This study determined that the absolute and relative CSAs of most trunk and lower limb muscles, excluding the QF and DF, were larger in sprinters than in non-sprinters. In particular, absolute CSAs of the PM and GM was 21.7 and 18.4%, respectively, higher in sprinters than in non-sprinters. In addition, the primary findings of this study showed that larger absolute and relative CSAs of the PM and GM correlated with better personal best 100 m sprint time in sprinters. Furthermore, a stepwise multiple regression analysis revealed that both CSAs of absolute PM and the relative GM were predictive variables of the personal best 100-m sprint time. These findings suggest that the PM and GM may be specific muscles for superior sprint performance for sprinters.
With regard to the PM, it is known to be a major muscle for performing hip flexion because of the largest among the hip flexors [15]. Hoshikawa et al. [16] reported that larger PM CSA is correlated with higher hip flexor maximal torque. Moreover, using a computer simulation, Dorn et al. [17] determined that the PM (i.e., which combined the psoas major and iliacus) was the highest torque component for performing the hip flexion and contributed to rapidly accelerating the leg forward during sprinting. Furthermore, we and others previously reported that larger PM CSA is correlated with better sprint performance (e.g., personal best 100-m sprint time) in sprinters [7, 10,11,12]. Therefore, the present finding corroborates the results of these previous studies by showing positive correlations between absolute and relative PM CSAs and personal best 100-m sprint time in sprinters. The findings of our and other studies suggest that the PM is an important muscle for achieving superior sprint performance in sprinters.
With regard to the GM, it is known to be a major muscle for performing hip extension because of the largest among the hip extensors [4, 18]. Tayashiki et al. [19] reported a positive correlation between the GM thickness and hip extensor maximal torque, but this correlation did not reach significance. Moreover, Bartlett et al. [18] determined that an increase in the electromyographic activity of the GM is related to increased sprint velocity when sprinting. In addition, the GM plays an important role in decelerating the forward swing of the leg during the latter half of the swing phase and stabilizing the trunk against flexion while sprinting [17, 20]. Furthermore, the computer simulation study, by Dorn et al. [17], determined that an increase in step frequency from a slow running to maximal sprinting is principally achieved by increasing the work of the hip extensor muscles, especially the GM, during the latter half of the swing phase. The increased step frequency is necessary to increasing sprint velocity during spirting [12, 21, 22]; thus, larger GM plays an important role in achieving better sprint performance, potentially by enhancing step frequency. Despite these previous findings, the relationship between GM size and sprint performance in sprinters remains poorly understood. Sugisaki et al. determined that greater muscle volume (MV) of the GM is correlated with better personal best 100 m sprint time in sprinters [10]. Therefore, the present finding corroborates their result by showing positive correlations between the absolute and relative GM CSAs and personal best 100 m sprint time in sprinters. Altogether, in addition to the PM, the GM is an important muscle for achieving superior sprint performance in sprinters.
In addition to the GM, the HAM, which is a biarticular muscle that extends the hip and flexes the knee, is known to be another major muscle among the hip extensors. The HAM is often considered a key muscle for achieving superior sprint performance in sprinters [23]. However, we and others previously reported the absence of relationship between the HAM CSA and sprint performance (e.g., personal best 100 m sprint time) in both groups of junior and adults sprinters [7, 9, 12]. Therefore, the present finding corroborates the results of these previous studies by showing no correlations between the absolute and relative HAM CSAs and personal best 100-m sprint time in adult sprinters. The findings of our and other studies suggest that the HAM may not be an important muscle for achieving superior sprint performance in sprinters.