Biomedical subjects

J Massion

Publications and source records attributed to J Massion.

At least 37 records · Page 2Linked to original sources

PubMed1999

Forearm postural control during unloading: anticipatory changes in elbow stiffness.

In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the central command for antagonist-muscle coactivation and the equilibrium angle to be the estimation of the reciprocal command for a shift of invariant characteristics of the joint. In the experiments, a load applied to the forearm was released. The subjects were instructed to maintain their forearm in the initial horizontal position. Five sessions of approximately twenty trials each were carried out by eight subjects. During two "control" series, the load release was triggered by the experimenter. During three "learning" series, the load supported by one forearm was released by the subject's other hand. The elbow-joint angle, the angular acceleration, and the external load on the postural forearm were recorded. These recordings as well as anthropometric forearm characteristics were used to calculate the elbow-joint torque (which we called "experimental"). Linear regression analysis was performed to evaluate the equilibrium angle, joint stiffness, and viscosity at each trial. The "theoretical" torque was calculated using a linear spring equation with the found parameters. The good agreement observed between experimental and theoretical joint-torque time courses, apart from the very early period following unloading, argues in favor of the idea that the movement was mainly performed under a constant central command presetting the joint stiffness and the equilibrium angle. An overall increase in the stiffness occurred simultaneously with a decrease in the equilibrium angle during the "learning" series in all the subjects. This suggests that subjects learn to compensate for the disturbing effects of unloading by increasing the joint stiffness. The mechanism possibly responsible for the presetting of the central control parameters is discussed.

Cognition↗

PubMed1999

Acquisition of anticipatory postural adjustments in a bimanual load-lifting task: normal and pathological aspects.

Anticipatory adjustments of forearm posture are associated with a voluntary load-lifting movement in bimanual load-lifting tasks. Three aspects of these adjustments are analyzed: their goal, their central organization, and their acquisition. The goal of the anticipatory adjustment in this task is to minimize the perturbation of forearm posture that occurs during unloading. The central organization is based on two parallel controls responsible, respectively, for the lifting movement of the moving forearm and the anticipatory postural adjustment of the postural forearm, their coordination depending on a central timing signal. The acquisition of the anticipatory postural adjustment was tested using a paradigm where the voluntary movement performed by one hand triggered, via an electronic switch, the load release of the postural forearm. It was achieved after 40-60 trials and was not graded as a function of the voluntary movement parameters, but of the disturbance of the postural arm about to occur. The learned anticipation was not transferred when, after a first acquisition session with one forearm as the postural forearm, a second learning session was performed with the other forearm as the postural forearm. The acquisition was tested in Parkinsonian and in hemiparetic patients with capsular lesion. The highest acquisition deficit was observed in hemiparetic patients, when the contralateral forearm was the postural forearm; the deficit was less important when the ipsilateral arm was postural. Surprisingly, the anticipatory postural adjustments in hemiparetic patients were rather well preserved when the natural load-lifting task was tested. These results suggest that the basal-ganglia SMA circuit and M1 premotor areas are important in the acquisition process.

Adaptation, Physiological↗

PubMed1999

Long-term adaptation of postural control in microgravity.

Orbital microgravity represents a unique environment, which allows the isolation of variables assumed to be involved in the mechanism of body positioning in space. In this context, the alignment of the trunk axis along allocentric references and the positioning of the body center of mass inside the supporting base compete for the role of the primary-controlled variable when assuming erect posture. This paper reports the quantitative evaluation of the postural strategies exhibited by two subjects with feet fixed to the floor of the space module along a 4-month period of exposure to microgravity. With respect to previous findings in parabolic flights and short term space missions, the analysis focused on long-term process of sensorimotor adaptation to weightlessness. Results show that while trunk-axis orientation is preserved and used as a stable postural frame of reference, the positioning of the body center of mass appears to be significantly biased backward and turns out to be involved in a long-term process of adaptation throughout the entire flight towards the re-emergence of a typically terrestrial postural regulation compatible with equilibrium.

