Incorrect exercise load

bro you have wrong hr zones, there's no bug

As surprising as it is, the watch does not use your HR zones to calculate the training effect.

The training effect is entirely based on Excess Post-exercise Oxygen Consumption (EPOC) dynamics during the workout.

EPOC is estimated during the workout based on HR, pace/power when available (pace/power greatly improves anaerobic effect estimation) using Rest HR and Max HR as reference (VO2 Max model).

Heart rate zones are just guideposts for the user to target a certain outcome.

If the time spent in HR zones is not consistent with the EPOC evaluation there can be several reasons:

- the Max HR value is wrong, which impacts VO2 Max and EPOC, and the entire HR/Pace relationship model (used for performance condition, stamina, training effect, load, targets for daily suggestions, etc.)

- the resting HR is wrong (uncommon but possible if the user doesn't wear the watch at night)

- the HR recorded during the exercise is flawed (common with the wrist HR, or a dry chest strap)

- the pace recorded is wrong (mostly impacting anaerobic effect, because of GPS reception, etc.)

Given the screenshot where you show a bunch of VO2 Max workouts, either your are way overexercising, or there is a problem with your VO2 Max data.

The problem is that there is no clear way to "reset" the models.

First, make sure your Max HR is correct. How did you determine yours?

Second, always wear a chest strap.

Third, keep a balanced training focus, follow daily suggestions and from time to time, replace the target intervals with maximal effort steady during the duration. Over time, this will feed good representative data to the watch.

Another way is to do a factory reset and to not connect the watch to your phone or the web for a couple of weeks. The watch will rebuild its model from scratch. I did this recently, and it was not much of a pain. After the reset I got a new high VO2 Max estimate, and it is slowly going back (down) to the estimate I had before the reset.

Thank you for your considered and detailed reply, I appreciate it.

To answer your question regarding my max HR, I obtained this by viewing my previous hard runs over the past year. I use HRR% to get my current HE Zones. My resting HR I check regularly first thing in the morning in bed when I awake. 
You mentioned wearing the watch whilst asleep determines the resting HR, but is this a true resting HR as the heart rate is always lower when asleep?

You mentioned over exercising as a lot of my runs are V02 max, however half of them should’ve been base runs in HRZ 2, and a few tempo/threshold runs not recorded as such.

I have since completed some zone 2 runs and the watch has successfully characterised them as such. I try to do 75% of my training in zone 2, and mix that up with tempo/threshold runs. I don’t do any interval training so never get into the Anaerobic zone. I’m 61 and basically just run to keep fit and love the solitude of just running.

The watch has continually rated my runs differently to what I expect. 

I tried running in a chest strap, not a Garmin one unfortunately, I have had a Polar H10 for a few years, but my HR kept dropping out on runs, my watch seems to be a lot more reliable, I did try fresh batteries which made no difference, I’m wondering if a Garmin chest strap would be the same, possibly where I run the signal is not great?

Also Garmin won’t recognise the Polar chest strap for taking a LTH test which is a pain.

Anyway, the last three runs have been rated correctly so I’ll see how it goes from here.

6871473 said:

I obtained this by viewing my previous hard runs over the past year

The Max HR is higher than any peak HR of any activity, most likely. It is rare that you get to Max HR. If you are a trained runner, take your peak HR of the fastest 5k you ran and add 5bpm. This should be very close to the actual Max HR.

6871473 said:

is this a true resting HR as the heart rate is always lower when asleep?

The watch will take an average resting HR anyway, and sleep periods are included.

6871473 said:

I have had a Polar H10 for a few years,

I have both, and I prefer the H10.

6871473 said:

my watch seems to be a lot more reliable

That means there is a problem with the H10. If batteries are not the problem, then the strap is. Even if you rinse your strap everytime you use it, expect 12-18mo of life if you run/exercise and sweat a bit every other day.

6871473 said:

Also Garmin won’t recognise the Polar chest strap for taking a LTH test which is a pain.

It should. Also a sign there is a problem with the strap.

If you care about the accuracy of the training metrics, wear a chest strap.

Etupes25 said:

The watch will take an average resting HR anyway, and sleep periods are included.

This is good info thank you. My hard runs were 5k runs so I will re-evaluate my max hr as you suggest.

Etupes25 said:

That means there is a problem with the H10. If batteries are not the problem, then the strap is. Even if you rinse your strap everytime you use it, expect 12-18mo of life if you run/exercise and sweat a bit every other day.

Yes, my strap is older than you suggest, even though I do rinse after run I think you may be right, I will order a new strap. 
You say the Polar H10 works for the LTH test? I will retry this once my new strap arrives.

Etupes25 said:

The watch will take an average resting HR anyway, and sleep periods are included.

Ok, this is something I didn’t realise. Again I will adjust my resting HR as required.

Thanks again