Body battery
What's available today as a percentage of your own 90-day baseline, not an athlete's. High, medium, low — thresholds chosen for bodies whose baseline shifts with the season, the cycle, the flare.
Energy Module · For ME/CFS & variable energy
Energy tracking for bodies that vary.
You felt okay on Tuesday. By Thursday you lost the week. Body Insights reads what your Apple Watch already records — HRV, RHR, sleep, wrist temperature — and tells you, in plain language, what today actually has in it.
Get Body Insights
iPhone + Apple Watch. Free for core features.
The Tuesday-Thursday math that most energy apps miss.
You feel okay on Tuesday, so you do the laundry, take the call, run the errand. Thursday you can't get off the couch. The training-app math runs backward — yesterday's effort is what emptied today's account.
For ME/CFS, long COVID, chronic Lyme, fibromyalgia, perimenopause, post-illness recovery, energy isn't a number to maximize. It's a budget to spend honestly. Most "body battery" features were calibrated on healthy athletes — they reward activity with readiness and count rest as a deficit.
Body Insights was built around the shift. Same Apple Watch data, different lens. Today's number is what's available. Knowing what you have is the goal.
Built for variable energy, not athletic energy.
Built for ME/CFS, Long COVID, chronic Lyme, chronic EBV, fibromyalgia, POTS, autoimmune flares, perimenopause, and post-illness recovery — and anyone whose energy doesn't follow a clean line.
Apps built around training cycles assume yesterday's effort earns today's capacity. With post-exertional malaise, that math runs in reverse. The honest read is the opposite — and that's the lens the whole app was tuned to.
Rest counts as a plan. There is no streak to break, no ring to close, no badge for grinding through a crash.
Read your energy, tomorrow morning
Free for core features. No card needed.
For people who want the science.
Everything below is what an honest ME/CFS-aware energy read should tell you. If you're comparing apps, you're in the right place.
What we read from your Apple Watch.
Apple Watch records the signals. Body Insights reads and interprets them. We don't measure anything ourselves — we translate what's already in Apple Health.
Energy curve
The W-shaped daily rhythm from a dual-process model (circadian Process C plus sleep-pressure Process S). Cognitive peak and physical peak surface as separate windows — they rarely land at the same hour.
HRV trend
Overnight HRV against your own 14-day baseline. A drop of more than 10% is one of the steadier signals that today has less in it.
Sleep recovery
Sleep stages, efficiency, and fragmentation from last night, folded into the morning read. The 8-hour night that didn't restore shows up here.
Wrist temperature shift
A multi-night climb of 0.3°C or more above baseline is part of the early-warning read. It can precede an infection or a flare by one to three days.
Pacing recommendation
One sentence each morning. Take it slow. Move gently. Today has more in it. The numbers are visible if you want them. The recommendation is in words.
Pacing, not pushing.
Rest is part of the plan, not a failure of it. The morning recommendation can say take it slow and mean it. For ME/CFS in particular, the evidence on graded exercise has shifted — pacing and energy-envelope work are the approaches the Workwell Foundation and the 2015 IOM report on ME/CFS have anchored on for years. The app reflects that.
If your morning read says low, the suggestion isn't push through and check back. It's a smaller envelope for the day — light activity, longer breaks, food, water, the things that protect tomorrow's account. If your read says higher, the suggestion is to use the window gently, with cognitive and physical peaks visible so you can match the task to the hour.
The point isn't optimization. It's a body that gets through the week intact.
What ME/CFS looks like in the data.
A few of the patterns we surface, and what they tend to mean. We surface the pattern — we don't diagnose.
HRV drop with RHR rise
Overnight HRV down more than 10% from your 14-day baseline, paired with resting heart rate up two or more beats. Often the first sign of an oncoming crash or PEM episode.
Wrist temperature climb
A multi-night climb of 0.3°C or more above baseline. Can precede an infection or a flare by one to three days.
Sleep architecture flattening
Deep and REM proportions compressing while time-in-bed stays normal. The 8-hour night that didn't restore.
Day-after exertion signature
HRV and energy-curve depression for 24 to 72 hours after a higher-output day. This is the PEM window made visible.
Body Insights vs Apple Health, Oura, Whoop, and symptom-tracker apps.
You're probably here because one of these didn't fit. The honest comparison.
| Apple Health | Oura / Whoop | Visible / Bearable | Body Insights | |
|---|---|---|---|---|
| Reads HR, HRV, sleep | Yes | Yes (own ring) | Manual entry | Yes (Apple Health) |
| Tuned for variable baselines | No | No (athlete-default) | N/A | Yes |
| Body battery view | No | Partial | No | Yes |
| Overnight glucose fusion | No | No | No | Yes (optional) |
| Plain-language morning read | No | Partial | Symptom-led | Yes |
| Pacing-first framing | No | No | Yes | Yes |
| Subscription | None | $6–30 / month | Free / paid tiers | Free for core |
| Extra hardware | None | Ring or strap | None | None |
Oura and Whoop are real products built by careful people, for a different reader. Visible and Bearable are good companions for symptom logging and are honest about being self-report tools — they don't read your watch data. Body Insights sits in the gap. We read the sensor data your Apple Watch already collects, through a chronic-illness lens, and translate it into a sentence you can act on.
Questions you're probably asking.
What is ME/CFS?
Myalgic encephalomyelitis / chronic fatigue syndrome — a serious, long-term illness defined by profound fatigue not relieved by rest, post-exertional malaise, unrefreshing sleep, and cognitive impairment. The 2015 IOM report established the modern criteria.
Is this app for long COVID too?
Yes. Long COVID and ME/CFS share enough physiology — PEM, autonomic dysregulation, sleep disturbance — that the same pacing-first read works for both.
What does PEM look like in the data?
Often a 24-to-72-hour depression in HRV, a rise in resting heart rate, a flattened energy curve, and a smaller body-battery capacity for the days after a higher-output day. One bad day isn't PEM. A multi-day shape is.
Do I need a CGM?
No. Without one, the metabolic-energy layer drops out cleanly and the rest of the read still works. With one, overnight glucose variability folds in — useful in perimenopause and post-viral recovery.
How is this different from Visible or Bearable?
Those are symptom-logging tools — you tell them how you feel. Body Insights is a sensor-data read — we interpret what your watch already wrote down. The two pair well.
How much does it cost?
Free for core energy features, including the body battery view and the morning recommendation. A paid tier unlocks deeper analytics and predictive features. No card needed to start.
Your energy data stays yours.
On-device. No account. No subscription required. No data sold. Ever.
- Reads from Apple Health
- Stays on your iPhone
- You choose what to share
Read your energy, tomorrow morning.
Free for core energy insights. Premium adds deeper analytics and predictive features.
