Biomedical subjects

R G Meulenbroek

Publications and source records attributed to R G Meulenbroek.

At least 19 recordsLinked to original sources

PubMed2001

Effects of sitting versus standing and scanner type on cashiers.

In the retail supermarket industry where cashiers perform repetitive, light manual material-handling tasks when scanning and handling products, reports of musculoskeletal disorders and discomfort are high. Ergonomics tradeoffs exist between sitting and standing postures, which are further confounded by the checkstand design and point-of-sale technology, such as the scanner. A laboratory experiment study was conducted to understand the effects of working position (sitting versus standing) and scanner type (bi-optic versus single window) on muscle activity, upper limb and spinal posture, and subjective preference of cashiers. Ten cashiers from a Dutch retailer participated in the study. Cashiers exhibited lower muscle activity in the neck and shoulders when standing and using a bi-optic scanner. Shoulder abduction was also less for standing conditions. In addition, all cashiers preferred using the bi-optic scanner with mixed preferences for sitting (n = 6) and standing (n = 4). Static loading of the muscles was relatively high compared with benchmarks, suggesting that during the task of scanning, cashiers may not have adequate recovery time to prevent fatigue. It is recommended that retailers integrate bi-optic scanners into standing checkstands to minimize postural stress, fatigue and discomfort in cashiers.

Adult↗

PubMed2001

End-point constraints in aiming movements: effects of approach angle and speed.

The present study focuses on two trajectory-formation models of point-to-point aiming movements, viz., the minimum-jerk and the minimum torque-change model. To date, few studies on minimum-jerk and minimum torque-change trajectories have incorporated self- or externally imposed end-point constraints, such as the direction and velocity with which a target area is approached. To investigate which model accounts best for the effects on movement trajectories of such--in many circumstances - realistic end-point constraints, we adjusted both the minimum-jerk and the minimum torque-change model so that they could generate trajectories of which the final part has a specific direction and speed. The adjusted models yield realistic trajectories with a high curvature near movement completion. Comparison of simulated and measured movement trajectories show that pointing movements that are constrained with respect to final movement direction and speed can be described in terms of minimization of joint-torque changes.

Arm↗

PubMed2001

Multijoint grasping movements. Simulated and observed effects of object location, object size, and initial aperture.

Studies of human prehension have revealed characteristic patterns of grasping kinematics. We sought to gain insight into the determinants of those patterns by means of a computer simulation and accompanying behavioral experiment concerning multijoint, planar grasping behavior. The simulation was based on a recent theory of posture-based motion planning which hypothesizes that movement preparation entails time-limited, multiple task-constraint satisfaction. Prehension was modeled with a stick-figure animation involving 12 series of 81 grasping movements. Circular objects to be grasped were located at three angles (45 degrees, 90 degrees, and 135 degrees) and at three distances (20 cm, 30 cm, and 40 cm) relative to the initial location of the hand in the workplane. Additionally, three object sizes (2 cm, 4 cm, and 6 cm in diameter) and three initial aperture sizes (0.3 cm, 3.3 cm, and 7.0 cm) were used. Analyses of the simulated grasping movements focused on the time course of the hand opening, the tangential velocity of the wrist, and the rotations of the joints in the arm, hand, and fingers. The results showed that the model accurately mimicked detailed kinematics of prehension observed in earlier studies. With respect to the frequently reported relationship between object size and hand opening, the simulations further revealed an effect of initial aperture. This predicted effect was confirmed in an experiment in which four participants performed analogous planar grasping tasks. An analysis of the time course of the opening of the hand showed that maximum aperture covaried with initial aperture. A conclusion of this work is that a major determinant of grasping kinematics is avoidance of collisions with objects that are to be grasped.

Adult↗

PubMed2001

Planning reaching and grasping movements: the problem of obstacle avoidance.

