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Maurice R. Yeadon and Grant Trewartha

The goal of this study was to investigate the control strategy employed by gymnasts in maintaining a hand balance. It was hypothesized that a “wrist strategy” was used in which perturbations in the sagittal plane were corrected using variations in wrist flexor torque with synergistic shoulder and hip torques acting to preserve a fixed body configuration. A theoretical model of wrist strategy indicated that control could be effected using wrist torque that was a linear function of mass center displacement and velocity. Four male gymnasts executed hand balances and 2-dimensional inverse dynamics was used to determine net joint torque time histories at the wrist, shoulder, and hip joints in the sagittal plane. Wrist torque was regressed against mass center position and velocity values at progressively earlier times. It was found that all gymnasts used the wrist strategy, with time delays ranging from 160 to 240 ms. The net joint torques at the shoulder and hip joints were regressed against the torques required to maintain a fixed configuration. This fixed configuration strategy accounted for 86% of the variance in the shoulder torque and 86% of the variance in the hip torque although the actual torques exceeded the predicted torques by 7% and 30%, respectively. The estimated time delays are consistent with the use of long latency reflexes, whereas the role of vestibular and visual information in maintaining a hand balance is less certain.

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Courtney M. Butowicz, Julian C. Acasio, and Brad D. Hendershot

Despite these larger global motions, nonlinear techniques that evaluate local kinematic variability may elucidate the underlying postural control strategies. 6 – 8 Trunk stability is dependent upon appropriate neuromuscular control to support passive spinal structures and control responses to internal and

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Christoph Schütz, Matthias Weigelt, Dennis Odekerken, Timo Klein-Soetebier, and Thomas Schack

Previous studies on sequential effects of human grasping behavior were restricted to binary grasp type selection. We asked whether two established motor control strategies, the end-state comfort effect and the hysteresis effect, would hold for sequential motor tasks with continuous solutions. To this end, participants were tested in a sequential (predictable) and a randomized (nonpredictable) perceptual-motor task, which offered a continuous range of posture solutions for each movement trial. Both the end-state comfort effect and the hysteresis effect were reproduced under predictable, continuous conditions, but only the end-state comfort effect was present under nonpredictable conditions. Experimental results further revealed a work range restriction effect, which was reproduced for the dominant and the nondominant hand.

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Tyler R. Keith, Tara A. Condon, Ayana Phillips, Patrick O. McKeon, and Deborah L. King

The Star Excursion Balance Test (SEBT) is a valid and reliable measure of dynamic postural control. Center of pressure (COP) behavior during the SEBT could provide additional information about direction-dependent SEBT balance strategies. The purpose of this study was to quantify spatiotemporal COP differences using COP area and velocity among three different SEBT reach directions (anterior, posteromedial, posterolateral). The anterior direction COP velocity was significantly lower than both posterior directions. However, the anterior COP area was significantly greater than posterior. Based on COP behavior, the anterior and posterior reach directions appear to use different postural control strategies on the SEBT.

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Fabio A. Almeida, Renae L. Smith-Ray, Rain Van Den Berg, Patti Schriener, Mike Gonzales, Pierre Onda, and Paul A. Estabrooks

Within the busy clinic visit and multiple preventive guidelines to follow, the rate of physician referral for physical activity (PA) is disappointing. This study used an interrupted time-series design to determine the effect of a simple stimulus control strategy to increase physician referrals for PA when compared to standard care before and after exposure to the stimulus control intervention. The number of referrals (N = 218 total) per week was significantly higher during weeks when the stimulus control intervention was used (p < .01). Approximately 77% of participants referred during standard care weeks initiated a PA program while 67% of those referred during stimulus control weeks initiated PA. These rate differences were significant (p < .05). Nonetheless, the number of individuals who initiated PA was greater during stimulus control weeks than during usual care weeks (p < .05; 9.8 vs. 5.6), due to the larger total volume of referrals. We concluded that stimulus control interventions targeting physician referrals are a practical method for enhancing participation in PA programs.

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Andrew H. Huntley, John L. Zettel, and Lori Ann Vallis

A simultaneous turn and step motion is a vital component of many complex movements and may provide insight into age related balance and stability deficits during a weight transfer task. In this study, nine young adults and ten healthy, community dwelling older adults performed a simultaneous “turn and step” task from a quiet standing position under two self-selected speeds, self-paced and as quickly and efficiently as possible. Whole-body center of mass was estimated to investigate stability, segmental coordination, and variability. Older adults performed the task with greater variability, however they were unable to alter stability nor segmental coordination across the self-selected speeds; absence of this modulation portrays a trade-off between stability and manoeuvrability. An increase in variability with no observed directional differences suggests that the simultaneous turn and step task may be a sensitive discriminatory motor task helpful in elucidating the adoption of altered control strategies used by elderly populations.

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Murielle Grangeon, Cindy Gauthier, Cyril Duclos, Jean-Francois Lemay, and Dany Gagnon

The study aimed to (1) compare postural stability between sitting and standing in healthy individuals and (2) define center-of-pressure (COP) measures during sitting that could also explain standing stability. Fourteen healthy individuals randomly maintained (1) two short-sitting positions with eyes open or closed, with or without hand support, and (2) one standing position with eyes open with both upper limbs resting alongside the body. Thirty-six COP measures based on time and frequency series were computed. Greater COP displacement and velocity along with lower frequency measures were found for almost all directional components during standing compared with both sitting positions. The velocity, 95% confidence ellipse area, and centroidal frequency were found to be correlated between unsupported sitting and standing. Despite evidenced differences between sitting and standing, similarities in postural control were highlighted when sitting stability was the most challenging. These findings support further investigation between dynamic sitting and standing balance.

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Assane E.S. Niang and Bradford J. McFadyen

The present study investigated the adaptations of specific power bursts during the combined contexts of the proximity (lead vs. trail limb) and height of an obstruction in relation to limb elevation versus progression. Ten young, adult, male subjects walked at their natural speed during unobstructed walking and the bilateral avoidance of moderate and high obstacles. Hip flexor generation power was unaffected by obstacle height for the leading limb and always delayed for the trailing limb. The knee extensor absorption power burst at toe-off was also eliminated for the trailing limb and was found to reappear in mid-swing. Few differences were seen for ankle push-off power. The results suggest that the hip joint is dedicated to limb advancement only, while the knee joint is directly involved in limb elevation and the control of multiarticular effects.

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

objectives in the DF control strategy, to answer these questions. Methods Search Strategy The information search was realized using the following databases: PubMed, Embase (ScienceDirect), Web of Science, Scopus, and SPORTDiscus (EBSCO). The terms were combined according to the following combination: (a

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Francis M. Grover, Valéria Andrade, Nicole S. Carver, Scott Bonnette, Michael A. Riley, and Paula L. Silva

.P. , & Schöner , G. ( 2002 ). Motor control strategies revealed in the structure of motor variability . Exercise and Sport Sciences Reviews, 30 ( 1 ), 26 – 31 . 10.1097/00003677-200201000-00006 Latash , M.L. , Scholz , J.P. , & Schöner , G. ( 2007