In this study, the characteristics of step length increase during the acceleration phase of the 100 m dash were examined in elementary school students and senior male sprinters (athletes) by means of segmented regression analysis of the step length per height (SL index). The 100 m running times of the 24 athletes analyzed ranged from 10.12 to 11.19 s, and those of the 25 elementary school students ranged from 14.51 to 20.70 s. The SL index at the maximum running speed (SL index･vmax) ranged from 0.99 to 1.41 height times.
The results showed that the characteristics of step length increase during the acceleration phase of the 100 m dash were indicated by three regression lines (L1, L2, and L3). The SL index･vmax was determined by the number of steps to which the regression lines L1 and L2 was extended in the case of athletes and L1 in the case of elementary school students，respectively. The trend of increasing step lengths of L2 and L3 was almost constant among elementary school students and athletes, regardless of the SL index･vmax. On the other hand, the increasing trend of L1 was found to be greater in athletes than in elementary school students, but it varied with the number of steps taken in L1 section. Furthermore, a method for setting a specific target step length to increase the SL index･vmax was also proposed, taking such characteristics into consideration.
