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ABSTRACT: OBJECTIVES: We investigated the pattern of activity of the tibialis anterior (TA), soleus (SOL) and peroneus longus (PER) muscles of both legs during tandem stance, in order to highlight their respective role in maintaining balance. METHODS: Twelve young healthy subjects were asked to stand with feet in line for successive 15s-epochs, on a dynamometric platform with (EO) and without (EC) vision. EMG was recorded from the six muscles simultaneously. Collected signals were displacement of the centre of feet pressure (CoP) and EMG. Variables calculated for each recorded epoch were mean level, variability and distribution between legs of EMG, and cross-correlation between EMG and CoP traces and between EMG of homonymous muscles. RESULTS: CoP motion was larger along the medio-lateral (M-L) than antero-posterior (A-P) axis, and larger with EC than EO particularly in the M-L axis. Muscle activity was larger in the rear than in the front leg, as expected, except for PER. Activity increased with the increase in M-L CoP oscillations, except for SOL, which was tonically active, both legs, regardless of the amplitude of the oscillations. Manipulating vision had no effect on the variability of the EMG for equal mean levels of activity, for any muscle. Cross-correlation between EMG of rear leg muscles and M-L CoP sway gave higher coefficients for TA and PER than SOL, and appropriate time-delays between TA or PER and CoP motion, indicating a role of these muscles in the control of M-L sway. Except for the tonically active SOL, the homonymous muscles of the two legs were active out-of-phase, indicating a mutual push-pull action of the pairs. This was confirmed by the reciprocal activation of TA and PER of the same leg. CONCLUSIONS: Overall, in spite of a large inter-trial and inter-subject variability, the neural command to the leg muscles during tandem stance implies a task-sharing rule, whereby SOL keeps the body upright while the reciprocal PER and TA activities produce the alternate impulses necessary for body stabilization in the frontal plane. SIGNIFICANCE: Knowledge of the normal mode of control of balance in frontal plane can foster new investigation in both posture and gait control, in addition to offering tools for understanding balance problems of elderly persons and patients at risk of fall.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 01/2013; · 3.12 Impact Factor
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ABSTRACT: Despite numerous studies addressing the issue, it remains unclear whether the triceps surae muscle group generates forward propulsive force during gait, commonly identified as 'push-off'. In order to challenge the push-off postulate, one must probe the effect of varying the propulsive force while annulling the effect of the progression velocity. This can be obtained by adding a load to the subject while maintaining the same progression velocity.
Ten healthy subjects initiated gait in both unloaded and loaded conditions (about 30% of body weight attached at abdominal level), for two walking velocities, spontaneous and fast. Ground reaction force and EMG activity of soleus and gastrocnemius medialis and lateralis muscles of the stance leg were recorded. Centre of mass velocity and position, centre of pressure position, and disequilibrium torque were calculated.
At spontaneous velocity, adding the load increased disequilibrium torque and propulsive force. However, load had no effect on the vertical braking force or amplitude of triceps activity. At fast progression velocity, disequilibrium torque, vertical braking force and triceps EMG increased with respect to spontaneous velocity. Still, adding the load did not further increase braking force or EMG.
Triceps surae is not responsible for the generation of propulsive force but is merely supporting the body during walking and restraining it from falling. By controlling the disequilibrium torque, however, triceps can affect the propulsive force through the exchange of potential into kinetic energy.
