共查询到20条相似文献,搜索用时 15 毫秒
1.
P. J. Stapley Thierry Pozzo G. Cheron Alexander Grishin 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1999,129(1):134-146
The whole-body center of mass (CoM) has been classically regarded as the stabilized reference value for human voluntary movements
executed upon a fixed base of support. Axial synergies (opposing displacements of head and trunk with hip segments) are believed
to minimize antero-posterior (A/P) CoM displacements during forward trunk movements. It is also widely accepted that anticipatory
postural adjustments (APAs) create forces of inertia that counteract disturbances arising from the moving segment(s). In the
present study, we investigated CoM stabilization by axial synergies and APAs during a whole-body reaching task. Subjects reached
towards an object placed on the ground in front of them in their sagittal plane using a strategy of coordinated trunk, knee,
and hip flexion. The reaching task imposed constraints on arm-trajectory formation and equilibrium maintenance. To manipulate
equilibrium constraints, differing conditions of distance and speed were imposed. The comparison of distance conditions suggested
that axial synergies were not entirely devoted to CoM stabilization: backward A/P hip displacements reduced as head and trunk
forward A/P displacements increased. Analysis of upper- and lower-body centers of mass in relation to the CoM also showed
no strict minimization of A/P CoM displacements. Mechanical analysis of the effects of APAs revealed that, rather than acting
to stabilize the CoM, APAs created necessary conditions for forward CoM displacement within the base of support in each condition.
The results have implications for the CoM as the primary stabilized reference for posture and movement coordination during
whole-body reaching and for the central control of posture and voluntary movement.
Received: 14 July 1998 / Accepted: 23 May 1999 相似文献
2.
Although previous studies have shown pointing errors and abnormal multijoint coordination in seated subjects with Parkinson's disease (PD) who cannot view their arm, the extent to which subjects with PD have problems using proprioception to coordinate equilibrium maintenance and goal-oriented task execution has not been adequately investigated. If a common motor program controls voluntary arm pointing movements and the accompanying postural adjustments, then impairments of proprioceptive integration in subjects with PD should have similar effects on pointing and body center of mass (CoM) control with eyes closed. Ten standing subjects with PD (OFF-medication) and 10 age-matched control (CTR) subjects pointed to a target with their eyes closed and open. Although pointing accuracy was not significantly different between groups, body CoM displacements were reduced in subjects with PD, but not in CTR, when eyes were closed. In addition, with eyes closed, PD subjects showed reduced temporal coupling between pointing and CoM velocity profiles and reduced spatial coupling between pointing and CoM endpoints. This poor coupling with eyes closed could be related to the PD subjects' increased jerkiness of CoM displacements. The different effects of eye closure between CTR and PD subjects on the CoM displacements, but not pointing accuracy, are consistent with separate motor programs for the pointing and postural components of this task. Furthermore, the decoupling between the two movement components in subjects with PD when they could not use vision, suggests that the basal ganglia are involved in the integration of proprioceptive information for posture–movement coordination. 相似文献
3.
Silvia Hua Julia A. Leonard Alicia J. Hilderley Paul J. Stapley 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2013,227(1):63-78
This study investigated whether postural configuration has a significant effect upon the kinematics of arm movements when humans performed unconstrained reach movements to visual targets. Eight subjects were required to reach to static visual targets (unperturbed REACH movements) or correct reach movements when the position of a target unexpectedly changed during the execution of a planned movement (perturbed reaches, or online corrections, OC). Subjects were required to execute REACH and OC movements in sitting and standing (STAND) positions. The height of the targets, distance from the right shoulder (acromion) and eccentricity in terms of the body midline were standardized between the two postural conditions before movements begun. Unperturbed REACH movements were executed to a central target placed at 130 % of outstretched arm length, along the midline (0°). Perturbed (OC) movements involved subjects initiating an arm movement to the 0° target upon its illumination. Two hundred milliseconds after the onset of the hand movement, the 0° target was extinguished and the target at 60° to the right of the midline (still at 130 % outstretched arm distance) illuminated. Subjects had to correct their reach movements online to the new target. Results demonstrated that, despite evident differences in postural kinematics between the four experimental conditions (e.g. pelvis obliquity and trunk/pelvis rotation), postural configuration had little or no effect upon the endpoint kinematics of the finger. Most importantly, the STAND position, with its greater postural constraints, did not affect the time taken to initiate an OC, nor did it lengthen the time taken to complete the REACH or OC movements. Our results suggest, therefore, that postural constraints are accounted for by the central nervous system when executing complex arm reaching movements. 相似文献
4.
