Motor Control Research Research Articles

ELITE-S2: the multifactorial movement analysis facility for the International Space Station

Experimental observations of adaptation processes of the motor control system to altered gravity conditions can provide useful elements to the investigations on the mechanisms underlying motor control of human subject. The microgravity environment obtained on orbital flights represents a unique experimental condition for the monitoring of motor adaptation. The research in motor control exploits the changes caused by microgravity on the overall sensorimotor process, due to the impairment of the sensory systems whose function depends upon the presence of the gravity vector. Motor control in microgravity has been investigated during parabolic flights and short-term space missions, in particular for analysis of movement-posture co-ordination when equilibrium is no longer a constraint. Analysis of long-term adaptation would also be very interesting, calling for long-term body motion observations during the process of complete motor adaptation to the weightlessness environment. ELITE-S2 is an innovative facility for quantitative human movement analysis in weightless conditions onboard the International Space Station (ISS). ELITE-S2 is being developed by the Italian Space Agency, ASI is to be delivering the flight models to NASA to be included in an expressed rack in US Lab Module in February 2004. First mission is currently planned for summer 2004 (increment 10 ULF 2 ISS).

Multijoint movement control: the importance of interactive torques

The underlying mechanisms of the neural control of movement have long been explored, with a focus primarily on central control aspects and often overlooking the intrinsic mechanical properties of the motor system. To fully understand the control and regulation of movements, the biomechanical properties of the moving subject, specifically interactive torques, must be considered in the design, evaluation, and interpretation of empirical data. We first discuss the difficulty of extrapolating information from a wide variety of tasks due to their varying inherent task constraints. Examples are subsequently given where a biomechanical perspective provides a more informative interpretation of existing data. Finally, we focus on research examining the role of interactive torques with a discussion of how discoordinated movements may be explained by an inability to modulate interactive torques. Inclusion of biomechanical considerations in motor control research is a step toward incorporating multilevel methodologies and interpretations into the field, and providing a more comprehensive understanding of the neural control and regulation of movement.

Virtual reality and physical rehabilitation: a new toy or a new research and rehabilitation tool?

Virtual reality (VR) technology is rapidly becoming a popular application for physical rehabilitation and motor control research. But questions remain about whether this technology really extends our ability to influence the nervous system or whether moving within a virtual environment just motivates the individual to perform. I served as guest editor of this month's issue of the Journal of NeuroEngineering and Rehabilitation (JNER) for a group of papers on augmented and virtual reality in rehabilitation. These papers demonstrate a variety of approaches taken for applying VR technology to physical rehabilitation. The papers by Kenyon et al. and Sparto et al. address critical questions about how this technology can be applied to physical rehabilitation and research. The papers by Sveistrup and Viau et al. explore whether action within a virtual environment is equivalent to motor performance within the physical environment. Finally, papers by Riva et al. and Weiss et al. discuss the important characteristics of a virtual environment that will be most effective for obtaining changes in the motor system.

A critical evaluation of the force control hypothesis in motor control.

The ability to formulate explicit mathematical models of motor systems has played a central role in recent progress in motor control research. As a result of these modeling efforts and in particular the incorporation of concepts drawn from control systems theory, ideas about motor control have changed substantially. There is growing emphasis on motor learning and particularly on predictive or anticipatory aspects of control that are related to the neural representation of dynamics. Two ideas have become increasingly prominent in mathematical modeling of motor function--forward internal models and inverse dynamics. The notion of forward internal models which has drawn from work in adaptive control arises from the recognition that the nervous system takes account of dynamics in motion planning. Inverse dynamics, a complementary way of adjusting control signals to deal with dynamics, has proved a simple means to establish the joint torques necessary to produce desired movements. In this paper, we review the force control formulation in which inverse dynamics and forward internal models play a central role. We present evidence in its favor and describe its limitations. We note that inverse dynamics and forward models are potential solutions to general problems in motor control--how the nervous system establishes a mapping between desired movements and associated control signals, and how control signals are adjusted in the context of motor learning, dynamics and loads. However, we find little empirical evidence that specifically supports the inverse dynamics or forward internal model proposals per se. We further conclude that the central idea of the force control hypothesis--that control levels operate through the central specification of forces--is flawed. This is specifically evident in the context of attempts to incorporate physiologically realistic muscle and reflex mechanisms into the force control model. In particular, the formulation offers no means to shift between postures without triggering resistance due to postural stabilizing mechanisms.

