Postural Responses to Achilles Tendon Vibration Depend on Feet Positioning.

Mechanical vibration of the Achilles tendon is widely used to analyze the role of proprioception in postural control. The response to this tendon vibration (TV) has been analyzed in the upright posture, but the feet positions have varied in past research. Moreover, investigators have addressed only temporal parameters of the center of pressure (CoP). We investigated the effect of TV on both temporal and spectral characteristics of the CoP motion. Eighteen healthy young adults, stood barefoot, with one foot on each side of a dual platform, wearing glasses with opaque lenses. We applied 20 seconds of Achilles TV (bilaterally with inertial vibrators at a frequency of 80 Hz and an amplitude of .2-.5 mm). We analyzed CoP signals pre-vibration (PRE,4-seconds), during vibration (VIB,20 seconds), and after vibration cessation (REC,20 seconds). We repeated this protocol in natural and standardized positions (15° feet angular opening). For determining CoP amplitude and velocity, we divided the 20 seconds into five phases of four seconds each and calculated spectral parameters for the whole 20-second signals. There was an adaptation process in the speed of the CoP mediolateral (p < .01) and anteroposterior (p < .01) and in the displacement of the CoP anteroposterior (p < .01), with higher values in the VIB condition. Velocity and displacement decreased progressively in the REC condition. Median and peak frequencies were higher in the VIB condition when compared to the REC condition, but only in the mediolateral direction (p = .01). The standardized foot position led to increased speed in CoP mediolateral, anteroposterior, and mediolateral displacement (p < .01). CoP spectral characteristics were not affected by foot positioning. We concluded that adaptation of CoP motion in the presence of TV and after its cessation are observable both in time and frequency domains. Feet positioning influenced CoP motion in the presence of TV and after its cessation but it did not affect its spectral characteristics.

Organization of postural equilibrium in several planes in ballet dancers.

This study analyzed the balance strategies of ballet dancers during postural equilibrium in three single leg balance conditions with and without vision and regard to age. Dancers participating formed two groups of 20 dancers each, one aged between 8 and 16 years (young group) and the other aged between 17 and 30 years (adult group). Ground reaction forces (GRFs) (mediolateral (ML), anteroposterior (AP) components, vertical (V)) were recorded. Results analysis enabled us to extract some spatiotemporal data for each component of the GRF (number of GRF oscillations, variability and impulses). Young dancers are characterized, compared to adult dancers, by an instability combined with an increase of oscillations number and a decrease variability mainly visible on the ML component. In the two groups, the absence of vision implies an increase of AP, ML and V impulsions and GRF variability. Balance with the gesturing limb to the rear increases the age and vision effect compared to balances with the limb forward or to the side. Young dancers are less efficient at controlling their balance than adult dancers. This observation may be related to the number of hours practicing dance, which differs between groups. The dancers have a visual dependence to control the postural balance.

Gait initiation reflects the adaptive biomechanical strategies of adolescents with idiopathic scoliosis.

BACKGROUND: The dynamics behavior of patients with idiopathic scoliosis obviously requires some biomechanical compensatory strategies. Our objective is to analyze the ground reaction forces (GRF) exerted during gait initiation in order to determine the dynamic consequences of idiopathic scoliosis. METHODS: Ten adolescent girls suffering from idiopathic scoliosis with a right thoracic curvature (Cobb>15°) and 15 healthy adolescents participated in this study. Two force plates were used to record the ground force evolution for the right and left limbs tested during gait initiation. RESULTS: Whichever limb was used to initiate gait, gait initiation duration was found to be significantly longer in persons with scoliosis than in healthy subjects. In the scoliosis group (SG), the impulses, occurrences and forces values were also greater than in healthy subjects. Under the stance foot, the anteroposterior and vertical forces were always increased. Under the swing foot, the SG showed the same characteristics associated to decreased mediolateral impulses parameters. Even greater differences were observed between these two groups in terms of peak occurrences during left-limb gait initiation. The intragroup comparisons only unveiled very few differences between the two limbs for the control group (CG), whereas significantly higher values were recorded for the group of scoliosis patients when gait was initiated with the left limb rather than with the right one. CONCLUSION: For patients with scoliosis specific dynamic behavior adjustment are made during gait initiation patterns, for both limbs in order to maintain balance during gait to compensate for their spine deformation. Patients with scoliosis always showed slower dynamic patterns than healthy controls. These results show the importance of including specific evaluation and dynamic physical rehabilitation for patients with idiopathic scoliosis.

Lateral steps reveal adaptive biomechanical strategies in adolescent idiopathic scoliosis.