Thierry Pozzo Joseph McIntyre Guy Cheron Charalambos Papaxanthis 《Neuroscience letters》1998,240(3):464-162
End-effector trajectory formation was studied during a reaching movement using the whole body. The movements of various parts of the body were measured with the optoelectronic ELITE system. Wrist reaching movement paths showed noticeable curvatures. The analysis of various marker onset latencies revealed that the wrist was the last to move, always after the head, knee or trunk, suggesting a subordinate role of the focal component with respect to the primary role of the equilibrium component. These results suggest that reaching wrist movements are subjected to whole-body equilibrium constraints in addition to constraints placed upon end-effector kinematics or the dynamic optimization of upper-limb movements. 相似文献
5.
Patron J Stapley P Pozzo T 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2005,165(1):84-96
Previous experiments by our group in normal gravity (1 G) have revealed spatial relationships between postural and focal components of whole-body reaching and pointing movements. We suggested that these relationships could be explained partly through the use of gravity to displace the CoM and attain the object or target position. In this study we compared human whole-body reaching in 1 G and microgravity (0 G) in order to more fully investigate how gravity contributes to strategies adopted for task execution and to determine possible invariant temporal relationships between multiple segments. Whole-body reaching movements made from the standing position in two experimental conditions of execution speed (naturally paced and as fast as possible) were recorded during periods of 1 G and 0 G in parabolic flight. Overall, at each speed of reaching, movement times were significantly slower when performed in 0 G than in 1 G for two of the three subjects, but all subjects were able to produce significantly faster movements in 0 G than in 1 G. Despite similar general trends across subjects observed in 1 G, angular displacements of reaching movements performed in 0 G differed greatly between subjects. There were changes at all joints, but above all at the shoulder and the ankle. However, despite a high intersubject and intratrial variability in 0 G, in both gravity conditions all subjects demonstrated times to peak curvilinear velocity for the finger (end effector) and the whole-body centre of mass (CoM) that coincided, regardless of the speed of execution. Moreover, cross-correlations between multiple segment curvilinear velocities and those of the CoM revealed tight, highly correlated temporal relationships between segments proximal to the CoM (which was expected). However, for more distal segments, the correlations were weaker, and the movements lagged behind movements of the CoM. The major and most interesting finding of this study was that although the finger was the most distal within the segment chain, with respect to the CoM, it was highly correlated with the CoM (0.99–0.98, all conditions) and with no time lag. Despite the large intersubject and interenvironmental variability recorded in this study, temporal relationships between postural task components (CoM displacements) and those of the focal movement (end-effector trajectory) were consistently conserved. 相似文献
6.
Human quiet stance is often modeled as a single-link inverted pendulum pivoting only around the ankle joints in the sagittal plane. However, several recent studies have shown that movement around the hip joint cannot be negligible, and the body behaves like a double-link inverted pendulum. The purpose of this study was to examine how the hip motion affects the body kinematics in the sagittal plane during quiet standing. Ten healthy subjects were requested to keep a quiet stance for 30 s on a force platform. The angular displacements of the ankle and hip joints were measured using two highly sensitive CCD laser sensors. By taking the second derivative of the angular displacements, the angular accelerations of both joints were obtained. As for the angular displacements, there was no clear correlation between the ankle and hip joints. On the other hand, the angular accelerations of both joints were found to be modulated in a consistent anti-phase pattern. Then we estimated the anterior–posterior (A–P) acceleration of the center of mass (CoM) as a linear summation of the angular acceleration data. Simultaneously, we derived the actual CoM acceleration by dividing A–P share force by body mass. When we estimated CoM acceleration using only the angular acceleration of the ankle joint under the assumption that movement of the CoM is merely a scaled reflection of the motion of the ankle, it was largely overestimated as compared to the actual CoM acceleration. Whereas, when we take the angular acceleration of the hip joint into the calculation, it showed good coincidence with the actual CoM acceleration. These results indicate that the movement around the hip joint has a substantial effect on the body kinematics in the sagittal plane even during quiet standing. 相似文献
7.