PLoS ONE 01/2013; 8(1):e52943. · 4.09 Impact Factor
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ABSTRACT: Early Parkinson's disease (PD), in which the motor disorder is mostly unilateral, allows to investigate the presence of side-related pathophysiological changes in the responses to balance perturbations prior to any confounding effect of therapy. These patients offer the possibility of answering the question whether the initial abnormalities affect spinal circuits or supra-spinal sensori-motor loops. Toe-down rotation of a supporting platform evokes in standing subjects a double-burst medium-latency response (MLR) in the stretched tibialis anterior (TA) muscle. The former burst (MLR1) is fed by group II spindle fibres through a spinal circuit, the latter (MLR2) travels through supraspinal pathways. This perturbation was used to separately test both reflex pathways in both the unaffected and affected side. Ten patients with unilateral PD (7 of which de-novo) and 10 normal subjects (NS) were recruited. 1. Body sway and centre of feet pressure (CFP) were recorded during quiet standing; 2. Rotations of the supporting platform were administered with both legs on the platform during free stance (Control) and 3. While holding onto a stable rail (Holding); 4. Separate perturbations to either leg (Leg-on or Leg-off) were also delivered to avoid the effect of concurrent ipsi- and contralateral inputs on MLR. The EMG of TA and Sol muscles were recorded bilaterally. 1. Position and sway of CFP were similar in NS and PD. 2. Under Control condition, there were no differences in area of TA MLR1 and MLR2 of both limbs between NS and PD. 3. During Holding, both bursts were reduced in amplitude in both NS and PD, but less so for the MLR1 on the PD affected side. 4. During single-leg perturbation, both bursts were reduced in amplitude in both NS and PD, both ipsi- and contralateral to the perturbation; however, in PD, MLR2 was much less reduced in the unperturbed affected side Leg-off. The differences in the responses to stretch between NS and early PD are not accounted for by changes in postural attitude, or by different amplitudes of the Control responses. The asymmetrical reduction of the MLR1 by Holding in PD indicates mostly unilateral impairment of the descending pathways modulatory to spinal group II circuits. Single-leg perturbation unveils a larger excitability of the supraspinal loop mediating the MLR2 on the affected side. These changes are early markers of basal ganglia malfunctions, and are related to both their descending effect on the spinal cord and their ascending influence onto the cortex.
Experimental Neurology 07/2012; 237(2):407-17. · 4.70 Impact Factor
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ABSTRACT: Fifteen patients with Charcot-Marie-Tooth type 1A (CMT1A) disease and 46 normal controls were studied. In the patients, leg
muscle strength, touch-pressure, vibration and joint position sense were reduced; lower limb ten-don reflexes were absent
in 12 or markedly decreased. Motor and sensory conduction velocity (CV) of leg nerves was either reduced or not measurable.
The Neurological Disability Score and the Neuropathy Score were obtained from clinical and electrophysiological examination,
respectively. Tilt of a supporting platform elicited short- (SLR) and medium-latency (MLR) responses to stretch in the foot
muscle flexor digitorum brevis (FDB) in controls. In the patients, the former response was absent and the latter delayed.
These findings are in keeping with the known loss of large-diameter myelinated fibres, with relative sparing of the smaller
fibres. The MLR delay was fully accounted for by the slowed CV of the motor fibres. The MLR afferent time was similar to that
in normal subjects. Body sway area (SA) during quiet stance was recorded with eyes open or closed, and with feet apart or
together. Under all postural and visual conditions, SA was within normal range in the less severely affected patients, but
was moderately increased in the patients with a more severe neuropathy score. Across all patients, no correlation was found
between SA and muscle force, motor CV, touch pressure, vibration and joint position sense, considered either separately or
as an aggregate. We suggest that: (1) functional integrity of the largest afferent fibres is not necessary for appropriate
equilibrium control during quiet stance and (2) any unsteadiness is related to additional functional alterations in smaller
fibres, most likely group II spindle afferent fibres.
Experimental Brain Research 04/2012; 135(2):155-162. · 2.39 Impact Factor
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ABSTRACT: Sudden addition or removal of visual information can be particularly critical to balance control. The promptness of adaptation of stance control mechanisms is quantified by the latency at which body oscillation and postural muscle activity vary after a shift in visual condition. In the present study, volunteers stood on a force platform with feet parallel or in tandem. Shifts in visual condition were produced by electronic spectacles. Ground reaction force (center of foot pressure, CoP) and EMG of leg postural muscles were acquired, and latency of CoP and EMG changes estimated by t-tests on the averaged traces. Time-to-reach steady-state was estimated by means of an exponential model. On allowing or occluding vision, decrements and increments in CoP position and oscillation occurred within about 2s. These were preceded by changes in muscle activity, regardless of visual-shift direction, foot position or front or rear leg in tandem. These time intervals were longer than simple reaction-time responses. The time course of recovery to steady-state was about 3s, shorter for oscillation than position. The capacity of modifying balance control at very short intervals both during quiet standing and under more critical balance conditions speaks in favor of a necessary coupling between vision, postural reference, and postural muscle activity, and of the swiftness of this sensory reweighing process.