In this article, we review a model of the movement-planning processes that people use for direct reaching, reaching around obstacles, and grasping, and we present observations of subjects' repeated movements of the hand to touch 2 target locations, circumventing an intervening obstacle. The model defines an obstacle as a posture that, if adopted, would intersect with any part of the environment (including the actor himself or herself). The model finds a trajectory that is likely to bring the end-effector to the target by means of a one-or two- stage planning process. Each stage exploits the principles of instance retrieval and instance generation. In the first stage, a goal posture is identified, and the trajectory of a direct transition to that posture is tested for collision. If the direct movement has no collision, the movement to the target is immediately executed in joint space. If, however, the direct movement is foreseen to result in a collision, a second planning stage is invoked. The second planing stage identifies a via posture, movement through which will probably avoid the collision. Movement to and from the via posture is then superimposed on the main movement to the target so that the combined movement reaches the target without colliding with intervening obstacles. We describe the details of instance retrieval and instance generation for each of these planning stages and compare the model's performance with the observed kinematics of direct movements as well as movements around an obstacle. Then we suggest how the model might contribute to the study of movements in people with motor disorders such as spastic hemiparesis.

Adult↗

PubMed2001

Planning reaching and grasping movements: simulating reduced movement capabilities in spastic hemiparesis.

In this paper we describe how a theory of posture-based motion planning recently applied to human grasping may contribute to the understanding of grasping pathology. The theory is implemented as a computer model rendered as a stick-figure animation capable of generating realistic multi-joint grasping movements. As shown here, the model can also be used to simulate grasping movements whose kinematics resemble those of grasps performed by people with spastic hemiparesis. The simulations demonstrate effects of: (a) reduced ranges of motion of arm joints on the size of the reachable workspace, (b) awkward starting postures on the time course of the hand closing around an object, (c) increased costs of joint rotations on movement time, and (d) addition of noise to biphasic joint rotations on the low-velocity phase of wrist transport.

Arm↗

PubMed2001

Planning reaching and grasping movements: theoretical premises and practical implications.

This paper presents the background, premises, and results of a model of movement planning. The model's central claims are fourfold: (a) A task is defined by a set of prioritized requirements, or what we call a constraint hierarchy; (b) movement planning works first by specifying a goal posture and then by specifying a movement to that goal posture; (c) movements have characteristic forms; and (d) movements can be shaped through simultaneous performance of different movements, even by the same effector. We review the model and then speculate on its implications for clinical concerns, especially spasticity

Arm↗

PubMed2000

Comfort constrains graphic workspace: test results of a 3D forearm model.

Human movement performance is subject to many physical and psychological constraints. Analyses of these constraints may not only improve our understanding of the performance aspects that subjects need to keep under continuous control, but may also shed light on the possible origins of specific behavioral preferences that people display in motor tasks. The goal of the present paper is to make an empirical contribution here. In a recent simulation study, we reported effects of pen-grip and forearm-posture constraints on the spatial characteristics of the pen tip's workspace in drawing. The effects concerned changes in the location, size, and orientation of the reachable part of the writing plane, as well as variations in the computed degree of comfort in the hand and finger postures required to reach the various parts of this area. The present study is aimed at empirically evaluating to what extent these effects influence subjects' graphic behavior in a simple, free line-drawing task. The task involved the production of small back-and-forth drawing movements in various directions, to be chosen randomly under three forearm-posture and five pen-grip conditions. The observed variations in the subjects' choice of starting positions showed a high level of agreement with those of the simulated graphic-area locations, showing that biomechanically defined comfort of starting postures is indeed a determinant of the selection of starting points. Furthermore, between-condition rotations in the frequency distributions of the realized stroke directions corresponded to the simulation results, which again confirms the importance of comfort in directional preferences. It is concluded that postural rather than spatial constraints primarily affect subjects' preferences for starting positions and stroke directions in graphic motor performance. The relevance of the present modelling approach and its results for the broader field of complex motor behavior, including the manipulation of tools, is indicated briefly.

Adult↗

PubMed2000

Kinematics of fast hemiparetic aiming movements toward stationary and moving targets.

