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Priscilla Augusta Monteiro Ferronato and José Angelo Barela

This study identified and quantified rambling and trembling properties of the postural control system of children 4–12 years of age. Forty five children of varying ages (4-, 8-, and 12-years) and 15 adults stood upright on a force plate and performed 5 trials with and 5 trials without vision with each trial lasting 30 s. Center of pressure, rambling, trembling, mean sway amplitude, and predominant frequency were obtained. Results revealed that the displacement of the center of pressure and overall rambling trajectories were age-related with younger children swaying more than older children and adults. Similarly, overall trembling trajectories for younger children were larger compared with older children and adults. These results suggested that a younger child’s larger body sway mostly results from difficulties using sensory information when estimating overall body position and velocity in an upright stance and is less a result from the noise in the postural control system.

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Hendrik Reimann, Tyler Fettrow and John J. Jeka

showed a similar effect in their healthy legs, but not in their amputated legs. This can be interpreted as an active control mechanism in the sense described above. Additional evidence that humans use the lateral ankle strategy to maintain balance during locomotion comes from a study by Reimann et

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Grace C. Bellinger, Kristen A. Pickett and Andrea H. Mason

involve different motor control mechanisms, an idea referred to as the two primitives theory ( Sternad et al., 2013 ; van Mourik & Beek, 2004 ). This theory would also allow for separate motor planning of the two components of the dual task. The purpose of this study is, therefore, to examine the

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Popi Sotiriadou, Jessie Brouwers, Veerle De Bosscher and Graham Cuskelly

Previous studies acknowledge the importance of sporting organizations’ developing partnerships with clubs for athlete development purposes. However, there are no studies that address the way partnerships influence athlete progression and pathways. This study explores interorganizational relationships (IORs) between a tennis federation and tennis clubs in their efforts to improve player development processes. Document analysis and semistructured interviews with representatives from clubs and the Flemish federation were used. The findings show that the federation and the clubs engaged in IORs to achieve reciprocity and efficiency. The federation anticipated gaining legitimacy and asymmetry, and clubs expected to develop stability. Formal and informal control mechanisms facilitated IOR management. The conceptual model discussed in this study shows the types of IOR motives, management, and control mechanisms that drive and influence the attraction, retention/ transition, and nurturing processes of athlete development.

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M.A. Urbin

Goal-directed movement is possible because the cortical regions regulating movement have continuous access to visual information. Extensive research from the various domains of motor control (i.e., neurophysiology, neuropsychology, and psychophysics) has documented the extent to which the unremitting availability of visual information enables the sensorimotor system to facilitate online control of goal-directed limb movement. However, the control mechanism guiding appreciably more complex movements characterized by ballistic, whole-body coordination is not well understood. In the overarm throw, for example, joint rotations must be optimally timed between body segments to exploit the passive flow of kinetic energy and, in turn, maximize projectile speed while maintaining accuracy. The purpose of this review is to draw from the various research domains in motor control and speculate on the nature of the sensorimotor control mechanism facilitating overarm throwing performance.

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Leanna Ferrand and Slobodan Jaric

The purpose of this study was to explore the effects of handedness on coordination of grip (G) and load (L) forces in static bimanual manipulation tasks. Participants (N = 10) exerted various L profiles against an externally fixed hand-held device based on presumably open-loop and closed-loop neural control mechanisms, (i.e., mediated and not mediated, respectively, by sensory feedback). Average G/L ratio and the coupling of G and L (i.e., stability of the G/L ratio and correlation between G and L) were separately assessed in each hand. The results revealed a lower average G/L ratio in the non-dominant hand suggesting a more economical grip, while the indices of G and L coupling were similar in two hands. The dominant and non-dominant hand failed to reveal relative advantages in the tasks predominantly based on open- and closed-loop control mechanisms, respectively. We conclude that, due to the static nature of the tested tasks, the particular advantage of the non-dominant hand in G and L coordination could be in line with the recently proposed specialization of the non-dominant limb for control of position. However, the overall results are not in line with classic views of the prevailing open- closed-loop neural mechanisms in the control of the dominant and nondominant limb, respectively.

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Patrick J. DiRocco, Jane E. Clark and Sally J. Phillips

The purpose of the study was to determine if mildly mentally retarded (MMR) children followed the same developmental sequence of coordination for the propulsive phase of the standing long jump as their nonhandicapped (NH) peers. Subjects for the study included 39 MMR and 90 NH children, ages 4-7 years. Each subject was filmed performing several standing long jumps. Jumping patterns were analyzed from the film records, and distance jumped also was determined from the film. Results indicated that the arm and leg patterns of coordination proposed for NH children by Clark and Phillips (1985) were comprehensive enough to include the MMR children. In spite of similar patterns of coordination, the age group means for the distance jumped by the MMR subjects were 2 to 3 years behind their NH peers. Two explanations are offered for this deficit in distance jumped: first, there may be differences in coordination between the arm and leg action, and second, there may be differences in control mechanisms.

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Erik A. Wikstrom and Robert B. Anderson

The purpose of this investigation was to determine if stereotypical patterns of gait initiation are altered in those with posttraumatic ankle osteoarthritis. Ten subjects, five with unilateral ankle osteoarthritis and five uninjured controls, participated. Subjects completed the SF-36 and Ankle Osteoarthritis Scale to quantify self-reported disability as well as 10 dual-limb static stance trials and 10 gait initiation trials with each leg. Center of pressure outcomes were calculated for static balance trials while the peak center of pressure excursions were calculated for each phase of gait initiation. The results indicate greater self-reported disability (P < .05) and worse static postural control (P < .05) in the ankle osteoarthritis group. Nonstereotypical patterns were also observed during the first and third phases of gait initiation in those with ankle osteoarthritis. The results of this pilot study suggest that supraspinal motor control mechanisms may have changed in those with posttraumatic ankle osteoarthritis.

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Vennila Krishnan and Slobodan Jaric

Coordination of the hand grip (G; acting normally to the grasping surface) and load forces (L; acting in parallel) in bimanual static tasks was studied. L symmetry (either the magnitude or direction) and frequency were manipulated in healthy participants (N = 14). More complex tasks (i.e., the higher frequency and/or asymmetric ones) revealed expected deterioration in both the task performance (accuracy of the prescribed L force profiles) and force coordination (G/L ratio and G-L correlation) suggesting importance of L frequency and symmetry in prehension activities. However, the same tasks revealed a more prominent deterioration of interlimb than the within-limb force coordination. This could be interpreted by two partly different and noncompeting neural control mechanisms where the coordination of interlimb forces may be based on ad-hoc and task-specific muscle coordination (often referred to as muscle synergies) while the within-limb coordination of G and L could be based on more stable and partly reflex mechanisms.

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Joan E. Deffeyes, Regina T. Harbourne, Wayne A. Stuberg and Nicholas Stergiou

Sitting is one of the first developmental milestones that an infant achieves. Thus measurements of sitting posture present an opportunity to assess sensorimotor development at a young age. Sitting postural sway data were collected using a force plate, and the data were used to train a neural network controller of a model of sitting posture. The trained networks were then probed for sensitivity to position, velocity, and acceleration information at various time delays. Infants with typical development developed a higher reliance on velocity information in control in the anterior-posterior axis, and used more types of information in control in the medial-lateral axis. Infants with delayed development, where the developmental delay was due to cerebral palsy for most of the infants in the study, did not develop this reliance on velocity information, and had less reliance on short latency control mechanisms compared with infants with typical development.