Enhanced Hoffman-reflex in human soleus muscle during exposure to microgravity environment

Takeshi Nomura, Fuminori Ka wano, Akihiko Ishihara, Yuzo Sato, Genyo Mitarai, Satoshi Iwase, Atsunori Kamiya, Tadaaki Mano, Yoshinobu Ohira

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Responses of Hoffman-reflex in the soleus muscle to changes of gravity levels created by parabolic flight of a jet airplane were investigated in four healthy male subjects. The subjects maintained a sitting position with seat belts fastened, keeping the anterior ankle and posterior knee angles at ∼135°. The gravity levels were altered from 1- to 2-G, and then microgravity was created for ∼20 s. The levels were recovered from 1.5- to 1-G during the descending phase. The time interval between the stimulation and either M- or H-wave was not influenced by the changes in gravity levels. The amplitude of the M-wave during hyper- and microgravity was identical to that obtained at 1-G. However, the H-wave amplitude was increased when the subjects were exposed to microgravity (∼four times vs. 1-G level). The H/M ratio was also elevated during microgravity. Further, such a phenomenon was maintained throughout the 20 s of microgravity exposure. Hypergravity at 1.5- or 2-G had no effect on the H-wave amplitude. It is suggested that an acute exposure to microgravity increases the excitability of the soleus motor pool and the increased excitability is restored immediately when the gravity level is elevated.

Original languageEnglish
Pages (from-to)55-57
Number of pages3
JournalNeuroscience Letters
Issue number1
Publication statusPublished - Dec 4 2001
Externally publishedYes


  • Hoffman-reflex
  • Human soleus muscle
  • Hyper- and microgravity
  • Parabolic flight

ASJC Scopus subject areas

  • Neuroscience(all)


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