J. L. Vercher G. Magenes C. Prablanc G. M. Gauthier 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1994,99(3):507-523
This study investigated whether the execution of an accurate pointing response depends on a prior saccade orientation towards the target, independent of the vision of the limb. A comparison was made between the accuracy of sequential responses (in which the starting position of the hand is known and the eye centred on the target prior to the onset of the hand pointing movement) and synergetic responses (where both hand and gaze motions are simultaneously initiated on the basis of unique peripheral retinal information). The experiments were conducted in visual closed-loop (hand visible during the pointing movement) and in visual openloop conditions (vision of hand interrupted as the hand started to move). The latter condition eliminated the possibility of a direct visual evaluation of the error between hand and target during pointing. Three main observations were derived from the present work: (a) the timing of coordinated eye-head-hand pointing at visual targets can be modified, depending on the executed task, without a deterioration in the accuracy of hand pointing; (b) mechanical constraints or instructions such as preventing eye, head or trunk motion, which limit the redundancy of degrees of freedom, lead to a decrease in accuracy; (c) the synergetic movement of eye, head and hand for pointing at a visible target is not trivially the superposition of eye and head shifts added to hand pointing. Indeed, the strategy of such a coordinated action can modify the kinematics of the head in order to make the movements of both head and hand terminate at approximately the same time. The main conclusion is that eye-head coordination is carried out optimally by a parallel processing in which both gaze and hand motor responses are initiated on the basis of a poorly defined retinal signal. The accuracy in hand pointing is not conditioned by head movement per se and does not depend on the relative timing of eye, head and hand movements (synergetic vs sequential responses). However, a decrease in the accuracy of hand pointing was observed in the synergetic condition, when target fixation was not stabilised before the target was extinguished. This suggests that when the orienting saccade reaches the target before hand movement onset, visual updating of the hand motor control signal may occur. A rapid processing of this final input allows a sharper redefinition of the hand landing point. 相似文献
8.
Mars F Archambault PS Feldman AG 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,150(4):515-519
Recent studies have shown that the hand-pointing movements within arm's reach remain invariant whether the trunk is recruited
or not or its motion is unexpectedly prevented. This suggests the presence of compensatory arm-trunk coordination minimizing
the deflections of the hand from the intended trajectory. It has been postulated that vestibular signals elicited by the trunk
motion and transmitted to the arm motor system play a major role in the compensation. One prediction of this hypothesis is
that vestibular stimulation should influence arm posture and movement during reaching. It has been demonstrated that galvanic
vestibular stimulation (GVS) can influence the direction of pointing movements when body motion is restrained. In the present
study, we analyzed the effects of GVS on trunk-assisted pointing movements. Subjects either moved the hand to a target or
maintained a steady-state posture near the target, while moving the trunk forward with the eyes closed. When GVS was applied,
the final position of the hand was deviated in the lateral and sagittal direction in both tasks. This was the result of two
independent effects: a deviation of the trunk trajectory and a modification of the arm position relative to the trunk. Thus,
the vestibular system might be directly involved not only in the control of trunk motion but also in the arm-trunk coordination
during trunk-assisted reaching movements.
Electronic Publication 相似文献
9.
Visual control of reaching movements without vision of the limb 总被引:5,自引:3,他引:2
C. Prablanc D. Pélisson M. A. Goodale 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1986,62(2):293-302
The spatial and temporal organization of hand and eye movements were studied in normal human subjects as they pointed toward small visual targets. The experiment was designed to assess the role of information about target position in correcting the trajectory of the hand when view of the hand was not available. To accomplish this, the duration of target presentation was systematically varied across blocks of trials. The results of this experiment showed that pointing movements were about 3 times more accurate when the target was present throughout the entire pointing movement, than when the target disappeared shortly after the hand movement had begun. These data indicate that pointing movements made without view of the limb are not purely preprogrammed but instead, are corrected during their execution. These modifications to the motor program are smoothly integrated into the ongoing movement and must depend upon comparing visual information about the position of the target with nonvisual information about the position of the limb. The source of this non-visual information was not directly established in the present experiment but presumably must be derived from kinesthetic reafferences and/or efference copy. 相似文献
10.