The H-reflex as a tool in neurophysiology: its limitations and uses in understanding nervous system function.

The Hoffmann reflex (H-reflex) is extensively used as both a research and clinical tool. The ease with which this reflex can be elicited in several muscles throughout the body makes it an attractive tool. This review discusses some of the important limitations in using the H-reflex. In particular, the inaccurate but widely held assumptions that the H-reflex (1). represents the monosynaptic reflex of the Ia afferent onto homonymous motoneurons, and (2). can be used to measure motoneuronal excitability are addressed. The second part of this review explores the utility of the H-reflex as a neural probe in neurophysiology and motor control research. Applications ranging from the investigation of the functional organization of neural circuitry to the study of adaptive plasticity in spinal structures in health and disease suggest that the H-reflex will continue to be an extensively used tool in motor control neurophysiology.

Computational motor control and human factors: modeling movements in real and possible environments.

An aim of human factors research is to have models that allow for the advance design of user-friendly environments. This is still a distant dream because existing models are not yet sufficiently sophisticated. Models in the domain of motor control are a case in point, but recent developments in computational motor control suggest that the gap between the current state of modeling in this area and the desired state is shrinking. To illustrate this point, we review principles of motor control research that any model of motor control must accommodate. Then we describe a model that captures many of the capacities of actors in the everyday world, including the capacity to reach for objects in different ways depending on factors such as the ease with which different joints can rotate, the required speed of movement, and whether obstacles are present. The model relies on the ideas that goal postures are internally specified before movements are generated, that tasks are defined with flexibly ordered constraint hierarchies, and that movements can be shaped according to task demands. Actual or potential applications of this research include designing and testing possible environments where motor components play a key role.

Effectiveness of neuromotor task training for children with developmental coordination disorder: a pilot study.

The aim of this pilot study was to evaluate the effectiveness of a Neuromotor Task Training (NTT), recently developed for the treatment of children with Developmental Coordination Disorder (DCD) by pediatric physical therapists in the Netherlands. NTT is a task-oriented treatment program based upon recent insights from motor control and motor learning research. Ten children with DCD (intervention group) were tested before and after 9 and 18 treatment sessions on the Movement ABC and a dysgraphia scale in order to measure the effectiveness of treatment on gross and fine motor skills in general and handwriting in particular. Five children (no-treatment control group) were tested twice with a time lag of nine weeks on the Movement ABC in order to measure spontaneous improvement. No improvement was measured for the children in the notreatment control group, whereas a significant improvement was found for children in the intervention group for both quality of handwriting and performance on the Movement ABC after 18 treatment sessions.

PI Control with Anti-Windup in a Nonlinear Phase-Locked Loop

A simple PI controller with anti-windup (PIAW controller) has been developed to control the relative phase between the vibrations of an adaptive tuned vibration absorber (ATVA) and a primary mass to which the ATVA has been attached. The controller and dynamic system combination acts as a phase-locked loop (PLL). This paper compares the PIAW controller with a traditional PLL. In both cases, the forward loop contains a static nonlinearity in series with a linear plant. A benefit of the PIAW controller is that if high gains are used to achieve rapid response times, stability is still guaranteed. While PIAW controller usage has so far been restricted to the ATVA problem in the area of adaptive-passive vibration control, it is anticipated that the controller will have further application in other areas of vibration and motion control research.

