Simon J. Bennett

Goal-Directed Aiming: Two Components but Multiple Processes

This article reviews the behavioral literature on the control of goal-directed aiming and presents a multiple-process model of limb control. The model builds on recent variants of Woodworths (1899) two-component model of speed-accuracy relations in voluntary movement and incorporates ideas about dynamic online limb control based on prior expectations about the efferent and afferent consequences of a planned movement. The model considers the relationship between movement speed and accuracy, and how performers adjust their trial-to-trial aiming behavior to find a safe, but fast, zone for movement execution. The model also outlines how the energy and safety costs associated with different movement outcomes contribute to movement planning processes and the control of aiming trajectories. Our theoretical position highlights the importance of advance knowledge about the sensory information that will be available for online control and the need to develop a robust internal representation of expected sensory consequences. We outline how early practice contributes to optimizing strategic planning to avoid worst-case outcomes associated with inherent neural-motor variability. Our model considers the role of both motor development and motor learning in refining feed-forward and online control. The model reconciles procedural and representational accounts of the specificity-of-learning phenomenon. Finally, we examine the breakdown of perceptual-motor precision in several special populations (i.e., Down syndrome, Williams syndrome, autism spectrum disorder, normal aging) within the framework of a multiple-process approach to goal-directed aiming.

Skill acquisition in sport: some applications of an evolving practice ecology

This paper builds on recent theoretical concerns regarding traditional conceptualizations of the skill acquisition process. The implications for the process of practice in sport contexts are explored with reference to the information-processing approach to motor behaviour and the newer ecological paradigm. Issues are raised with current principles of practice based on traditional theoretical ideas. A practice strategy that gives greater weight to the guided exploration of the practice workspace jointly defined by the properties of the individuals subsystems, the specific task and the environment is advocated. Such a constraints-led perspective supersedes previous distinctions between rudimentary and voluntary skills. Sports scientists, coaches, teachers and movement rehabilitation therapists are invited to review current practices in the light of recent theoretical advances from the ecological perspective.

Research design and statistics in biomechanics and motor control

Biomechanics and motor control researchers measure how the body moves and interacts with its environment. The aim of this review paper is to consider some key issues in research methods in biomechanics and motor control. The review is organized into four sections: proposing, conducting, analysing and reporting research. In the first of these, we emphasize the importance of defining a worthy research question and of planning the study before its implementation to prevent later difficulties in the analysis and interpretation of data. In the second section, we cover selection of trial sizes and suggest that using three trials or more may be beneficial to provide more ‘representative’ and valid data. The third section on analysis of data concentrates on effect size statistics, qualitative and numerical trend analysis and cross-correlations. As sample sizes are often small, the use of effect size is recommended to support the results of statistical significance testing. In using cross-correlations, we recommend that scatterplots of one variable against the other, with the identified time lag included, be inspected to confirm that the linear relationship assumption underpinning this statistic is met and, if appropriate, that a linearity transformation be applied. Finally, we consider important information related to the issues above that should be included when reporting research. We recommend reporting checks or corrections for violations of underpinning assumptions, and the effect of these checks or corrections, to assist in advancing knowledge in biomechanics and motor control.

Vertical jump coordination: fatigue effects

PURPOSE The aim of this study was to investigate the segmental coordination of vertical jumps under fatigue of the knee extensor and flexor muscles. METHODS Eleven healthy and active subjects performed maximal vertical jumps with and without fatigue, which was imposed by requesting the subjects to extend/flex their knees continuously in a weight machine, until they could not lift a load corresponding to approximately 50% of their body weight. Knee extensor and flexor isokinetic peak torques were also measured before and after fatigue. Video, ground reaction forces, and electromyographic data were collected simultaneously and used to provide several variables of the jumps. RESULTS Fatiguing the knee flexor muscles did not reduce the height of the jumps or induce changes in the kinematic, kinetic, and electromyographic profiles. Knee extensor fatigue caused the subjects to adjust several variables of the movement, in which the peak joint angular velocity, peak joint net moment, and power around the knee were reduced and occurred earlier in comparison with the nonfatigued jumps. The electromyographic data analyses indicated that the countermovement jumps were performed similarly, i.e., a single strategy was used, irrespective of which muscle group (extensor or flexors) or the changes imposed on the muscle force-generating characteristics (fatigue or nonfatigue). The subjects executed the movements as if they scaled a robust template motor program, which guided the movement execution in all jump conditions. It was speculated that training programs designed to improve jump height performance should avoid severe fatigue levels, which may cause the subjects to learn and adopt a nonoptimal and nonspecific coordination solution. CONCLUSION It was suggested that the neural input used in the fatigued condition did not constitute an optimal solution and may have played a role in decreasing maximal jump height achievement.

Postural sway and active balance performance in highly active lower-limb amputees.

Buckley JG, O’Driscoll D, Bennett SJ: Postural sway and active balance performance in highly active lower-limb amputees. Am J Phys Med Rehabil 2002;81:13–20. ObjectiveTo determine the balance performance of active lower-limb amputees during quiet standing and under dynamic conditions. DesignCenter-of-pressure excursions during quiet standing and the standing balance performance on a single axis stabilimeter was assessed in six unilateral lower-limb amputees and six able-bodied controls. Stabilimeter trials were repeated with subjects standing so that pivoting occurred either in the anteroposterior or mediolateral direction or in the mediolateral direction but with vision occluded. ResultsCenter-of-pressure excursions were significantly greater (P < 0.05) for amputees in both the mediolateral and anteroposterior directions. During all stabilimeter tests, amputees spent significantly less time in balance than able-bodied controls (P < 0.05), and this was attributed to a nonsignificant increase in the average time the stabilimeter spent in contact with the ground. Group differences in the average time of contact in the anteroposterior test condition were meaningful (effect size, 1.19). ConclusionsAmputees had poorer static and dynamic balance than able-bodied controls. Amputees had a greater problem controlling dynamic balance in the anteroposterior direction than the mediolateral direction. Findings highlight the importance of the ankle in maintaining balance in situations that involve body movements in the sagittal plane.

