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David A. Rosenbaum

The development of mathematical tools for describing dynamical systems has made it possible to characterize forms of behavior that could not be characterized before. This represents progress, but the enterprise runs the risk of being nothing more than curve fitting if investigators fail to identify the physical, biological, or psychological mechanisms which are common to systems that follow the same dynamical regime and which are not common to systems that do not follow the same dynamical regime.

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Joseph Hamill, Jeffrey M. Haddad and William J. McDermott

Variability is a critical aspect of a dynamical systems analysis. Because there are a number of numerical techniques that can be used in such an analysis, the calculation of variability has several issues that must be addressed. The purpose of this paper is to present a variety of quantitative methods for investigating variability from a dynamical systems perspective. The paper is divided into two major sections covering discrete and continuous methods. Each of these sections is subdivided into two sections. Within discrete methods, we discuss, first, the calculation of the discrete relative phase from a time-series history of two parameters and, second, the use of return maps. Using continuous methods, we present procedures for using angle-angle plots in the evaluation of relative phase. We then discuss the use of phase plots in the calculation of the continuous relative phase. Each of these methods presents unique problems for the researcher and the method to be used is determined by the nature of the question asked.

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Christophe Gernigon, Fabienne d’Arripe-Longueville, Didier Delignières and Grégory Ninot

Based on the dynamical systems perspective, the present study aimed to explore how states of involvement toward mastery, performance-approach, and performance-avoidance goals (Elliot & Church, 1997) flow, are interrelated, and are activated during a practice judo combat. Using a retrospective video recall method, two male national level judo competitors expressed on a computer their moment-to-moment level of involvement toward each goal. Self-confrontation interviews also based on the video were immediately conducted. Analyses of variance revealed differences in levels of each goal between periods of the combat. Windowed cross-correlation analyses showed that the patterns of relationships between the time series of the different goals considered two-by-two included either high positive, high negative, or zero correlations, depending on the moment. Qualitative data analyses supported these findings and suggested that goal involvement states emerged and fluctuated according to the ecological constraints of the situation, such as the initial contextual conditions and the course of action.

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Patrick O. McKeon and Jay Hertel

Column-editor : Michael G. Dolan

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Patrick O. McKeon

Edited by John Parsons

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Kathleen M. Haywood and Kathleen Williams

This study examined tennis serving in older adult tennis players. Twenty-two older adults, divided into younger and older halves, were videotaped serving five “first” serves. Dominant shoulder flexibility also was measured. From the videotape, servers were classified into developmental levels and their resultant ball impact velocity was calculated. An Age × Gender (2 × 2) mixed model MANOVA yielded no significant differences between the age groups or between men and women in flexibility, ball impact velocity, or movement pattern. A few combinations of the developmental levels of elbow and forearm/racket action were used by the majority of servers. Regular practice might consolidate older adults in these attractor movement patterns, making them more resilient to change than with less practiced skills. These results suggest practice in older adulthood favorably affects performance by resulting in consistency of movement pattern and maintenance of movement pattern, flexibility, and ball impact speed.

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Eliane Mauerberg-deCastro

This article uses an anchor metaphor to explain the dynamic interplay between the human body's active uses of nonrigid tools to mediate information about its adjacent environment to enhance postural control. The author used an “anchor” system (e.g., ropes attached to varying weights resting on the floor) to test blindfolded adults who performed a restricted-balance task (30 s one-foot standing). Participants were tested while holding the anchors under a variety of weight conditions (125 g, 250 g, 500 g, and 1 kg) and again during a baseline condition (no anchors). When compared with the baseline condition, there was a significant reduction in the amount of body sway across the anchor conditions. The author found that mechanical support provided by the anchor system was secondary to its haptic exploratory function and that an individual can use the anchoring strategy with a dual purpose: for resting and for reorientation after intrinsic disruptions.

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Anne R. Schutte and John P. Spencer

The timed-initiation paradigm developed by Ghez and colleagues (1997) has revealed two modes of motor planning: continuous and discrete. Continuous responding occurs when targets are separated by less than 60° of spatial angle, and discrete responding occurs when targets are separated by greater than 60°. Although these two modes are thought to reflect the operation of separable strategic planning systems, a new theory of movement preparation, the Dynamic Field Theory, suggests that two modes emerge flexibly from the same system. Experiment 1 replicated continuous and discrete performance using a task modified to allow for a critical test of the single system view. In Experiment 2, participants were allowed to correct their movements following movement initiation (the standard task does not allow corrections). Results showed continuous planning performance at large and small target separations. These results are consistent with the proposal that the two modes reflect the time-dependent “preshaping” of a single planning system.

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Kenneth G. Holt and Suh Fang Jeng

This paper presents some of the ways we are attempting to understand why physically challenged children adopt the movement patterns they do. It focuses on the skill of walking and compares non-neurologically disabled persons with children with cerebral palsy. A multidisciplinary approach is advocated in which the tools of biomechanics, physiology, and dynamical systems theory are explored. Traditional biomechanics of children with cerebral palsy tend to be descriptive in nature. More recent methods include both traditional biomechanical and dynamical systems approaches to understand why physically challenged children adopt the gait patterns they do. The concept of self-optimization is introduced as a way to motivate the investigations. Mechanical energy conservation, minimal metabolic cost, normality, and stability are discussed as some of the potential optimality criteria. Optimality criteria measurement including several methods of analysis of stability are discussed, and preliminary results of findings in the three groups are reported.