In vivo determination of subject-specific musculotendon parameters: applications to the prime elbow flexors in normal and hemiparetic subjects

Objective. This study aimed at estimating the musculotendon parameters of the prime elbow flexors in vivo for both normal and hemiparetic subjects. Design. A neuromusculoskeletal model of the elbow joint was developed incorporating detailed musculotendon modeling and geometrical modeling. Background. Neuromusculoskeletal modeling is a valuable tool in orthopedic biomechanics and motor control research. However, its reliability depends on reasonable estimation of the musculotendon parameters. Parameter estimation is one of the most challenging aspects of neuromusculoskeletal modeling. Methods. Five normal and five hemiparetic subjects performed maximum isometric voluntary flexion at nine elbow positions (0°–120° of flexion with an increment of 15°). Maximum flexion torques were measured at each position. Computational optimization was used to search for the musculotendon parameters of four prime elbow flexors by minimizing the root mean square difference between the predicted and the experimentally measured torque-angle curves. Results. The normal group seemed to have larger maximum muscle stress values as compared to the hemiparetic group. Although the functional ranges of each selected muscle were different, they were all located at the ascending limb of the force–length relationship. The muscle optimal lengths and tendon slack lengths found in this study were comparable to other cadaver studies reported in the literature. Conclusion. Subject-specific musculotendon parameters could be properly estimated in vivo. Relevance Estimation of subject-specific musculotendon parameters for both normal and hemiparetic subjects would help clinicians better understand some of the effects of this pathological condition on the musculoskeletal system.

WATER HYDRAULICS MOTION CONTROL-POSSIBILITIES AND CHALLENGES

Water hydraulics is a growing technology area mainly due to environmental, safety and cleanness reasons. Water hydraulic systems have proved to be the best technology alternative in some industrial sectors such as food, processing, paper, steel and power industry. The main challenges for water hydraulics technology are proper design, good reliability and controllability at a reasonable price level. When these requirements are fulfilled, water hydraulic systems should be fully competitive to other systems.The objective of water hydraulics motion control research is to improve the controllability of the systems. This paper considers the current possibilities and challenges in water hydraulics motion control. Component technology is shortly discussed, including control valves and actuators. After the component technology, the present control methods in water hydraulics motion control are explained. The challenges in position, velocity and force control are exemplary described. Finally, two examples of new water hydraulic motion control systems are presented: Example 1. Positioning system with on/off valves, Example2. Cavitation free proportional pressure relief valve for water systems.

Development of a method for measuring movement-related effort: biomechanical considerations and implications for Fitts' law.

An emerging view in motor control research is that voluntary movements typically require little effort. Nonetheless, there is no agreed-upon method for measuring movement-related effort. To pursue such a method, we conducted two experiments. In the first, participants oscillated the forearm about the elbow in the horizontal plane at different frequencies. After performing each task, they gave an effort rating. The forearm movements caused a cursor to move back and forth between two targets on a computer screen, and we changed the gain of the system, requiring different angular displacements to produce the same cursor displacement, thus keeping the visual demands the same while varying the motor demands. Surprisingly, the ratings increased as the amplitudes of forearm rotation decreased, and the performance scores that participants received were also worse the smaller the amplitudes of forearm rotation. The latter result suggests that participants simply rated as effortful those movements for which knowledge of results indicated poor performance. To seek a more direct link between motor activity and rated effort, in the second experiment we asked participants to oscillate the forearm about the elbow in the horizontal plane at different metronome-specified frequencies, but we allowed participants to generate whatever angular displacements they wished to incur different levels of prescribed effort. With this procedure, we found that angular velocity was proportional to prescribed effort. The simplicity of this outcome suggests that the method used in the second experiment can be used in the future as a means of evaluating biomechanically related effort. The surprising finding of the first experiment suggests that Fitts' Law depends both on perception and on motor control.

Evaluation of dynamic balance among community-dwelling older adult fallers: A generalizability study of the limits of stability test

Objective:To establish reliability estimates of the 75% Limits of Stability® Test (75% LOS test) when administered to community-dwelling older adults with a history of falls. Design:Generalizability theory was used to estimate both the relative contribution of identified error sources to the total measurement error and generalizability coefficients. A random effects repeated-measures analysis of variance (ANOVA) was used to assess consistency of LOS test movement variables across both days and targets. Setting:A motor control research laboratory in a university setting. Participants:Fifty community-dwelling older adults with 2 or more falls in the previous year. Main Outcome Measures:Spatial and temporal measures of dynamic balance derived from the 75% LOS test included average movement velocity, maximum center of gravity (COG) excursion, end-point COG excursion, and directional control. Results:Estimated generalizability coefficients for 2 testing days ranged from .58 to .87. Total variance in LOS test measures attributable to inconsistencies in day-to-day test performance (Day and Subject × Day facets) ranged from 2.5% to 8.4%. The ANOVA results indicated that no significant differences were observed in the LOS test variables across the 2 testing days. Conclusions:The 75% LOS test administered to older adult fallers on 2 consecutive days provides consistent and reliable measures of dynamic balance.

