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PubMed2000

The effect of age on the attentional demands of postural control.

A dual-task paradigm was used to determine the attentional demands of several postural control tasks in 16 older women (age, 71.5+/-3.4 years) and 14 young women (age, 25.5+/-2.4 years). Older women had slower verbal reaction times (VRT) compared with the younger women and increased reaction time more from a sitting to standing posture. Compared with the younger women, older women required more cognitive resources to maintain a simple eyes open standing posture versus an eyes open seated posture. Further, older women had significantly greater VRT during the dual-task conditions compared with younger women. However, VRT did not significantly change as the difficulty of the primary task increased in either group. These data have implications for older adults who may be at risk for falls in situations where they may be engaged in concurrent tasks, even when those tasks are considered automated and/or lower order operations.

Accidental Falls↗

PubMed2000

A rapid upward step challenges medio-lateral postural stability.

A rapid step up was compared with a rapid step forward to assess the challenge they posed to postural stability in the medio-lateral (ML) direction. The center of pressure (COP) motion, and hip abductor muscle activity were compared between the two tasks in nine young healthy subjects. Analysis revealed that in the step up task there was a greater range and velocity of medio-lateral COP motion, an earlier gluteus medius onset time and a larger magnitude of gluteus medius activity than in the step forward task. The step up task appears to provide a greater challenge to ML postural stability than a step forward and thus may be an appropriate paradigm for the investigation of medio-lateral postural instability.

Adult↗

PubMed2000

Invariant sway properties in children.

The ability to maintain upright body posture depends on the biomechanical properties of a body and on the execution of control programs. The aim of this study was to determine how the structural growth of the human body, between ages 7-18, affects spontaneous sway parameters and to determine how the visual feedback positional task changes body sway parameters. The selected parameters of postural sway were evaluated in 57 children aged 7-18, while they stood with their feet together for 30 s. The experiment consisted of two different tasks: free standing with no feedback (No feedback), and free standing with additional visual feedback (Feedback). No statistically significant correlation between sway parameters and developmental factors (body height, body mass, and age) in the No Feedback task was found. Statistically significant correlations were found between age and most of the sway parameters in the Feedback task. The execution of voluntary feedback resulted in an increase in the total sway (20%), while the total area decreased nearly two-times. The invariance of sway amplitude supports the view that the same activation patterns can be utilized by children aged 7-18, despite the changes in body dimensions.

Adolescent↗

PubMed2000

An improved technique for the extraction of stochastic parameters from stabilograms.

An improved characterization of the dynamics of postural sway can provide a better understanding about the functional organization of the postural control system as well as a more robust tool for postural pattern recognition. To this aim, a novel parameterization was applied to the stabilogram diffusion analysis formerly proposed by Collins and De Luca [Collins JJ, De Luca CJ. Open-loop and closed-loop control of posture: a random-walk analysis of center-of-pressure trajectories. Exp Brain Res 1993;95:308-18] that considered the act of maintaining posture as a stochastic process. The main purpose of the present technique was to overcome some drawbacks of the model presented by Collins and De Luca that may restrain its potential application in clinical practice. The approach uses a unique non-linear model to describe the center of pressure (COP) dynamics that reduces the number of parameters and decreases their intra-subject variability; consequently, fewer trials are required to perform reliable estimates of stochastic parameters and this is of particular importance for subjects that cannot afford many repeated measurements because of age or pathology. Four new statistical mechanics parameters (NSMP) were computed on the log-log stabilogram diffusion plots and their estimates were compared in terms of reliability and sensitivity to the visual conditions with: (1) a minimal set of four summary statistic scores (SSS); and (2) the six statistical mechanics parameters (SMP) proposed by Collins and De Luca. All four NSMP showed at least a fair-to-good reliability (intraclass correlation coefficient, ICC>0.49) while SMP (ICC>0.20) showed some poor reliability. A better overall reliability was also observed with respect to SSS. Moreover, only NSMP had a similar score for eyes open and eyes closed conditions. Three out of four NSMP were also significantly sensitive to eyes open or closed conditions (P<0.001) while only three out of six SMP were sensitive to operating conditions (P<0.01).

