RESULTS: Linear Kinematics

Joint Position.The majority of the displacement of the hip joint occurred in the vertical direction, with negligible horizontal displacement. Maximum vertical displacement was 0.89 m and 0.80 m for the female and male jump, respectively. This corresponds to the lowest position of the hip during the preparatory phase. The minimum hip displacements were 0.22 m for the female jump and 0.09 m for the male jump. These displacements occur at the maximum height of each jump (relative to the ground) 1.22 m for the female jump and 1.36 m for the male jump. The female jumped 73.5% of her total body height and the male jumped 76.3% of his total body height. The male had a higher relative and absolute jump height. The maximum displacement in the horizontal direction was 0.11m for the female jump and 0.13m for the male jump. The vertical component was the primary contributor to the total displacement.

Figure 8. Position of the hip joint in female jump (left) and in male jump (right). The thinnest line is the combined horizontal and vertical displacement of the hip. The narrow dashed line represents horizontal displacement, while the wide dashed line represents vertical displacement. Increasing values on the y-axis in the positive direction represent upward motion in the vertical direction with respect to the reference markers which were placed at a vertical height of 1.45m off of the ground. Increasing values on the y-axis also represent forward motion in the horizontal direction with respect to the reference markers, which were placed 1.37m apart.

Joint velocity.Similar to the hip displacement, the vertical velocity component was the most important factor in determining the resultant velocity. This was shown by a maximum vertical velocity of 2.8 m/s and a maximum combined velocity of 2.8 m/s in the male jump. The female jump maximum vertical velocity was 4.2 m/s and the horizontal component was 0.83 m/s resulting in a maximum combined velocity of 4.28 m/s. These data show that the horizontal component was negligible. The maximum vertical velocity occurred in both subjects during the push-off phase before the maximum jump height was attained.

Figure 9. Velocity of the hip joint in female jump (left) and male jump (right). The thinnest line is the combined horizontal and vertical velocity of the hip. The narrow dashed line represents horizontal velocity, while the wide dashed line represents vertical velocity. Positive values on the y-axis indicate upward velocity in the vertical direction. Positive values on the x-axis represent forward velocity in the horizontal direction.

Center of mass. The male subject had a higher absolute center of mass (CM) than the female subject. In addition, both subjects' center of mass were anterior to the ankle joint, with the male's CM being slightly more anterior than the female's CM.

Figure 10. Location of the center of mass (CM) in the female jump (left) and the male jump (right). Stick figures represent the lower body, including the thigh, shank and foot segments.