Human movement science 04/2011; 30(2):172-89. · 2.15 Impact Factor
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ABSTRACT: We investigated the adaptation of balancing behavior during a continuous, predictable perturbation of stance consisting of 3-min backward and forward horizontal sinusoidal oscillations of the support base. Two visual conditions (eyes-open, EO; eyes-closed, EC) and two oscillation frequencies (LF, 0.2 Hz; HF, 0.6 Hz) were used. Center of Mass (CoM) and Center of Pressure (CoP) oscillations and EMG of Soleus (Sol) and Tibialis Anterior (TA) were recorded. The time course of each variable was estimated through an exponential model. An adaptation index allowed comparison of the degree of adaptation of different variables. Muscle activity pattern was initially prominent under the more challenging conditions (HF, EC and EO; LF, EC) and diminished progressively to reach a steady state. At HF, the behavior of CoM and CoP was almost invariant. The time-constant of EMG adaptation was shorter for TA than for Sol. With EC, the adaptation index showed a larger decay in the TA than Sol activity at the end of the balancing trial, pointing to a different role of the two muscles in the adaptation process. At LF, CoM and CoP oscillations increased during the balancing trial to match the platform translations. This occurred regardless of the different EMG patterns under EO and EC. Contrary to CoM and CoP, the adaptation of the muscle activities had a similar time-course at both HF and LF, in spite of the two frequencies implying a different number of oscillation cycles. During adaptation, under critical balancing conditions (HF), postural muscle activity is tuned to that sufficient for keeping CoM within narrow limits. On the contrary, at LF, when vision permits, a similar decreasing pattern of muscle activity parallels a progressive increase in CoM oscillation amplitude, and the adaptive balancing behavior shifts from the initially reactive behavior to one of passive riding the platform. Adaptive balance control would rely on on-line computation of risk of falling and sensory inflow, while minimizing balance challenge and muscle effort. The results from this study contribute to the understanding of plasticity of the balance control mechanisms under posture-challenging conditions.
Human movement science 03/2011; 30(2):262-78. · 2.15 Impact Factor
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ABSTRACT: To assess the efficacy of a balance rehabilitation treatment by using both a powered platform on which subjects stand and specific physical exercises (EXs).
Crossover trial.
Physical and rehabilitation medicine department in Italy.
Patients (N=33) with balance disorders (14 vestibular origin, 19 peripheral neuropathy origin).
Patients underwent powered platform then EX treatment (n=17); the other 16 received the same treatments in reverse order. powered platform consisted of balancing on a sinusoidally oscillating powered platform (in anteroposterior and laterolateral directions in separate trials) with eyes open and closed. A physical therapist administered Cawthorne-Cooksey EXs for patients with vestibular disorders and modified Frenkel EXs for patients with neuropathy. Treatment lasted 1 hour a day for 10 consecutive days, except for the weekend.
Body sway area, subjective score of stability, balance and gait scores, and amplitude of head displacement while balancing on the oscillating powered platform were recorded before, (t0) after the first (t1), and after the second treatment (t2), regardless of the powered platform or EX order.
On average, all participants improved balance regardless of the order of treatments, and more so at t2 than t1. Improvement was observed by using instrumental evaluations and balance and gait scales. In both patient groups, powered platform treatment proved to be as effective as EX in improving balance. This effect was stronger in patients with vestibular disorders, independently of order of treatment.
Balance rehabilitation with either EX or powered platform is effective in patients with balance disorders of vestibular or neuropathic origin. These findings point to the value of either or both physical EXs and powered platform in increasing stability and potentially decrease the risk of falling in patients with neuropathy, for whom few results are documented in the literature.
Archives of physical medicine and rehabilitation 12/2010; 91(12):1869-77. · 2.18 Impact Factor
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ABSTRACT: Curved walking requires complex adaptations, including shift of body weight to counteract the ensuing centrifugal force, and the production of strides of different length between legs. We hypothesized that gait capacities would be more stressed in hemiparetic patients than in healthy subjects when walking along curved, compared with straight, trajectories.
Twenty chronic, stabilized stroke patients and 20 healthy subjects walked along straight or curved trajectories. Mean cadence and gait velocity were off-line computed from video recordings. An electronic walkway detected asymmetry of single support and degree of foot yaw angle at mid-stance. Centre of pressure during standing was recorded by posturography.