Adult↗

PubMed1999

Kinematic synergies and equilibrium control during trunk movement under loaded and unloaded conditions.

The aim of the present investigation was to study the adaptation of the kinematic synergy responsible for equilibrium control during upper trunk movements to a 10-kg load added to the subject's shoulders. Five adult subjects were asked to bend their upper trunk forward to an angle of 35 degrees and then to hold the final position for 3 s, first without any load and then with a 10-kg load fixed to their shoulders. The final anteroposterior CM positions 400 ms after the movement offset, the time course of the anteroposterior center of mass (CM) shift during the movement, the EMG pattern of the main muscles involved in the movement and the initial CP shift were studied under both unloaded and loaded conditions. 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 final anteroposterior position of the CM changed little if at all in the presence of the additional load, and that the anteroposterior CM shift was minimized throughout the duration of the movement; (2) the kinematic synergy was still characterized, in the presence of the additional load, by a strong coupling between the angle changes, as indicated by the fact that the first principal component (PC1) accounted for more than 99% of the hip, knee and ankle joint movements. A change was observed, however, in the ratio between the angles: the ankle extension increased, thus compensating for the additional theoretical forward CM shift that the additional load could be expected to cause; (3) the lack of change in the initial backward CP shift observed under loaded condition as well as the lack of change of the initial agonist EMG bursts suggest that the initial feedforward control of the kinematic synergy was not affected in the presence of the additional load. An increase in the antagonist bursts, presumably reflecting an adaptation of the kinematic synergy, was observed during the late phase of the movement; and (4) it is concluded that the adaptation of the kinematic synergy to the load was due to a specific change in the feedback control during the braking phase of the movement which presumably increases the ankle joint extension and consequently causes an increased backward shift of the hip which compensates for the forward shift due to the load.

Adult↗

PubMed1999

Reorganization of equilibrium and movement control strategies in patients with knee arthritis.

The purpose of this study was to identify changes in equilibrium and movement control strategies in patients with arthritis of the knee. These strategies were expected to be different from those of healthy subjects because of the impairments caused by knee arthritis. The different phases of a side step were studied in patients with severe knee arthritis using a movement analysis system and force-plates. The duration of the postural phase and the intensity of the horizontal ground reaction forces during the postural phase were increased when the pathological limb was the supporting one. The monopodal phase was shortened on the pathological leg. These results show that knee arthritis patients develop new posturomotor strategies mainly aimed at shortening the monopodal phase when the affected leg is the supporting one. This movement analysis method enables quantification of differences that cannot be observed on clinical examination between knee arthritis patients and control subjects, and provides additional information to the usual clinical evaluation scales.

Aged↗

PubMed1999

[Influence of knee replacement arthroplasty on modalities of weight transfer during the lateral step].

INTRODUCTION: The aim of this work was to study the relations between equilibrium and movement in patients after total knee arthroplasty. A previous study, conducted in patients with unilateral knee osteoarthritis, had shown that the timing of the events occurring during a side-step was modified in an asymmetrical way according to the supporting leg with respect to the affected one. METHOD: A kinetic and kinematic analysis was performed in a population of 9 patients before and after total knee arthroplasty and in 11 control subjects, using an ELITE system and two AMTI force-plates. The different phases (i.e. postural, monopodal, landing and stabilization) of a side step were studied. RESULTS AND DISCUSSION: Before surgery, the postural phase was longer and the monopodal phase was shorter in knee arthritis patients when the affected leg was the supporting one than when the sound leg was supporting. Total step duration and landing-stabilization phase duration were longer in patients no matter which leg was supporting than in control subjects. After total knee arthroplasty, the postural phase remained longer when the operated leg was supporting than when the sound leg was supporting. Altered proprioception can provide an explanation for this result. However, the duration of the postural phase decreased significantly when the operated leg was supporting as compared to when the affected leg was supporting before surgery. The duration of the monopodal phase was the same when the operated leg was supporting than when the sound limb was supporting and increased significantly as compared to when the affected leg was supporting before surgery. This result can be related to the decrease of pain which was observed in all patients after surgery. The duration of the landing-stabilization phase and the total movement duration remained longer in patients after surgery no matter which leg was supporting than in control subjects. CONCLUSION: This study shows that relations between equilibrium and movement tend to become symmetrical with respect to the leg used as supporting one in patients after undergoing total knee arthroplasty but remain different from those of control subjects. This movement analysis method enables to determine and to quantify differences in patients before and after undergoing total knee arthroplasty and thus provides additional information for the functional evaluation of patients with total knee prosthesis.

