What to track
The signals that matter most in ME/CFS are ones that can warn of a crash a day or two before it hits, or flag an infection early:
- Overnight heart rate variability (HRV). In a study of 4,244 people with Long COVID, ME/CFS and related illnesses using the Visible app, a higher morning heart rate and lower HRV predicted worse fatigue, brain fog and crashes later that day.1 Another study found HRV among the best predictors of next-day fatigue,2 and in Long COVID, HRV stays depressed for about 24 hours after exertion.3 Many patients report the warning comes a day or two ahead; the published evidence so far shows same-day and next-day prediction.
- Resting heart rate. A rise can signal over-exertion or illness.
- Respiratory rate and skin temperature. Useful for spotting infections early.
- Sleep
- Real-time heart rate during activity. This is the key pacing tool.
A simple daily log
You don’t need a device. Each night, record:
- Energy today (0–10)
- Brain fog today (0–10)
- Crash? (yes/no)
- What I did. A few words.
- Sleep quality
- Changes. Any new supplement, medication or dose, with the date.
After 4–8 weeks, compare weekly averages. You’ll start to see which activities cost the most and whether any treatment is helping. It’s also powerful evidence to show a doctor.
Devices compared
Prices are as at September 2026 and change often; check the maker’s site.
| Device | Price (AUD) | Good for ME/CFS | Watch out for |
|---|---|---|---|
| Visible app + armband4,5 | Paid tier includes a Polar-made armband | Built for ME/CFS and Long COVID pacing. Real-time heart rate alerts, a daily “PacePoints” energy budget, HRV, symptom and medication tracking, monthly reports for doctors, optional research participation (its data has produced peer-reviewed studies). In a survey of 1,301 users, 77% reported improvement, though with no comparison group.6 | Armband form factor |
| Garmin Cirqa (screenless band, launched July 2026)7 | US$199.99 RRP, no subscription | “Body Battery” and stress tracking are widely used for pacing in the ME/CFS community. Up to ~10 days of battery. Wristband or armband. | The Garmin Connect app is dense, which is hard on brain-fog days. New product. |
| Whoop 5.0 | Membership only (annual plans; check current pricing) | Mature HRV and recovery tracking; comfortable to wear 24/7 | No ME/CFS mode. Its “Strain/Recovery” model assumes an athlete, so a “green” day prompts you to push harder. No PEM concept or real-time stop alert. |
| Google Fitbit Air8 | A$199, includes 3 months of Google Health Premium | Cheapest option. Screenless, light, ~1 week of battery, sleep tracking, HRV, breathing rate, skin temperature | Limited without the paid Premium tier. The AI coach sets activity goals that may not suit pacing. |
Before you buy, check it has
- Real-time high heart rate alerts during activity. The single most useful feature.
- Overnight SpO₂ (blood oxygen). Not diagnostic, but trends can support a request for a sleep study.
- A simple app you can use on a foggy day
Signs a treatment might be working
When something helps in ME/CFS, it usually shows up in your data a week or two before you notice it:
- Resting heart rate trending down a few beats
- Morning HRV trending up
- Fewer over-limit days at the same activity level
- Fewer and shorter crashes
References
- Digital physiological biomarkers predict within-person symptom changes in complex chronic illness Observational
- Wearable-derived predictors of next-day fatigue in post-viral illness Observational
- Wearable heart rate variability monitoring, autonomic dysfunction and post-exertional malaise in Long COVID Observational
- Visible: illness management for ME/CFS and long COVID News
- Visible: the pacing app for people with ME/CFS and long COVID News
- Self-reported outcomes among users of a pacing app for ME/CFS and long COVID Observational
- Meet CIRQA smart band: the screen-free health and fitness tracker from Garmin News
- Google Fitbit Air News