Axial rotation in Parkinson's disease.

AIMS: To investigate the ability of patients with Parkinson's disease to perform a rotation around the longitudinal axis of the body. Three questions were raised. Is body rotation impaired in Parkinson's disease? Is there a level of the kinematic chain from the head to the foot at which the impairment is more severe? Is the deficit related to the general slowness of movement in Parkinson's disease? METHODS: Kinematic data were recorded. The temporal organisation of body rotation during gait initiation was analysed in 10 patients with Parkinson's disease, who were all at an advanced stage of the disease and had all experienced falls and freezing during their daily life, and in five controls. The latency of the onset of the rotation of each segment was measured by taking the onset of the postural phase of step initiation as reference value. Locomotor variables were also analysed. RESULTS: Body rotation was found to be impaired in patients with Parkinson's disease, as the delay in the onset of the rotation of each segment is greater than that in controls. Moreover, a specific uncoupling in the onset of shoulder and pelvis segment rotation was seen in patients. This impairment of rotation is not related only to the general slowness of movements. CONCLUSION: Patients with Parkinson's disease were found to have an impairment of posturo-kinetic coordination and impaired capacity to exert appropriate ground reaction forces to orient the pelvis in space.

Kinematic synergy adaptation to an unstable support surface and equilibrium maintenance during forward trunk movement.

The aim of this investigation was to study the adaptation to an unstable support surface of kinematic synergy responsible for equilibrium control during upper trunk movements. Eight 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 in a standard condition, with two feet on the ground and the second, on a rocking platform swinging in the sagittal plane. The movement characteristics (duration, amplitude, and mean angular velocity of the trunk), the time course of the antero-posterior center of mass (CM) shift during the movement, and the EMG pattern of the main muscles involved in the movement were studied under the two experimental conditions. Kinematic synergy was quantified by performing a principal component analysis on the hip, knee, and ankle angle changes occurring during the movement. The results indicate that (1) the CM shift from the very onset of the movement remains controlled during performance of the forward trunk movement when the equilibrium constraints were increased; (2) the principal component analysis of the hip, knee, and ankle angle changes occurring during the movement showed a transition from one principal component (PC(1)) in the standard condition to two components in the rocking platform condition; (3) the greatest contribution of PC(1) (weight coefficients) was located at the hip level in both the standard and rocking platform conditions, while the greatest contribution of PC(2) in the rocking platform condition was located at the ankle level; and (4) the EMG pattern underlying kinematic synergy is modified. It is concluded that a simple adaptation of kinematic synergy by changing the weight coefficients of each pair of joints participating in the movement is no longer sufficient when the equilibrium constraints increase and, rather, disturbs equilibrium. The CNS has to provide two parallel controls, one to perform the trunk movement and the other to preserve equilibrium.

Behavioral outcomes following below-knee amputation in the coordination between balance and leg movement.

Lateral leg movement is accompanied by opposite movements of the supporting leg and trunk segments. This kinematic synergy shifts the center of mass (CM) towards the supporting foot and stabilizes its final position, while the leg movement is being performed. The aim of the present study was to provide insight in the behavioral substitution process responsible for the performance of this kinematic synergy. The kinematic synergy was assessed by the principal component analysis (PCA) applied to both hip joints and supporting ankle joint. Patients after unilateral below-knee amputation and control subjects were asked to perform a lateral leg raising. The first principal component (PC(1)) accounted for more than 99% of the total angular variance for all subjects (amputees and controls). PC(1) thus well represents the possibility to describe this complex multi-joint movement as a one degree of freedom movement with fixed ratios between joint angular time course. In control subjects, the time covariation between joints changes holds during all phases of the leg movement (postural phase, ascending and braking phases). In amputees, PC(1) score decreased during the ascending phase of the movement (i.e. when the body weight transfer is completed, while the movement is initiated). We conclude that a feedback mechanism is involved and discuss the hypothesis that this inter-joint coordination in amputees results from a failure in the pre-setting of the inter-joint coupling.

Goal directed locomotion and balance control in autistic children.

This article focuses on postural anticipation and multi-joint coordination during locomotion in healthy and autistic children. Three questions were addressed. (1) Are gait parameters modified in autistic children? (2) Is equilibrium control affected in autistic children? (3) Is locomotion adjusted to the experimenter-imposed goal? Six healthy children and nine autistic children were instructed to walk to a location (a child-sized playhouse) inside the psychomotor room of the pedopsychiatric centre located approximately 5 m in front of them. A kinematic analysis of gait (ELITE system) indicates that, rather than gait parameters or balance control, the main components affected in autistic children during locomotion are the goal of the action, the orientation towards this goal and the definition of the trajectory due probably to an impairment of movement planning.

Coordination of axial rotation and step execution: deficits in Parkinson's disease.