Humans↗

PubMed2000

Quantitative analysis of neutral body posture in prolonged microgravity.

The experiment was performed during a 6-month space flight and focused on the quantitative three-dimensional description of the Neutral Body Posture (NBP) and of subjects' spine anthropometry in Erect Posture (EP). The NBP joint angles' configuration is described along the long-term microgravity exposure and compared with respect to previous in-flight collected data. Observed spinal length modification during EP in-flight is related to on-ground investigations focused on circadian anthropometrical fluctuations. The flattening of the spinal lumbar lordosis and thoracic kyphosis is also described. Even though only two subjects were studied, this analysis points out the maturity of the opto-electronic technology for the quantitative analysis of posture in microgravity and confirms the need of enriching the anthropometrical database of human postures in weightlessness for the design optimization of permanently inhabited space modules.

Adult↗

PubMed2001

Postural control: visual and cognitive manipulations.

Numerous questions exist regarding the utilization of sensory information for postural control. Past research has established the possibility that cognitive tasks requiring visual perception may affect the processing of visual information used for postural control. The purpose of this study was two fold: (1) to investigate the effects of varying demands of visual perception and (2) to evaluate the effects of performing a cognitive task on postural control in healthy, young adults (N=30). Three posture-related dependent variables were recorded during the manipulation of two independent variables (eye movement and modality of presentation of a cognitive task). The two levels of eye movement were movement and no movement, while the three levels of modality of presentation were visual, auditory, and none. A 2x3 repeated measures ANOVA was applied to the data to investigate the presence of group differences. Significantly more variability was observed in the no cognitive condition than the visual and the auditory for medial-lateral (M--L) COP variability. Additionally, the eye movement condition revealed significantly greater M--L COP variability than the no eye movement condition. No differences were observed between the visual and auditory conditions for any dependent variable. Therefore, the greatest COP variability was observed in the eye movement and no cognitive condition. Further, an interesting relationship between the measures of COP variability and sway velocity was described.

Adult↗

PubMed2001

The translating platform paradigm: perturbation displacement waveform alters the postural response.

The translating platform paradigm is widely used to investigate the regulation of upright standing and locomotion. This study investigated how the displacement waveform characteristics underlying the translating platform perturbation are revealed in the resulting postural response. Eight participants experienced a series of backward-directed perturbations using a hydraulically driven forceplate. Two ranges of platform displacement (5 and 15 cm) in combination with two peak velocities (40 and 60 cm/s) were achieved using three distinct waveforms for platform displacement: (a) RAMP: ramp onset and ramp offset, (b) Ramp-to-Parabola (R-P): ramp onset with parabolic offset and (c) SINE: sine-wave onset with sine wave offset. Our findings indicated that the unique and distinctive acceleration and deceleration characteristics that result from the three different platform displacement waveforms significantly altered the postural response to the perturbation.

Adult↗

PubMed2001

Attention influences sensory integration for postural control in older adults.

This study investigated the influence of attention on the sensory integration component of postural control in young and older adults. Eighteen young and 18 older healthy subjects performed information-processing tasks during different postural challenge conditions. Postural conditions included seated, standing on a firm surface, standing on a sway-referenced floor, and standing on a sway-referenced floor while viewing a sway-referenced scene. During each condition, reaction time (RT) was measured during two simple and one inhibitory RT tasks. For the inhibitory task, the time required to inhibit an action was derived, termed the inhibitory time (IT). Performing a RT task was associated with increased postural sway in older subjects, but not in young subjects. The greatest influence of RT task on sway of older subjects was found during the sway-referenced floor/sway-referenced scene condition. Conversely, postural condition had an influence on RT task performance in both young and older subjects. The IT was increased in both young and older subjects only during the sway-referenced floor/scene condition. These results suggest that the sensory integration component of postural control in particular seems to require attention. Further, our data suggest that attentional processes related to inhibitory control are engaged when sensory integration requirements are high.

