Hardware
sEMG-RD
The sEMG devices consisted of two primary subcomponents: a digital compute capsule and an analogue wristband (Extended Data Fig. 1). The digital compute capsule comprised the battery, antenna for Bluetooth communication and a printed circuit board that contained a microcontroller, an analogue-to-digital converter and an inertial measurement unit. The analogue wristband comprised discrete links that each housed a multilayer rigid printed circuit board that contained the low-noise analogue front-end circuits and gold-plated electrodes. We manufactured the sEMG-RD device in four sizes. The analogue front end applied 20-Hz high-pass and 850-Hz low-pass filters to the data.
These printed circuit boards were inserted into Nylon 12 PA 3D printed housings and then strung together with a multilayer flexible printed circuit board along with a strain-relieving fabric. An elastic nylon cord was routed continuously between the links and was tied together at the wristband gap to form a clasp and tensioning mechanism. Finally, the digital compute capsule was connected to the analogue wristband through a connector on the flexible printed circuit board and fastened together with screws for mechanical stability. The device underwent a biocompatibility testing process to ensure its safety. The band is easily donned at the wrist with the only requirements being that the compute capsule is on the dorsal side and the gap is near the ulna bone.
Data collection
MRI scan
To visualize the position of the sEMG-RD’s electrodes relative to wrist anatomy, we collected a high-resolution anatomical MRI scan (Siemens Magnetom Verio 3T) from a consenting participant’s right forearm. We collected axial scans along the forearm, beginning from just distal to the wrist and ending just distal to the elbow. The scan was collected pursuant to an IRB governed study protocol conducted by Imperial College London.
Participant experience
All data collection was done at either Meta’s internal data-collection facilities or at third-party vendor sites. Study recruitment and participant onboarding was performed according to protocol(s) approved by an external IRB (Advarra). All studies began by providing the participants with information about the study protocol and asking them to review and sign an IRB-reviewed consent form before beginning the study. The participants were provided with the opportunity to ask questions before their participation and were able to discontinue their participation at any time. On-site research administrators monitored participants during the study protocol(s) to ensure participant well-being. The participants were financially compensated for their time participating in the study.
Collection at scale
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