Portable quantum-sensor magnetomyography decodes fine hand movements

Abstract

Optically pumped magnetometers (OPMs) are compact quantum sensors that can measure the magnetic fields generated by muscle activity (magnetomyography, MMG) without skin contact. This contact-free alternative to surface electromyography (EMG) has remained mostly confined to magnetically shielded rooms and simple tasks, limiting translation. Here, we show that a portable OPM-MMG system operated inside a compact magnetic shield can robustly decode fine finger movements and recover EMG-like muscle activation patterns. Eight participants executed flexion-extension combinations spanning 15 finger actions while we recorded triaxial MMG and bipolar EMG concurrently. MMG supported robust multi-class and finger-specific decoding, recovering a representational geometry that closely matched EMG. Orientation analyses showed that components orthogonal to the muscle axis contributed most significantly to discriminability, providing actionable guidance for OPM array design. Our results show that OPM-MMG in a portable shielded environment preserves task-relevant neuromuscular information and approaches EMG-level structure without skin contact or a magnetically shielded room. Our findings open a path toward hygienic, rapid-setup assessment and human-machine interfacing in clinics and rehabilitation settings.