ABE, T., K. KUMAGAI, and W. F. BRECHUE. Fascicle length of leg muscles is greater in sprinters than distance runners. Med. Sci. Sports Exerc., Vol. 32, No. 6, pp. 1125–1129, 2000.
Purpose: The purpose of this study was to compare architectural characteristics of leg muscles of sprinters and distance runners.
Methods: Skeletal muscle architectural characteristics were studied in 23 elite male 100-m sprinters (SPR, 10.0–10.9 s for 100 m), 24 elite male distance runners (DR, 13.5–14.5 min for 5000 m), and 24 untrained male controls. Fascicle pennation angle and isolated muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured in vivo by ultrasound, and fascicle length was estimated.
Results: Standing height and upper and lower limb lengths were similar among the groups. Body weight was significantly greater in SPR than in either DR or controls, which were similar. Muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles was significantly greater in SPR than in either DR or controls, which were similar. In all muscles, pennation angle was similar between SPR and controls, but less than DR. Fascicle length of the vastus lateralis muscle (absolute and relative to limb length) was greatest in SPR and least in DR with control values being between the athlete groups. Fascicle length of the gastrocnemius medialis muscle (absolute and relative to limb length) was greater in SPR than in either DR or controls, which were similar. Fascicle length of the gastrocnemius lateralis muscle (absolute and relative to limb length) was significantly greater in SPR than DR. Absolute fascicle length in gastrocnemius lateralis muscle was similar between DR and controls; however, relative to limb length DR was significantly less.
Conclusion: Greater fascicle length and lesser pennation angle observed in leg muscles of SPR, compared with DR, would appear to favor shortening velocity as required for greater running speed.
Muscle fiber shortening velocity is a reasonable parameter for the determination of sprint running performance. Velocity of shortening is determined by biochemical (myosin ATPase activity) (4,22) and architectural (fiber length; the number of sarcomeres in series) (7,21,24) properties. Most studies regarding sprint running performance and capacity for shortening velocity have focused on biochemical properties. Several studies (5,8) have demonstrated that elite male and female sprinters have a high percentage of fast-twitch muscle fibers in leg muscles and that maximum running speed is significantly correlated with percentage of fast-twitch fibers (18). Further, maximum contraction velocity of knee extensor muscles is related to the percentage of fast-twitch fibers (26). Similar relationships between sprint running performance and muscle fiber type composition or fiber type specific enzyme activities have been seen in animals (e.g., lizard (10)). In contrast, athletes in endurance events have a high percentage of slow fibers (5,8) and a relatively slow maximal velocity of shortening in the corresponding leg muscles.
Biochemical factors, e.g., myosin ATPase activity, are important determinants of muscle shortening velocity. However, muscle architecture has been shown to modulate these biochemical effects (21,27). Differences in maximal shortening velocity among muscles are closely associated with differences in muscle fascicle length (number of sarcomeres in series) and pennation angle (27). Therefore, it is theoretically plausible that muscle architecture may be closely associated with sprint performance. To the best of our knowledge, there is no information concerning the role of muscle architecture in determining sprint performance (14). Recently, we showed that muscle fascicle lengths were similar among a cross-section of height-matched female and male athletes, yet there was a tendency for track sprinters or athletes with the fastest sprint time to have relatively longer fascicle lengths (2,3). Thus, the purpose of this study was to compare muscle architectural characteristics of athletes from extremes of the speed/power continuum for runners; 100-m sprinters and distance runners (10-km or marathon).