Effect of length change in muscle fibers on conduction velocity in human motor units

Length and conduction velocity were determined in muscle fibers belonging to the single motor unit (right m. vastus medialis) in the living human body. A new method was developed for measuring the length of fibers, i.e., the muscle length was defined to be the distance between the starting point of...

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Bibliographic Details
Published inJapanese journal of physiology Vol. 36; no. 4; p. 773
Main Author Morimoto, S
Format Journal Article
LanguageEnglish
Published Japan 1986
Subjects
Adult
Humans
Knee Joint - physiology
Male
Motor Neurons - physiology
Muscles - anatomy & histology
Muscles - innervation
Muscles - physiology
Neural Conduction
Time Factors
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Summary:Length and conduction velocity were determined in muscle fibers belonging to the single motor unit (right m. vastus medialis) in the living human body. A new method was developed for measuring the length of fibers, i.e., the muscle length was defined to be the distance between the starting point of excitation (motor end-plate) and the distal end of muscle fibers belonging to the particular motor unit. Both points were decided by analyzing the shape of the spike potentials of the motor unit recorded by surface electrodes. The length increased by about 70% (ranging from 48% to 97%) when changing the knee angle from fully extended to the fully flexed position, whereas the conduction velocity decreased by about 26% (ranging from 17 to 36%). It can be considered that the decrease of the conduction velocity when increasing the length of the muscle fibers was mainly due to the decrease in fiber diameter.
ISSN:0021-521X
DOI:10.2170/jjphysiol.36.773