Sergei V. Adamovich Philippe S. Archambault Mohammad Ghafouri Mindy F. Levin Howard Poizner Anatol G. Feldman 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,138(3):288-303
Movements of different body segments may be combined in different ways to achieve the same motor goal. How this is accomplished by the nervous system was investigated by having subjects make fast pointing movements with the arm in combination with a forward bending of the trunk that was unexpectedly blocked in some trials. Subjects moved their hand above the surface of a table without vision from an initial position near the midline of the chest to remembered targets placed within the reach of the arm in either the ipsi- or contralateral workspace. In experiment 1, subjects were instructed to make fast arm movements to the target without corrections whether or not the trunk was arrested. Only minor changes were found in the hand trajectory and velocity profile in response to the trunk arrest, and these changes were seen only late in the movement. In contrast, the patterns of the interjoint coordination substantially changed in response to the trunk arrest, suggesting the presence of compensatory arm-trunk coordination minimizing the deflections from the hand trajectory regardless of whether the trunk is recruited or mechanically blocked. Changes in the arm interjoint coordination in response to the trunk arrest could be detected kinematically at a minimal latency of 50 ms. This finding suggests a rapid reflex compensatory mechanism driven by vestibular and/or proprioceptive afferent signals. In experiment 2, subjects were required, as soon as they perceived the trunk arrest, to change the hand motion to the same direction as that of the trunk. Under this instruction, subjects were able to initiate corrections only after the hand approached or reached the final position. Thus, centrally mediated compensatory corrections triggered in response to the trunk arrest were likely to occur too late to maintain the observed invariant hand trajectory in experiment 1. In experiment 3, subjects produced similar pointing movements, but to a target that moved together with the trunk. In these body-oriented pointing movements, the hand trajectories from trials in which the trunk was moving or arrested were substantially different. The same trajectories represented in a relative frame of reference moving with the trunk were virtually identical. We conclude that hand trajectory invariance can be produced in an external spatial (experiment 1) or an internal trunk-centered (experiment 3) frame of reference. The invariance in the external frame of reference is accomplished by active compensatory changes in the arm joint angles nullifying the influence of the trunk motion on the hand trajectory. We suggest that to make a transition to the internal frame of reference, control systems suppress this compensation. One of the hypotheses opened to further experimental testing is that the integration of additional (trunk) degrees of freedom into movement is based on afferent (proprioceptive, vestibular) signals stemming from the trunk motion and transmitted to the arm muscles. 相似文献
11.
Pigeon P Yahia LH Mitnitski AB Feldman AG 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2000,131(3):336-349
Previous studies addressing the problem of the control of multiple degrees of freedom have examined the influence of trunk movement on pointing movements within the arm's reach. Such movements may be controlled by two functionally independent units of coordination (synergies): one involving only arm joints and producing the hand trajectory to the target (the transport synergy), and the other coordinating trunk and arm movements leaving the hand trajectory unchanged (the compensatory synergy). The question of whether or not this functional subdivision depends on visual feedback was addressed in the present study. We also tested whether or not the motor effects of different synergies are summated as independent components, a control strategy called "superposition." Finally, we investigated whether or not the relationship between different degrees of freedom within each synergy could be considered linear resulting in proportional changes in different joint angles. Seated subjects produced fast, uncorrected arm movements to an ipsi- or a contralateral target in the direction of +/-45 degrees to the sagittal midline of the trunk. Targets could be reached using the arm alone (control trials) or by combining the arm motion with a forward or backward trunk motion produced by hip flexion or extension (test trials), with and without visual feedback. The shape of the hand trajectory, its direction and tangential velocity, movement precision, joint angles and the sequence of the trunk and hand recruitment and de-recruitment were measured. In both visual conditions, the direction of the hand trajectory observed in control trials was generally preserved in test trials. In terms of sequencing, even in the absence of vision, the trunk movement was initiated before the onset of and outlasted the hand shift, indicating that the potential influence of the trunk on the hand movement was compensated by rotations in the elbow and shoulder joint. The analysis of other variables also implied that the effects of trunk recruitment on the hand trajectory were minor compared to those which could be observed if these effects were not compensated by appropriate changes in the arm joint angles. It was concluded that an arm-trunk compensatory synergy is present in pointing movements regardless of visual feedback. Principal component analysis showed that the relationship between elbow, shoulder and hip joint angles in individual arm and combined arm-trunk movements cannot be considered linear, implying that this relationship is adjusted according to the changing arm geometry. The changes in each arm joint angle (elbow, shoulder) elicited by a forward trunk bending in one block of trials were compared with those elicited by a backward bending in another block, whereas the hand moved to the same target in both blocks. These changes were opposite but of similar magnitude. As a result, for each moment of movement, the mean joint angle obtained by averaging across two directions of trunk motion was practically identical to that in control trials in which the trunk was motionless. It is concluded that the transport and arm-trunk compensatory synergies are combined as independent units, according to the principle of superposition. This principle may simplify the control of the coordination of a redundant number of degrees of freedom. 相似文献
12.
