Stress score

What your watch knows about your stress

Your wearable can't read your mind, but it can read your nervous system. Stress scores are derived from heart rate variability patterns: when your body is under stress (physical or mental), the timing between heartbeats becomes more rigid and predictable. Less variability = more stress. Garmin's score, built by Firstbeat, samples that every few minutes all day on a 0 to 100 scale; Fitbit's Stress Management Score turns it around so that higher is better; Polar's Nightly Recharge and Oura's daytime stress read the same signal with their own scales. The physiology underneath is identical: how far the autonomic nervous system has swung toward fight-or-flight.

Physical stress, not just emotional

Here's something important: a high stress score doesn't necessarily mean you're worried about something. Physiological stress includes exercise, illness, poor sleep, caffeine, dehydration, alcohol, heat and even a heavy meal. Your body doesn't distinguish between "I'm nervous about a presentation" and "I ran 10k this morning"; both show up in the data. The score is honest about load and blind to its cause, which is why the same afternoon can read as stressful on the watch and calm in your head.

Reading the scale

On Garmin's scale, which most people mean when they say "stress score":

• 0 to 25: rest. Where sleep and a quiet evening should sit
• 26 to 50: low. A normal working day for most people
• 51 to 75: medium. Concentration, a commute, an argument, a meal, the hour after coffee
• 76 to 100: high. Exercise (which the watch excludes from the daily average), acute stress, fever

The daily average is less useful than three other views: the overnight level, which should be in the rest band and rises with alcohol, late meals and illness; the share of the day in rest, which should be a meaningful slice even on a working day; and the duration of high blocks, since an hour at 80 after a hard conversation is normal and a whole afternoon there is not.

How to interpret it

Look at patterns, not single readings. A high score after exercise is normal and expected. A consistently elevated score during rest days or sleep is worth paying attention to; it could mean you're not recovering properly, getting sick, or chronically overstressed. Three specific patterns are worth knowing:

• Orange nights. Overnight stress that stays in the medium band means the body did not switch into recovery. The usual causes, in order: alcohol, a late large meal, an evening session, heat, the first day of an infection
• No rest all day. A day with under an hour in the rest band, repeated across a week, is the signature of chronic load; in the index it shows up as a high daily average and a battery that never recharges
• Stress that will not fall after exercise. Normally the score drops back within an hour or two of a session. When it stays up into the evening, the session was harder than the plan, or recovery is behind

Where the watch gets it wrong

The score needs clean beat-to-beat data. A loose strap, a tattoo under the sensor, cold hands or a lot of arm movement produce gaps and spikes that are not stress. Some medicines, beta blockers in particular, hold heart rate and HRV in a narrow range and make the score read low regardless of what is happening. And because the scale is personal, a value that means "medium" for one person is "high" for another; the comparison that matters is against your own usual day.

In MyBodyAI

Stress data feeds the Stress Load index, which reads the average and the peaks of the day's stress channel, the drain and overnight recharge of Body Battery where the watch has it, awake time during sleep and the direction of the trend, over an adaptive window of the last 5 days, widened to 10 only when those five hold no stress reading at all, so that daily noise is smoothed without an old bad week hanging around. It also feeds the Recovery, Nervous System and Overtraining indices. The goal isn't zero stress; it's making sure you have enough recovery to balance the load.