Quiet eye duration and gun motion in elite shotgun shooting.

INTRODUCTION No literature exists to document skill-related differences in shotgun shooting and whether these may be a function of eye movements and control of gun motion. We therefore conducted an exploratory investigation of the visual search behaviors and gun barrel kinematics used by elite and subelite shooters across the three shotgun shooting subdisciplines. METHODS Point of gaze and gun barrel kinematics were recorded in groups of elite (n = 24) and subelite (n = 24) shooters participating in skeet, trap, and double trap events. Point of gaze was calculated in relation to the scene, while motion of the gun was captured by two stationary external cameras. Quiet eye (final fixation or tracking gaze that is located on a specific location/object in the visual display for a minimum of 100 ms) duration and onset were analyzed as well as gun motion profiles in the horizontal and vertical planes. RESULTS In skeet, trap, and double trap disciplines, elite shooters demonstrated both an earlier onset and a longer relative duration of quiet eye than their subelite counterparts did. Also, in all three disciplines, quiet eye duration was longer and onset earlier during successful compared with unsuccessful trials for elite and subelite shooters. Kinematic analyses indicated that a slower movement of the gun barrel was used by elite compared with subelite shooters. CONCLUSIONS Overall, stable gun motion and a longer quiet eye duration seem critical to a successful performance in all three shotgun disciplines.

Observational modeling effects for movement dynamics and movement outcome measures across differing task constraints : A meta-analysis

The authors conducted a meta-analysis of the observational modeling literature to quantify overall between-participants treatment effects obtained when movement behaviors are acquired. Effects were obtained and reported separately for movement dynamics (MD) and movement outcome (MO) measures. The overall mean observational modeling treatment effects (δ u Bi ) were 0.77 and 0.17, respectively, for MD and MO measures. The effects reflected a significant advantage of observational modeling over practice-only control conditions. Most important, the magnitude of the obtained effects was far stronger for MD than for MO measures, confirming a distinctive response to observational modeling during motor learning. The advantage for MD measures over observational modeling measures was replicated for different types of tasks. Observational modeling was particularly beneficial for serial tasks (δ u Bi = 1.62 and 0.61, respectively, for MD and MO). There were slightly reduced effects for continuous tasks (δ u Bi = 1.01 and 0.51, respectively, for MD and MO) and smaller to medium-sized effects for discrete tasks (δ u Bi = 0.56 and 0.10, respectively, for MD and MO). The authors discuss those findings with reference to the visual perception perspective on observational modeling, i.e., that demonstrations primarily convey relative motions required to approximate modeled movement behaviors.

Joint torques and dynamic joint stiffness in elderly and young men during stepping down

OBJECTIVE To compare the joint torque pattern and dynamic joint stiffness at the knee and ankle in elderly and young men during stepping down. BACKGROUND Adequate joint stiffness is critical during the single support phase to control forward and downward body momentum. DESIGN Six active elderly men (mean 67.7) and six young men (mean 23.6) of similar body mass and height, were filmed stepping down from one force platform to another. Repeated trials were undertaken at three different step heights (200, 250, and 300 mm). METHOD Joint torques were determined for the ankle and knee of the support limb throughout the single support phase. The gradient of the joint torque-angle graph was calculated to define dynamic joint stiffness of the ankle and knee in two phases; (I) from initiation of movement until heel-off of the supporting limb, and (II) from heel-off of the supporting limb to contra-limb touch down. RESULTS Maximum ankle torque values were lower in the elderly and occurred at a larger dorsiflexion angle (P<0.05). Knee torque patterns were similar in both groups. Phase I ankle stiffness was significantly less in the elderly (4.0-5.2 Nm/ degrees ) at all step heights compared to the young (7.6 - 8.7 Nm/ degrees ). In both groups ankle stiffness in Phase II increased with step height, while knee joint stiffness decreased. CONCLUSIONS The different torque pattern and lower dynamic ankle stiffness in the elderly, particularly for Phase I, suggested an altered control strategy. These findings highlight the importance of dynamic ankle joint stiffness in stepping down. RELEVANCE Understanding how the elderly step down may be important in developing strategies to prevent falls.

General motor representations are developed during action-observation

This study was designed to examine the generality of motor learning by action-observation. During practice, action-observation participants watched a learning model (e.g., physical practice participants) perform a motor sequence-timing task involving mouse/cursor movements on a computer screen; control participants watched a blank screen. Participants transferred to either a congruent (same mouse-cursor gain), or an incongruent (different mouse-cursor gain) condition. As predicted, motor sequence timing was learned through action-observation as well as physical practice. Moreover, transfer of learning to an incongruent set of task demands indicates that the motor representation developed through observation includes generalised visual-motor procedures associated with the use of feedback utilization.

Information-movement coupling: Implications for the organization of research and practice during acquisition of self-paced extrinsic timing skills

Information‐movement coupling is a fundamental concept, integral to theorizing on the coordination of goal‐directed activity in ecological psychology. In this paper, we examine the implications of this concept for the design of experimental research and the organization of practice during the acquisition of movement coordination in sport tasks. The task vehicle for our analysis is interceptive actions, in particular self‐paced extrinsic timing tasks exemplified by serving in sports such as volleyball. Recent research highlighting the relevance of information‐movement coupling for the process of practice in sport is discussed. We conclude that information‐movement coupling represents an important principle for the structural organization of research and practice in self‐paced extrinsic timing tasks and that further work is required to verify its significance across a range of sport movements.