Lilian Fautrelle Bastien Berret Enrico Chiovetto Thierry Pozzo François Bonnetblanc 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2010,203(1):147-158
The aim of this study was to determine whether the timing of the muscular synergies was influenced by the reduction of the base of support when we initiate a whole body reaching movement. To answer this question, we performed a principal component analysis on electromyographic activities of 24 muscles recorded on the leg, the trunk, and the arm. Our results demonstrated that during the initiation of the whole body pointing movement, only three principal components accounted for at least 95% of the variance for the overall muscular data, both when the equilibrium constraints were normal and when the base of support was reduced. These principal components were strongly correlated despite the fact that the center of mass forward displacement and the center of pressure backward displacements significantly decreased when the base of support was reduced. It suggests that the central nervous system did not change the overall timing of the muscular synergies when new equilibrium constraints were introduced in the task but was rather able to tune their amplitude as evidenced by the modification of the center of mass and center of pressure displacements. 相似文献
13.
Berrigan F Simoneau M Martin O Teasdale N 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2006,170(2):255-264
We examined the interaction between the control of posture and an aiming movement. Balance control was varied by having subjects
aim at a target from a seated or a standing position. The aiming difficulty was varied using a Fitts’-like paradigm (movement
amplitude=30 cm; target widths=0.5, 1.0, 2.5 and 5 cm). For both postural conditions, all targets were within the reaching
space in front of the subjects and kept at a fixed relative position with respect to the subjects’ body. Hence, for a given
target size, the aiming was differentiated only by the postural context (seated vs. upright standing). For both postural conditions,
movement time (MT) followed the well-known Fitts’ law, that is, it increased with a decreasing target size. For the smallest
target width, however, the increased MT was greater when subjects were standing than when they were seated suggesting that
the difficulty of the aiming task could not be determined solely by the target size. When standing, a coordination between
the trunk and the arm was observed. Also, as the target size decreased, the center of pressure (CP) displacement increased
without any increase in CP speed suggesting that the subjects were regulating their CP to provide a controlled referential
to assist the hand movement. When seated, the CP kinematics was scaled with the hand movement kinematics. Increasing the index
of difficulty led to a strong correlation between the hand speed and CP displacement and speed. The complex organization between
posture and movement was revealed only by examining the specific interactions between speed–accuracy and postural constraints. 相似文献
14.
Constanze Hesse Tristan T. Nakagawa Heiner Deubel 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2010,202(4):837-850
Our study examined the effects of performing a pointing movement with the left hand on the kinematics of a simultaneous grasping
movement executed with the right hand. We were especially interested in the question of whether both movements can be controlled
independently or whether interference effects occur. Since previous studies suggested that eye movements may play a crucial
role in bimanual movement control, the effects of different fixation strategies were also studied. Human participants were
either free to move their eyes (Experiment 1) or they had to fixate (Experiment 2) while doing the task. The results show
that bimanual movement control differed fundamentally depending on the fixation condition: if free viewing was allowed, participants
tended to perform the task sequentially, as reflected in grasping kinematics by a delayed grip opening and a poor adaptation
of the grip to the object properties for the duration of the pointing movement. This behavior was accompanied by a serial
fixation of the targets for the pointing and grasping movements. In contrast, when central fixation was required, both movements
were performed fast and with no obvious interference effects. The results support the notion that bimanual movement control
is moderated by fixation strategies. By default, participants seem to prefer a sequential behavior in which the eyes monitor
what the hands are doing. However, when forced to fixate, they do surprisingly well in performing both movements in parallel. 相似文献
15.
