How avg vigorous minutes for last 4 weeks are calculated?

I have the same question. Under fitness age my 4 week average for vigorous minutes shows as 66. However, If I look under Intensity Minutes it has numbers of 128, 68, 123 and 69 for vigorous minutes for each of the last 4 seven day periods. By my reckoning that should be an average of 97 minutes per week.

Unfortunately, the Fitness Age FAQ (What Does Fitness Age Mean in Garmin Connect? | Garmin Customer Support) only speaks about Vigorous Days, and does not provide any insight of the aspect of Vigorous Minutes, so I am afraid nobody will tell you how exactly they are calculated. I can only speculate that the algorithm either does not count vigorous minutes from days not recognized as Vigorous (not having a minimum of 5 continuous vigorous minutes), or that it even discards any intervals that are shorter than 5 continuous vigorous minutes.

Although I am not at all sure, whether it is really so, the solution that works for me quite well, is increasing the number of vigorous minutes, and trying to keep the higher effort for at least 5 continuous minutes, and preferably every day. 

As per the support article trux linked, a vigorous day is a day which has at least 5 continuous vigorous minutes. So even if you run 3 days a week for at least 30 minutes, not all of those days may qualify as “vigorous”.

According to Garmin’s fitness age “science” (marketing) page:

https://www.garmin.com/en-CA/garmin-technology/health-science/fitness-age/

• Aim for at least 5 vigorous intensity minutes in a 30-minute time period to achieve your vigorous intensity objective for that day.

Yes it’s annoying that there are two different definitions. Clearly the former satisfies the latter, but not vice versa.

I have no idea where the mismatch for avg vigorous minutes is coming from tho. Trux’s speculation could explain it, but who knows? I agree that the lack of transparency here is annoying, too.

3045303 said:

If so, how can i plan and monitor my exercise progress for fitness age reduction if it is not transparent?

Personally I don’t get too hung up on the metrics Garmin provides, except to monitor trends over time.

If you really care about fitness age, I can tell you what the targets are, having exceeded the minimum vigorous minutes/days targets on the Fitness Age page. (Once you exceed the vigorous minutes/days targets, the page no longer shows you your 4 week average, it only shows you the minimum targets.)

- Vigorous Minutes: Maintain at least 75 min/wk

- Vigorous Days: Maintain at least 3 days/wk

Yeah, this is kind of implied on the support page.

Sounds trite, but you could just slowly ramp up your weekly exercise time until you hit these numbers.

Thank you all for answers!

Probably most useful for me would be "don’t get too hung up on the metrics Garmin provides, except to monitor trends over time" ;)

If 30+min nonstop running 3 times a week at pace 6min/km and pulse 160+ does not qualify for "- Vigorous Minutes: Maintain at least 75 min/wk / - Vigorous Days: Maintain at least 3 days/wk", then that description is totally confusing!

3045303 said:

If 30+min nonstop running 3 times a week at pace 6min/km and pulse 160+ does not qualify for "- Vigorous Minutes

It may be better not ony for the vigorous Intensity Minutes, for the Fitness Age, and for the stats, but especially also for your health, fitness, performance, and for you progress, if you do a bit longer, and much less intensive workouts. It is best keeping the majority of your runs in the low aerobic mode (Z2). Even that is usually sufficient for getting plenty of vigorous minutes. With the default IM settings, and with the 7 days avg Resting HR of around 50-60 bpm (common at an average person), you start getting the Vigorous Intensity Minutes already at the HR of around 100-120 bpm, so it is not such a big problem to get couple of tens of them in average daily, even without killing yourself with short runs where you push your HR to the lactate threshold or even higher. Not only it makes the recovery longer, but it also may lead to health problems, or to injuries, while not bringing much progress. Have a look at some YT videos speaking about "low heart rate running", "Maffettone method", etc. Trying to push hard at every run is a classical mistake when starting to run. Even elite athletes spend the majority of their training time in low HR zones.