Exercise, Recovery & Readiness

Exercise is deeply connected to the balance of mind and body. When you move, your autonomic nervous system stirs; when you rest, it returns — and this very back-and-forth can be observed in the form of HRV (heart rate variability). On this page, we gently explain the relationship between exercise and HRV, with sources, and introduce how Feelmo watches over it.

First, why is HRV related to exercise?

HRV is the slight fluctuation in the interval between one heartbeat and the next (the R-R interval). This fluctuation mainly reflects the work of the parasympathetic nervous system (the side that rests the body). Because exercise moves this autonomic balance considerably, HRV becomes a gentle window that tells you "what state your body is in right now."

For more, please also see What is HRV?.

Exercise grows HRV

Meta-analysis has reported that regular aerobic exercise is associated with higher resting HRV (especially the parasympathetic component) (Sandercock et al., 2005). The view is that as the body adapts to exercise, the heart becomes more able to "fluctuate."

Rather than chasing each day's score with highs and lows, this is a change that comes into view when you gaze slowly over a long yardstick of several weeks to several months. Nothing is decided in a single day, so we hope you can read it with your shoulders relaxed.

The rhythm of load and recovery

On the other hand, right after hard exercise, HRV temporarily drops and returns as you recover. The body responds to the load of exercise and then rebuilds itself — and observing the rise and fall of this rhythm, as a way to gauge "how recovered am I today?", has spread in the athletic world (Plews et al., 2013).

Figure: an illustration of overnight HRV temporarily dipping after a hard load and returning with recovery. The dotted line is your own baseline. The figure is illustrative, not actual measurements.

How to read these ups and downs

• HRV dropping after a single bout of load is also evidence that your body is responding properly. The drop itself is not a bad thing.
• What matters is whether it returns properly afterward. A quick return means recovery is progressing; a slow return may be a sign that "today, let's rest a little more."
• The method of monitoring exercise status with autonomic indicators has also been examined in systematic review and meta-analysis (Bellenger et al., 2016).
• What matters is not a single day's value but the trend from your own baseline. That said, how to read a rise or fall in HRV is not straightforward, and it has been reported that its meaning can change depending on context (sleep, physical condition, temperature, stress, and so on) (Plews et al., 2013). Don't judge from a single number — please gaze at it as a flow.

How Feelmo handles it

Feelmo is not an app that "guesses your emotions"; it is a daily companion that gently watches over the balance of your autonomic nervous system. The principle is that rather than deciding your mood or feelings, it observes how settled your body is.

The relationship between daily behavior — including exercise — and HRV is also read in the context of this Balance score (0–100).

How the Balance score works

• It is calculated from HRV (heart rate variability / the fluctuation of R-R intervals) derived from Apple Watch.
• The score is built mainly around multiple HRV-derived clues, measurement quality, and movement from your own baseline.
• It is read in this direction: low = fluctuating, high = settled.
• This is the most important part: it is not a number for comparing yourself with others. Read it only as the difference from your own baseline. Even if it dips a little after exercise, that is something to view as a deviation from your own "usual."

For more, please see Balance score and The idea of a baseline.

The score is translated into a "facial expression"

Rather than making you stare at the numbers themselves, Feelmo translates them into the facial expressions of 6 companions (Genki/Energetic, Odayaka/Calm, Futsuu/Neutral, Fuan/Anxious, Panku/Overwhelmed, Tsukare/Tired) and places them beside you. For example, if "Tsukare/Tired" shows its face the morning after you pushed hard, it is not blaming you — it is a word of observation saying "let's take it easy today." It is a touch designed to stay close to you gently, without making firm assertions (The 6 Companions).

Checking "whether it works for you"

"Is this amount of exercise, or this way of resting, really helping my balance?" — Feelmo Premium's habit-impact analysis, Which habits help you, tries to answer that question. Inside the Kokoro Report's "This week's insight," it individually compares whether habits such as exercise or breathing actually move "your own" balance. Not generalities, but confirmation with the data of you alone (Which habits help you).

How indicators are integrated and assembled into a score is the core of our proprietary Feelmo analysis logic, and is not disclosed, as a trade secret. That said, the idea of "reading it around multiple HRV-derived clues, as the difference from your own baseline" is exactly as written here.

Here's how you can use it

1. Exercise as usual, and at night sleep with your Apple Watch on.
2. The next morning, gaze at the balance gauge and the 6 expressions on the home screen.
3. If it leans toward "Tsukare/Tired," don't overdo it — gently settle with breathing or light activity (Breathing Techniques).
4. As you keep this up, your own "load → recovery" rhythm gradually comes into view. Premium's long-term trends and autonomic trajectory reflect that flow even more carefully (Feelmo Premium).

Not to push you, but to help you settle. Not to be tossed around by numbers, but to grow friendly with your own rhythm — that is Feelmo's wish.

References

1. Sandercock GR, Bromley PD, Brodie DA. Effects of exercise on heart rate variability: inferences from meta-analysis. Medicine & Science in Sports & Exercise. 2005;37(3):433–439.
2. Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Medicine. 2013;43(9):773–781.
3. Bellenger CR, Fuller JT, Thomson RL, Davison K, Robertson EY, Buckley JD. Monitoring Athletic Training Status Through Autonomic Heart Rate Regulation: A Systematic Review and Meta-Analysis. Sports Medicine. 2016;46(10):1461–1486.