A study of biomechanical variables in the countermovement jump and the drop jump performed by female intercollegiate athletes
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The purpose of this study was to investigate differences in selected biomechanical parameters during countermovement (CMJ) and drop (DJ) jumps. A secondary purpose was to descriptively compare the performances of the two jump conditions. Two sagittal view high speed videocameras filmed 25 female intercollegiate basketball and volleyball athletes performing CMJs and DJs. One CMJ, one DJ, and a static squat jump matched with each jump condition were selected and analyzed. A two factor repeated measures ANOVA was used to analyze the jump conditions performed by two sport groups. Based on the results of the statistical analysis, it was concluded that: (a) both sport group's body center of mass descended faster during the DJ (p< .0001) and further during the CMJ (p.0007), and the volleyball group descended faster (p .003) and further (p< .0001) under both jump conditions; (b) eccentric (p< .0001) and concentric (p.001) time periods were longer for the CMJ for both sport groups; (c) the percentage of simultaneity and utilized stored elastic energy were not significantly different for either jump condition or sport group; and (d) peak jump heights were similar for jump conditions and sport groups. Descriptive statistics were computed on demographic data and five kinematic variables. The two sport groups were similar in demographic profile. Based on the statistical results it was concluded that: (a) knee and hip flexion remained relatively consistant within 10 of 1.57 rad (90) for all conditions except volleyball's CMJ, and CMJ's hip flexion was greater; (b) CMJs followed a proximal. to distal sequential pattern, whereas, the DJs had no definable pattern; (c) CMJ's first time delays were shorter than the second, whereas, DJ time delays were inconsistant; (d) CMJ’s segmental maximum velocities were higher; and (e) shared positive contributions between the trunk and thigh were greater than the thigh and shank.