Aged↗

PubMed1998

Axial synergies in parkinsonian patients during voluntary trunk bending.

During upper trunk movements, the axial kinematic synergies (opposite movements of upper and lower segments) preserve the balance by minimizing the antero-posterior center of gravity (CG) shift due to the movement. Forward and backward upper trunk movements were analyzed in a population of parkinsonian patients (PD) that were subject to falling, in order to determine whether an impaired control of the kinematic synergies might explain the falling. Ten PD (stage III-IV of the Hoehn and Yahr classification; Hoehn MM, Yahr MD. Parkinsonism: onset, progression and mortality. Neurology 1967;17;427-432) were compared to seven age-matched control subjects (CS). Kinematic analysis and force platform recordings were carried out. Principal Component (PC) analysis was performed to measure the coupling between hip, knee and ankle joint angles during the movement. (1) In both PD and CS, the first principal component (PC1) was found to account for 98% or more of the joint angles changes, which indicates that there exists a strong coupling between the angles during the movement; however, the part of the movement not accounted for by PC1 was twice as high in PD as in CS. (2) The intertrial variability between the angle ratios was about twice as high in PD as in CS. (3) The absolute value of the antero-posterior CG shift occurring during the movement significantly increased in PD in the case of backward movements, both fast and slow. (4) As a high correlation was found between actual CG shift and its estimation based on the observed interjoint coordination, the increased CG shift in PD was related to unproper set of ratios between joint angles. It was concluded that the control of the kinematic synergy is preserved on the whole in PD, with an increased variability and unproper set of the ratios between joint angular changes. This may lead to CG shifts to beyond the support surface, especially in backward bending. Copyright 1998 Elsevier Science B.V.

Journal Article↗

PubMed1998

Axial synergies during human upper trunk bending.

Upper trunk bending movements were accompanied by opposite movements of the lower body segments. These axial kinematic synergies maintained equilibrium during the movement performance by stabilizing the center of gravity (CG), which shifted on average across all the subjects by 1 +/- 4 cm in the anteroposterior direction and thus always remained within the support area. The aim of the present investigation was to provide an insight into the central control responsible for the performance of these synergies. The kinematic analysis was performed by the method of principal components (PC) analysis applied to the covariation between ankle, knee and hip joint angles and compared with CG shifts during upper trunk bending. Subjects were asked to perform backward or forward upper trunk bending in response to a tone. They were instructed to move as fast as possible or slowly (2 s), with high or low movement amplitudes. PC analysis showed a strong correlation between hip, knee and ankle joint changes. The first principal component (PC1) representing a multijoint movement with fixed ratios between joint angular changes, accounted, on average, for 99.7% +/- 0.2% of the total angular variance in the forward trunk movements and for 98.4% +/- 1.4% in the backward movements. The instructed voluntary regulation of the amplitude and velocity of the movement was achieved by adapting the bell-shaped profile of the velocity time course without changes in interjoint angular relations. Fixed ratios between changes in joint angles, represented by PC1, ensured localization of the CG within the support area during trunk bending. The ratios given by PC1 showed highly significant dependence on subjects, suggesting the adaptability of the central control to each subject's biomechanical peculiarities. Subject's intertrial variability of PC1 ratios was small, suggesting a stereotyped automatic interjoint coordination. When changing velocity and amplitude of the movement, the ratios remained the same in about half the subjects while in others slight variations were observed. A weak second principal component (PC2) was shown only for fast movements. In forward movements PC2 reflected the early knee flexion that seems related to the disturbances caused by the passive interaction between body segments, rather than to the effect of a central command. In fast backward movements, PC2 reflected the delay in hip extension relative to the movement onset in the ankle and knee that mirrors intersubject differences in the initiation process of the axial synergy. The results suggest that PC1 reflects the centrally controlled multijoint movement, defining the time course and amplitude of the movement and fixing the ratios between changes in joint angles. They support the hypothesis that the axial kinematic synergies result from a central automatic control that stabilizes the CG shift in the anteroposterior direction while performing the upper trunk bending.