To determine why parkinsonian patients (PP) present some difficulties to initiate locomotion, a diagonal step has been investigated in two tasks in five control subjects (CS) and in ten PP. In the first task, the subjects had to perform one diagonal step without change in their orientation (WR); in the second task, they had to perform one diagonal step with a body rotation in the step direction (RO). The defended hypothesis is that the gait initiation deficits in Parkinson disease are a consequence of their difficulties to coordinate al the component of a complex movement. The analysed parameters were the duration of the postural and movement phases, the step length and velocity, and the amplitude of the horizontal ground reaction forces during each phase. Compared to CS, the PP showed a lengthening of the postural phase, a decrease in the step length and velocity and a reduction of the horizontal forces. The comparisons between the performances obtained in the WR versus those obtained the RO show in CS that the performances remained unchanged, whereas in PP the performances were significantly more altered in the RO. It illustrates the specific deficit occurring in PP while performing complex tasks where coordination between several components has to be achieved simultaneously.

Specific functions of the motor cortex in reorganizing coordinations during motor training in animals and humans.

The involvement of the motor cortex in learning movements has recently attracted much attention. One aspect of motor learning is the inhibition of innate synergies which interfere with performance of the acquired movement. Various models of operant responses in dogs have demonstrated the critical role of the motor cortex in the reorganization and inhibition of interfering synergies during learning. The role of the motor cortex and corticospinal influences in the formation of new coordinations in humans was studied here in patients with organic lesions of the cerebral circulation involving the internal capsule, using postural coordination and movements in a bimanual unloading response as an example. Formation of the forearm stabilization response was deeply lesioned on the afflicted side. Some degree of impairment was also seen on the ipsilateral side, but it was no different from the level of learning impairment in patients with lesions not involving the internal capsule or in patients with parkinsonism. The existence of specific contralateral influences of the motor cortex and non-specific descending influences on the process of motor learning is proposed.

Reorganization of equilibrium and movement control strategies after total knee arthroplasty.

This work was aimed at identifying changes in posturomotor control strategies in patients with unilateral total knee arthroplasty. Using kinetic and kinematic data, a previous study had revealed that, during a side step, patients with unilateral knee arthritis showed a shortened monopodal phase and a lengthened postural phase when the affected leg was the supporting one. It was expected that these strategies would be modified after undergoing total knee arthroplasty. Postoperatively the durations of the monopodal phase and of the postural phase became similar when the operated limb was supporting and when the sound limb was supporting. Concerning the upper body movements, the same asymmetrical results as before surgery were observed. Hence, patients with total knee arthroplasty exhibit posturomotor strategies which, although they become close to normal, remain asymmetrical. The durations of the monopodal and of the postural phases could be considered to assess the results of total knee arthroplasty.

Euromir 95 T4 experiment 'Human Posture in microgravity': global results and future perspectives.

After 7 years of studies on Euromir 95 T4 experiment 'Human Posture in microgravity' dataset, some important remarks can be proposed for best exploiting future experimental campaigns as well as for neurophysiological investigations on-ground. The main focus of such experiments was to monitor the process of learning and adapting to the new environment in performing complex voluntary movements. Euromir 95 was the first quantitative investigation with high technology instrumentation (ELITE-S) involving two subjects starting from 15 days after the launch until 5 months of mission. Results confirm the excellent capability of mutation of motor planning by the central nervous system (CNS) in order to best exploit environmental constraints and advantages. Under this view, the results offer a unique cue for improving the design of rehabilitation processes in motor pathologies.

Motor coordination in weightless conditions revealed by long-term microgravity adaptation.

The functional approach to studying human motor systems attempts to give a better understanding of the processes behind planning movements and their coordinated performance by relying on weightlessness as a particularly enlightening experimental condition. Indeed, quantitative monitoring of sensorimotor adaptation of subjects exposed to weightlessness outlines the functional role of gravity in motor and postural organization. The recent accessibility of the MIR Space Station has allowed for the first time experimental quantitative kinematic analysis of long-term sensorimotor and postural adaptation to the weightless environment though opto-electronic techniques. In the frame of the EUROMIR'95 Mission, two protocols of voluntary posture perturbation (erect posture, EP; forward trunk bending, FTB) were carried out during four months of microgravity exposure. Results show that postural strategies for quasistatic body orientation in weightlessness are based on the alignment of geometrical body axes (head and trunk) along external references. A proper whole body positioning appears to be recovered only after months of microgravity exposure. By contrast, typically, terrestrial strategies of co-ordination between movement and posture are promptly restored and used when performing motor activities in the weightless environment. This result is explained under the assumption that there may be different sensorimotor integration processes for static and dynamic postural function and that the organisation of coordinated movement might rely stably on egocentric references and kinematics synergies for motor control.

