Charge 6 AZM differ after doing same workouts

[amray77]

I workout (nearly) daily and track my AZM.  While I do rotate my workouts, I generally use the same core group of workouts.  I have noticed, over time, that I will see substantially different AZM's for the same exercise on some days.  On these days, I am sweaty and breathing hard so I assume my body is working as it does on other days.  On these days, I may see 1/2 to 1/3 of the number of AZM's as I see on "typical" days.  This seems to be inversely proportional to my readiness number --- when my readiness is lower, my AZM's are also lower.  Intuitively, it seems like if my readiness is down that my body should be working HARDER to do the same exercise.  This is just the opposite of what I am seeing.

I have been tracking AZM's for almost 2 years, so this is not a new thing.

Any insights are greatly appreciated.

Moderator Edit: Clarified subject

[RiekoC]

Hello @amray77 

My apologies if you have already checked out this help page on Active Zone Minutes (<-- click link) and this one on Readiness Score (<-- click link)

Since Active Zone Minutes are based on your tracked heart rate being in a certain range, have you had a chance to look at your heart rate graph in the Exercise tile? That would show what heart rate ranges were tracked by your Fitbit. It could be that on the days that you have lower AZMs, your device tracked more minutes in the Moderate range (1 AZM/minute) than Vigorous or Peak ranges (2 AZM/min).

[amray77]

I have reviewed how this is supposed to work — AZM’s are earned when the heart rate elevates into higher ranges…as I understand my RHR being the baseline for measurement.   And this makes sense —- we are trying to put demand on our heart and the AZM is a good measurement.   I track and monitor both my RHR and my AZM’s.

My confusion comes when I have days where I am unable to raise my heart rate with the same activities that normally raise it.  One would think “yes!  Fitness is helping.”   But there is more to the story:  on the days when I am not getting the expected (and typical) elevation, my readiness number is LOW.   If I do the exact same workout as I did two days prior, I will see half (or less) of the AZM’s.  My heart rate simply is not elevating, even though I feel like I have worked hard.  This happens at the same time my Readiness score decreases.

It is almost like when my body is experiencing fatigue, my heart rate just doesn’t respond.  A protective mechanism?  A glitch in measurement?

I have been watching this for at least 6 months, trying to figure out the relationship.  It seems opposite of what I would expect.

[Rich_Laue]

You mentioned over time. If you are doing the same exercises, the same way, and your heart muscles are creating stronger and ande efficient. It is possible that your heart doesn't have to work as hard, and a lower AZM number will be reported 

[amray77]

Again, this make sense but still doesn't totally explain it.  When the AZM's drop off (again, same workouts), I always jokingly say "It's hell getting fit!"...which seems to make sense.  HOWEVER, this drop coincides always with the drop in readiness.  For example, I'll do a workout, get 30 AZM's.  I repeat, although I do mix them up some, but will typically see 30.  Right until my Readiness drops and then so do the AZM's I get from the same workout.  When the readiness score goes back to "Excellent", I will get the 30 again.

Right now, my readiness score is 45...which is "Good".  On this morning workouts, I earned a total of 15 AZM's.  When my readiness score is "Excellent", I will get 50 AZM's for the same exercises.  It truly seems like it is much much harder to get AZM's when my readiness is lower.  If this is true...why is that?