### Abstract

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 language | English |
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Pages (from-to) | 284-289 |

Number of pages | 6 |

Journal | Journal of Electromyography and Kinesiology |

Volume | 20 |

Issue number | 2 |

DOIs | |

Publication status | Published - Apr 2010 |

### Keywords

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

### ASJC Scopus subject areas

- Neuroscience (miscellaneous)
- Biophysics
- Clinical Neurology

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## Cite this

*Journal of Electromyography and Kinesiology*,

*20*(2), 284-289. https://doi.org/10.1016/j.jelekin.2009.02.007