Adaptation, Physiological↗

PubMed1998

Postural reorganization of weight-shifting in below-knee amputees during leg raising.

The position of the center of gravity (CG) is a reference value that is controlled by the nervous system during the performance of movements. In order to maintain equilibrium, leg movement is preceded by a shift of the CG towards the supporting side. This CG shift is initiated by an early displacement of the center of pressure (CP) towards the moving leg. This characteristic CP thrust partly results from the activity of a distal muscle in the leg to be moved: the gastrocnemius medialis (GM). The aim of this study was to determine how this weight-shifting is initiated when the distal muscles are missing, as in amputees, and to identify any change in the central command. Experiments were performed on ten subjects: five below-knee amputees with no pathology and five control subjects. While standing, the subjects were instructed to raise one leg laterally as fast as possible to an angle of 45 degrees and to maintain the final position. The same weight-shifting strategy was used by both groups, whereas local adaptations associated with the behavior occurred. When the GM is lacking, an early tensor-fasciae-latae (TFL) burst is observed just prior to and associated with the onset of the lateral CP change. This moving-leg abductor may be responsible for initiating the thrust at a proximal level when that leg is still on the ground. In addition, upon analyzing the lateral displacement of the CP, two modes of CP shift were detected. The first CP-shift mode has been previously described and the second mode (which we term here the pre-pushing mode) was used by both amputees and controls. The prepushing mode consisted of two thrusts: an early thrust onto the ground was exerted by the leg about to become the supporting leg followed by the previously described thrust exerted by the leg about to be raised. The early thrust, which could be exerted by either the sound or prosthetic leg, may have increased the efficiency of the second, classical thrust by initiating a swing.

Adult↗

PubMed1998

Postural control systems in developmental perspective.

How can the adult postural organisation be elucidated using an ontogenetic approach, and what questions can be raised about ontogenesis starting from the organisation of adult posture? These questions will be addressed taking three aspects of postural organisation. The first is the internal representation of erect posture, including the role played by the various sensory inputs in this representation. The second aspect relates to the variables which are controlled during erect posture: is it the body orientation with respect to the vertical or the localisation of the centre of gravity with respect to the feet which is controlled? The third aspect concerns the coordination between posture, equilibrium and movement, focusing on the role played by an internal representation of the external world and its interactions with the body segments in organising the anticipatory postural adjustments. The central organisation of coordinated control will also be considered. Each of these aspects will be discussed in relation to ontogenetic considerations.

Humans↗

PubMed1998

Body orientation and control of coordinated movements in microgravity.

The present paper focuses on the organization of posture and movement under normal and microgravity conditions. Two reference values subserving the control of erect posture and the performance of movements are analyzed. The first is 'geometrical' in nature and corresponds to the orientation of a body segment with respect to the external world. The second reference value, which involves the mass and inertia of the body segments, is the position of the centre of mass with respect to the foot support area. The reorganization of these parameters which occurs under microgravity is discussed in the framework of a hierarchical model of posture. Suggestions are made for training procedures which could be used to prevent loss of balance from occurring in astronauts on landing after long space flights.

Humans↗

PubMed1998

[Methods of shifting body weight in patients with knee arthroses].

