Muscle fiber conduction velocity in human vastus lateralis during isometric contractions. Relation to muscle fiber composition / 体力科学

ABSTRACT

Relationship between muscle fiber conduction velocity and muscle fiber composition was studied in vastus lateralis of well-trained athlete students, who differed considerably regarding their fiber type distribution with averaged 69.2% fast twitch (FT) muscle fibers for sprinters (12 male subjects) and 39.7% FT muscle fibers for distance runners (7 male subjects) . Measurement of muscle fiber conduction velocity during brief and maintained isometric contraction was made directly, using the zero-crossing time delay method between two surface myoelectric signals. Muscle fiber conduction velocities increased 4.40 to 4.84 m/sec for sprinters and 3.91 to 4.31 m/sec for distance runners as developing force increased from 25 to 100% maximum voluntary contraction (MVC) . The correlation coefficients between conduction velocity and % FT fibers were 0.59, 0.63, 0.64 and 0.84 for 25, 50, 75 and 100% MVC, respectively. During maintained at 50% of MVC conduction velocities in sprinters decreased linealy from 4.77 to 4.38 m/sec and in distance runners decreased from 4.11 to 3.96 m/sec at only last stage. It was suggested that the individual difference in conduction velocity was caused by different muscle fiber composition and that the changes of conduction velocity depended on the recruitment of muscle fibers.