title: Contraction history produces task-specific variations in spinal excitability in healthy human soleus muscle.
abstract: BACKGROUND
  In human movements muscles lengthen and then shorten, or occasionally shorten and then lengthen, but it is unclear whether the nature of neural activation of the initial phase influences the neural state of the subsequent phase. We examined whether contraction history modulates spinal excitability in the healthy human soleus muscle.
  
  
  METHODS
  Subjects performed six blocks of 10 repetitions of four muscle actions consisting of specific combinations of passive shortening (PAS), and passive lengthening (PAL), shortening contraction (SHO), and lengthening contraction (LEN); that is: (1) SHO+PAL; (2) PAS+LEN; (3) PAS+PAL; and (4) SHO+LEN.
  
  
  RESULTS
  Compared with baseline, the H-reflex increased in the block of 300-400 s after SHO+PAL and decreased in the block of 0-100 s after PAS+LEN and SHO+LEN.
  
  
  CONCLUSIONS
  Our results suggest that spinal excitability is potentiated during a muscle action preceded by muscle shortening, but it becomes depressed during a muscle action preceded by muscle lengthening.
authors.affiliation: Motor Control and Biomechanics Laboratory, Graduate School of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa 359-1192, Japan. azusa-gold@toki.waseda.jp
authors.forename: Azusa
authors.initials: A
authors.lastname: Uematsu
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Sekiguchi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Tibor
authors.initials: T
authors.lastname: Hortobágyi
authors.forename: Shuji
authors.initials: S
authors.lastname: Suzuki
mesh_terms: D000328:Adult; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009470:Muscle Spindles / Q000502:physiology; D009129:Muscle Tonus / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D055815:Young Adult