Mathematical equation of fusion index of tetanic contraction of skeletal muscles

S. Watanabe, T. Kitawaki, Hisao Oka

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The fusion index (FI) is an index that can evaluate the tetanic progression of the skeletal muscles. Although the FI-frequency curve (FFC), which is obtained by changing the stimulation frequency, is greatly affected by muscle fiber type and fiber compositions, there are no reports of a mathematical equation that can express the FFC. In this study, the FFC was measured for the gastrocnemius, vastus intermedius, and soleus muscles of rats, and the mathematical equation (FFC-equation) was proposed. The FFC-equation (FI(f)) was proportional to the h-th power of f, and was in inverse proportion to the sum of the h-th power of k and the h-th power of f. f was the stimulation frequency, k was the stimulation frequency at 50% of FI, and h reflected the gradient of FFC. As a result, the approximated curve produced by the FFC-equation corresponded with the measured FFC. k reflected the fiber compositions and h represented the ratio of relaxation time to contraction time of the twitch contraction. The calcium ion fluctuation in muscle plasma may be described by the FFC-equation obtained from the experimental data.

Original languageEnglish
Pages (from-to)284-289
Number of pages6
JournalJournal of Electromyography and Kinesiology
Issue number2
Publication statusPublished - Apr 2010


  • Fiber type
  • Fusion index
  • Muscle force
  • Tetanic contraction
  • Twitch contraction

ASJC Scopus subject areas

  • Neuroscience (miscellaneous)
  • Biophysics
  • Clinical Neurology


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