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Shane J. Gore, Brendan M. Marshall, Andrew D. Franklyn-Miller, Eanna C. Falvey and Kieran A. Moran

When reporting a subject’s mean movement pattern, it is important to ensure that reported values are representative of the subject’s typical movement. While previous studies have used the mean of 3 trials, scientific justification of this number is lacking. One approach is to determine statistically how many trials are required to achieve a representative mean. This study compared 4 methods of calculating the number of trials required in a hopping movement to achieve a representative mean. Fifteen males completed 15 trials of a lateral hurdle hop. Range of motion at the trunk, pelvis, hip, knee, and ankle, in addition to peak moments for the latter 3 joints were examined. The number of trials required was computed using a peak intraclass correlation coefficient method, sequential analysis with a bandwidth of acceptable variance in the mean, and a novel method based on the standard error of measurement (SEMind). The number of trials required across all variables ranged from 2 to 12 depending on method, joint, and anatomical plane. The authors advocate the SEMind method as it demonstrated fewer limitations than the other methods. Using the SEMind, the required number of trials for a representative mean during the lateral hurdle hop is 6.

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Mark L. Latash

Living systems may be defined as systems able to organize new, biology-specific, laws of physics and modify their parameters for specific tasks. Examples include the force-length muscle dependence mediated by the stretch reflex, and the control of movements with modification of the spatial referent coordinates for salient performance variables. Low-dimensional sets of referent coordinates at a task level are transformed to higher-dimensional sets at lower hierarchical levels in a way that ensures stability of performance. Stability of actions can be controlled independently of the actions (e.g., anticipatory synergy adjustments). Unintentional actions reflect relaxation processes leading to drifts of corresponding referent coordinates in the absence of changes in external load. Implications of this general framework for movement disorders, motor development, motor skill acquisition, and even philosophy are discussed.

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Jason M. Avedesian, Tracey Covassin and Janet S. Dufek

the need for further LE biomechanical exploration in concussed athletes. In DuBose et al, 19 altered LE stiffness measures were based upon one testing trial per limb, even though a minimum of 4 landing trials are recommended for landing performance stability. 24 Lapointe et al 22 did not analyze

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Andrew D. Nordin and Janet S. Dufek

demands (BW25˙H25) from selection as the first testing condition for participant safety. 16 , 23 , 27 Ten blocked landing trials were carried out in each condition (9 used during analysis), providing performance stability, 29 with adequate rest between trials and condition blocks to minimize fatigue. 16

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James Hackney, Jade McFarland, David Smith and Clinton Wallis

achieve performance stability of selected ground reaction force variables during landing . Journal of Sports Science & Medicine, 6 ( 1 ), 126 . PubMed ID: 24149234 Kopell , N. , & Howard , L.N. ( 1975 ). Bifurcations and trajectories joining critical points . Advances in Mathematics, 18 ( 3

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Cynthia J. Wright, Nico G. Silva, Erik E. Swartz and Brent L. Arnold

) precluded the averaging of multiple trials per participant since the assumption of performance stability would not be met. The use of a single helmet design limits generalizability to other helmet styles, and skill transfer between styles in novice learners is yet unknown. However, the existing literature