000150817 001__ 150817 000150817 005__ 20251017144654.0 000150817 0247_ $$2doi$$a10.1109/TNSRE.2025.3531054 000150817 0248_ $$2sideral$$a142859 000150817 037__ $$aART-2025-142859 000150817 041__ $$aeng 000150817 100__ $$aGrison, Agnese 000150817 245__ $$aMotor unit sampling from intramuscular micro-electrode array recordings 000150817 260__ $$c2025 000150817 5060_ $$aAccess copy available to the general public$$fUnrestricted 000150817 5203_ $$aRecordings of electrical activity from muscles allow us to identify the activity of pools of spinal motor neurons that send the neural drive for muscle activation. Decoding motor unit and motor neuron activity from muscle recordings can be performed by high-density (HD) electrode systems, both non-invasively (surface, HD-sEMG) and invasively (intramuscular, HD-iEMG). HD-sEMG recordings are obtained by grids placed on the skin surface while HD-iEMG signals can be acquired by micro-electrode arrays. While it has been shown that HD-iEMG allows the accurate decoding of a larger number of motor units when compared to HD-sEMG, the dependence of motor unit yield on the parameters of the micro-electrode arrays is still unexplored. Here, we used recently developed HD-iEMG electrodes to record from hundreds of recording sites within the muscle. This allowed us to investigate the impact of electrode number, inter-electrode distance, and the number of muscle insertions on the ability to sample motor units within the muscle. Specifically, we recorded both HD-sEMG and HD-iEMG from the Tibialis Anterior muscle of two healthy subjects at various contraction intensities (10%, 30%, and 70% of maximum voluntary contraction, MVC). For the first time, we present intramuscular recordings with more than 140 electrodes inside a single muscle, achieved through multiple implants of high-density micro-electrode arrays. Through systematic offline analyses of these recordings, we tested different electrode configurations to identify optimal setups for accurately capturing motor unit activity. The results revealed that the density of electrodes in the micro-electrode arrays is the most critical factor for maximising the number of identified motor units and ensuring very high accuracy. Comparisons between intramuscular and surface recordings also confirmed that HD-iEMG consistently captures larger and more stable numbers of motor units across subjects and contraction levels. These results undersc... 000150817 536__ $$9info:eu-repo/grantAgreement/EC/HORIZON EUROPE/101077693/EU/Extracting the Human Motor Null Space from Muscles - A new framework to measure human neural activity/ECHOES$$9info:eu-repo/grantAgreement/EC/H2020/810346/EU/Natural Integration of Bionic Limbs via Spinal Interfacing/Natural BionicS$$9This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 810346-Natural BionicS$$9info:eu-repo/grantAgreement/ES/MICINN/CNS2022-135366 000150817 540__ $$9info:eu-repo/semantics/openAccess$$aby$$uhttps://creativecommons.org/licenses/by/4.0/deed.es 000150817 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/publishedVersion 000150817 700__ $$0(orcid)0000-0001-8439-151X$$aIbáñez Pereda, Jaime$$uUniversidad de Zaragoza 000150817 700__ $$aFarina, Dario 000150817 7102_ $$15008$$2800$$aUniversidad de Zaragoza$$bDpto. Ingeniería Electrón.Com.$$cÁrea Teoría Señal y Comunicac. 000150817 773__ $$g33 (2025), 620-629$$pIEEE trans. neural syst. rehabil. eng.$$tIEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING$$x1534-4320 000150817 8564_ $$s4769677$$uhttps://zaguan.unizar.es/record/150817/files/texto_completo.pdf$$yVersión publicada 000150817 8564_ $$s3870730$$uhttps://zaguan.unizar.es/record/150817/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada 000150817 909CO $$ooai:zaguan.unizar.es:150817$$particulos$$pdriver 000150817 951__ $$a2025-10-17-14:37:34 000150817 980__ $$aARTICLE