PEM Tracker
Free · in development

A crash is a metabolic event.
Fitness apps see a rest day.

Cross-section of the inner mitochondrial membrane Oxidant rises through the matrix toward a phospholipid bilayer. Glutathione moves down to meet it and the two cancel out before it arrives. As the glutathione reserve is drawn down, fewer interceptions happen and the oxidant begins striking the membrane; peroxidation then spreads outward from each impact, because a damaged lipid attacks the lipid beside it. The reserve is regenerated and the bombardment stops while the membrane is still damaged, and only after that does membrane integrity begin to recover. Glutathione pool Regenerating costs NADPH Intermembrane space Matrix Cardiolipin chain reaction

A fraction of the oxygen your mitochondria use leaves as oxidant rather than water — constantly, even at rest. The matrix answers with SOD2 and glutathione, which neutralise it before it reaches the bilayer. Every interception spends reserve, and spent glutathione has to be regenerated at a cost in NADPH — so how fast the reserve comes back matters as much as how much oxidant arrives. Outrun it and the oxidant gets through instead: cardiolipin peroxidises, and because a damaged lipid abstracts a hydrogen from its neighbour, one hit becomes a spreading front. The order is the point. The reserve refills and the attack stops — but the membrane is still damaged, and rebuilding it is far slower than spending the reserve was. So there is a stretch where nothing is attacking you any more and you are still not better.

Membrane integrity · cardiolipin
Antioxidant reserve · glutathione
About this illustration

Schematic, not a reading, and a simplified one: superoxide does not really cross the matrix, the defence is a relay rather than a single catch, and vitamin E does much of the chain-breaking inside the bilayer itself. Oxidative stress has been reported in ME/CFS for decades, but cardiolipin peroxidation specifically has never been demonstrated in it — that part is extrapolated from general redox biology. PEM Tracker scores heart-rate variability, resting heart rate and temperature from your wearable. It does not measure glutathione or cardiolipin, and no wearable does.

Where this sits, and my bias in it. ME/CFS has no settled cause. Three lines of research carry most of the weight: immune dysfunction and post-infectious persistence; impaired energy metabolism in the mitochondria; and neurological and autonomic dysregulation. The panel above illustrates the second. I find it the most persuasive of the three — that is a preference, plainly stated, not a verdict, and I hold the other two to be just as credible. Nothing in this tool depends on any of them being right.

Post-exertional malaise is systemic. It moves heart rate variability, resting heart rate, respiration and body temperature — often a day or more before you consciously register that anything has gone wrong.

A fitness tracker is not built to look for that. It reads a crash day as a lazy day: fewer steps, a goal missed, a reminder to move more. Nothing in that reading separates resting because you chose to from resting because your body has stopped cooperating.

PEM Tracker is being built to be a clear lens on exactly that — your wearable's own signals paired with what you actually felt each day, on one timeline, with an estimate calibrated to you rather than to a population average.

Devices it reads
OuraRing Gen 3 · Gen 4 · Gen 5
FitbitAir · Edge · Charge 6 · Charge 5 · Charge 4 · Luxe · Sense 2 · Sense · Versa 4 · Versa 3
GooglePixel Watch 2 · 3 · 4 · 5
Recommended buys (ECG enabled devices)Pixel Watch 5 · Fitbit Charge 6 · Fitbit Edge

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Free. This is a small personal project — not a commercial product, not a medical device, and not diagnostic. It can be wrong, and it does not replace care from a clinician. It is invite-only while it is being built.

You will see an "unverified app" warning. That is expected. Google's verification for health data needs a paid security audit every year, which this small project skips. Choose Advanced, then Go to pem.multiwebz.com. Only your name and email address are requested at this step.