Intramuscular fiber conduction velocity and muscle fascicle length in human vastus lateralis.

Muscle fascicle length and muscle fibre conduction velocity are thought to be important parameters for power performance. It might be expected that faster muscle fibre conduction velocities would compensate for longer fascicle lengths to increase the speed of action potential propagation along the elongated fibres. However, the relationship between muscle fascicle length and muscle fibre conduction velocity (MFCV) remains unknown. The aim of the present study was to explore the relationship between average vastus lateralis MFCV and average fascicle length. In seventeen moderately-trained healthy male physical education students (age 23.4 ± 3.1 years, body height 178 ± 5.5 cm, body mass 82.7 ± 6.9 kg, BMI 24.6 ± 1.5 kg∙m-2) resting MFCV was measured with intramuscular microelectrodes while muscle architecture was evaluated with ultrasonography. Fascicle length was highly correlated with total MFCV (r: 0.923, p = 0.000), maximum MFCV (r: 0.949, p = 0.000), and MFCV of the fastest (r: 0.709, p = 0.001), but not of the slowest fibres (r: 0.131, p = 0.616). No significant correlations were also found between vastus lateralis thickness or fascicle angle with any of MFCV parameters (r: 0.145 - 0.430; R2 < 0.130; p > 0.05). These data indicate that average MFCV is associated with average fascicle length in vastus lateralis muscle in different individuals. It seems that participants with longer fascicle lengths have also higher muscle fibre conduction velocities.