[A specific function of the motor cortex in the reorganization of coordination in motor learning in animals and humans]. / Spetsificheskaia funktsiia motornoi kory v reorganizatsii koordinatsii pri dvigatel'nom obuchenii u zhivotnykh i cheloveka.

The findings suggest that a particular function of MCx in motor learning involves suppression of synergies and co-ordination which interferes with acquisition of new motor patterns. Experimental animal models based on inhibition of certain natural synergies or reflexes in the process of learning new co-ordination have been developed where the MCx is responsible for inhibition of natural motor patterns. Following the MCx lesion the natural synergies dominate again and the learned movement cannot be adequately performed. Similar disturbances occur after combined lesions of the premotor and parietal associative cortex or after lesions of the cerebellar nuclei. However, after the associative cortex or cerebellar lesions the recovery of learned co-ordinations is possible. This suggests the inhibition of inappropriate synergies or co-ordination during motor learning is a specific function of the MCx, the latter taking part in organisation of new co-ordination between posture and movement in humans as well.

Biomechanical analysis of movement strategies in human forward trunk bending. I. Modeling.

Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance during the movement, we decided to model an extreme case, called "optimal bending", in which the movement is performed without any center of pressure displacement at all, as if standing on an extremely narrow support. The "optimal bending" is used as a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and hip) model of the human body and is performed in terms of "eigenmovements", i.e., the movements along eigenvectors of the motion equation. They are termed "ankle", "hip", and "knee" eigenmovements according to the dominant joint that provides the largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle) eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments. An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion units--the hip and ankle eigenmovements--are responsible for the movement and for equilibrium maintenance, respectively.

Biomechanical analysis of movement strategies in human forward trunk bending. II. Experimental study.

The large mass of the human upper trunk, its elevated position during erect stance, and the small area limited by the size of the feet, stress the importance of equilibrium control during trunk movements. The objective of the present study was to perform a biomechanical analysis of fast forward trunk movements in order to understand the coordination between movement and posture. The analysis is based on a comparison between experimentally observed bending and hypothetical "optimal bending" performed on an infinitely narrow support, as presented in a companion paper. The experimental data were obtained from 16 subjects who performed fast forward bending while standing on a wide platform or on a narrow beam. The analysis is performed by decomposition of the movement into three dynamically independent components, each representing a movement along one of the three eigenvectors of the motion equation. The eigenmovements are termed "hip", "ankle", and "knee" eigenmovements, according to the dominant joint. The experimentally observed movement is characterized mainly by the hip and ankle eigenmovements, whereas the knee eigenmovement is negligible. Similarly to the "optimal bending" the ankle eigenmovement starts earlier and lasts longer than the hip eigenmovement. An early forward acceleration of the center of gravity in the ankle eigenmovement is caused by anticipatory changes in the ankle joint torque. This clarifies the role of the early tibialis anterior burst and/or soleus inhibition usually observed in electromyographic recordings during forward bending. The results suggest that the hip and the ankle eigenmovements can be treated as independently controlled motion units aimed at functionally different behavioral goals: the bending per se and postural adjustment. It is proposed that the central nervous system has to control these motion units sequentially in order to perform the movement and maintain equilibrium. It is also suggested that the hip and ankle eigenmovements can be regarded as a biomechanical background for the hip and ankle strategies introduced by Horak and Nashner (1986) on the basis of electromyographic recordings and kinematic patterns in response to postural perturbations.

Static and dynamic postural control in long-term microgravity: evidence of a dual adaptation.

The adaptation of dynamic movement-posture coordination during forward trunk bending was investigated in long-term weightlessness. Three-dimensional movement analysis was carried out in two astronauts during a 4-mo microgravity exposure. The principal component analysis was applied to joint-angle kinematics for the assessment of angular synergies. The anteroposterior center of mass (CM) displacement accompanying trunk flexion was also quantified. The results reveal that subjects kept typically terrestrial strategies of movement-posture coordination. The temporary disruption of joint-angular synergies observed at subjects' first in-flight session was promptly recovered when repetitive sessions in flight were analyzed. The CM anteroposterior shift was consistently <3-4 cm, suggesting that subjects could dynamically control the CM position throughout the whole flight. This is in contrast to the observed profound microgravity-induced disruption of the quasi-static body orientation and initial CM positioning. Although this study was based on only two subjects, evidence is provided that static and dynamic postural control might be under two separate mechanisms, adapting with their specific time course to the constraints of microgravity.

Equilibrium and movement control strategies in trans-tibial amputees.

