The purpose of this study was to investigate the influence of the prestretching speed and strength of the thigh extensors during take-off phase on the jumping height in vertical jump. Five males performed the following several vertical jumps : squatting jump (SJ) from a static knee bending position ; counter movement jump (CMJ) with a preparatory counter-movement ; drop jump (DJ) from the five different heights (20, 40, 60, 80 and 100cm) on to the platform followed immediately by a vertical jump. All of these jumps were performed on the force-platform (Kistler) with the arms kept at the back. The jumping motions were recorded with the high-speed video tape recorder (NAC : HSV-200) from subject\u27s side at 200 f. p. s.. The results obtained from this study were summarized as follows : 1) The highest height of rise of center of gravity was obtained in CMJ. 2) When observing the result only in the DJs, the highest jumping performance was obtained in the DJ from a height of 40cm. 3) An average velocity of center of gravity during down phase in CMJ which showed the highest performance was 0.71m・sec^. 4) Prestretching force in CMJ was higher than that in SJ, but on the other hand it was lower than that in DJs. 5) Both angles of the knee and hip joints at the maximal knee bending position in CMJ which showed the highest performance were about 70 degrees
