How to upload manual treadmill activities to watch?

The watch will not use those activities in its calculations even if you in some way get them to the watch. Log your treadmill runs with the watch. Calibrate and save after each run. 

VO2 max is not calculated for treadmill runs.

Well, the best and simplest would be recording your runs with your Garmin watch. Finally that's what the watch and the app were made for.

However, if you can get the activity file from iFit or Strava in the FIT file format, then you could upload them over the USB cable directly to the folder //GARMIN/NewFiles/ on the watch, but it is uncertain it will have any impact on the metrics like Training Status, etc, anyway. Very unlikely it would impact VO₂max or the Hill Endurance. You need to make true runs for that (unless the iFit file simulates the outdoor data perfectly, which I doubt).

Using the watch to record the treadmill run really is not a great option on the type of running I'm doing on the treadmill.

If you are doing a load of hill reps I want to see what elevation I've done, what intervals at what percentage incline etc, and what speed at each interval. Just recording it on a watch gives you none of this and won't add to any stats.

Whilst I get your point trux about it not been as accurate as outside, you can't think that doing 5 miles at 12% gradient with a high heart rate is not significantly different to a flat 5 miles on a treadmill. Ideally I'd like the stats from Garmin to reflect the level of effort for that session.

Treadmills are a great tool for training for hills as just by there nature they offer infinite inclines! If I wanted to do 3,000ft of climb on an evening outside I'd have to drive to the lake district or something.

The fact that all the speed, interval, incline and HR data sits in iFit but can't be easily imported into the Garmin infrastructure is just well baffling.

Degtheleg said:

you can't think that doing 5 miles at 12% gradient with a high heart rate is not significantly different to a flat 5 miles on a treadmill.

Indeed I do not think it is the same, but the watch will see the increased effort on your HR, HRV, respiratory rate, etc., too, and will adjust the relevant metrics accordingly. The watch does not really need the information about the slope.

Still, as I wrote, you can try uploading the files directly to the watch. Another solution that could perhaps work for you, is using Zwift or another 3rd party app with better integration with Garmin, instead of iFit. Or asking iFit to make their app compatible with Garmin Connect in the same way as other 3rd party services did. A partial list of them is in the following article, though this list is for indoor cycling. AFAIK Zwift works for virtual running as well, and perhaps some of the other apps too. Then there are also indoor rowing apps like Concept2 with the full integration to Garmin.

What Software Applications Are Compatible With Tacx Smart Trainers? | Garmin Customer Support

trux said:

Indeed I do not think it is the same, but the watch will see the increased effort on your HR, HRV, respiratory rate, etc., too, and will adjust the relevant metrics accordingly. The watch does not really need the information about the slope.

I'm unsure how my watch would handle that data? Would it not just think I'm very unfit and knock my stats down? Without knowing the elevation it might think I simply am blowing out my **** whilst doing a few slow miles?

I suppose if not all stats are accurately adjusted some are better than none.

In terms of iFit integration, I've read contradicting reports about compatibility issues, so I would not like to say on whose side the fault of lack of integration lies, but as I say I have no issue in exporting the activities and manually adding them through Garmin connect. The issue I have is those manual activities not then been reflected in the data on the watch.

Degtheleg said:

I'm unsure how my watch would handle that data? Would it not just think I'm very unfit and knock my stats down?

AFAIK the only metrics that consider the pace are the the LTHR and the VO₂max, and those are not measured indoors anyway, so no, it will not have any negative impact.

Degtheleg said:

I would not like to say on whose side the fault of lack of integration lies

Seeing the number of certified 3rd parties with the full integration, I think it is rather clear that Garmin does have their API ready for it.

Degtheleg said:

The issue I have is those manual activities not then been reflected in the data on the watch.

Manual imports cannot help, since the data must be processed by the watch. There is no processing in Garmin Connect. Did you already try what I suggested - uploading the activity FIT files to the device? I cannot guarantee it will work with iFit files, but there is a chance.

trux said:

Zwift works for virtual running as well,

Looking at Zwift Runn kit, it looks like I can add that to the treadmill and it will accurately monitor pace and incline. As I've got Zwift for the bike in any case this might give me a good option as the stats from Zwift on the bike are exactly the sort of stats I want to see from the treadmill. I.e. HR pace, elevation etc over the course of the activity.

I think doing an iFit programme on the treadmill, but recording the data on Zwift, which then uploads it to Garmin and Strava might be the best work around as virtual rides appear on my watch as well.

Unlike on a PC, on a Mac you need to install Android File Transfer, or similar tool for accessing MTP drives.

Accessing the Garmin Folder of a Garmin Device on a Mac Computer | Garmin Customer Support