Dip In Fitness Numbers Across the Board

Has anyone else noticed a change in their fitness results since the latest firmware?

I have observed a somewhat profound dip in performance numbers since about the time the latest firmware was pushed out.

Example: 
Here are the numbers from a Bikram yoga class on Oct. 5th.
These are typical numbers from my many years with this activity.

Contrasted with the numbers from the two weeks since (this one is actually the higher of the two weeks since the 5th):

This is just one example, but there are several others, be it power lifting, strength training, cardio, etc.
I could post several others, but I'm trying not to test everyone's patience and attention span.

Suffice it to say that all activities typically are down sometimes several hundred calories. 

It seems to me (and this is just a theory) that something has changed in the way heart rate is being measured.
This can effect the amount of calories being burned, which in turn effects your training load (which is down considerably), which effects your "Fitness Age" (which is UP, and admittedly a bullsh*t value).

Here's Training Load as of this morning.  Of course it is way down from my normal numbers. Both numbers are usually in the 450-500 range.

The only "scientific controls" that I can apply here are 1.) my training has not changed in any dramatic way (in some cases I have been advancing) and 2.) these numbers have not changed to this degree in the many years I have been tracking my fitness with FitBit, Apple Watch and now Garmin.

I know not to treat these numbers as Gospel (I feel as strong as ever - maybe stronger), especially Fitness Age, but we trust these devices to be consistent in their manner of gathering information so that we can use those numbers to make the necessary adjustments to our fitness activities.

Ok - rant off.

  • I don't see any significant change in indicated calories lately. I have however noticed that two seemingly similar training sessions can be rewarded with very different training load. Typically low load if I am in good shape, and higher load if I haven¨t done that training for a while. Heartbeat is quite similar, but the watch indicates (correctly) longer rest time and higher load. I guess this is based on Firstbeat EPOC measurements (look it up).

  • Thanks for the reply. 

    I don't think the EPOC theory applies to me, however, as this is a sudden change across the board after about 12 years of tracking fitness with assorted devices. The results until recently had all been similar.

    Suddenly after all this time my training load is drastically down. 

    Have I suddenly become an Olympiad?
    My workouts continue to be exhausting, so I don't think I've crossed into elite training territory.

    Again, the numbers aren't carved in stone, but they should be somewhat consistent. 

  • No change for me. The only cardio exercise I've been doing in 2025 is a 5k on the treadmill at 10km/h, that I do a few times a week. My average HR for this exercise is extremely predictable (90% of the time between 150 and 154). My calorie burn as advertised by my FR255 has been stable, between 290 and 310. See below a chart. I am on the latest version, v25.06.