Compared with linear walking, the velocity of curved walking was not significantly smaller in patients, and was independent of affected body side or direction of rotation. It was inversely correlated with paretic limb weakness, asymmetry of single support, and shift of centre of pressure toward the healthy side. External rotation of the paretic foot relatively favoured curved walking toward the paretic side.
Curved locomotion is defective in stabilized stroke patients, but impairment is not dependent on direction of rotation, indicating a shared task between legs or occurrence of effective functional adaptation. These findings advocate rehabilitation exercises targeting complex gait adaptations, including curved walking.
Journal of rehabilitation medicine: official journal of the UEMS European Board of Physical and Rehabilitation Medicine 10/2010; 42(9):858-65. · 1.88 Impact Factor
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ABSTRACT: During the administration of timed bilateral alternate vibration to homonymous leg or trunk muscles during quiet upright stance, Parkinsonian (PD) patients undergo cyclic antero-posterior and medio-lateral transfers of the centre of foot pressure. This event might be potentially exploited for improving gait in these patients. Here, we tested this hypothesis by applying alternate muscle vibration during walking in PD.
Fifteen patients and 15 healthy subjects walked on an instrumented walkway under four conditions: no vibration (no-Vib), and vibration of tibialis anterior (TA-Vib), soleus (Sol-Vib) and erector spinae (ES-Vib) muscles of both sides. Trains of vibration (internal frequency 100 Hz) were delivered to right and left side at alternating frequency of 10% above preferred step cadence.
During vibration, stride length, cadence and velocity increased in both patients and healthy subjects, significantly so for ES-Vib. Stance and swing time tended to decrease. Width of support base increased with Sol-Vib or TA-Vib, but was unaffected by ES-Vib.
Alternate ES vibration enhances gait velocity in PD. The stronger effect of ES over leg muscle vibration might depend on the relevance of the proprioceptive inflow from the trunk muscles and on the absence of adverse effects on the support base width.
Trunk control is defective in PD. The effect of timed vibratory stimulation on gait suggests the potential use of trunk proprioceptive stimulation for tuning the central pattern generators for locomotion in PD.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 11/2009; 121(2):240-7. · 3.12 Impact Factor
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ABSTRACT: In patients with spastic hemiparesis, centre of foot pressure (CoP) is shifted toward the unaffected limb during quiet stance. We hypothesised that abnormal gait features would correlate with the degree of asymmetry during stance. In 15 patients and 17 normals we recorded CoP and body sway by a force platform and measured spatial-temporal variables of gait with pedobarography. In patients CoP was shifted toward the unaffected limb and sway was larger than in normals. CoP position was associated with the decrease in strength of the affected lower-limb muscles. Spatio-temporal variables of gait were also affected by the disease. Cadence and velocity were decreased, duration of single support on the unaffected limb and of double support were increased with respect to normals. The degree of impairment of gait variables correlated with CoP. We found a negative relationship between velocity or cadence and CoP, and a positive relationship between duration of single support and CoP in the unaffected but not in the affected limb. Duration of double support correlated positively with CoP. CoP asymmetry during both standing and walking suggests that postural and gait problems share some common neural origin in hemiparetic patients. This asymmetry affects gait performance by increasing the time and effort needed to shift body weight toward the affected limb. The degree of postural asymmetry measured by stabilometry is associated with the level of impairment of gait variables.
Gait & posture 04/2009; 30(1):5-10. · 2.58 Impact Factor
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ABSTRACT: We hypothesized that gait capacities would be more stressed in patients with Parkinson's disease (PD) when walking along curved than straight trajectories, owing to the complex adaptations required for this walking task. Twenty on-phase patients with PD and 20 healthy subjects walked eyes-open along straight and curved trajectories for 1 minute at self-paced cadence and velocity. Step frequency along straight and curved trajectories was computed from video-recordings of the lower limbs. Step frequency was not affected by trajectory shape in either patients with PD or healthy subjects. Distances run by the patients were shorter than normal under both conditions. However, in PD, distances were relatively shorter during curved than straight walking; therefore, decreased distances in PD were connected with decreased mean step length (as the ratio between distance and step number). No correlation was found between the above mentioned variables and the severity or duration of the disease or the frequency of falls. Walking along curved trajectories can highlight impaired gait control in on-phase patients with PD, and can be suitable for the routine evaluation of possible walking disorders when straight walking is not significantly affected.
