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

groups of athletes 8 , 9 , 12 and after different training programs. 13 – 16 The shape of the force–time curve influences the shapes of the resultant velocity– and displacement–time curves, which can also be included in a TPA, 8 – 10 , 15 thus providing a more comprehensive analysis of CMJ performance

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Christopher K. Rhea, Jed A. Diekfuss, Jeffrey T. Fairbrother and Louisa D. Raisbeck

level. During the external focus condition, participants were instructed to focus on keeping the floor level. Data Collection and Processing Center of pressure displacement time series data were collected at 100 Hz (leading to 3,000 data points per trial) and filtered with a fifth-order low

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Oren Tirosh and W.A. Sparrow

Analysis of human gait requires accurate measurement of foot-ground contact, often determined using either foot-ground reaction force thresholds or kinematic data. This study examined the differences in calculating event times across five vertical force thresholds and validated a vertical acceleration-based algorithm as a measure of heel contact and toe-off. The experiment also revealed the accuracy in determining heel contact and toe-off when raw displacement/time data were smoothed using a range of digital filter cutoff frequencies. Four healthy young participants completed 10 walking trials: 5 at normal speed (1.2 m/s) and 5 at fast speed (1.8 m/s). A 3D optoelectric system was synchronized with a forceplate to measure the times when vertical force exceeded (heel contact) or fell below (toe-off) 10, 20, 30, 40, and 50 N. These were then compared and subsequently used to validate an acceleration-based method for calculating heel contact and toe-off with the displacement/time data filtered across a range of four cutoff frequencies. Linear regression analyses showed that during both normal and fast walking, any force threshold within 0 to 50 N could be used to predict heel-contact time. For estimating toe-off low force thresholds, 10 N or less should be used. When raw data were filtered with the optimal cutoff frequency, the absolute value (AbsDt) of the difference between the forceplate event times obtained using a 10-N threshold and the event times of heel contact and toe-off using the acceleration-based algorithms revealed average AbsDt of 10.0 and 16.5 ms for normal walking, and 7.4 and 13.5 ms for fast walking. Data smoothing with the non-optimal cutoff frequencies influenced the event times computed by the algorithms and produced greater AbsDt values. Optimal data filtering procedures are, therefore, essential for ensuring accurate measures of heel contact and toe-off when using the acceleration-based algorithms.

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John J. McMahon, Shannon Murphy, Sophie J.E. Rej and Paul Comfort

Purpose:

Gross measures of countermovement-jump (CMJ) performance are commonly used to track maturational changes in neuromuscular function in rugby league (RL). The purpose of this study was to conduct both a gross and a more detailed temporal-phase analysis of the CMJ performances of senior and academy RL players, to provide greater insight into how neuromuscular function differs between these groups.

Methods:

Twenty senior and 14 academy (under-19) male RL players performed 3 maximal-effort CMJs on a force platform, with forward dynamics subsequently employed to allow gross performance measures and entire kinetic– and kinematic–time curves to be compared between groups.

Results:

Jump height (JH), reactive strength index modified, concentric displacement, and relative concentric impulse (C-IMP) were the only gross measures that were greater for senior players (d = 0.58–0.91) than for academy players. The relative force- and displacement–time curves were similar between groups, but the relative power– and velocity–time curves were greater (d = 0.59–0.97) for the senior players at 94–96% and 89–100% of the total movement time, respectively.

Conclusions:

The CMJ distinguished between senior and academy RL players, with seniors demonstrating greater JH through applying a larger C-IMP and thus achieving greater velocity throughout the majority of the concentric phase and at takeoff. Therefore, academy RL players should train to improve triple (ie, ankle, knee, and hip) extension velocity during the CMJ to bring their JH scores in line with those attained by senior players.

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Paige E. Rice, Herman van Werkhoven, Edward K. Merritt and Jeffrey M. McBride

the minimum acceptable criterion (countermovement hop = .94; 20-cm drop hop = .79; 30-cm drop hop = .91; 40-cm drop hop = .85). 25 The eccentric phase of each hop was defined as the downward slope of the displacement–time curve from the time at which the sum of both force plates (Bertec) exceeded 0 N

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Salman Nazary-Moghadam, Mahyar Salavati, Ali Esteki, Behnam Akhbari, Sohrab Keyhani and Afsaneh Zeinalzadeh

C. Sprott from the Physics Department of Wisconsin University, Madison, WI. The LyE estimates the separation rate of infinitesimally close trajectories. The LyE for angular knee displacement time series (sagittal plane) was measured using the Wolf algorithm. 10 We did not filter the knee kinematic

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Alejandro Pérez-Castilla, Belén Feriche, Slobodan Jaric, Paulino Padial and Amador García-Ramos

power from the directly recorded displacement-time data using the inverse dynamic approach. 7 Note that the successive manipulation of raw data typically increases measurement errors. 6 In this regard, the linear velocity transducer reduces the steps needed to calculate the variables of

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Masafumi Terada, Megan Beard, Sara Carey, Kate Pfile, Brian Pietrosimone, Elizabeth Rullestad, Heather Whitaker and Phillip Gribble

original COP displacement time series ( Jehu, Paquet, & Lajoie, 2017 ; Yamagata, Ikezoe, Kamiya, Masaki, & Ichihashi, 2017 ). While we explored examining differences in SampEn calculated with the original COP displacement time series between the groups, there were no between-group differences in SampEn

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Sahar Boozari, Mohammad Ali Sanjari, Ali Amiri and Ismail Ebrahimi Takamjani

subject leaves the ground. The CoM displacement time series were calculated by double trapezoidal integration of the acceleration curve. The acceleration curve was, in turn, calculated by dividing force time series by body mass. 12 (3) Maximum power (MP): the maximum amount of power in the power

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Philip W. Fink, Sarah P. Shultz, Eva D’Hondt, Matthieu Lenoir and Andrew P. Hills

-SF; Novel GmbH, Munich, Germany) sampled at 10 Hz. Multifractal Analysis For each trial, displacement of COP was calculated as the Euclidean distance between the COP at a given time and the initial COP position. The displacement time series was differentiated to find the change in displacement between time