The aim of the present study was to gain insight into the control that hemiparetic subjects have over fast, unimanual aiming movements. Twelve hemiparetic subjects with cerebral palsy and twelve healthy subjects were asked to hit, as quickly as possible, stationary and moving targets projected onto a frontoparallel screen. The task was performed with the nonpreferred (spastic/nondominant) and preferred (nonspastic/dominant) arm. Although the pattern of kinematics of hemiparetic subjects generally corresponded with that reported in earlier reaching and grasping studies, the commonly observed prolonged movement time of the nonpreferred arm as compared to the preferred arm was absent. The spatial variability of the lateral hand displacements toward stationary targets was highest in the spastic arm of the hemiparetic subjects, indicating diminished motion stability. Even though hemiparetic subjects were expected to be unable to adjust their movements flexibly to the position and the velocity of a moving target, they used an initial estimate of where moving targets would be hit in the same way as the healthy subjects did, i.e., they started aiming toward a position in front of the target. In both subject groups, this spatial estimate and the movement time (MT) varied as a function of target velocity, suggesting that the use of target-velocity information in hitting moving targets is unaffected in spastic hemiparetic subjects. The results are related to possible deficits in the regulation of cocontraction underlying movement stability.

Adolescent↗

PubMed1999

Coordination of reaching and grasping by capitalizing on obstacle avoidance and other constraints.

Reaching and grasping an object can be viewed as the solution of a multiple-constraint satisfaction problem. The constraints include contact with the object with the appropriate effectors in the correct positions as well as generation of a collision-free trajectory. We have developed a computational model that simulates reaching and grasping based on these notions. The model, rendered as an animation program, reproduces many basic features of the kinematics of human reaching and grasping behavior. The core assumptions of the model are: (1) tasks are defined by flexibly organized constraint hierarchies; (2) manual positioning acts, including prehension acts, are first specified with respect to goal postures and then are specified with respect to movements towards those goal postures; (3) goal postures are found by identifying the stored posture that is most promising for the task, as determined by the constraint hierarchy, and then by generating postures that are more and more dissimilar to the most-promising stored posture until a deadline is reached, at which time the best posture that was found during the search is defined as the goal posture; (4) depending on when the best posture was encountered in the search, the deadline for the search in the next trial is either increased or decreased; (5) specification of a movement to the goal posture begins with straight-line interpolation in joint space between the starting posture and goal posture; (6) if an internal simulation of this default movement suggests that it will result in collision with an obstacle, the movement can be reshaped until an acceptable movement is found or until time runs out; (7) movement reshaping occurs by identifying a via posture that serves as a body position to which the actor moves from the starting posture and then back to the starting posture, while simultaneously making the main movement from the starting posture to the goal posture; (8) the via posture is identified using the same posture-generating algorithm as used to identify the goal posture. These processes are used both for arm positioning and, with some elaboration, for prehension. The model solves a number of problems with an earlier model, although it leaves some other problems unresolved.

Avoidance Learning↗

PubMed1998

Exploitation of elasticity in copying geometrical patterns: the role of age, movement amplitude, and limb-segment involvement.

An experiment is reported in which 12 adults and 12 10-year-old children copied three-segment geometrical patterns under various size and limb-segment involvement instructions. Next to an assessment of movement pauses, analyses of pen-tip displacements focused on: (1) the accuracy of size reproduction, (2) movement time, and (3) ratio of peak-over-mean velocity. A low value of the latter measure was considered to reflect the adoption of a cyclical movement regime facilitating the exploitation of elastic properties of muscles and tendons during execution. Subjects generally produced size overshoots which, particularly for the children, were most pronounced for small patterns. These effects were accompanied by prolonged movement times. Peak-over-mean velocity ratios were smallest in adults, in large patterns, and when the arm instead of the hand was required as effector. Although adults paused more frequently than children, pause durations were similar in both groups. It is suggested that fast movements with low peak-over-mean velocity ratios reflect successful attempts by subjects to exploit the elasticity of muscles and tendons. These attempts are accompanied in the present task, however, by an increased risk of having to pause between subsequent segments of a movement sequence, possibly for energy-dissipation reasons.