INTRODUCTION: The aim of this work was to study movement control strategies in patients with knee arthritis. These strategies were expected to be different from healthy subjects because of deficiencies due to knee arthritis (i.e. pain, altered proprioception). METHOD: A kinetic and kinematic analysis was performed in a population of 10 patients with unilateral knee arthritis and in 11 age-matched control subjects, using an ELITE system and two AMTI force-plates. The different phases of a side step were studied. RESULTS: The timing of the movement was different in the two populations. The postural phase was longer and the monopodal phase was shorter in knee arthritis patients when the affected leg was the supporting one than when the sound leg was supporting. Total step duration and landing-stabilization phase duration were longer in knee arthritis patients than in healthy subjects. CONCLUSION: This movement analysis method enables to determine and to quantify differences between knee arthritis patients and control subjects. Clinical examination cannot identify these differences. Movement analysis methods bring up additional information to usual clinical evaluation scales and could be used for evaluation of the results of total knee arthroplasty.

Aged↗

PubMed1997

Voluntary head stabilization in space during oscillatory trunk movements in the frontal plane performed in weightlessness.

The ability voluntarily to stabilize the head in space during lateral rhythmic oscillations (0.59+/-0.09 Hz) of the trunk has been investigated during microgravity (microG) and normal gravity (nG) conditions (parabolic flights). Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, during phases of either microG or nG. The main result was that head orientation with respect to vertical may be stabilized about the roll axis under microG with, as well as without vision, despite the reduction in vestibular afferent and muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as was previously reported. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may in fact be organized on the basis of either dynamic vestibular afferents or a short-term memorized postural body schema.

Acoustic Stimulation↗

PubMed1997

Is the erect posture in microgravity based on the control of trunk orientation or center of mass position?

In the present experiments carried out in microgravity two questions were addressed. First, when the subject was instructed to adopt a vertical erect posture in microgravity with his feet fixed to the floor of the space cabin, would he control anteroposterior position with respect to the ankle joint axis of the "vertical projection" of his center of mass (CM) or trunk axis orientation with respect to the "vertical" (perpendicular to the floor of the space cabin)? Secondly, is CM anteroposterior position regulated during upper trunk movements in microgravity, in the absence of equilibrium constraint? Two subjects were tested in a long-term space flight. Video camera recordings were performed and analyzed off line. The results show that during erect vertical posture in microgravity, the trunk axis with respect to the "vertical" is inclined some 7 degrees forward. The anteroposterior position of the CM "vertical" projection is not shifted forward, as might be expected in view of the trunk inclination, but remains close to the ankle joint axis. At the end of the upper trunk forward or backward bending movement, the final position of the vertical CM projection remains close to the ankle joint axis in microgravity. These results are interpreted as indicating that CM anteroposterior position continues to be accurately controlled in microgravity; the forward inclination of the trunk axis observed in microgravity is interpreted as being due to a misevaluation of the "vertical" axis on the basis of biased information from proprioceptive inputs.

Analysis of Variance↗

PubMed1996

Balance control during lateral arm raising in humans.

The aim of the present study was to determine (i) whether the centre of gravity (CG) shift resulting from the mechanical effect of arm raising in the frontal plane is minimized in standing subjects and (ii) whether this putative minimization is affected by the support conditions (unipedal vs bipedal) and/or by adding a load (3.5 kg) to the moving hand. Our results indicate first that a CG control does exist during bipedal stance (compensating for 31% of the mechanical shift), which increases markedly in unipedal stance (73%) and secondly, that an additional load is compensated for solely in the case of unipedal stance (81%).

Adult↗

PubMed1996

Is the center of gravity controlled during upper trunk movements?

The question was addressed in this study as to whether the kinematic synergy responsible for equilibrium control during upper trunk movements may involve an actual evaluation of the weight of the body segments. Five adult subjects were asked to bend the upper trunk forward or backward to an angle of about 35 degrees, first without any load and then with a 10 kg load fixed to their shoulders. The center of gravity (CG) shift in the sagittal direction which occurred at the end of the movement was compared versus without a load. Two patterns of CG shift were identified. In the first pattern shown by three subjects in forward and three in backward trunk bending, the CG shift remained the same, while in the other pattern (two subjects for forward and two for backward trunk bending), the CG shift increased by an amount corresponding to the purely mechanical effect of the load. These results indicate that the actual weight of the segments may be evaluated on the basis of sensory inputs and may be responsible for a change in the kinematic synergy which preserves the CG control during the upper trunk movement.