INTRODUCTION: Adolescent idiopathic scoliosis (characterized by a morphological deformation of the trunk) prompts the development of new postural control strategies. This adaptation has an influence on the dynamics of motor behaviour. The present study analysed ground reaction forces during lateral stepping in order to highlight the dynamic consequences of idiopathic scoliosis. MATERIAL AND METHODS: Ten adolescents suffering from idiopathic scoliosis with right thoracic curvature (Cobb angle>or=15 degrees) and 15 healthy adolescents participated in the study. We used two force platforms to record ground reaction forces for the right and left legs during large and small lateral steps (LSs). RESULTS: Our results revealed intergroup and interlimb differences for both types of step. For small LSs, right-side (i.e. convexity side) initiation induced a significant increase in the ground reaction force impulse during the postural phase for the scoliotic group, when compared with the control group. For large LSs, left-side (i.e. concavity side) initiation induced a significant increase in ground reaction force impulse during the landing phase only. Patients always displayed slower dynamic behaviour than healthy controls. For both stepping sides, the asymmetry index (AI) was higher in the scoliotic group than in the control group (0.2or=85 in the scoliotic group versus 0.124.4 in the control group). Furthermore, the scoliotic group showed a significant increase in the variability of the dynamic parameters (>8%). CONCLUSION: In scoliotic subjects, lateral stepping prompts specific dynamic behaviour affecting both limbs, in order to maintain balance during movement despite spinal deformation. This stepping task could be used in future studies to identify specific motor strategies.

Effect of aging on the coordination between equilibrium and movement: what changes?

This investigation studies the effect of aging on the coordination between equilibrium and trunk movement. Eight young adults and seven adults at the end of middle age bent their trunk forward and stabilized their position. The center of mass shift was studied as an indicator of equilibrium control as was the electromyographic pattern of the main muscles involved in the movement. The kinematic strategy responsible for both the movement and equilibrium control was quantified by performing a principal components analysis on the hip, knee, ankle angle changes occurring during the movement. We observed that the effect of aging can be detected early. It is not expressed as a deterioration of equilibrium control but rather as "over control". The kinematic strategy is modified, the central command adapted. These results could express the onset of a lesser ability to simplify the coordination between equilibrium and movement as young adults leading to its deterioration in the elderly.

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.

[Temporal, kinetic and kinematic asymmetry in gait initiation in one subject with hemiplegia]. / Asymétries chronométriques, cinétiques et cinématiques de l'initiation de la marche chez un sujet hémiplégique.

OBJECTIVE: To investigate the temporal, kinetic and kinematic asymmetry of gait initiation in one subject with hemiplegia with an equinus varus foot. MATERIAL AND METHODS: A kinetic analysis with two AMTI force plates and a kinematic analysis with an ELITE optoelectronic system of gait initiation were performed in one subject with hemiplegia. RESULTS: The duration of the gait initiation phases was asymmetrical. The monopodal phase was shorter when the affected lower limb was supporting than when the healthy one was supporting. The propulsion resulted from the force exerted on the healthy lower limb. The distribution of body weight on the lower limbs was asymmetrical. Body weight support was more important on the healthy side than on the affected side. Maximal extension of the ankle on the hemiplegic side occurred during the swing phase. Ground clearance was increased by elevating the knee higher on the affected side than on the healthy side during the swing phase. Initial contact with the floor was performed with the foot flat on the affected side. CONCLUSION: This preliminary study has shown that gait initiation in one subject with hemiplegia was asymmetrical in kinetics and kinematics. The results concerning kinematics have not been reported previously for gait initiation in subjects with hemiplegia. The study of gait initiation should allow for better understanding postural and movement control strategies developed by patients with hemiplegia.

[Posture and movement analysis and sports medicine]. / Analyse de la posture et du mouvement et médecine du sport.

The use of posture and movement analysis methods has developed during the past 15 years. These methods are of special interest in the field of sport sciences and have allowed to improve the understanding of physiology of posture and movement in athletes. More recently these methods have been used in the field of sport medicine. In some cases, they have helped to identify abnormalities which cannot be seen on standard clinical examination and to understand the mechanism of lesions occurring during sport activities. For the future these methods should provide useful information for understanding the physiopathology of lesions, for developing prevention of pathologies related to sport and for elaborating and assessing new treatment protocols in the field of sport medicine.

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.

[Biomechanical consequences of a knee osteoarthritis on the opposite lower limb]. / Conséquences biomécaniques d'une gonarthrose unilatérale sur le membre inférieur opposé

UNLABELLED: The aim of this work was to study the compensatory strategies built up by patients with unilateral knee arthritis during stair descent. These compensatory strategies might induce increased biomechanical constraints on the unaffected knee. METHOD: A kinetic and kinematic analysis was performed in 11 patients with unilateral knee arthritis and in 14 control subjects using an ELITE system and two force-plates. The peak of vertical ground reaction forces when landing on the reception force-plate, the time to reach the peak and the duration of the different phases of the movement were studied during stair descent. RESULTS: The peak of vertical ground reaction forces was more important when landing on the unaffected limb than when landing on the affected limb. The time to reach this peak was longer in patients than in controls no matter which side was supporting. The duration of the single support phase was longer on the unaffected limb than on the affected limb. DISCUSSION AND CONCLUSION: This work has shown that patients with unilateral knee arthritis develop new strategies during stair descent. These new strategies imply increased biomechanical constraints on the unaffected limb and might favor arthritis on the sound side. These results support the idea that rehabilitation protocols of patients with unilateral knee arthritis should also involve the unaffected limb.

