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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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Jukka T. Viitasalo, Pekka Luhtanen, Harri V. Mononen, Kare Norvapalo, Leena Paavolainen and Matti Salonen

A new instrument, the photocell contact mat (PCM), was developed to measure ground contact time and flight time as well as step and stride frequency as a function of running time or running distance. The purpose of this study was to evaluate the validity and accuracy of PCM measurements against simultaneous force platform measurements. Effects of striking pattern (sprinter or long-distance), running velocity, and height of the PCM from ground level on the contact parameters were analyzed. One male sprint runner and one male distance (marathon) runner volunteered as subjects. The time difference between the PCM and force platform determinations linearly increased as a function of the PCM height and decreased as a function of running velocity (except for the lowest 10 mm PCM height). The low coefficients of variation found between corrected PCM contact times and force platform contact times suggested that the PCM is an accurate instrument to measure ground contact times.

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Ewald M. Hennig, Thomas L. Milani and Mario A. Lafortune

Ground reaction force data and tibial accelerations from a skin-mounted transducer were collected during rearfoot running at 3.3 m/s across a force platform. Five repetitive trials from 27 subjects in each of 19 different footwear conditions were evaluated. Ground reaction force as well as tibial acceleration parameters were found to be useful for the evaluation of the cushioning properties of different athletic footwear. The good prediction of tibial accelerations by the maximum vertical force rate toward the initial force peak (r 2 = .95) suggests that the use of a force platform is sufficient for the estimation of shock-absorbing properties of sport shoes. If an even higher prediction accuracy is required a regression equation with two variables (maximum force rate, median power frequency) may be used (r 2 = .97). To evaluate the influence of footwear on the shock traveling through the body, a good prediction of peak tibial accelerations can be achieved from force platform measurements.

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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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Abbigail Ristow, Matthew Besch, Drew Rutherford and Thomas W. Kernozek

motion capture system (Motion Analysis Corp, Santa Rosa, CA). Kinetic data were collected at 1800 Hz using a force platform (model 4080; Bertec Corporation, Columbus, OH). All data were filtered with a 15-Hz low-pass Butterworth filter. Prior to completing the single-leg hopping tasks, participants

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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

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Antonio Dello Iacono, Marco Beato and Israel Halperin

print January 4, 2019]. J Strength Cond Res . PubMed ID: 30615009 doi:10.1519/JSC.0000000000003005 30615009 27. Moir GL . Three different methods of calculating vertical jump height from force platform data in men and women . Meas Phys Educ Exerc Sci . 2008 ; 12 ( 4 ): 207 – 218 . doi:10