C. Christensen, D. Everton, K. Rencher, J. Ryan, B. Lee, W.M. Denning

Brigham Young University - Idaho, Rexburg, ID

Vertical jump height is used as a measure of overall health and power and is vital to performing many jumping sports. It is important to understand how lower-extremity kinematics influence vertical jump height performance. PURPOSE: The aim of this research is to explore the relationship between peak knee flexion angle and maximum vertical jump height. METHODS: Seventeen able-bodied subjects (5 Female, 12 Male; mass = 85.8 ± 18.7kg, height = 1.8 ± 0.1m) performed six maximum vertical jumps. Before jumping, markers were placed on the lateral aspect of the mid-thigh (midway between lateral epicondyle of femur and greater trochanter), the lateral epicondyle of the femur, and lateral aspect of the lower leg (midway between lateral epicondyle of femur and lateral malleolus). Peak knee flexion angle was determined by finding the relative angle between the lower and upper leg during counter- movement. After marker placement, subjects jogged in place for 40 seconds as a warmup. Next, vertical jump height was determined. Each subject jumped maximal hitting the tiles on the Vertec. A two-minute rest period was given between each jump. The highest three jump heights were used for analysis. A video camera recorded (120 fps) lower-extremity movement. Maximum knee flexion angle was determined using video uploaded in a freeware motional analysis software (Kinovea 0.8.15). Linear and curvilinear regressions were used to determine the relationship between knee flexion angle and vertical jump height. RESULTS: Average vertical jump height was 17.9 ± 4.3 in. Average peak knee flexion angle was 97.2 ± 10.5°. Based on the curvilinear regression, knee flexion angle significantly correlated with maximum jump height (r = 0.6; p = 0.49). In this model, knee angle accounted for 35% of the variance in jump height with a prediction equation of Y = -0.017x2+3.264x-136.54. Linear regression analysis was not significant. CONCLUSION: There is a significant relationship between maximal jump height and peak knee flexion angle. A knee flexion angle between 87 and 107 degrees was shown to maximize vertical jump height. Training athletes to achieve a knee flexion angle within this range is suggested. Further a prediction equation using knee flexion angle may be used to estimate jump height when no other methods are available.

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