This study was aimed at identifying changes in equilibrium and movement control strategies in trans-tibial amputees (TTA) related to both the biomechanical changes and the loss of afferent inflow. The coordinations between equilibrium and movement were studied in traumatical TTA and in controls during transition from bipedal to monopodal stance. TTA failed to perform the task in a high percentage of trials both when the sound and the prosthetic limb were supporting. Significant differences were also found between TTA and controls in the duration of the weight transfer phase, in the length of the initial centre of pressure (CP) displacement and in the electromyographic (EMG) patterns. Despite adaptive posturomotor control strategies, transition from bipedal to monopodal stance remains a difficult task to perform for TTA, both when the supporting limb is the affected one and when the sound one is. The results of this study are discussed with respect to the rehabilitation programme and the prosthesis design for transtibial amputees.

Lateral leg raising in patients with Parkinson's disease: influence of equilibrium constraint.

Patients with Parkinson's disease often have difficulty maintaining postural stability. This impairment is attributed to postural adjustment deficits. We studied the postural adjustments associated with the performance of two complex tasks which differed only in the final equilibrium constraints. Ten patients with Parkinson's disease and six age-matched control subjects were asked to raise one leg laterally to an abduction angle of approximately 45 degrees as fast as possible to the right or left in random order. In the first series of tests, the subjects were instructed to maintain the leg at 45 degrees, whereas in the second series they were instructed to place their foot back on the ground. Recordings included ground reaction forces and kinematics. In the patients with Parkinson's disease the final posture for the first task was never maintained. The strategy used to shift the body weight was different for the two groups. In control subjects, it was initiated by a whole body rotation around the ankle followed by a trunk inclination around the hip. Conversely, in patients with Parkinson's disease, the shift of the body weight was initiated by a trunk inclination around the hip and then by a whole body rotation around the ankle. The amplitude of the trunk inclination toward the supporting side was smaller than in the control subjects. The second task with less severe equilibrium constraints was, on the whole, better performed by the patients even though the same postural adjustment deficits were present.

Asymmetry of gait initiation in patients with unilateral knee arthritis.

OBJECTIVE: To identify how patients with knee arthritis modify their equilibrium and movement control strategies during gait initiation. DESIGN: Observational study. SETTING: University hospital movement analysis laboratory. PARTICIPANTS: Twelve patients with unilateral knee arthritis and 12 healthy control subjects. MAIN OUTCOME MEASURES: Durations of the phases of gait initiation (ie, postural, monopodal, and double-support phases), center-of-pressure displacements, ground reaction forces, pelvic velocity, step length, and knee range of motion were measured using a movement analysis system and force plates. RESULTS: Gait initiation was slower in patients than in controls no matter which leg was the supporting one. In patients, the durations of the postural and the monopodal phases were modified in an asymmetrical way according to the leg used as the supporting one. The postural phase was lengthened and the monopodal phase was shortened when the affected leg was the supporting one. Opposite effects were observed when the sound leg was supporting. Step length, knee range of motion, and maximal pelvic velocity were reduced in patients whatever the side of the supporting leg. CONCLUSION: Gait initiation is an asymmetrical process in unilateral knee arthritis patients, who develop adaptive posturomotor strategies that shorten the monopodal phase on the affected leg.

Kinematic synergy adaptation to microgravity during forward trunk movement.

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.

Forward versus backward oriented stepping movements in Parkinsonian patients.

The primary purpose of this paper was to compare the effect of reversing the direction of step initiation in Parkinson's disease. Forward (FDS) and backward (BDS) oriented stepping initiation analyses were conducted on combined kinematic and kinetic data recorded on Parkinsonian patients (PD) and healthy age-matched subjects. Two successive phases were examined: a postural phase from T1 (onset of the center of pressure [CP] displacement) to T2 (onset of the malleolus displacement), which was followed by a stepping phase from T2 to T3 (end of the malleolus displacement; i.e., the end of the step). In healthy subjects, the duration of the postural phase remained unchanged regardless of the direction in which the step was initiated. The stepping phase duration and the first step length were reduced in BDS in comparison with FDS. In both tasks, the absolute value of the horizontal force in sagittal plane (Fx) remained unchanged. The maximal velocity of the iliac crest marker (estimated whole body center of gravity [CG]) in the sagittal plane (Vmax CG) remained within the same range regardless of direction of stepping. In Parkinsonian patients, the duration of the postural phase was markedly prolonged in both tasks in comparison with healthy subjects. The mean duration of stepping phase was approximately the same as in normal subjects, but the first step length was considerably reduced, as were horizontal force (Fx) and Vmax CG. This impairment, which was due to a decrease in the propulsive forces, was significantly more pronounced in BDS that in FDS.

[Influence of knee replacement arthroplasty on modalities of weight transfer during the lateral step]. / Influence de l'arthroplastie totale de genou sur les modalités de transfert du poids du corps au cours du pas latéral.

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.

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.