Adult↗

PubMed1998

Geometric features of workspace and joint-space paths of 3D reaching movements.

The present study focuses on geometric features of workspace and joint-space paths of three-dimensional reaching movements. Twelve subjects repeatedly performed a three-segment, triangular-shaped movement pattern in an approximately 60 degrees tilted horizontal plane. Task variables elicited movement patterns that varied in position, rotational direction and speed. Trunk, arm, hand and finger-tip movements were recorded by means of a 3D motion-tracking system. Angular excursions of the shoulder and elbow joints were extracted from position data. Analyses of the shape of 3D workspace and joint-space paths focused on the extent to which the submovements were produced in a plane, and on the curvature of the central parts of the submovements. A systematic tendency to produce movements in a plane was found in addition to an increase of finger-tip path curvature with increasing speed. The findings are discussed in relation to the role of optimization principles in trajectory-formation models.

Adult↗

PubMed1998

The stability of pen-joint and interjoint coordination in loop writing.

This study is concerned with pen-joint and interjoint coordination in handwriting. In particular, it focuses on the stability of coordination as a means to find the locus of coordination control in the arm-pen effector system. Twelve subjects generated loop sequences of varying length at various positions on the baseline of writing. Joint excursions and pen-tip displacements were recorded by means of a 3D-motion tracking system. The coordination stability of 15 pairs of 6 mechanical degrees of freedom (d.f.s) of the arm-pen effector system was investigated by means of relative phase analyses. Pen-joint coordination between horizontal pen-tip displacements and wrist excursions was found to be most stable; that between vertical pen-tip displacements and finger excursions was considerably less stable. Interjoint coordination was generally less stable than pen-joint coordination, and most stable between the wrist and the elbow. Sequence length and its position on the line differentially affected the coordination stability of the d.f. combinations. The results are discussed in relation to assumptions about joint coordination in writing as expressed by computational handwriting models.

Adult↗

PubMed1998

Functional properties of graphic workspace: assessment by means of a 3D geometric arm model.

Computer simulations aimed at assessing functional characteristics of the graphic workspace are presented. The simulations involve a 10-df kinematic model of the distal part of the writing arm, and yield the effective workspace of the pen tip under two types of kinematic constraints. The first constraint involves fixing the forearm under various pronation angles, the second governs the protrusion of the pen tip from the finger tips. The effective workspace is analyzed in terms of the effort required to reach the various locations in it, where effort is defined in terms of the joint angles adopted by the wrist and fingers to reach each location. The simulation results show agreements between the distribution of required effort over the workspace and known stroke-direction preferences in drawing. Furthermore, they predict shifts in the biases that are thought to lead to these preferences as a function of both hand pronation and pen protrusion.

Biomechanical Phenomena↗

PubMed1998

Low-frequency periodicity in the coordination of progressive handwriting.

The paper addresses the question how the effector segments are coordinated during handwriting, in particular as a function of the left-to-right progression within words. It studies the phase relations between wrist and finger-joint rotations during a repetitive graphic task (long words consisting of letters 'e'), and it subjects the resulting continuous phase-relation plots to autocorrelation analysis. A novel phenomenon, viz. that of low-frequency (1-Hz) periodicity, is observed which presumably reflects adjustments of the coordination pattern about once per second, i.e., after every three or four letters 'e'. Moreover, word length and word position are found to affect this periodicity in a predictable manner. These results are related to those of an earlier study which used an ad-hoc method of analysing wrist-finger coordination adjustments. The paper underlines the value of phase-relation analysis for certain graphic tasks, but it also points out its limitations for this purpose.

Adolescent↗

PubMed1998

Path curvature in workspace and in joint space: evidence for coexisting coordinative rules in aiming.

