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Anderson Nascimento Guimarães, Herbert Ugrinowitsch, Juliana Bayeux Dascal, Alessandra Beggiato Porto and Victor Hugo Alves Okazaki

in the range of motion during the practice and developed a pattern of control adapted to the environment and task constraints. CC = cross correlation; AAG = angle–angle graphic; PPG = position–position graphic; PTG = position–time graphic, JROM = joint range of motion; PRAV = pick range of angular

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Joanne Smith, Madeleine Grealy and Gert-Jan Pepping

We investigated a general theory accounting for the guidance of ongoing movements in an interceptive reaching task. The aim was to assess the premise of tau-coupling that the coupling constant k, the ratio of taus (τs) of motion gaps between hand and object, reflects the kinematics of the on-going movement. The spatial and temporal constraints of the interceptive action were manipulated in three task conditions. While the time dependent counterpart of k, K(t) exhibited task effects, k itself could not distinguish between task manipulations. K(t) showed large variability during the initial acceleration phase, small variability during the rest of the movement, and task dependent changes during the final deceleration phase of interception. The findings highlight the importance of clarifying what constitutes as t-coupling.

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Mohsen Shafizadeh, Jane Manson, Sally Fowler-Davis, Khalid Ali, Anna C. Lowe, Judy Stevenson, Shahab Parvinpour and Keith Davids

organisation of structured, stimulating environment” ( Nithianantharajah & Hannan, 2006 ). The authors conceptualized an enriched environment to be assessed in an exercise context (a) with familiar environmental and task constraints, (b) with less explicit information provided by a support practitioner and

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Jason C. Laffer, Aaron J. Coutts and Job Fransen

Movement Science, 55 , 229 – 239 . PubMed ID: 28846855 doi:10.1016/j.humov.2017.08.012 10.1016/j.humov.2017.08.012 Dicks , M. , Button , C. , & Davids , K. ( 2010 ). Examination of gaze behaviors under in situ and video simulation task constraints reveals differences in information pickup for

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David W. Eccles, Susanne E. Walsh and David K. Ingledew

The objective of this study was to gain an understanding of expert cognition in orienteering. The British orienteering squad was interviewed (N = 17) and grounded theory was used to develop a theory of expert cognition in orienteering. A task constraint identified as central to orienteering is the requirement to manage attention to three sources of information: the map, the environment, and travel. Optimal management is constrained by limited processing resources. However, consistent with the research literature, the results reveal considerable adaptations by experts to task constraints, characterized primarily by various cognitive skills including anticipation and simplification. By anticipating the environment from the map, and by simplifying the information required to navigate, expert orienteers can circumvent processing limitations. Implications of this theory for other domains involving navigation, and for the coaching process within the sport, are discussed.

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Weiyun Chen, Inez Rovegno, John Todorovich and Matt Babiarz

The purpose of this study was to describe third grade children’s movement responses to dribbling tasks taught by four accomplished teachers and how children’s dribbling varied with changes in task constraints. Children in four intact classes were videotaped during three dribbling lessons as part of their physical education program. Videotapes were analyzed to provide descriptions of children’s movement responses. Typically, when children dribbled while walking or jogging they controlled the ball, pushed with finger pads, and looked at the ball. When dribbling tasks were more difficult, in general, there was less ball control and more slapping with palms (less mature patterns) while at the same time more instances of children lifting their heads to look up (a more mature pattern). Task constraints had differential impacts on different dribbling elements. One implication is that teachers need to consider this differential impact in designing practice conditions and in selecting assessment tasks.

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Graham E. Caldwell and Li Li

In this commentary we question whether the relationship between muscle activity and joint moments is the same for natural motor tasks as for controlled experimental situations. An important consideration in this regard is the identification of the correct electromechanical delay (EMD) for comparing EMG and joint moment data. Data from recent cycling studies are used to illustrate the importance of EMD, and how changing task constraints can alter the relation between muscle activity and joint moment balance for bi-articular antagonist pairs.

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Neil Anderson and Chris Button

Control of static posture is constrained by multiple sensory inputs, motor ability, and task constraints. Development of static postural control across the lifespan can be analyzed effectively using nonlinear analyses of center of pressure (CoP) time series, including approximate and sample entropy. In this paper, the key findings from studies using nonlinear analysis tools are reviewed to describe the development of postural control. Preschool children learn to adopt relatively unstable postures (e.g., standing) in which the regularity of CoP initially increases as a consequence of restricting mechanical degrees of freedom. As children age, CoP regularity decreases as degrees of freedom are released, thus enabling a more functional, adaptable type of postural control. Changes to sensory inputs or task constraints also affect the regularity of CoP sway. For example, removing vision, adding vibration, or imposing dual-task conditions affect performer’s CoP regularity differently. One limitation of approximate and sample entropy analysis is the influence of different input parameters on the output and subsequent interpretation. Ongoing refinement to entropy analysis tools concern determining appropriate values for the length of sequence to be matched and the tolerance level used with CoP data.

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Sean Clark, Peter W. Iltis, Crystal J. Anthony and Andrea Toews

Despite widespread use of the functional-reach (FR) and limits-of-stability (LOS) tests, comparisons of postural strategies and postural limits for these tests have not been previously reported. The purpose of this study was to compare postural strategies as determined by cross-correlation analyses of trunk and lower leg angular displacements and postural limits as assessed by maximum center-of-gravity (COG) excursions as older adults at low fall risk completed the FR and LOS tests. Fourteen older adults completed three FR and LOS trials while standing on a Balance Master® force platform. Results indicated that despite relatively similar instructions to reach or lean as far as possible without losing balance or altering the base of support, their performance differed with regard to postural strategies employed and maximum COG excursions produced. These findings suggest that because of differences in task constraints, FR and LOS tests should not be used interchangeably.

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Michael A. Riley, Suvobrata Mitra, Thomas A. Stoffregen and Michael T. Turvey

We examined the potentially exploratory and performatory nature of postural sway. Subjects stood upright or leaned forward, with eyes open or closed. Postural data were analyzed using a statistical mechanics analysis of center of pressure (COP) trajectories, which examines the fractional Brownian nature of postural sway. Positive correlations (persistence) over short time scales are hypothesized to reflect exploratory behavior, and negative correlations (antipersistence) over long time scales are hypothesized to reflect performatory behavior. When leaning, subjects exhibited decreased levels of persistence (decreased correlation) and increased levels of antipersistence (increased correlation) than when upright. With eyes open, subjects showed decreased levels of persistence and decreased levels of antipersistence than with eyes closed. Effects of vision were more pronounced when leaning. Evidence for direction-specific exploration (based upon root mean square variability analysis) was considered. Task-specificity and trade-offs between biomechanical and task constraints in models of postural control were discussed.