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Douglas W. Powell, Anburaj Muthumani and Ruiping Xia

Bradykinesia is a cardinal symptom of Parkinson’s disease (PD). Both aging and disease are shown to be associated with decreased adaptability to environmental stresses characterized by reduced complexity (or increased regularity) of biorhythms. The purpose of this study was to investigate the regularity of movement in individuals with PD, and the effect of dopaminergic medication. Nine subjects with PD and eight controls performed wrist flexion/extension movements at maximal velocity and range of motion. Subjects with PD were tested under two medication conditions. Approximate entropy (ApEn) was calculated to assess the regularity of the movement, with the smaller value associated with the greater regularity. Data revealed that subjects with PD had lower ApEn values than controls. Medication did not alter the ApEn values. These findings demonstrate that impaired voluntary movement in individuals with PD is associated with increased regularity of movement and this exaggerated regularity appears less sensitive to anti-PD medication.

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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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Andrew M. Murray, Joong Hyun Ryu, John Sproule, Anthony P. Turner, Phil Graham-Smith and Marco Cardinale

Purpose:

Running performance is influenced by the interaction of biomechanical and physiological factors. Miniaturized accelerometers worn by athletes can be used to quantify mechanical aspects of running and as a noninvasive tool to assess training status and progression. The aim of this study was to define and validate a method to assess running regularity and allow the estimation of an individual’s oxygen uptake (V̇O2) and/or blood lactate—[La]b—based on data collected with accelerometers and heart rate.

Methods:

Male adolescent endurance athletes completed an incremental submaximal aerobic stage test where V̇O2 and [La]b were measured. The test was terminated when [La]b concentration at the end of the stage exceeded 4 mmol/L. Two wireless triaxial accelerometers were placed on participants’ right shank and lower back throughout the test. The root mean square (RMS) and sample entropy (SampEn) were calculated for the vertical, mediolateral, and anteroposterior components of acceleration.

Results:

There were significant positive correlations of acceleration and entropy variables with [La]b and V̇O2, with moderate to high coefficients (r = .43–.87). RMS of the shank acceleration was the most highly related with both physiological variables. When the accelerometer was attached on the trunk, SampEn of the vertical acceleration had the strongest relationship with V̇O2 (r = .76, P < .01).

Conclusions:

The described method analyzing running complexity may allow an assessment of gait variability, which noninvasively tracks V̇O2 and/or [La]b, allowing monitoring of fatigue or training readiness for trained adolescent individuals.

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Pascal Madeleine

This laboratory study investigated seated computer work before and after prolonged constrained sitting. Discomfort ratings and kinetic and kinematics data were recorded in nine healthy males performing computer work for 5 min before and after 96 min of sitting. The displacement of the center of pressure (CoP) in anterior-posterior and medial-lateral directions and lumbar curvature (LC) were calculated. The root mean square, standard deviation, and sample entropy values were computed from the CoPs and LC signals to assess the magnitude, amount of variability, and regularity of sitting dynamics, respectively. The discomfort increased for the buttocks (p = .02).The standard deviation and sample entropy values of the CoPs and LC signals, respectively, increased (p < .04) and decreased (p < .004) whereas the root mean square remained unchanged (p > .15) after prolonged constrained sitting compared with before. This present study showed that during seated computer work, prolonged constrained sitting affected the amount of variability and the regularity of sitting postural control, whereas the magnitude was not affected. The importance of the dynamics of sitting control may challenge the idea of a static and ideal seated posture at work.

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William P. Berg and Michael R. Hughes

Muscle activation was measured using EMG in 28 males (n = 28) while participants caught visually identical balls of known and unknown weights (50, 1.32, 2.18, and 2.99 kg) under variable (1–10s) and constant (3s) foreperiods. EMG integrals were computed for three time intervals before the catch (anticipatory), and one after (compensatory). Load uncertainty caused the CNS to use an anticipatory strategy characterized by preparation to catch balls of an unknown weight by utilizing about 92% of the muscle activation used to catch the heaviest possible ball under the known weight condition. The CNS appeared to scale anticipatory muscle activation to afford an opportunity to catch a ball of an unknown weight between .50 and 2.99 kg. The constant 3s foreperiod, which permitted temporal anticipation, did not influence the anticipatory neuromotor strategy adopted by the CNS to cope with load uncertainty. Load uncertainty also altered compensatory neuromotor control in catching.

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Ugo H. Buzzi and Beverly D. Ulrich

The purpose of this study was to examine the dynamic stability of two groups of children with different dynamic resources in changing contexts. The stability of the lower extremity segments of preadolescent children (8–10 years old) with and without Down syndrome (DS) was evaluated as children walked on a motorized treadmill at varying speeds. Tools from nonlinear dynamics, maximum Lyapunov exponent, and approximate entropy were used to assess the behavioral stability of segmental angular displacements of the thigh, shank, and foot. Our results suggest that children with DS show decreased dynamic stability during walking in all segments and that this might be a consequence of inherently different subsystem constraints between these groups. Differences between groups also varied, though not uniformly, with speed, suggesting that inherent differences could further constrain the behavioral response to changing task demands.

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Yoshifumi Kijima, Ryoji Kiyama, Masaki Sekine, Toshiyo Tamura, Toshiro Fujimoto, Tetsuo Maeda and Tadasu Ohshige

, Tamura, Minato, & Kanaya, 2015 ). In a gait analysis using a tri-axial accelerometer attached to the lumbar region, the disturbance of the trunk during walking was estimated by the root mean square (RMS; Sekine et al., 2013 ), and the gait regularity and symmetry were estimated by the autocorrelation

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Tsuyoshi Saida, Masayuki Kawada, Daijiro Kuroki, Yuki Nakai, Takasuke Miyazaki, Ryoji Kiyama and Yasuhiro Tsuneyoshi

). Previous studies have reported that patients with knee OA with severe deformities, as assessed by the Kellgren and Lawrence classification, walked with greater asymmetry than those with mild deformities ( Iijima, Eguchi, Aoyama, & Takahashi, 2019 ). In addition, regularity of gait, indicating the degree of

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

coper cohorts. It is possible that LAS copers may be able to rely on somatosensory information when visual input is removed more effectively than those with CAI, which could provide valuable insight into these two cohorts with a history of LAS. SampEn has been used as the application of a regularity

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John J. Jackson

Sport has a multitude of organizations, which are social systems organized for the attainment of particular types of goals. Organizations are characterized by divisions of labor, power, and communication responsibilities through which regularities such as task allocation, supervision, and coordination are developed. Such regularities constitute the organization’s structure, which is described here in terms of formal relations and communication.