Motor neuron pools of synergistic thigh muscles share most of their synaptic input

Christopher M. Laine, Eduardo Martinez Valdes, Deborah Falla, Frank Mayer, Dario Farina

Research output: Contribution to journalArticlepeer-review

75 Citations (Scopus)


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 (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.
Original languageEnglish
Pages (from-to)12207-12216
Number of pages10
JournalThe Journal of Neuroscience
Issue number35
Publication statusPublished - 2 Sept 2015


  • EMG
  • motor units
  • muscle synergy
  • partial coherence
  • quadriceps


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