I’ll tell you what I know about it.
First, set your activity level accurately, the monitor will later adjust them based on data it gets but the better your first guess the better the results will be.
The epoc number is based off of your heart rate variability, if you’re an engineering type then you’ll most properly realize it as the taking the fourier transform of your hr data series and then looking at certain frequency bands which have been established as relevant. If you’re not th emath type then think of it this way, a steady hr is not exactly steady, there is always some variation up or down. The hr may ride and fall slowly, or quickly or both slowly and quickly and they kinda lay one on top of the other and it adds up to a ver complex pattern. All that rising and falling has been hypothesized to mean something.
Specifically these guys have some data that shows that if you take the right frequency of rising and falling, do some math on it and add it all up, it will give the current value of your post exercise oxygen consumption. If you were to stop exercising at that very minute, how much EXTRA oxygen will you burn above your normal resting level between the point you stop exercising and the point your metabolism gets back to normal.
The biggest weakness of their system is that it doesn’t take into account lactate threshold, it turn out that lactate threshold hr is a rather important number if you want to predict epoc from hr data. So what they do is they estimate your lactate threshold based on your activity class. Based on how much exercise you get they take a stab at what your lactate threshold will be compared to your max hr. As I said, after you build up some data the softare will automatically adjust it for you.
Now, here’s where the levels come into it. Each epoc number is classified as maintaining, gaining, or overreaching for an activity class. You can check as you go to see where you are on that scale so as to A make sure you are getting something out of the workout or B make sure you are not overdoing it.
In practice there are two funny things about it that mean you can’t just live and die by the epoc number. First is that it nly records the highest number for the session, if you start the workout with some hard intervals get your epoc number up to say 100 and then ride easy for another 2 hours, it will still show 100 as the epoc number for that ride. In effect according to that number, the last two hours of riding didn’t count, we both know it actually does count for something.
The other thing is that the epoc method really favors intensity over volume. Now there is some wisdom to this and depending on the specifics you could easily make the case that this is the way to go for some people. However, you have to use your noodle and not go all hard all the time even if the epoc number stays low for your long workouts. This is in the training with epoc book as well.
I have the older t6, so it calculates the epoc afterward, not during the workouts. It’s an interesting number and I do look at it but it has never really told me anything I didn’t already know.
All in all it is a decent non-linear training quantification method, not particularly outstanding in any way in my opinion. One big drag about it is that in contrast to trimps or even tss and govss, it is harder to guess at the epoc number of a workout you did without the watch on. In case you did a workout and didn’t remember your watch.
NOTE: If you want to get hr while swimming, get yourself a suunto memory belt to go with your watch. It is a heart rate belt with an internal memory that also will display on your watch when you have it on. So you can get post hoc hr data after the swim. Nice for a tri race where you want to know what sort of hr you had for the swim.