The honest ceiling of the 'sensor + frequency' idea: a real measured signal, a defined active ingredient — resonance breathing at ~0.1 Hz — and a meta-analytic effect on anxiety and stress. The biofeedback loop GUIDES the breathing; the breathing is the mechanism. It belongs in the same atlas as the devices that claim a real signal, a defined mechanism, and a measured effect — and have none.
Origin & lineage
Resonance-breathing / baroreflex biofeedback lineage (Lehrer, Vaschillo, and others).
Claimed mechanism
Slow breathing at the ~0.1 Hz baroreflex resonance frequency, guided by real-time HRV feedback, increases vagal / autonomic modulation.
Plausibility
Plausible / established (narrow) — a real, measured signal and a defined active ingredient.
Evidence — grade B
Goessl 2017 (Psychol Med; within g=0.81, vs-control g=0.83, stress/anxiety); Lehrer 2020 SR+MA (58 RCTs); Pizzoli 2021 (g=0.38, depression); Lehrer 2017 (mechanism). Moderate effect for anxiety/stress; the active ingredient is resonance breathing, guided — not caused — by the feedback.