Ivan Toni Maurizio Gentilucci Marc Jeannerod Jean Decety 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1996,111(3):447-454
In this study the influence of visual scene on both arm end point accuracy and spatial path kinematics was evaluated. Eight subjects, immersed in a virtual environment, were required to point to one of ten targets located at two distances and in five directions. Targets were presented in frameworks of different complexity. The simplest framework was constituted by a uniform background, the most complex framework was constituted by a perspective-arranged grid. In the other two conditions it consisted of lines having a direction parallel to either the subject's sagittal or frontal body axis. Movements were executed without vision of both target and framework. The results showed that pointing movements were hypometric in all conditions. No difference in end point localization was observed between movements executed after presentation of the simplest and the most complex scenes. However, hypometria significantly increased when the scene was formed by lines parallel to the subject's sagittal axis. Visual information on the scene was also used to specify hand path parameters. Trajectory curvature increased with decreasing complexity of the framework. Correspondingly, the pointing kinematics varied. Taken together, these results suggest that visual analysis of cues surrounding the target can influence both target localisation and hand path planning. However, scene complexity is directly related only to determining trajectory curvature. We conclude that planning an arm movement consists of at least two processes: target localisation and hand path specification. Environmental visual cues forming the scene are taken into account differently during the two processes. 相似文献
16.
Verrel J Cuisinier R Lindenberger U Vuillerme N 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2011,210(2):313-324
Neck muscle vibration (NMV) during upright standing is known to induce forward leaning, which has been explained as a global
response to the (illusory) perception of a lengthening of the dorsal neck muscles. However, the effects of NMV both at the
level of individual joints and on whole-body postural coordination, and its potential modulation by vision, have not yet been
analyzed in detail. Eight healthy young adult participants completed a total of ten trials each, with a 10-s period of unperturbed
standing followed by a 10-s period of NMV. Participants were instructed to stand “as still as possible”. This postural task
was executed under two visual conditions: eyes open (EO) and eyes closed (EC). Postural responses were measured in terms of
center of pressure (CoP) and center of mass (CoM) profiles, and whole-body kinematics. Responses to NMV at the level of individual
body segments and joints were assessed by decomposing the time series into linear trends and residual fluctuations. Inter-segmental
coordination was analyzed using a decorrelation technique, assessing motor-equivalent stabilization of four task-related variables:
CoM position, trunk orientation, as well as head position and orientation. NMV induced a general forward leaning response
under both visual conditions, visible in CoP, CoM, segment positions and orientations. Locally, NMV induced a pronounced extension
of the atlanto-occipital joint. Residual fluctuations were higher with EC and unaffected by NMV. Coordination analysis showed
that stabilization of different body parts was differentially affected by NMV. Head orientation was consistently stabilized
across all conditions, with weaker coordination in the EC condition. In contrast, motor-equivalent stabilization of CoM and
head position, and trunk orientation was only observed during no-vibration periods. Taken together, our results demonstrate
specific effects of vision and proprioception on different aspects of local and global postural control. While perturbed neck
proprioception seemed to affect the postural “set point” (inducing forward leaning), vision appeared to mainly serve in noise
reduction (residual fluctuations) and control of head orientation. 相似文献
17.
The aim of this study was to investigate how humans correct ongoing arm movements while standing. Specifically, we sought to understand whether the postural adjustments in the legs required for online corrections of arm movements are predictive or rely on feedback from the moving limb. To answer this question we measured online corrections in arm and leg muscles during pointing movements while standing. Nine healthy right-handed subjects reached with their dominant arm to a visual target in front of them and aligned with their midline. In some trials, the position of the target would switch from the central target to one of the other targets located 15°, 30°, or 45° to the right of the central (midline) target. For each target correction, we measured the time at which arm kinematics, ground reaction forces, and arm and leg muscle electromyogram significantly changed in response to the target displacement. Results show that postural adjustments in the left leg preceded kinematic corrections in the limb. The corrective postural muscle activity in the left leg consistently preceded the corrective reaching muscle activity in the right arm. Our results demonstrate that corrections of arm movements in response to target displacement during stance are preceded by postural adjustments in the leg contralateral to the direction of target shift. Furthermore, postural adjustments preceded both the hand trajectory correction and the arm-muscle activity responsible for it, which suggests that the central nervous system does not depend on feedback from the moving arm to modify body posture during voluntary movement. Instead, postural adjustments lead the online correction in the arm the same way they lead the initiation of voluntary arm movements. This suggests that forward models for voluntary movements executed during stance incorporate commands for posture that are produced on the basis of the required task demands. 相似文献
18.
