FUKASHIRO, SENSHI and MITSUMASA MIYASHITA. An estimation of the velocities of three take-off phases in 18-m triple jump.Med. Sci. Sports Exerc., Vol. 15, No. 4, pp. 309–312, 1983. The purposes of this study were to estimate the take-off velocities necessary to gain a given distance on the triple jump by adopting three hypotheses and to investigate the external force vectors during the jump's supporting phase. The total distance corresponding to the varying combinations of horizontal and vertical velocities at take-offs were calculated based on these hypotheses. The calculated velocities of the body's center of gravity coincided well with the observed total distance, even though the velocities were slightly underestimated. There was a significant correlation between the run-up velocity and the total distance (r=0.91,P< 0.001). From these results, the run-up and take-off velocities and the external force vectors for an 18-m jump were estimated. It might be said that the 18-m jumper must gain great run-up velocity (10.7 m·s-1) and exert forces during each supporting phase which are 3.6–4.4 times the body weight, resulting in a force-vector angle of about 101° at each take-off.