AbstractThis study aimed to clarify the composition of the phases (acceleration, full sprint, and velocity endurance) in the 50-m sprint as performed by elementary school students, focusing on changes in running velocity. The subjects were 169 boys and 178 girls in theˆrst to sixth grades of elementary school, who performed a 50-m sprint from a standing start. Running velocity was measured using a laser distance meter, which was synchronized with a video camera that recorded the entire sprint. It was found that the running time of the total sprint was signiˆcantly shorter and that maximal velocity was signiˆcantly higher for higher-grade than for lower-grade students. The distances of the acceleration phase and full sprint phase were signiˆcantly longer for higher-grade than for lower-grade students, but there was no signiˆcant diŠerence in the duration of these phases by grade. However, both the distance and duration of the velocity endurance phase were signiˆcantly shorter for highergrade than for lower-grade students.Step length in the acceleration, full sprint, and velocity endurance phases was longer for higher-grade than for lower-grade students. However, step frequency at each phase tended to be almost equal or slightly lower for higher-grade than for lower-grade students. The SL index for higher-grade boys tended to be higher than for lower-grade boys. However, for girls, there was little diŠerence in the SL index at each phase for second-grade students or above. Taken together, the results indicate that the velocity endurance phase comprises the majority of the 50-m sprint when performed by lower-grade students. However, for higher-grade students, the velocity endurance phase is shorter due to the relative increases in the acceleration and sprint phases. This suggests that the distance of the acceleration and full sprint phases aŠects the distance and duration of the velocity endurance phase.
Sprinters adjust the arrangement of their starting blocks prior to a race, but there is no clear standard for arranging the blocks. It is unclear at present how the arrangement changes the forces applied to the blocks and consequently affects performance coming off them. The purpose of this study was to investigate the effects of the arrangement of the starting blocks on the forces applied to them. Forces applied by a sprinter to the front and the rear starting block as well as to the ground on the first step were measured using three force platforms for 18 different arrangements of block spacing. The results indicated that the amount of the impulse applied in starting posture to both the front and rear starting blocks changed little between the 18 arrangements. Likewise, no substantial change occurred in the forces applied to the ground on the first step. However, as the distance between the front and rear blocks changed, the ratio of the impulse applied to the front and rear blocks changed: as the block spacing was increased, the impulse applied to the front block during starting posture decreased while that at the rear block increased. In addition, changing the distance from the starting line to the front block influenced the relation between the block spacing distance and the forces applied to the two starting blocks.
The role of the starting block in sprinting and its in‰uence on a crouch start. Japan J. Phys. Educ. Hlth. Sport Sci. 60: 667 684, December, 2015 AbstractStarting blocks are required for sprint starts in competitive races. Here, we examined the functional role of starting blocks at the start of a sprint. The participants were 9 sprinters (height: 174.8 ±3.7 cm; weight: 69.0±4.5 kg; personal best 100 m time: 10.89±0.34 s) who performed 2 kinds of sprint start: a crouch start with starting blocks (BS), and a crouch start without starting blocks (CS). Two force plates were placed under each block or under the participants' feet in the BS or CS, respectively, and were used to measure the force applied to the starting blocks or to the ground. Another 2 force plates were placed to measure the ground reaction force of theˆrst and second steps after block clearance. The sampling frequency for these measurements was 1 kHz, and kinematic data were recorded using 4 high speed cameras at 250 frames/s. Time from the start signal to take-oŠ of the second step was signiˆcantly longer for CS than for BS, but there was no signiˆcant inter-group diŠerence in the point of touchdown of the second step. The method of increasing the horizontal velocity of the center of gravity diŠered signiˆcantly by group and power in the horizontal direction during the block clearance phase, being signiˆcantly less for CS than for BS. Consequently, the horizontal impulse applied to the ground in CS was signiˆcantly less than that applied to the starting blocks in BS, and the duration of force application in CS was signiˆcantly longer. Furthermore, the horizontal impulse applied by the rear foot in CS was signiˆcantly less than that applied to the rear block in BS, and the horizontal impulse applied during the double stance phase in CS was signiˆcantly less than that in BS. These factors aŠect the extensional and rotational movements in the block clearance phase. Taken together, these results indicate that the crouch start can be eŠective when starting blocks are used. Therefore, starting blocks can be regarded as an essential tool for enhancing sprint start performance.
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