Stress Monitor
The Stress Monitor tracks your cardiovascular stress level in real time throughout the day, providing a continuous picture of how much your body is being taxed — beyond just your workouts.
Physiological stress and the heart
Stress — whether from exercise, work pressure, poor sleep, or illness — activates the sympathetic nervous system, which elevates heart rate and blood pressure. The cardiovascular system cannot distinguish between different types of stress; all stressors drive heart rate above the resting baseline.
This makes heart rate a useful, continuous proxy for total physiological load. When your heart rate is elevated relative to your resting baseline without intentional exercise, it indicates that your body is under some form of stress — this could be the immune system fighting off an infection, caffeine stimulation, dehydration, or psychological stress.
For athletes, monitoring non-exercise stress is important because high background stress reduces the body's ability to absorb training and recover effectively. Two athletes with the same workout can have very different total stress loads depending on what else is happening in their lives.
How Flux measures stress
Flux reads your heart rate continuously from Apple Health throughout the day during periods of non-exercise. The Stress Monitor provides a panorama of your stress only during times when you are not working out or engaged in intentional physical activity. Each reading is compared against your personal resting heart rate baseline and maximum heart rate, using a model that produces a stress score from 0 to 100:
A heart rate at or below your resting baseline results in a stress score of 0. As your heart rate increases above baseline, the stress score rises proportionally. A heart rate approaching your maximum produces a stress score near 100.
The real-time score is displayed as a circular gauge on the dashboard. The detail view shows a full timeline chart of stress across the day, as well as a 7-day daily average trend.
Stress Monitor vs. Strain Score
These two metrics are related but serve different purposes:
Stress Monitor
Real-time, moment-to-moment cardiovascular arousal. Updates throughout the day. Captures both exercise and non-exercise stress (work, emotions, illness, etc.).
Strain Score
Cumulative daily cardiovascular training load. An end-of-day metric that quantifies the total volume and intensity of all active minutes.
Interpreting your stress level
Relaxed state. Your heart rate is near baseline and your body is in a restorative physiological state.
Normal active state. Light exercise, mental engagement, or mild life stress. Generally not a concern.
Your heart rate is notably elevated. This may reflect moderate exercise, dehydration, caffeine, or psychological stress.
Significant cardiovascular activation. Likely intense exercise or acute stress. If at rest, consider rest, hydration, or stress management.
Practical uses
- Monitor elevated resting heart rate in the morning — it may be an early sign of illness or under-recovery.
- Track your stress trend over 7 days to identify chronically elevated periods.
- Use the timeline chart to see how different activities (workouts, work meetings, meals) affect your stress level.
- Correlate high non-exercise stress with low recovery scores the next morning.