title: Non-uniform recruitment along human rectus femoris muscle during transcutaneous electrical nerve stimulation.
abstract: OBJECTIVE
  To test the hypothesis that motor units with different axonal excitability levels are localized in specific portions of the rectus femoris (RF) muscle using transcutaneous electrical nerve stimulation.
  
  
  METHODS
  M-waves were elicited by transcutaneous electrical nerve stimulation and detected from 24 sites along longitudinal line of the muscle. The stimulation was applied to the femoral nerve, and the current level was gradually increased.
  
  
  RESULTS
  The central locus activation, which is calculated from the spatial distribution of M-waves, appeared at the proximal regions at low stimulation level and then moved to the middle site of the muscle with an increase in the stimulation level. The results reveal that groups of motor units activated at different stimulation levels are located in different positions in the proximal-distal muscle direction.
  
  
  CONCLUSIONS
  Our results suggest that motor unit properties in proximal and other regions are not uniform within the RF muscle.
authors.affiliation: Laboratory of Neuromuscular Biomechanics, School of International Liberal Studies, Chukyo University, Yagotohonmachi, Showa-ku, Nagoya, 466-8666, Japan. wkohei@lets.chukyo-u.ac.jp.
authors.forename: Kohei
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Laboratory of Neurophysiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
authors.forename: Motoki
authors.initials: M
authors.lastname: Kouzaki
authors.affiliation: Graduate School of Education and Human Development, Nagoya University, Nagoya, Japan.|Japan Society for the Promotion of Science, Tokyo, Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Ando
authors.affiliation: Graduate School of Education and Human Development, Nagoya University, Nagoya, Japan.|Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Akima
authors.affiliation: Laboratory of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Moritani
mesh_terms: D000293:Adolescent; D000328:Adult; D019054:Evoked Potentials, Motor; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D004561:Transcutaneous Electric Nerve Stimulation
keywords: Bi-articular muscles; M-wave; Multi-channel surface electromyogram; Neuromuscular compartment