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.

[Postural and locomotor evaluation of normal pressure hydrocephalus: a case report]. / Troubles posturaux et locomoteurs dans l'hydrocéphalie à pression normale: intérêt de l'analyse chez un patient.

Generally, the diagnosis of idiopathic normal pressure hydrocephalus (NPH) is raised in elderly patients with an association of gait disturbances, cognitive impairment, urinary incontinence and widening of the ventricles. Gait disturbances appear as the predominant clinical symptom of NPH, and may precede other symptoms. The main objectives of this study were to determine the effect of ventriculoperitoneal shunt (VPS) on gait and to compare the results obtained in HPN with those obtained in Parkinson's disease (PD). The performance of a patient with NPH on specific postural and locomotion tasks was analyzed during three successive experimental sessions: the first one before VPS, the second one week after VPS and the third three months after VPS. The patient was instructed to walk at his natural speed and also to maintain postural control for one minute. Four gait parameters (mean velocity, stride length, cadency and step width) were calculated for each session to assess the subject's performance. In this NPH patient there was a significant improvement in gait performance before and after VPS. This improvement concerned mean velocity, stride length and step cadency but did not involve the width component which remained unchanged. Before VPS, the NPH patient walked slower and with a shorter stride length than a group of patients with PD. After VPS his performance was better than the PD group except for cadency. Step width remained longer for the HPH patient than in PD patients for all three sessions. From this study, it appears that gait in idiopathic NPH exhibits a specific temporospatial pattern distinct from that in PD or normal age-matched controls. Changes in gait can be evaluated shortly after treatment of NPH. Gait disorders, excepting dynamic balance, may normalize as soon as one week after surgery.

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.

[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.

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.

Visual control of locomotion in Parkinson's disease.

The effect of placing parallel lines on the walking surface on parkinsonian gait was evaluated. To identify the kind of visual cues (static or dynamic) required for the control of locomotion, we tested two visual conditions: normal lighting and stroboscopic illumination (three flashes/s), the latter acting to suppress dynamic visual cues completely. Sixteen subjects with idiopathic Parkinson's disease (nine males, seven females; mean age 68.8 years) and the same number of age-matched controls (seven males; nine females, mean age 67.5 years) were studied. During the baseline phase, Parkinson's disease patients walked with a short-stepped, slow velocity pattern. The double limb support duration was increased and the step cadence was reduced relative to normal. Under normal lighting, visual cues from the lines on the walking surface induced a significant improvement in gait velocity and stride length in Parkinson's disease patients. With stroboscopic illumination and without lines, both groups reduced their stride length and velocity but the changes were significant only in the Parkinson's disease group, indicating greater dependence on dynamic visual information. When stroboscopic light was used with stripes on the floor, the improvement in gait due to the stripes was suppressed in parkinsonian patients. These results demonstrate that the perceived motion of stripes, induced by the patient's walking, is essential to improve the gait parameters and thus favour the hypothesis of a specific visual-motor pathway which is particularly responsive to rapidly moving targets. Previous studies have proposed a cerebellar circuit, allowing the visual stimuli to by-pass the damaged basal ganglia.

Strategies of segmental stabilization during gait in Parkinson's disease.

This study compared the postural strategies adopted by patients with Parkinson's disease (PD; n = 16) during locomotion to those of elderly controls (n = 16). We focused mainly on the head and trunk stabilization modes in sagittal and frontal planes. Subjects were asked to walk at their natural speed on an uniformly gray, flat ground. Gait data were recorded before and 1 h after L-dopa intake and were analyzed by an automatic motion analyser (Elite system). The modes of segmental stabilization adopted by each group were determined by means of the anchoring index, associated with cross-correlation functions between angular movements of pairs of segments. The major findings were: (a) PD patients generally had shorter step length, greater step width, and slower gait velocity than the healthy elderly. (b) No difference in angular dispersion of any anatomical segment studied was observed between the two groups. (c) PD patients had adopted a strategy of head stabilization on the shoulder ("en bloc" functioning of the head-shoulder unit) about the roll axis only. (d) PD patients displayed head and shoulder angular movements around the roll axis that were more correlated than those of controls, confirming their more en bloc functioning. (e) Shoulder and hip were equally stabilized in space in the two groups around the roll axis. (f) There was no difference between the two groups about the pitch axis where an en bloc functioning of the whole trunk was shown. These results are discussed with respect to the similarities observed between the visuo-locomotor PD performances and those of children.

[Methods of shifting body weight in patients with knee arthroses]. / Modalités de transfert du poids du corps chez le patient gonarthrosique.

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.