Sprint workout has tempo training effect

It happened again today. The daily suggested workout was "Anaerobic": 7 1:00 intervals with recovery in between, plus warm up and cool down. I did the workout and again my device calculated a "Tempo" primary benefit. 

https://connect.garmin.com/modern/activity/7805283792

I think the issue is that the aerobic training effect calculated at the end of the workout is consistently higher than that predicted on the daily suggested workout. Why is it consistently so far wrong?

Yannis77 said:

And how does the watch interpret the muscles load? Via raw speed?

I also try to start 5 sec earlier in order to maximize speed.

For anaerobic efforts, the algorithm is really looking at how quickly the HR increases, rather than how high it goes or how fast you go.

To register a higher anaerobic TE, you should make your sprints harder, not longer.

Exactly. For me its really easy to reach 2.0 and then its getting harder. Up to 3.0 is reachable for me on most anaerobic activities. Have not reached 4.0 yet though...

This is a screen shot from my last easy run (classed as Base run) which i did include 1 hard interval. Reached 1.9 anaerobic score and recieved 20 anaerobic points for that interval.

I have similar effects, but I wonder if it matters from the actual training point of view, or if it's just a Garmin "bookkeeping" thing.

So what if I don't rest enough between the sprint sets, and I jog slowly instead of walking, for example. The aerobic load will increase (according to the watch). But was my training actually "worse" ?  I guess I will have a bit more training load than the watch anticipated. So what ? Maybe it just means that I did both (aerobic and anaerobic), but I will still see physical progress if I continue training like this.

I guess my question is: should I really try to optimize the numbers that the watch is giving me because they help me make my training better ? Am I missing out something, if I miss the targets (not in terms of speed and duration of the sprint block, but rather that I strain the aerobic a bit more than planned).

Let's not forget that the point should be to improve our running capabilities, not pleasing the Fenix :-)

I found the maximum anaerobic TE on the Fenix 6 low compared to the Fenix 5 Plus used previously, and found max HR to be set higher than I guess it should be, so I set it to (220 - age) which is a bit of an arbitrary value, but more reasonable. And now anaerobic TE has gone up. 

That said, I don't pay too much attention to these metrics, and use Runalyze.com to plan and review my training.  

I had the same daily suggested workout today and this time I did get a "Sprint" primary benefit. I executed it pretty much the same way but managed to get the anaerobic training effect up to 2.7.

connect.garmin.com/.../7859890577

This is just a general statement that I've found personally about the suggested workouts. I've been following them for a little while now mainly to change up my normal routine.  One is I wear a HRM-Run chest strap (old one with snaps) as it's better than the on board for accuracy IMHO.  And the other thing that has helped me obtain the goals the watch is asking for (base, sprints, tempo, threshold) is by changing the "Target Type" from pace to heart rate.  That helps me focus on what the watch is suggesting better.  It's is different for me to target HR over pace but has become more natural as time goes on.  It's much easier to hit 'base' runs when I just follow the  HR and not worry about pace.

I do still get crossover between tempo and threshold at times, but for sprints, those seem to be very solidly recorded as sprints, same for base, and recovery runs.

I fail to see how you can do a sprint or intervals workout based on a HR target. The steps are too short for my heart rate to hit the target. So I do those with a pace target. HR target works better for threshold and tempo workouts with longer steps.