Straps and getting started

Polar H10. Today's Load was developed using the Polar H10 as its reference chest strap. Independent ECG-referenced studies support the accuracy of its RR-interval measurements at rest.

Movesense HR+ and Medical. Both have ECG-referenced evidence for beat-to-beat measurement. Movesense Medical has also been validated against a 12-lead ECG for standard HRV measures and DFA α1.

CooSpo H808S. Peer-reviewed evidence shows excellent agreement with the Polar H10 for HR and HRV in resting conditions. Its HRV agreement deteriorates during running, which is less relevant to Today's Load because the protocol does not involve exercise or locomotion.

Other chest straps can pair too, and show as Unverified: they work if they send true beat-to-beat data, but we can't vouch for their beat-timing quality. A reading taken with one is labelled as such, on the reading itself, for as long as it exists.

In this tier today: Polar H9, Garmin HRM 200 (beat-to-beat output independently confirmed), Garmin HRM-Dual, Wahoo TRACKR, Suunto Smart HR Belt, and the inexpensive Magene, XOSS, Decathlon and other CooSpo belts. They may be excellent. Nobody has published the comparison that would let us say so.

Garmin HRM-Pro. Published ECG-referenced evidence raises concerns for the type of resting beat-to-beat variability Today's Load depends on. In one ECG-referenced study, a measure of resting RR-interval variability was approximately 24% lower with the Garmin HRM-Pro than with ECG.

Polar Verity Sense, Polar OH1, COROS armband. Optical sensors that send no beat-to-beat intervals over the standard service at all.

Watches and optical armbands in general. Optical armbands and watches can't feed the measurement. Optical sensors detect peripheral pulse-related optical changes rather than the heart's electrical activity. Most send no beat-to-beat data at all, and a sensor that never streams beats can't finish pairing.

Wear it properly. Wet the electrodes and wear the strap snug against your chest — it only wakes on skin contact. If it will not pair, close the strap's own vendor app first; most straps allow only a limited number of connections.

Measure before anything else. First thing after waking, before coffee and before training. Caffeine, food and movement all genuinely move your autonomic state, so measuring at the same point each morning is what makes one day comparable with the next.

Twelve minutes, lying and standing. The app tells you when to move and paces your breathing in the second half. You do not have to time anything.

Your first morning counts as much as your hundredth. The decision is computed from that morning's beats against fixed limits. The engine holds no personal baseline and learns nothing about you over time, so there is no warm-up period to sit through and no reading that is thrown away as calibration.

Measuring regularly still changes what you get, in two specific ways. A progression day is only offered when a run of recent mornings has been clear, so it cannot appear on your first. The trends become more informative as more consistent mornings accumulate. Measuring under the same conditions each morning is what makes the trends readable.