Three layers, and most arguments happen because people stand on different ones.
Layer one — the sensors. Largely fine. Resting heart rate and HRV measured at rest agree closely with ECG (concordance ~0.91 and ~0.94 in independent testing).
Layer two — the score itself. A 2025 review examined every piece of public documentation for 14 composite scores across 10 manufacturers and found that none disclosed its algorithmic formula, with few providing peer-reviewed validation. There is no published criterion standard for 'readiness', so there is nothing to validate the score against. A separate 2025 paper makes the sharper point: proving a device's raw interbeat intervals are accurate does not prove the displayed number is, because undisclosed processing sits in between.
Layer three — acting on it. This is the marketed claim. A 2024 scoping review found eleven studies that adjusted training session-to-session based on readiness; not one used a commercial composite score. A ClinicalTrials.gov search returns no registered trial using a wearable readiness score to prescribe training.
Why reproducibility drifts. Test-retest reliability and cross-device concordance have never been published — nobody has reported whether two devices on the same person on the same night agree on the decision. Scores are also silently versioned: algorithms change between app releases with no changelog, so an athlete's April and July numbers may not be the same measurement.
The inferential error to watch for. The favourable HRV-guided training literature is routinely borrowed to support this claim. That research used supervised chest-strap lnRMSSD with a published decision rule. A black-box 0–100 number is a different intervention.
On the largest dataset. 389 professional golfers over 35,140 monitored nights is a real contribution — but it was authored by the manufacturer's own scientists on the manufacturer's own data, and it is observational. Higher scores co-occurring with better golf is equally consistent with the score being a downstream marker of good sleep and fitness.
- One review's funding/COI could not be retrieved (405/403); a co-author has commercial interests in the adjacent HRV-app space.
- One systematic review of a major brand is a preprint and was unretrievable — it should not be weighted as peer-reviewed regardless.
- No peer-reviewed validation of one major brand's battery-style score was located at all. Treat as zero located evidence, not as negative evidence.
- Doherty C, et al. (2025). Transl Exerc Biomed 2(2):128–144 — 14 scores, 10 manufacturers ↗
- Ibrahim AH, Beaumont CT, Strohacker K (2024). Int J Exerc Sci 17(5):382–404 — scoping review ↗
- Dial MB, et al. (2025). Physiol Rep 13(23):e70706 — transparency argument ↗
- Grosicki GJ, et al. (2025). Int J Sports Physiol Perform 21(2):180–191 — vendor-authored, n=389 ↗
- Miller DJ, et al. (2020). J Sports Sci 38(22):2631–2636 — PSG validation ↗
- v1 · 2026-07-26 · Initial grade.
SSMT. "Adjusting training according to a proprietary composite readiness score improves training outcomes compared with not using it." Claim SSMT-2026-0004 v1, graded 2026-07-26. https://sportssciencetech.com/c/SSMT-2026-0004