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.

Re-evaluating Rudolf Laban's choreutics.

The choreutic conception of kinesthetic-motor space originally proposed by Rudolf Laban is given psychological validation through comparisons with similar conceptual models in spatial cognition and motor control research. Highly differentiated systems of reference are distinguished. Spatial paths are mentally represented as a series of locations linked into polygonal trajectories. Map-like images of the kinesphere' are structured with polyhedral networks. A fundamental practice consists of transforming spatial information with various operations (rotation, reflection, sizing, etc.). Loci are linked into spatial 'scales' which provide symmetrical solutions to geometric puzzles such as the traveling salesman problem and those devised by Hamilton (Icosian game) and Euler (Koenigsberg bridge problem). In the body these are considered to be prototypes for spatial paths used during adjustments of dynamic equilibrium. The choreutic conception of polyhedral body space is especially similar to the trajectory formation model. The choreutic principal of topological forms deflecting across various kinespheric nets is analogous to N. Bernstein's description of the "net of the motor field ... as oscillating like a cobweb in the wind." These commonalities indicate that further critical reviews of "choreutic laws" might be valuable in suggesting conceptual models and analytical tools for movement study in cognitive science.

Postural sway characteristics in women with lower extremity arthritis before and after an aquatic exercise intervention

Objective: To examine the reliability of postural sway assessment in women with lower extremity arthritis and to ascertain the effects of an aquatic exercise intervention program on these measures.Design: The reliability of postural sway measures was analyzed by within-subjects (Subject times Trial) analysis of variance (ANOVA). The effects of aquatic exercise were analyzed by repeated measures ANOVA using a planned comparison approach with an independent 2 × 2 (Group times Test) design.Setting: Testing in a motor control research laboratory; aquatic exercise in a warm water pool at an area YMCA.Participants: Volunteer sample, 24 women with lower extremity arthritis (rheumatoid [RA] n = 11, osteo [OA] n = 13) randomly assigned into an aquatic exercise group (n = 14) or control group (n = 10).Intervention: Postural sway measures under a two-legged stance test on two separate test days: day 1, pretest; day 2, posttest, administered after a 6-week aquatic exercise program.Results: Reliability correlation coefficients for postural sway measures ranged from .64 to .94 for both subject groups. Aquatic exercise subjects significantly reduced lateral sway and total sway area scores (by 18% to 30%) under both visual conditions after the 6-week intervention. Postural sway scores were significantly higher under the no-vision condition than under the vision condition in each group for both test sessions. Both OA and RA groups had normal sagittal/lateral ratio scores.Conclusion: Women with lower extremity arthritis can be reliably assessed on postural sway measures on a stable two-legged stance test. Although they had normal sagittal/lateral sway ratio scores (ie, scores typical for nonarthritic peers), vision played an important role in their postural stability for this balance task. Aquatic exercise reduced postural sway in women with lower extremity arthritis, as demonstrated by a two-legged stance test, and this exercise program appears to be a viable treatment for increasing postural stability in this population.