Movement Disorders 01/2009; 24(4):598-604. · 4.51 Impact Factor
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ABSTRACT: Neural circuits responsible for stance control serve other motor tasks as well. We investigated the effect of prior locomotor tasks on stance, hypothesizing that postural post-effects of walking are dependent on walking direction. Subjects walked forward (WF) and backward (WB) on a treadmill. Prior to and after walking they maintained quiet stance. Ground reaction forces and centre of foot pressure (CoP), ankle and hip angles, and trunk inclination were measured during locomotion and stance. In WF compared to WB, joint angle changes were reversed, trunk was more flexed, and movement of CoP along the foot sole during the support phase of walking was opposite. During subsequent standing tasks, WB induced ankle extension, hip flexion, trunk backward leaning; WF induced ankle flexion and hip extension. The body CoP was displaced backward post-WB and forward post-WF. The post-effects are walking-direction dependent, and possibly related to foot-sole stimulation pattern and trunk inclination during walking.
Arbeitsphysiologie 12/2008; 105(2):297-307. · 2.15 Impact Factor
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ABSTRACT: Patients suffering from Parkinson's disease (PD) have difficulties with control of stance, postural changes, and walking, seemingly depending on problems in central integration of proprioceptive information. We tested the hypothesis that alternate vibration of postural muscles can induce cyclic medio-lateral or antero-posterior sway in PD, mimicking that accompanying body progression during walking, thereby favoring the production of locomotor tasks. In 12 standing PD patients and 11 healthy subjects, we applied trains of vibratory stimuli, bilaterally in an alternating paradigm to soleus, tibialis anterior, or paravertebral muscles. The trains of stimuli were delivered at frequencies selected to be above, near, and below the normal walking rhythm. The displacement of the center of foot pressure (CoP) was recorded. In PD, sway area during unperturbed stance was just larger than in healthy subjects; shifts in CoP in response to vibration were preserved, regardless of the vibrated muscle pair; CoP oscillations along medio-lateral, but not antero-posterior direction, were coupled to the vibration trains; time to initiate and terminate the postural responses was normal. PD patients correctly integrate and exploit the vibration-induced proprioceptive inflow to produce body oscillations comparable to those occurring during walking. Vibratory stimulation can be safely and easily employed to provoke rhythmic postural changes in PD.
Movement Disorders 10/2008; 23(15):2186-93. · 4.51 Impact Factor
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ABSTRACT: We studied balance control in patients with cervical spondylosis, on the hypothesis that ataxia and changes in postural responses occur concurrently as a consequence of structural problems in the cervical cord. Subjects and patients: Seventeen patients and 17 healthy subjects were recruited. Based on magnetic resonance imaging, the patients were divided into 2 groups, with (n=9) and without (n=8) signs of myelopathy.
Body sway was recorded under quiet stance on a force platform. Postural perturbations evoked early and late responses in soleus and tibialis anterior.
Most patients showed increased body sway during stance, which was larger in cervical spondylosis with myelopathy than cervical spondylosis. Early postural responses in the soleus were not affected. Late responses in soleus and tibialis anterior were delayed in cervical spondylosis with myelopathy. Across all patients, latency of tibialis anterior late response was correlated with lower limb sensory impairment and amplitude of body sway.
Abnormal transmission through the cervical cord of proprioceptive input to supraspinal centres and of descending commands to caudal cord levels are accountable for ataxia in cervical spondylosis with myelopathy. Stabilometry may be an economic and easy way in a clinical and rehabilitative setting to distinguish severe from mild forms of cervical spondylosis prior to physical treatment and to help the differential diagnosis from other diseases featuring similar signs.
