I’ve given a subset of this topic a lot of thought - Is getting this information from [INSERT WEARABLE] going to effect my training or otherwise be actionable?
I started with Whoop. It gave me HRV and sleep statistics that seemed fairly accurate most of the time (and by accurate, they matched how I felt). Strain score while interesting, wasn’t as interesting to me. The action items I got from Whoop: 1) By quantifying certain the effects on certain things on my HRV, RHR, and sleep (alcohol, irregular sleep schedule, workouts in the morning vs evening, etc.), it changed some behaviors; and 2) on what I labeled “dead days” (when my Whoop recovery score was below 15), I did not workout at all.
I then got annoyed with the Whoop subscription model and the “walled garden” of information. I started looking at Garmin watches. The cost of Garmin led to some real consideration of whether: 1) there would be action items, 2) if it was just information gathering for curiosity’s sake, or 3) whether it was a gimmick I would ignore. I decided it would be either the first or second; it would also be a cycling computer (I now use extended display on my Edge); and it would be a central place to record and view all of my exercise. I ended up getting a Fenix 6s Sapphire.
Here is my take on the Garmin in the three weeks I’ve had it:
I wore it and the Whoop simultaneously for two weeks, and the Garmin gives similar measurements on HR, recovery, and sleep (the only material difference is in the measurement of “deep” sleep);
HRV on Whoop and Body Battery on Garmin correlate very closely each morning, except Garmin goes the extra step of adjusting throughout the day;
Garmin “Stress” measurements are seemingly accurate, useful, and very informative on how certain things affect my body;
the Garmin provides a lot more information than Whoop (I’m still trying to figure out the value of respiration rate and pulse ox, but I do like many of the others), and
Garmin is a central repository for all my workouts.
As to action items, I tend to use it like Whoop - when my Body Battery is very low (under 20), I don’t train at all. When bad habits creep up and affect sleep and recovery, I note them and make changes.
To get specifically to your question (yep, it took that many paragraphs) - whether to use “unproductive” or “overreaching” as a guide - I think it depends on your goals and how much you value the marginal gains from “perfection.”
I think the stat itself is probably some version of accurate (as accurate as a watch can be). Does that mean you’ll be incapable of completing TR workouts when your battery is low? Of course not. But does it mean you may not get as much gain from that workout as you would if you were “fresher” or that there is a better workout for you that day? Probably so. Will the difference between those two affect the average amateur’s performance or results? Probably not appreciably.
TrainerRoad is, by it’s own description, “structured training.” The plans are probably pretty dialed in for the middle of the bell curve. It is the opposite of Xert - the adaptable workout platform (and I’m not saying Xert is great at it; I’m just saying it advertises itself that way). Your Garmin is pointing out that you aren’t the middle of the bell curve. Again, will it materially matter to your training? It depends on how far from the middle you are, but probably not.
For me, on a low volume plan, I have some flexibility to listen to my Garmin. I have TR workouts on Tuesday, Thursday, and Saturday. If my “battery” is low on any one of those days, I can move the workout to the next (especially moving the Saturday to Sunday). This may be tougher with mid and high volume plans.
Whew. That was a lot. I’m also going to cross post some of this to the Whoop thread.