In this study we tried to establish whether point-to-point aiming movements are planned in workspace, joint space, or both. Eight right-handed subjects performed horizontal, vertical, and diagonal aiming movements on a transversal plane. Movements were performed at several speeds. Curvature variations of the hand and corresponding joint-space paths were investigated as a function of position, direction, and speed. Straightness of hand paths predominated for vertical movements but was systematically violated for horizontal and top-right to bottom-left movements. Furthermore, the hand-path curvature of the latter movements increased with speed. Joint-space paths showed more deviation from a straight line than hand paths except for top-left to bottom-right movements in which the paths were equally curved. A comparison of normalized path curvatures at the hand and joint level indicated that in aiming, the coordinative rule of straight-line production seems to apply to both workspace and joint-space planning. The present findings confirm Kawato's (1996) views that optimization processes operate concurrently at the two control levels of arm-trajectory formation under study.

Humans↗

PubMed1998

The timing of prehensile movements in subjects with cerebral palsy.

In this study, a paradigm is presented for the assessment of manual dexterity in subjects with cerebral palsy (CP) that divides the prehensile action into a 'time-to-contact' phase and a 'time-in-contact' phase. Two experiments were performed that determined the effect of object weight on the timing of both phases for the impaired hand and non-impaired hand of subjects with spastic hemiparesis (N = 14). In the first experiment, subjects had to reach for and lift a tube at their own preferred speed. The results showed that the prehensile deficit of the impaired limb is to a large degree manifested by a longer time spent in contact with the object before it was lifted. The time-in-contact phase was decreased after repeated lifts, suggesting that subjects with CP can control and modify force output in advance based on weight information from preceding lifts. In the second experiment speed of movement execution was stressed to examine whether the observed timing pattern of the first experiment is characteristic of prehensile movements of the paretic arm or represents a movement strategy adapted to the disorder. The results of the second experiment showed that subjects could comply with the instruction by reducing the absolute duration of both phases of the prehensile movement. Furthermore, the anticipation effects were eliminated to a large degree. In both experiments the time-in-contact phase was longer for the impaired limb. These results indicate a pathological constant in the time-in-contact phase for the impaired limb. This assumption is discussed in relation to the application of grip and lift forces during this phase. It is concluded that the paradigm is well suited for use in a practical setting as a simple and broad clinical test to assess the prehensile decrements of subjects with CP.

Adolescent↗

PubMed1996

Adaptation of a reaching model to handwriting: how different effectors can produce the same written output, and other results.

This report shows how a model initially developed for the control of reaching can be adapted for the control of handwriting. The main problem addressed by the model is how people can produce essentially the same written output with different effectors (e.g., the preferred or nonpreferred hand, the foot, or even the mouth). The model is based on the assumption that writers strive for invariant graphic outputs when they write with different effectors, when they write on surfaces with different orientations, or when they write large or small script; such output invariance is an essential requirement for later recognition of the written result. Given this assumption, the question is how the motor system enables the relevant effectors to generate the necessary pen strokes. The adapted model provides one possible answer to this question. It is first fully working model of multijoint activity underlying writing and related graphic tasks. We describe how the model differs from other models developed in the past, and we review the model's strengths and weaknesses.

Female↗

PubMed1996

Biomechanical and perceptual determinants of drawing angles.

This study focuses on perceptual and biomechanical determinants of the kinematics of angular drawing movements. Two experiments are reported in which twelve righthanded adults were asked to draw geometrical patterns consisting of three segments comprising either two acute or two obtuse angles. In Experiment 1, a lower frequency of pauses was observed in acute patterns and their segment length tended to be overestimated. The former effect is attributed to the exploitation of elasticity (Guiard, 1993). In order to evaluate whether the latter effect was due to perceptual factors, a second experiment was conducted. Twelve subjects drew a subset of the angular patterns under normal visual conditions and under conditions in which they could neither see their moving limb nor the resulting drawing trace. Again, subjects produced more pauses at obtuse than at acute angles and tended to overestimate the segment length in acute patterns. It is concluded that pauses are likely to occur between segments of discrete movement sequences when potential energy needs to be dissipated. When conditions arise that allow subjects to exploit elasticity, however, segment length tends to increase. The results of Experiment 2 confirm that these phenomena are independent from visual perception.

Adult↗