Heart rate on Epix 2 activity WAY TOO LOW

Me too. Seems to only be in the walk mode. (I don't run). Cardio is fine.
And before someone explains to me too that the watch isn't as accurate as the strap, that's not it.
The watch might be reading 110 and then drops to 62 in the walk app. That's a sleeping HR for me!!
When the watch behaves properly, it takes a few minutes to respond to me going up hill before it starts registering a sensible heart rate. This is not that problem.  That we all accept as some kooky short coming of garmin. This is different.

It's only started doing it in the last 2 weeks, I think.

Hey, I believe you. I went for a one-hour, 22-km bike ride today, virtually repeating one I did on the 20th, both on my ebike. The first one gave me a 'Tempo' training effect of 4.0 aerobic and 2.0 anaerobic, despite using 14.x% power on the ebike. Today's ride, done using just 5% bike power (meaning, I was putting in more effort), yielded a 'Base' training effect of 2.9 aerobic and zero anaerobic. When the results were ported to Runalyze, they showed a much stronger TRIMP performance on the ride with the greater boost from the ebike. Clearly, the watch is not delivering consistent results.

What you are referring to is Training Effect and this is very different to the effort you put in which is Training Load. 

Would be interested to know what the training load was for each activity as that is based on EPOC & HR (i.e. the actual overall effort you have put into it) and would probably show a different result. I have had activities with higher loads where the training effect is "lower" than other "higher" activities. I put lower and higher in quotes as they really aren't lower and higher its more of designation than true lower and higher - i.e. its not like training load which is a higher /lower metric. 

Would suggest reading this link on training load to better understand it and you will see why its not the same as Training Effect: https://www.garmin.com/en-US/blog/fitness/ask-expert-training-load/

Training effect (what you are talking about) determines the type of results you can expect and the types of performances you’ll be well prepared for in the future .i.e. its sneak peek at how each training session is expected to impact your future fitness levels. One of the most common uses of training effect is to coordinate and balance workouts that maintain and improve your current fitness level. 

Read this article on training effect and you can see why you despite working harder you may get a "lower" - its actually different - training effect; as this is more about how and what you did than the effort you have put in. Of course effort plays a role, but you can put max effort in and never get any anaerobic - you would just get high aerobic; on the other side you can cruise putting in little effort but then add a couple of sprints and you will receive some anaerobic training effect as that is what you done. https://support.garmin.com/en-GB/?faq=Vi2undejXR5Mmq662o4lO9

Would pay particular attention to this graph as I find it very useful in understanding how low and high aerobic work in conjunction with anaerobic based on how you work out:

(its in the link)

The point you missed is that the Training Effect differed so much over two consecutive rides that were basically the same. The only substantive difference between them is that the one that allegedly generated almost no Training Effect was the ride in which I used almost no battery power on the ebike (5% vs 14%). Two comparable rides done just days apart cannot generate very different Training Effects, and nothing in the articles suggests such a possibility. By the way, both rides most closely resembled the Lactate Threshold Intervals from the graph above, with the exception that the second ride (that generated less Training Effect) involved more effort as there was less battery assist. I fail to see how greater efforts leads to less impact.

The watch heart beat outside an activity is not updated very often. It is possible that the drop you see is just the change to real time measurement, aside from possible other changes like watch position (if your strap is too loose, the reading might be off when you don't pay attention to the measurement, lags on the watch display, but when you rise your watch to check, the sensor is in the correct position and the reading is real time).

Of course, if you are using a chest strap, this suggestion is a moot point :-)

I am confused by the fact that the TRIMP  is higher on the ride where the bike was assisting you more. Is TRIMP using the power data you are deploying or the power data that the bike is deploying?

I am just curious about how this works with an e-bike ;-)

WRT to your question, it is very hard to compare 2 different rides at the training effect level. Too many algorithmic layers on top of the raw heart data data, itself depending on physical condition that day.

Even if you reproduce the exact same interval based training workout, doing your best effort to replicate the same human power output pattern (heart rate is too fickle), you will not see exactly the same training effect numbers.

At least this has been my experience on power-based training plans on a trainer.

I am using anaerobic/aerobic numbers to ensure a balance in the training plan over time, not ride vs ride.

very difficult to tell unless you provide open links to both activities as per my point that while they may look similar on the summary level once you get into the detail it can be a very different case in point, especially as its mainly based off HR, unless you are saying that you had a linked bike power meter and the training effect was based off power meter not HR - in which case I would agree with you that something is incorrect? But if your impact is based off HR, really has nothing to do with how much bike power you used as there are too many other factors that can impact your HR. If you were in a lab and everything was the exact same, and having a coffee 5 mins before the two rides, you would get different benefits, as coffee will cause you to have a higher HR rate. Wind, how your were feeling on the day/energy levels, potentially fighting off flu/illness, or even muscles being tired could all give a day where you used more bike epower but your body worked harder on a day where you used less epower and hence would cause you to have a different load focus benefit.

This is part of the reason why i would prefer to see more RPE input options across all activities and not just running, swimming and cycling. Would also be great if off the back of that it provided an adjusted benefit (which while not being used for any metrics - could at least be used for comparitives.

Hello. I came across your post and found it that I have a very similar issue. Did you manage to find a solution to this?

thank you!