Intramuscular fibre conduction velocity and muscle fascicle length in human vastus lateralis

Abstract

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.

Weak Association between Vastus Lateralis Muscle Fiber Composition and Fascicle Length in Young Untrained Females

“…However, it has been recently reported that the variance of RFD performance between young recreationally active men, could be explained by the individuals’ maximal motor unit discharge rates and recruitment intervals [ 58 , 59 ]. As a final point, the lean body mass of the lower extremities seems to be the most important contributor of CMJ power and maximum isometric/dynamic maximum strength, while muscle fiber type composition and muscle architecture of the vastus lateralis have a lower importance, as has been previously reported in sedentary [ 26 ] and novice power-trained males [ 16 ].…”

“…The absence of any significant correlation between muscle fiber type proportion and muscle fascicle length was somewhat expected; according to the results of an earlier study in experimental animals [ 17 ]. In addition, the mechanical properties of each muscle, and thus power production, seem to depend primarily on the combination of fiber type distribution and size, e.g., %CSA, and not only on the number of type II fibers [ 26 , 42 , 43 , 44 ]. For example, it has been reported that in a world champion shot putter, with a predominance of type I muscle fibers (~60%), his hypertrophied type II muscle fibers occupied 67% of VL the area, making him able to achieve greater power and shot put performance, compared to another shot-putter with a predominance of type II fibers but with smaller type II fiber CSA [ 45 ].…”

“…Interestingly, power performance may be better explained by the combination of muscle size, muscle architecture, and fiber composition, instead of using each one of these parameters alone [ 16 ]. Furthermore, the propagation velocity of action potentials along the sarcolemma of muscle fibers, which is associated with power performance, is also closely correlated with both type II muscle fiber %CSA and muscle fascicle length [ 26 ].…”

“…Therefore, the possible link between muscle fiber composition and fascicle length may be better revealed in individuals with minimal exposure to resistance/power training, yet with high-power potential. For this reason, female university students participated in this study, since this group is less exposed to strength/power training [ 26 , 27 ]. Thus, the aim of the present study was to investigate the relationship between vastus lateralis muscle fiber length and fiber type composition in individuals with minimal exposure to systematic resistance/power training.…”

Rate of force development relationships to muscle architecture and contractile behavior in the human vastus lateralis

“…We speculate that the lack of correlations between fascicle length and RFD may be attributed to several physiological and methodological factors. Inter-individual variability in physiological factors affecting fast force production such as faster fibre conduction velocity 37 muscle fibre type 38 may affect the relative importance of the fibre length. Another reason could be related to how accurate fascicle length reflects the number of in-series sarcomeres, which may vary along fibres and the muscles 39 .…”