The aim of this study was to examine the influence of the velocity on the control of the final postural equilibrium in the movement of standing up into upside-down vertical posture on the hands. Seven expert gymnasts performed the movement on a force plate of large dimensions from which the kinematic of center of mass (CoM) was studied. The first result showed that the speed of CoM was increased in the vertical axis but did not change in the antero-posterior axis. The second result showed a reduction of the duration of the anticipatory postural adjustments (APA) conversely to the speed. This was in contrast to the movements performed in the natural erect stance. These results suggest firstly that the speed of CoM corresponds to a global strategic response linked to the body's posturo-kinetic capacity, and secondly that the reduction of the APA seems to be linked to the precariousness of the final equilibrium. 相似文献
19.
I. B. M. van der Fits A. W. J. Klip L. A. van Eykern M. Hadders-Algra 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,120(2):202-216
The present study evaluated the effect of different positions, which varied in the amount of bodily support, on postural control
during fast pointing movements. Fourteen adult subjects were studied in standing, various sitting and lying positions. Multiple
surface electromyograms (EMGs) of arm, neck, trunk and upper leg muscles and kinematics were recorded during a standard series
of unilateral arm movements. Two additional series, consisting of bilateral arm movements and unilateral arm movements with
an additional weight, were performed to assess whether additional task-load affected postural adjustments differently in a
sitting and standing position. Two pointing strategies were used – despite identical instructions. Seven subjects showed an
elbow extension throughout the movements. They used the deltoid (DE) as the prime mover (DE group). The other seven subjects
performed the movement with a slight elbow flexion and used the biceps brachii (BB) as the prime mover (BB group). The two
strategies had a differential effect on the postural adjustments: postural activity was less and substantially later in the
BB-group than in the DE group. Anticipatory postural muscle activity was only present in the DE group during stance. In all
positions and task-load conditions the dorsal postural muscles were activated before their ventral antagonists. The activation
rate, the timing and – to a lesser extent – the amplitude of the dorsal muscle activity was position dependent. The position
dependency was mainly found in the caudally located lumbar extensor (LE) and hamstrings (HAM) muscles. The EMG amplitude of
LE and HAM was also affected by body geometry (trunk and pelvis position). Position and body geometry had only a minor effect
on the activity of the neck and thoracic extensor muscles. This difference in behaviour of lower and upper postural muscles
suggests that they could serve different postural tasks: the lower muscles being more involved in keeping the centre of mass
within the limits of the support surface, and the upper ones in counteracting the reaction forces generated by movement onset.
Increasing task-load by performing bilateral movements and – to a minor extent – during loaded unilateral movements affected
the temporal and quantitative characteristics of the postural adjustments during standing and sitting in a similar way. The
effect was present mainly during the early part of the response (within 100 ms after prime mover onset). This suggests that
feedforward or anticipatory mechanisms play a major role in the task-specific modulation of postural adjustments.
Received: 9 April 1997 / Accepted: 9 October 1997 相似文献
20.
The aim of the present investigation was to see whether the kinematic synergy responsible for equilibrium control during upper trunk movement was preserved in absence of gravity constraints. In this context, forward trunk movements were studied during both straight-and-level flights (earth-normal gravity condition: normogravity) and periods of weightlessness in parabolic flights (microgravity). Five standing adult subjects had their feet attached to a platform, their eyes were open, and their hands were clasped behind their back. They were instructed to bend the trunk (the head and the trunk together) forward by approximately 35 degrees with respect to the vertical in the sagittal plane as fast as possible in response to a tone, and then to hold the final position for 3 s. The initial and final anteroposterior center of mass (CM) positions (i.e., 200 ms before the onset of the movement and 400 ms after the offset of the movement, respectively), the time course of the anteroposterior CM shift during the movement, and the electromyographic (EMG) pattern of the main muscles involved in the movement were studied under both normo- and microgravity. The kinematic synergy was quantified by performing a principal components analysis on the hip, knee, and ankle angle changes occurring during the movement. The results indicate that 1) the anteroposterior position of the CM remains minimized during performance of forward trunk movement in microgravity, in spite of the absence of equilibrium constraints; 2) the strong joint coupling between hip, knee, and ankle, which characterizes the kinematic synergy in normogravity and which is responsible for the minimization of the CM shift during movement, is preserved in microgravity. It represents an invariant parameter controlled by the CNS. 3) The EMG pattern underlying the kinematic synergy is deeply reorganized. This is in contrast with the invariance of the kinematic synergy. It is concluded that during short-term microgravity episodes, the kinematic synergy that minimizes the anteroposterior CM shift is surprisingly preserved due to fast adaptation of the muscle forces to the new constraint. 相似文献