The Physics of Impedance: Why Your Livenpace HMM1 Recording Failed
Update on Dec. 9, 2025, 4:55 p.m.
The Livenpace HMM1 manual contains a critical instruction that many users overlook or dismiss as a suggestion: “The chest strap needs to be wetted and tightened before wearing.”
From a forensic engineering standpoint, this is not a suggestion. It is a fundamental requirement of Bio-Instrumentation Physics. A significant number of negative reviews regarding “erratic readings” or “straight lines” are not hardware failures, but failures of the Electrode-Skin Interface.
The Stratum Corneum Barrier
The outer layer of human skin, the stratum corneum, is composed of dead skin cells. Electrically, it acts as a capacitor and a high-resistance insulator. The Livenpace HMM1 attempts to measure microvolt-level signals ($10^{-6}$ V) generated by the heart’s depolarization.
When the skin is dry, the impedance (electrical resistance) can exceed 100kΩ or even 1MΩ. This high impedance creates a voltage divider effect, drastically attenuating the signal before it even reaches the device’s sensor.
The “Wet Strap” Solution
Water (or better yet, conductive gel) acts as an electrolyte. It permeates the dead skin cells, creating conductive channels that lower the impedance to a manageable range (typically <5kΩ).
When a user wears the HMM1 with a dry strap, especially in winter or low-humidity environments, the device is essentially listening to static. The “AI Analysis” then receives 24 hours of noise, which it may hallucinate as arrhythmia or simply reject as “unclassifiable.”
The Adhesive Alternative
For users with chronically dry skin, or for those wearing the device during sleep (where the strap may dry out over 8 hours), the chest strap is mechanically inferior. The HMM1 supports disposable adhesive electrodes.
Engineering-wise, Ag/AgCl (Silver/Silver Chloride) adhesive electrodes are superior because they contain a wet gel column that maintains a stable electrolyte interface for days. Users serious about data quality should discard the strap and invest in medical-grade adhesive pads.