Age Factors↗

PubMed2001

Fingertip touch improves postural stability in patients with peripheral neuropathy.

The purpose of this work was to determine whether fingertip touch on a stable surface could improve postural stability during stance in subjects with somatosensory loss in the feet from diabetic peripheral neuropathy. The contribution of fingertip touch to postural stability was determined by comparing postural sway in three touch conditions (light, heavy and none) in eight patients and eight healthy control subjects who stood on two surfaces (firm or foam) with eyes open or closed. In the light touch condition, fingertip touch provided only somatosensory information because subjects exerted less than 1 N of force with their fingertip to a force plate, mounted on a vertical support. In the heavy touch condition, mechanical support was available because subjects transmitted as much force to the force plate as they wished. In the no touch condition, subjects held the right forefinger above the force plate. Antero-posterior (AP) and medio-lateral (ML) root mean square (RMS) of center of pressure (CoP) sway and trunk velocity were larger in subjects with somatosensory loss than in control subjects, especially when standing on the foam surface. The effects of light and heavy touch were similar in the somatosensory loss and control groups. Fingertip somatosensory input through light touch attenuated both AP and ML trunk velocity as much as heavy touch. Light touch also reduced CoP sway compared to no touch, although the decrease in CoP sway was less effective than with heavy touch, particularly on the foam surface. The forces that were applied to the touch plate during light touch preceded movements of the CoP, lending support to the suggestion of a feedforward mechanism in which fingertip inputs trigger the activation of postural muscles for controlling body sway. These results have clinical implications for understanding how patients with peripheral neuropathy may benefit from a cane for postural stability in stance.

Aged↗

PubMed2002

Effect of vibration-induced postural illusion on anticipatory postural adjustment of voluntary arm movement in standing humans.

We investigated the contribution of sensory signals arising from muscle proprioceptive receptors to anticipatory postural adjustments (APAs). During vibration applied to ankle (tibialis anterior; TA, soleus; Sol) or neck muscles, subjects generally describe having illusory sensations of whole-body movement, namely, whole-body movement in a backward and forward direction induced by vibration of the Sol or TA, respectively, and the front or back surface of the neck muscles, respectively. Preceding electromyographic (EMG) activity of the ipsilateral biceps femoris (BFi) muscle induced by rapid voluntary arm movement and the typical phenomenon of APA were changed dependent on these illusory whole-body movements, with preceding EMG activities of BFi appearing earlier in vibration applied to TA and later in vibration applied to Sol muscle. In vibration applied to the back surface of neck muscle, preceding EMG activities of BFi appeared earlier, as with vibration applied to TA. On the contrary, in vibration applied to the front surface of neck muscles, preceding EMG activities of BFi appeared later, as with vibration applied to Sol. Based on these results, we discuss changes in the central processing of proprioceptive signals used for coding of the spatial orientation of the body and its contribution to postural stabilization.

Adult↗

PubMed2002

Contributions of altered sensation and feedback responses to changes in coordination of postural control due to aging.

We used multivariate kinematics and joint torque measurements during dynamic posturography to determine the relative contributions of changes in overall control gain, relative weighting of sensors, and noise-like effects on posture control in the elderly. Our results show that sway coordination and amplitude both change with age, but that changes in overall feedback gains do not explain these differences. We propose that increased sway of elderly subjects in platform sway-referenced conditions is due to sensory noise or decreased ability to detect small motions of the platform, while increased sway during visual sway-referencing is due to re-weighting of the various sensors.

Adult↗

PubMed2002

Adaptation of vibration-induced postural sway in individuals with Parkinson's disease.

