failed to provide starting temperature for the run.

I really don't get it. The hour data is visible every time for the given day, why can't that be used for the activity even 2-3 hours after a phone connection?

The watch reloads the weather data every15-20 minutes (Active Weather Feature on Outdoor Handhelds | Garmin Support)