TY  - GEN
A1  - Martinez-Valdes, Eduardo
A1  - Negro, Francesco
A1  - Laine, Christopher M.
A1  - Falla, Deborah L.
A1  - Mayer, Frank
A1  - Farina, Dario
T1  - Identifying motor units in longitudinal studies with high-density surface electromyography
T2  - Converging clinical and engineering research on neurorehabilitation II
N2  - We investigated the possibility to identify motor units (MUs) with high-density surface electromyography (HDEMG) over experimental sessions in different days. 10 subjects performed submaximal knee extensions across three sessions in three days separated by one week, while EMG was recorded from the vastus medialis muscle with high-density electrode grids. The shapes of the MU action potentials (MUAPs) over multiple channels extracted from HDEMG decomposition were matched across sessions by cross-correlation. Forty and twenty percent of the MUs decomposed could be tracked across two and three sessions, respectively (average cross correlation 0.85 +/- 0.04). The estimated properties of the matched motor units were similar across the sessions. For example, mean discharge rate and recruitment thresholds were measured with an intra-class correlation coefficient (ICCs) > 0.80. These results strongly suggest that the same MUs were indeed identified across sessions. This possibility will allow monitoring changes in MU properties following interventions or during the progression of neuromuscular disorders.
Y1  - 2016
SN  - 978-3-319-46669-9
SN  - 978-3-319-46668-2
U6  - https://doi.org/10.1007/978-3-319-46669-9_27
SN  - 2195-3562
VL  - 15
SP  - 147
EP  - 151
PB  - Springer
CY  - Cham
ER  - 
TY  - JOUR
A1  - Laine, Christopher M.
A1  - Martinez-Valdes, Eduardo Andrés
A1  - Falla, Deborah
A1  - Mayer, Frank
A1  - Farina, Dario
T1  - Motor Neuron Pools of Synergistic Thigh Muscles Share Most of Their Synaptic Input
JF  - The journal of neuroscience
N2  - Neural control of synergist muscles is not well understood. Presumably, each muscle in a synergistic group receives some unique neural drive and some drive that is also shared in common with other muscles in the group. In this investigation, we sought to characterize the strength, frequency spectrum, and force dependence of the neural drive to the human vastus lateralis and vastus medialis muscles during the production of isometric knee extension forces at 10 and 30% of maximum voluntary effort. High-density surface electromyography recordings were decomposed into motor unit action potentials to examine the neural drive to each muscle. Motor unit coherence analysis was used to characterize the total neural drive to each muscle and the drive shared between muscles. Using a novel approach based on partial coherence analysis, we were also able to study specifically the neural drive unique to each muscle (not shared). The results showed that the majority of neural drive to the vasti muscles was a cross-muscle drive characterized by a force-dependent strength and bandwidth. Muscle-specific neural drive was at low frequencies (<5 Hz) and relatively weak. Frequencies of neural drive associated with afferent feedback (6 - 12 Hz) and with descending cortical input (similar to 20 Hz) were almost entirely shared by the two muscles, whereas low-frequency (<5 Hz) drive comprised shared (primary) and muscle-specific (secondary) components. This study is the first to directly investigate the extent of shared versus independent control of synergist muscles at the motor neuron level.
KW  - EMG
KW  - motor units
KW  - muscle synergy
KW  - partial coherence
KW  - quadriceps
Y1  - 2015
U6  - https://doi.org/10.1523/JNEUROSCI.0240-15.2015
SN  - 0270-6474
VL  - 35
IS  - 35
SP  - 12207
EP  - 12216
PB  - Society for Neuroscience
CY  - Washington
ER  -