Adaptation, Physiological↗

PubMed1996

Coordination between posture and movement in a bimanual load-lifting task: is there a transfer?

The present experimental series was designed to test the possibility that an anticipatory postural adjustment learned during the performance of a bimanual load lifting task may be transferred between the upper extremities. Eight seated subjects were asked to maintain horizontally one forearm (postural arm) loaded with a 1-kg load, which was fixed to the arm by means of an electromagnet. The unloading was triggered either by the experimenter pressing a switch (control) or by the subjects making a voluntary movement with their other arm (moving arm). In the latter case, the subject lifted a 1-kg load resting on a force platform with the moving hand, and the switching off was triggered when the force level reached a threshold of 0.5 kg. The maximum amplitude (MA) and the maximum velocity (MV) of the postural forearm elbow joint rotation occurring after the unloading were measured at each trial. The learning process was estimated by performing a regression analysis on each series of trials, using an exponential model, and from the intercept of the regression curve with the ordinate. 1. During the original learning session (three series of 20 trials), a decrease in MA and MV was found to occur both within the series and between the series during a session. 2. After the initial learning session, the sides of the postural and moving arm were interchanged to test whether any transfer had occurred. The first series of trials in the second session (transfer) and the last series of trials in the original learning session were compared and found to be significantly different in terms of the intercept (seven subjects in the case of MA, five subjects in the case of MV) and the slope (five subjects), indicating a lack of transfer. 3. The data recorded during the second transfer learning session indicated that learning occurred in all eight subjects in the case of MA and in six subjects in the case of MV. It was observed that the original learning session did not facilitate the second one. 4. The lack of transfer of the anticipatory postural adjustment observed in this task is discussed with reference to the data in the literature.

Conditioning, Psychological↗

PubMed1996

Impairment of posturo-kinetic co-ordination during initiation of forward oriented stepping movements in parkinsonian patients.

In order to differentiate between a specific impairment affecting gait initiation and a non-specific deficit in the postural adjustment which occurs prior to any forward oriented stepping movement, 3 forward oriented movements (FOMs), performed by a group of parkinsonian patients and a group of healthy age-matched subjects, were compared in the present study. These FOMs all consisted of initiating 1 step, but differed in their respective planning characteristics. The first consisted of initiating normal walking. The second consisted of initiating a single step, while the third was a visually guided task, consisting of placing the foot just behind a mark on the ground. In all 3 FOMs, the postural phase, i.e., the time elapsing between the initial shift of the center of pressure (CP) and the onset of the first step, was significantly longer in the patients than in the healthy subjects, whereas the duration of the subsequent movement phase, i.e., that of the first step, was within the same range in both groups. The horizontal reaction forces that led to a forward center of gravity (CG) acceleration during the postural phase were markedly reduced in the patients in all 3 FOMs, and the maximal velocity of the iliac crest marker, which corresponds approximately to that of the CG, decreased significantly in the patients. In addition, the length of the first step was significantly shorter in the patients than in the healthy subjects, in all 3 FOMs. The EMG pattern differed significantly between the patients and the healthy subjects; the amplitudes of the early tibialis anterior (TA) and vastus lateralis (VL) activations often decreased and were unilateral rather than bilateral. In addition, the gastrocnemius medialis (GM) burst associated with foot lift-off at the end of the postural phase was either absent or greatly reduced, thus suggesting that the co-ordination between the preparatory postural adjustment of the whole body and the actual stepping movement was impaired. The present results suggested that the lengthening of the postural phase is a common deficit in all FOM tasks in parkinsonian patients and is due to the impaired production of the requisite propulsive forces providing the forward acceleration of the CG. Consequently, a shortening of the first step length occurs. However, the step length is reduced less in the FOM tasks which provide some information about the goal of the first step (single step, visually guided step) than in a normal walking task, during which such information is missing. This suggests that although the stepping movement can be improved with the aid of any sensory cue about the end of the step in patients with Parkinson's disease, the postural phase will always be prolonged whichever FOM task they perform.

Aged↗