Age differences in postural sway during volitional head movement

Objective: To examine the role of a volitional self-paced head-turn movement on the postural sway characteristics of healthy young and elderly subjects. Design: Cross-sectional design. Setting: Motor control research laboratory. Subjects: Ten young adults and 10 elderly subjects. Main Outcome Measures: Postural sway characteristics of each subject were examined using a Kistler force platform. Each subject was tested under four experimental conditions: (1) static postural sway with vision; (2) static postural sway without vision; (3) postural sway with vision and self-paced head-turn movement; and (4) postural sway with no vision and a self-paced head-turn movement. Subjects performed six 15-second trials in each experimental condition. Dependent variables analyzed on each trial were mean sway amplitude (in millimeters), sagital sway standard deviation, lateral sway standard deviation, and frequency of sway (in hertz). Results: During the static conditions (eg, no voluntary movement), the young subjects produced significantly less postural sway than the elderly in both the vision condition (sway amplitude in the young, 3.80mm; in the elderly, 4.89mm) and the no-vision condition (young, 5.44mm; elderly, 5.95 mm). This increased sway was the result of greater lateral sway in the elderly for the vision condition (3.73 vs 2.68mm), and greater sagittal sway for the elderly in the no-vision condition (5.55 vs 4.70mm). There were no significant differences between the groups in the frequency of sway. When asked to initiate and complete the head-turn, elderly subjects significantly increased their mean sway amplitude and decreased their frequency of sway whereas the young subjects did not significantly alter their postural sway profiles. Conclusions: These results demonstrate different postural sway control strategies for young and elderly subjects when asked to perform volitional movements.

Precision hypothesis and the end-state comfort effect

Recently, motor control research has emphasized the planning of macroscopic aspects of control. In object manipulation studies, when participants complete a movement in a comfortable posture, an end-state comfort effect is attained. One explanation for this effect is the precision hypothesis, which states that precision increases when participants are in a comfortable position. This research directly tests the precision hypothesis in two experiments. In Experiment 1, participants picked up a dowel and touched a large or small target on a wall. For the second experiment, the same procedure was followed using a pinpoint target. The probability analyses of the first experiment indicated that the end-state comfort effect was magnified in the small target condition and that the point-of-change effect (Short and Cauraugh, 1997) appeared only when end-state comfort was magnified. Error analyses in Experiment 2 showed that participants were more accurate when in a more comfortable position. The present findings indicate that the precision hypothesis plays a significant role in the end-state comfort effect.

Chapter 21 Neuromuscular Strategies Underlying Ballistic Movements

Publisher Summary The major goal of motor control research is to advance the understanding of the central nervous system (CNS) mechanisms that bring about movement diversity. Such diversity results from two sources of variation: (1) the design of musculoskeletal elements that participate in movement and (2) the way these elements are activated by the CNS. Conceptually, the simplest approach to understanding how a neuromuscular system might generate a specific type of movement is to begin by studying the individual properties of its various components—for example, the muscle fiber (MF), the motor unit (MU), and the motoneurons (MNs). Eventually, a picture begins to emerge showing how the distinctive components might function during movement. For example, skeletal muscles are composed of MFs that have different morphological (e.g., lengths, diameters, and tapering profiles), physiological, and biochemical (e.g., contraction speed and fatigability) properties. Each of these properties and their various combinations confer certain capabilities on the muscle. The assembly of individual MFs with different properties to form whole MUs and whole muscles and the activation of this assembly of usually heterogeneous MFs and MUs by the CNS, at both segmental and supra-segmental levels, are some of the important questions to be addressed. This approach has been applied with great success to the groups of muscles that are involved in the cyclical patterns of muscle activation that are driven by central pattern-generating circuits (e.g., chewing, scratching, and locomotion). In contrast, much less is known about muscle systems that are involved in ballistic movements. This chapter discusses the design of the various musculoskeletal and neural elements that participate in ballistic head retraction—the chief escape response in turtles.

The abstracts of the 4th biennial motor control & human skill research workshop 5th–7th December 1997 Perth, Western Australia

(1998). The abstracts of the 4th biennial motor control & human skill research workshop 5th–7th December 1997 Perth, Western Australia. Australian Journal of Psychology: Vol. 50, No. 3, pp. 1-12.

Motor behavior and human skill: a multidisciplinary approach

Outlines recent research in motor control and human skill. Twenty chapters provide a forum for analyses of the many diverse theoretical approaches used in the understanding of motor control, including the cognitive, dynamical systems, computational and neurological approaches. Two special sections on motor development and motor disability are featured, including new findings for intervention programmes. One of the concluding chapters, Has ecological psychology delivered what it promised? by Jeff Summers, is followed by four commentaries. An information-processing approach is adopted in Part Two through the analysis of motor performance in terms of computational modelling. Research based on the dynamical systems approach is also presented.