A method for locating surface electromyography electrodes on the flexor carpi ulnaris

The flexor carpi ulnaris (FCU), a superficial forearm muscle which provides wrist flexion and ulnar deviation, is used in surface electromyography (sEMG) applications for clinical assessments, rehabilitation, and human-machine interfaces. Proper electrode location on the forearm muscles is imperative due to small signal amplitudes and susceptibility to interference and crosstalk, where poor placement can give ambiguous or erroneous results. Currently, no formal method exists for locating sEMG electrodes over the FCU muscle. General advice is to palpate and observe muscle movements, however, this depends on the practitioner’s experience-level, so can be subjective and inconsistent.
This paper presents a systematic method for locating sEMG electrodes on the FCU muscle using palpation of the pisiform bone and humeral medial epicondyle, and establishing the muscle line between. The technique’s efficacy was assessed using sEMG from three sites on the muscle belly, testing both arms of 10 participants, and analysing the resulting SNR, mean absolute value (MAV), and frequency spectrum. An electrode location at 80% of the distance from the pisiform is recommended to provide the highest median SNR and MAV across participants. These results provide guidance for locating a suitable and consistent sEMG site on the FCU that is less reliant on practitioner experience, which may benefit both clinical and biomedical engineering applications.