• B. Yu


INTRODUCTION Triple jump is one of the four jumping events in track and field. In a recent study, Yu and Hay (1996) reported a linear relationship between the gain in the vertical velocity (ΔvZ) and the Ioss in the horizontal velocity (Δvx) for individual athletes in the triple jump. This relationship indicates a horizontal-to-vertical velocity conversion during each support phase. An understanding of these effects appears to be essential for the understanding of the effect of phase ratio on the actual distance. The purpose of this study was to examine the effects of ΔvZ and the relationship between ΔvZ and Δvx on the horizontal-to-vertical velocity conversion during each support phase of the triple jump. METHODS Three-dimensional kinematic data were collected for at least four complete trials in the same competition for each athlete. The magnitudes of Δvx and ΔvZ during each support phase were detennined for each trial. The relationships between Δvx and ΔvZ were detennined for each athlete using a linear regression analysis with dummy variables. The slope of this linear function, A1 , was referred to as the horizontal-to-vertical velocity conversion coefficient. The horizontal-to-vertical velocity conversion rate (1) was defined as the ratio of the absolute value of Δvx to ΔvZ . The effects of ΔvZ , A1 , and other regression coefficients in the relationship between Δvx and ΔvZ on h was determined using a computer simulation procedure. RESULTS The magnitude of Δvx was a linear function of ΔvZ . The magnitude of h was a function of ΔvZ and A1. Positive correlations were found between the absolute value of A1 and ג , and between ΔvZ and ג . The greater was the magnitude of A1 , the more sensitive was h to ΔvZ . The magnitude of Avz had no significant effect on when h the absolute value of A1 was lower than 0.5. DISCUSSION The magnitude of A1 may be a reflection of some physical characteristics for a given athlete. It is an important parameter for determining optimum phase ratio for a given triple jumper (Yu and Hay, 1996). A hop dominated technique is optimum for an athlete with a low absolute value of A1. A jump-dominated technique is optimum for an athlete with a high absolute value of A1. The magnitude of A1 may also be a parameter for identifying elite long and triple jumpers. An athlete with low magnitude of A1 may be a potential elite long jumper, and an athlete with high magnitude of A1 may be a potential elite triple jumper. REFERENCE Yu, B. and Hay, J.G. (1996). Optimum phase ratio in the triple jump. Journal of Biomechanics, 29(10):
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