Journal of Rehabilitation Medicine 08/2008; 40(7):539-47. · 2.05 Impact Factor
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ABSTRACT: Processing of sensory information, timing operations and set-shifting can be affected in Parkinson's disease (PD) patients. We investigated their capacity and swiftness to pass from a kinaesthetic- to a vision-dependent behaviour during dynamic balancing on a continuously moving support base. Nineteen on-phase PD patients and 13 age-matched normal subjects stood on a platform continuously translating in the antero-posterior direction at 0.2 Hz. Body segment oscillations were identified by a stereophotogrammetric device and electromyogram (EMG) was recorded from tibialis anterior and soleus. Under constant visual conditions, both patients and normal subjects roughly stabilised head and trunk in space with eyes open (EO) but followed the platform displacement with eyes closed (EC). Amplitude and variability of the periodic EMG bursts were smaller with EO than EC. Constant visual-condition trials were intermingled with trials in which subjects opened (EC-EO) or closed (EO-EC) the eyes in response to an acoustic signal. Both patients and normal subjects changed kinematics and EMG patterns to those appropriate for the new visual condition. However, PD patients were slower in changing their behaviour under the EC-EO condition. These findings show abnormal temporal features in balancing strategy adaptation when shifting from kinaesthetic to visual reference in PD. The delay in the implementation of the vision-dependent behaviour was unexpected, given the advantage vision is supposed to confer to motor performance in PD. This condition may play a major role in the instability of patients performing dynamic postural tasks under changing sensory conditions.
Brain Research Bulletin 10/2007; 74(4):258-70. · 2.82 Impact Factor
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ABSTRACT: Can visual information be replaced by other sensory information in the control of static and dynamic equilibrium? We investigated the balancing behaviour of acquired and congenitally blind subjects (25 severe visually impaired subjects--15 males and 10 females, mean age 36 +/- 13.5 SD) and age and gender-matched normal subjects under static and dynamic conditions. During quiet stance, the centre of foot pressure displacement was recorded and body sway analysed. Under dynamic conditions, subjects rode a platform continuously moving in the antero-posterior direction, with eyes open (EO) and closed (EC). Balance was inferred by the movement of markers fixed on malleolus, hip and head. Amplitude of oscillation and cross-correlation between body segment movements were computed. During stance, in normal subjects body sway was larger EC than EO. In blind subjects, sway was similar under both visual conditions, in turn similar to normal subjects EC. Under dynamic conditions, in normal subjects head and hip were partially stabilized in space EO but translated as much as the platform EC. In blind subjects head and hip displacements were similar in the EO and the EC condition; with respect to normal subjects EC, body displacement was significantly larger with a stronger coupling between segments. Under both static and dynamic conditions, acquired and congenitally blind subjects had a similar behaviour. We conclude that long-term absence of visual information cannot be substituted by other sensory inputs. These results are at variance with the notion of compensatory cross-modal plasticity in blind subjects and strengthen the hypothesis that vision plays an obligatory role in the processing and integration of other sensory inputs for the selection of the balancing strategy in the control of equilibrium.
Brain 09/2007; 130(Pt 8):2097-107. · 9.46 Impact Factor
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ABSTRACT: Treadmill locomotion is different with respect to overground walking and may require an adapted control mode. The relevant neural computational effort may produce lasting effects encroaching upon the performance of a subsequent postural task. The hypothesis of the present study was that, contrary to overground walking, treadmill walking has effects on quiet stance variables, in the assumption that the imposed locomotor activity is more critical to stance control than natural walking. Nine young subjects performed three different walking sessions: treadmill with eyes closed, treadmill with eyes open, overground walking with eyes open. Body sway area and sway path and the position of the centre of foot pressure during stance were recorded by a dynamometric platform under control, post-walking and post-recovery conditions, alternatively with eyes closed and eyes open. At variance with overground walking, treadmill locomotion produced an effect on body orientation in space during the subsequent stance trials. This consisted in a forward inclination of the body, not accompanied by increased body sway, lasting for a few minutes. Presence or absence of vision during treadmill locomotion did not induce differences in the amplitude or time-course of the post-effect. We argue that body inclination would be the consequence of a change in the postural reference produced by a message arising from treadmill locomotion itself, possibly connected to particularities in the control mode of this type of walking.
Arbeitsphysiologie 07/2007; 100(3):331-9. · 2.15 Impact Factor
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ABSTRACT: Several observations support the notion that integration of neck proprioceptive input is impaired in cervical dystonia (CD). An example is the inconsistent or opposite to normal effect of lateral neck muscle vibration on body rotation during stepping. We hypothesized that lateral neck vibration produces abnormal responses also in a static task. Normal subjects and patients with CD stood quietly with eyes closed, without or with vibration applied to the sternocleidomastoid muscle, and center of foot pressure and body sway were recorded by a dynamometric platform. Patients had a larger than normal sway under control condition. They showed little or no postural responses to vibration. When body tilt occurred, it was rarely in the frontal plane as in normal subjects, but in the sagittal plane. No relationship existed between vibration-induced tilt during stance and body rotation during stepping. Therefore, in CD, proprioceptive neck input is less used for the construction of the postural vertical during quiet stance than it is used for the definition of the subjective straight ahead during a dynamic task.
