(5) USE THE HIGHEST DISPLACEMENT WHEN MEASURING VERTICAL JUMP CHARACTERISTICS

Purpose: High reliability but poor precision was previously found in our laboratory for several kinetic and kinematic variables obtained during vertical jumping. In those cases, data were averaged from multiple attempts over two sessions. However, although each attempt was designed to be a maximum effort, the fitness-trained individuals may have exhibited random jump-to-jump inconsistencies, that, when averaged, resulted in force, velocity, and power outputs that were unreflective of the individual’s performance. More consistent day-to-day results might be obtained by using the jump with the greatest displacement at each testing session for data extraction, a procedure analogous to the scoring done for field events in track and field competitions. Therefore, the purpose of this study was to determine the stability reliability and precision of peak vertical ground reaction force (PkvGRF), peak velocity (Pk Vel, absolute expression only), peak vertical power (PkPz), and concentric work (W) expressed as absolutes and normalized for body mass during countermovement vertical jumps based on the attempt from each session with the highest jump displacement. Methods: Sixty young, fitness-trained adults (31 men, 29 women), 18 to 35 years of age, performed three vertical jumps (CMVJ) on two occasions using a self-selected countermovement depth and constrained arm swing. A nine-camera 3D motion capture system (240 Hz, Qualisys Inc., Sweden) and force platform (1200 Hz, AMTI, Watertown, MA, USA) were used to collect 3D marker position data and vertical ground reaction force (vGRF) data for the right side of the body, respectively. Velocity (meters per second) was based on the center of mass displacement with respect to time. Power (watts) was calculated as the product of vGRF and center of mass vertical velocity. Concentric work (joules) was calculated from vGRF with respect to displacement starting at a point corresponding to the lowest center of mass and ending at toe-off. Except for velocity, all measures were expressed both as absolutes and normalized for body mass. Stability reliability (relative reliability) was determined using an intraclass correlation coefficient (two-way random model), and precision (absolute reliability) using both the standard error of measurement and the coefficient of variation percentage. Occasional marker data were corrupted resulting in some missing values. Results: See Table 1. Conclusions: For populations like the one used in this study, it appears that when the highest displacement from a series of countermovement vertical jumps is used, extracted peak vGRF, peak velocity, peak power, and concentric work are likely to be both reliable and precise. Practical Applications: These findings suggest for fitness-trained young men and women that a single session may be used to represent the extracted peak vGRF, peak velocity, peak power, and concentric work during the countermovement vertical jump having the highest displacement obtained from a series of jumps. Acknowledgements: None