Individual differences in 100-m-race performance cannot be explained by the muscularity of specific muscles, and 23% of the variability in the performance can be explained by the relative difference between the muscularity of gluteus maximus and quadriceps femoris; faster runners have a greater gluteus maximus relative to quadriceps femoris.

The ACTN3 R577X genotype has been found to associate with sprint/power phenotypes in all elite athlete cohorts investigated. This association has not been extensively studied in elite Asian athletes. The present study was undertaken to investigate the association between the ACTN3 R577X genotype and elite Japanese track and field athlete status. 299 elite Japanese track and field athletes (134 sprint/power athletes; 165 endurance/middle-power athletes) and 649 Japanese controls were genotyped for the ACTN3 R577X polymorphism. All athletes were of national or international level. Sprint/power athletes showed a higher frequency of RR + RX genotype than controls (111/134 [82.8%] vs. 478/649 [73.7%], P = 0.025 under the R-dominant model), while there was no significant difference between endurance/middle-power athletes and controls (126/165 [76.4%] vs. 478/649 [73.7%], P = 0.48 under the R-dominant model). Sprinters with the RR + RX genotype had significantly faster personal best times for the 100 m than those with XX genotype (10.42 ± 0.05 s vs. 10.64 ± 0.09 s, P = 0.042); no such association was found in the 400 m sprinters (47.02 ± 0.36 s vs. 47.56 ± 0.99 s, P = 0.62). ACTN3 R577X genotype is associated with sprint/power performance in elite Japanese track and field athletes, especially short sprint performance.

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In the present study, an ergometer (SErg) was developed to determine the force-velocitypower relationship in sprint running and to examine its applicability for assessing sprinting ability on the ground. The SErg consisted of a low friction belt, a rotary encoder, a force transducer attached to the runner's waist, and an electrical brake on the belt. The subjects (nine healthy and active men, including two sprinters: age, 22.6±2.1yrs; body height, 175.3 ±4.1cm; body weight, 74.1±9.3 kg) sprinted with maximal effort at fi ve loads that were generated by the braking force. The mean velocity (V) and force (F) were calculated where the mean belt velocity in six steps was maximal. In addition to the treadmill running, the subjects performed a 60m maximal sprint on the ground. From the F-V relationship, the value of the intercept on the V axis was regarded as estimated maximal velocity (eVmax). The maximal power (ePmax) was also calculated from V-P regression. The test-retest reliability of the eVmax and ePmax was high (ICC>0.79). The eVmax (8.25+/-0.89m/s) and ePmax (856.5+/-135.0W) were highly correlated to the maximal velocity (8.91+/-0.75m/s, r = 0.91) and acceleration (3.55+/-0.24m/s 2 , r =0.91), respectively, in the 60 m sprint on the ground. The present results indicate that the SErg can be applicable to determine the F-V-P relationship during sprint running and to estimate maximum velocity and acceleration in maximal ground sprinting.

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