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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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Liam P. Kilduff, Huw Bevan, Nick Owen, Mike I.C. Kingsley, Paul Bunce, Mark Bennett and Dan Cunningham

Purpose:

The ability to develop high levels of muscle power is considered an essential component of success in many sporting activities; however, the optimal load for the development of peak power during training remains controversial. The aim of the present study was to determine the optimal load required to observe peak power output (PPO) during the hang power clean in professional rugby players.

Methods:

Twelve professional rugby players performed hang power cleans on a portable force platform at loads of 30%, 40%, 50%, 60%, 70%, 80%, and 90% of their predetermined 1-repetition maximum (1-RM) in a randomized and balanced order.

Results:

Relative load had a significant effect on power output, with peak values being obtained at 80% of the subjects’ 1-RM (4466 ± 477 W; P < .001). There was no significant difference, however, between the power outputs at 50%, 60%, 70%, or 90% 1-RM compared with 80% 1-RM. Peak force was produced at 90% 1-RM with relative load having a significant effect on this variable; however, relative load had no effect on peak rate of force development or velocity during the hang power clean.

Conclusions:

The authors conclude that relative load has a significant effect on PPO during the hang power clean: Although PPO was obtained at 80% 1-RM, there was no significant difference between the loads ranging from 40% to 90% 1-RM. Individual determination of the optimal load for PPO is necessary in order to enhance individual training effects.

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Aaron T. Scanlan, Jordan L. Fox, Nattai R. Borges and Vincent J. Dalbo

Purpose:

Declines in high-intensity activity during game play (in-game approach) and performance tests measured pre- and postgame (across-game approach) have been used to assess player fatigue in basketball. However, a direct comparison of these approaches is not available. Consequently, this study examined the commonality between in- and across-game jump fatigue during simulated basketball game play.

Methods:

Australian, state-level, junior male basketball players (n = 10; 16.6 ± 1.1 y, 182.4 ± 4.3 cm, 68.3 ± 10.2 kg) completed 4 × 10-min standardized quarters of simulated basketball game play. In-game jump height during game play was measured using video analysis, while across-game jump height was determined pre-, mid-, and postgame play using an in-ground force platform. Jump height was determined using the flight-time method, with jump decrement calculated for each approach across the first half, second half, and entire game.

Results:

A greater jump decrement was apparent for the in-game approach than for the across-game approach in the first half (37.1% ± 11.6% vs 1.7% ± 6.2%; P = .005; d = 3.81, large), while nonsignificant, large differences were evident between approaches in the second half (d = 1.14) and entire game (d = 1.83). Nonsignificant associations were evident between in-game and across-game jump decrement, with shared variances of 3–26%.

Conclusions:

Large differences and a low commonality were observed between in- and across-game jump fatigue during basketball game play, suggesting that these approaches measure different constructs. Based on our findings, it is not recommended that basketball coaches use these approaches interchangeably to monitor player fatigue across the season.

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Nick Dobbin, Richard Hunwicks, Ben Jones, Kevin Till, Jamie Highton and Craig Twist

force platform with an immovable bar positioned to correspond with the second-pull clean position, just below the crease of the hip. 14 Participants are then instructed to pull as fast and hard as possible, enabling various kinetic measures to be quantified from ground-reaction forces. 15 , 16 With

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Robin Healy, Ian C. Kenny and Andrew J. Harrison

–time trace contained initial impact transients, that is, force peaks. Thirty seconds of rest were provided between trials to avoid any deleterious effects of fatigue on performance. 16 Drop jumps were performed from a box height of 0.3 m, with athletes landing on an AMTI NET force platform (Watertown, MA

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John J. McMahon, Paul A. Jones, Timothy J. Suchomel, Jason Lake and Paul Comfort

The Reactive Strength Index (RSI) accounts for the duration of force production to achieve a given jump height by dividing jump height by ground-contact time. 1 RSI is a more easily obtainable metric than force-platform-derived variables, and it provides greater insight into neuromuscular and

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Thomas Dos’Santos, Paul A. Jones, Jonathan Kelly, John J. McMahon, Paul Comfort and Christopher Thomas

subjects standing on a portable force platform (Kistler, Switzerland, Model 9286AA, SN 1209740) positioned on the center of the floor within a power rack. An immovable weightlifting bar (Werksan Olympic Bar, Werksan, Moorsetown, NJ, USA) was clamped down to the crash bars of the power rack with ratchet

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John J. McMahon, Paul A. Jones and Paul Comfort

Purpose:

To determine the concurrent validity and reliability of the popular Just Jump system (JJS) for determining jump height and, if necessary, provide a correction equation for future reference.

Methods:

Eighteen male college athletes performed 3 bilateral countermovement jumps (CMJs) on 2 JJSs (alternative method) that were placed on top of a force platform (criterion method). Two JJSs were used to establish consistency between systems. Jump height was calculated from flight time obtained from the JJS and force platform.

Results:

Intraclass correlation coefficients (ICCs) demonstrated excellent within-session reliability of the CMJ height measurement derived from both the JJS (ICC = .96, P < .001) and the force platform (ICC = .96, P < .001). Dependent t tests revealed that the JJS yielded a significantly greater CMJ jump height (0.46 ± 0.09 m vs 0.33 ± 0.08 m) than the force platform (P < .001, Cohen d = 1.39, power = 1.00). There was, however, an excellent relationship between CMJ heights derived from the JJS and force platform (r = .998, P < .001, power = 1.00), with a coefficient of determination (R 2) of .995. Therefore, the following correction equation was produced: Criterion jump height = (0.8747 × alternative jump height) – 0.0666.

Conclusions:

The JJS provides a reliable but overestimated measure of jump height. It is suggested, therefore, that practitioners who use the JJS as part of future work apply the correction equation presented in this study to resultant jump-height values.

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Caleb D. Bazyler, Satoshi Mizuguchi, Ashley A. Kavanaugh, John J. McMahon, Paul Comfort and Michael H. Stone

force platform can be used to monitor training adaptations in volleyball players and inform training prescription during a peaking phase. A few limitations of this study, albeit difficult in practice, were the lack of a control group and small sample size. Future research should develop a model to

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Jason D. Stone, Adam C. King, Shiho Goto, John D. Mata, Joseph Hannon, James C. Garrison, James Bothwell, Andrew R. Jagim, Margaret T. Jones and Jonathan M. Oliver

right and left end of the barbell. Three reflective markers (seventh cervical vertebra, bilateral anterosuperior iliac spine) were removed after the static trial. Kinetic data were obtained at a sampling frequency of 1200 Hz from bilateral force platforms (Advanced Medical Technology, Inc, Watertown, MA