What this measures
One figure for how much work your day contained, on the scale your own provider invented and capped where it chose. It is a position on that scale rather than an amount of anything, so the ceiling travels with every point.
How your device works it out
Your device watches your heart rate through the day and reduces what it saw to a single number. Every provider does that differently, so two devices watching the same day routinely produce figures that look nothing alike.
What generally moves it
The scale itself, above everything else. Then how long the device was worn, anything that moves your heart rate including heat and caffeine, where your local day starts and ends, and a provider revising its own scale.
Why Thriverence shows it
It is the other half of the picture your morning Readiness starts: Readiness is how you arrived, load is what the day then asked of you. It is never rescaled to make two providers comparable, because the figures were answers to differently shaped questions.
What it is not
This is not a judgement about how hard you trained and it is not comparable with anybody else. It is not a target, it is not a measure of health, and no figure here identifies a medical condition. Support resources are below if you want to speak to somebody.