Movement Disorders 04/2007; 22(4):498-503. · 4.51 Impact Factor
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ABSTRACT: Balance control under static and dynamic conditions was assessed in patients with Sensory Neuron Disease (SND) in order to shed further light on the pathophysiology of ataxia.
Fourteen patients with diabetic polyneuropathy and 11 with SND underwent clinical and neurophysiological evaluation, stabilometric recording of body sway during quiet stance with and without vision, stereometric analysis of body segment displacement while riding a platform translating in anterior-posterior direction with and without vision (dynamic condition), and EMG recording of leg muscle responses to abrupt stance perturbation produced by rotation of a supporting platform. The findings were compared to those of age matched normal subjects.
Clinical and neurophysiological evaluation revealed a more severe motor impairment in patients with diabetes than SND, while sensory impairment was superimposable. Some patients with SND had vestibular dysfunction of diverse severity. Body sway during stance was larger in patients with SND than diabetes with and without vision. In the stance perturbation condition, the latency of the long-loop EMG response to platform rotation was disproportionately increased with respect to the spinal response in the SND but not in diabetic patients. Under dynamic condition, patients with SND oscillated more than diabetic patients and several of them easily lost balance with eyes closed.
Patients with SND show severe unsteadiness under both static and dynamic conditions, particularly with eyes closed. The patchy sensory loss of SND, disrupting sensation from territories other than the lower limbs and possibly including the vestibular nerve, could be responsible for this instability. Ataxia is correlated to the abnormal latency of the muscle responses to stance perturbation. Since increased response latencies cannot be attributed to a vestibular deficit, the deterioration of equilibrium control would be ascribed mainly to the degeneration of the central branch of the afferent fibres.
Measures of body balance under quiet stance and dynamic conditions can provide relevant diagnostic information as to the pathophysiology and severity of ataxia and viability of the central branch of the sensory fibres, and help in separating patients with peripheral neuropathy from patients with loss of sensory neurones.
Clinical Neurophysiology 04/2007; 118(3):538-50. · 3.41 Impact Factor
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ABSTRACT: While balancing on a continuously antero-posterior (A-P) translating platform (10 cm, 0.5 Hz), the head normally oscillates with the platform without vision but is stabilized in space with vision. We estimated the time to shift from one to the other balancing behaviour when visual condition changed at some stage during the balancing trials. Ten subjects performed randomly 50 balancing trials (each lasting 18 s): 10 trials with eyes open (EO), 10 with eyes closed (EC), 15 in which participants started with EO and closed their eyes (condition EO-->EC) in response to an acoustic signal delivered during the trial, and 15 starting with EC and closing their eyes (EC-->EO) in response to the same signal. No other specific instruction was given. Displacements of malleolus, hip and head, and EMG from leg and axial muscles were recorded. Indexes of amplitude of A-P head and hip oscillation and of amplitude of EMG activity were computed. All variables were larger with EC than EO. On changing visual condition during the trial, the pattern of head and hip movement and of muscle activity turned into that appropriate for the new visual condition in a time-interval ranging from about 1 to 2.5 s. For each subject, the mean latency of the change in the balancing behaviour was assessed by statistical methods. On average, the latencies of kinematics and EMG changes proved to be longer for the EO-->EC condition than vice versa. Further, the latencies of the changes were also measured across all EO-->EC and EC-->EO individual trials. These values were clustered around particular epochs of the first few oscillation cycles following the shift in visual condition. The results show that subjects can rapidly adapt their balancing behaviour to the new visual condition. However, they appear to refrain from releasing the new behaviour were this unfit, and unfastened it at appropriate time in the next platform translation cycle. These findings reveal the temporal and spatial features of the automatic release of the new balancing strategy in response to a shift in the ongoing sensory set, and emphasize the swiftness in the change in balancing behaviour when subjects pass from a non-visual to a visual reference frame.
Experimental Brain Research 03/2007; 178(1):18-36. · 2.39 Impact Factor
