SlowpulseThis one has a genuinely two-sided answer, and missing the second side is how people end up alarmed by a number that was behaving exactly as expected.
The long timescale: training is associated with higher HRV
A 2024 review of the factors influencing HRV reports that regular physical activity and endurance training are associated with an increase in parasympathetic activity, and higher HRV with it. Resistance training showed no such change in otherwise healthy people.
So as a general pattern, someone who trains regularly tends to sit higher than they otherwise would. This is a slow adaptation measured over months, not something you can observe from one session.
The short timescale: a hard session lowers it
The same review reports that high-intensity training and competition decrease HRV. A hard effort raises heart rate and lowers variability for a period afterwards.
Both statements are true at once. Training raises your HRV over months, and lowers it for a while after each hard session.
This is why a single reading after a heavy day is close to meaningless, and why the days immediately after hard training are the worst possible moment to compare yourself to anyone.
Why this matters for a stress score
Here is the problem this creates for any app that watches these signals. Exertion produces almost exactly the pattern that tension does: heart rate up, HRV down, both at once. Judged on the numbers alone, a hill sprint and a difficult conversation look remarkably similar.
An app that ignores this is guaranteed to tell you that you are stressed every time you exercise, which is both wrong and quickly ignored — and an alert people ignore is worse than no alert.
How Slowpulse handles it
Slowpulse reads your active energy burned and your exercise minutes alongside the heart signals, and uses them to discount the score. The more the recent numbers indicate genuine physical effort, the less weight the heart-rate excursion carries. Past a threshold of exertion the score is pulled down substantially, on the reasoning that your body has an obvious explanation for the state it is in.
It is a deliberately simple correction rather than a clever one. But it is the difference between a score that means something on a rest day and a score that is really just an exercise detector.
It also means the score is most informative when you are not training — which, for noticing tension you had not consciously registered, is exactly when you want it to be.
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