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Gavin L. Moir, Alberto Garcia and Gregory B. Dwyer

Purpose:

To investigate the intersession reliability of selected kinematic and kinetic variables during countermovement vertical jumps (CMJs).

Methods:

Thirty-five men and 35 women performed CMJs on a force platform during four testing sessions each separated by 1 wk. Kinematic variables included time in the air (TIA), take-off velocity (TOV), total vertical displacement of the center of mass (TJH). and countermovement depth, whereas kinetic variables included positive impulse, negative impulse, vertical stiffness, and rates of force development. Systematic bias was assessed by calculating the 90% confidence interval of the change in the mean between consecutive testing sessions and between the first and final testing session for each variable. Coefficients of variation (CV) and intraclass correlation coefficients (ICC) were also calculated.

Results:

Systematic bias was observed only for peak rate of force development during the concentric phase of the movement. For TIA, TOV, and TJH, CV values ranged from 1.7% to 6.6%, with ICC values ranging from 0.82 to 0.97. The other variables showed greater variation (CV range: 1.7% to 39.9%; ICC range: 0.04 to 0.99). Only slight gender differences were found in the reliability statistics, and the reliability of most of the variables was diminished as the time between the testing sessions was increased.

Conclusion:

Even though practitioners can expect good reliability for jump height measured from a force platform in men and women, other kinematic and kinetic variables often assessed during vertical jumps may not be reliable.

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Philip X. Fuchs, Andrea Fusco, Jeffrey W. Bell, Serge P. von Duvillard, Cristina Cortis and Herbert Wagner

Purpose: To determine the effect of in-season differential training on volleyball spike-jump technique and performance in elite-level female players. Methods: During the season, spike jumps of 12 elite female players (Austrian Volleyball League Women) were recorded by 13 Qualisys Oqus cameras (250 Hz) and an AMTI force plate (1000 Hz). First measurement was made at the beginning of the investigation. Two identical measurements were repeated after a first and a second interval. The first interval served as control phase. The second interval was comparable in length and regular program but included differential training (6 wk, 8 sessions of 15–20 min) as a modified warm-up. It addressed specific performance determinants. Analyses of variances were calculated for the 3 measurements and for the development during control and intervention phase. Results: Initial jump height (0.44 [0.09] m) changed by −4.5% during the control phase and +11.9% during the intervention (P < .001, ηp2=.70). All approach variables, arm backswing, and velocity-conversion strategy improved compared with the control phase (Δ%: 6.1–51.2%, P < .05, ηp2=.40.80). Joint angles, countermovement depth, maximal angular velocities, and torso incline were not affected (Δ%: −2.9–9.1%, P = .066–.969, ηp2=.00.27). Conclusions: In-season differential training led to technical adaptations and increased spike-jump height in elite female players. The differential training program allowed players to experience a range of adaptability and to adjust toward an individual optimum in technical components of performance determinants. Coaches are encouraged to apply technical differential training to elite athletes and to target biomechanical performance factors specifically.

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Kym J. Williams, Dale W. Chapman, Elissa J. Phillips and Nick Ball

% (bodyweight) to 40% (loaded) of an athlete’s predicted 1RM at 10% increments performed in ascending order to provide a continual warm-up effect as load increased. 5 Athletes began each CMJ from an upright standing position and were instructed to use a self-selected countermovement depth to maintain constant

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Niall Casserly, Ross Neville, Massimiliano Ditroilo and Adam Grainger

placed on the hips. Countermovement depth was self-selected by the player before jumping as high as possible with hips and feet extended throughout flight to prevent tucking of the knees. 21 Postjump, each participant received verbal feedback upon their performance. Players were familiar with the CMJ