Postural control requires accurate integration of visual, vestibular, cutaneous, and proprioceptive sensory information. Previous research suggests that patients with Parkinson's disease (PD) may have difficulty with this integration process, particularly involving incongruent visual information. The purpose of this study was to determine whether PD patients also show difficulty in adaptation to erroneous proprioceptive information. Postural reactions to soleus muscle vibration were explored in 8 PD patients, 8 healthy elderly, and 8 young adults. Postural sway was recorded using an electromagnetic motion analysis system in four conditions (2 vision x 2 vibration) with four trials in each condition to test subjects' adaptation to the vibrator stimulus. The results showed that PD patients did adapt to the vibration across trials, similar to those of both control groups. It was concluded that PD patients in the early stages of the disease could override inaccurate proprioceptive inputs, relying more on true vestibular and/or visual information. These results suggest that the basal ganglia are not critical for this adaptation process in postural control.

Adaptation, Physiological↗

PubMed2003

The influence of external orthotic support on the adaptive gait characteristics of individuals with chronically unstable ankles.

External orthotic supports or braces are used clinically to treat individuals with chronically unstable ankles. Braces have efficacious effects on dynamic strength, passive tissue tension, and proprioception, but their effects on gait remains undetermined. The purpose of this study was to determine if overground locomotion, including walking up a step and a curb are influenced by orthotic device use. Twenty subjects, 10 with no previous injury and 10 with chronically unstable ankles, performed with no brace, a flexible brace and a semi-rigid brace while walking on a level surface, up a step and on a ramp. Differences were noted in kinematic and kinetic gait parameters between groups and between step and ramp conditions, suggesting that gait patterns vary between individuals who have had ankle sprain and those who have not. Few differences were noted between the brace and no brace conditions for both groups. Adding to the previously described efficacious benefits, we conclude that bracing does not alter selected gait parameters in individuals who have chronic ankle instability.

Adaptation, Physiological↗

PubMed2003

Anticipatory activation of postural muscles associated with bilateral arm flexion in subjects with different quiet standing positions.

We investigated changes in activation timing and magnitude of the postural muscles according to initial standing positions. The subjects were divided into three groups depending on the position of the center of foot pressure (CFP) during quiet standing, namely backward, middle, and forward. Subjects maintained standing postures at various CFP positions in the anteroposterior direction, and then started bilateral arm movement at their own pace. The activation magnitude of the biceps femoris (BF) and erector spinae (ES) did not differ among any of the initial CFP positions. In only the BF, the preceding action to the anterior deltoid (AD) was clearly observed at more forward CFP positions in the order of the forward, middle and backward groups. Between initial CFP positions adjacent to quiet standing posture, the smallest change was observed in the preceding activation time of the BF. Significant correlation was observed between the background activity and activation time in both the BF and ES.

Adult↗

PubMed2003

Postural sway increases with attentional demands of concurrent cognitive task.

The purpose of the present project was to determine whether postural sway varied with the difficulty of a concurrent unrelated cognitive task. Participants stood on a compliant surface under four conditions of varied attentional demand. Information reduction tasks (digit reversal, digit classification, counting backward by 3s) were used to quantify the attentional demands of the cognitive activity. Results showed attentional demands of the cognitive task impacted postural sway, with the most difficult cognitive task having the greatest influence.

Adolescent↗

PubMed2003

Mechanical effect of additional supports in a rocking on heels movement.

This study examined the influence of the addition of handles on postural adjustments associated to a rocking on heels movement. Upper and lower limb muscle EMG activities were recorded and the forces applied to the handles and beneath the feet were measured. Without handles, the anticipatory activation of the Gastrocnemius Medialis displaced the COP forwards, enabling the backward shift of the CG required to rock back on heels. This anticipatory postural activity disappeared with handles and was substituted by an EMG activity on the upper limbs. This activity engendered a forward and downward push on the handles, which largely contributed to create the dynamic conditions required to perform the movement.

Adult↗

PubMed2003

The steady-state postural response to continuous sinusoidal galvanic vestibular stimulation.

Galvanic vestibular stimulation (GVS) applied between the mastoids during quiet standing elicits postural sway. The aim of this study was to characterize the postural sway response to continuous sinusoidal GVS across various stimulus frequencies and amplitudes. Binaural bipolar sinusoidal GVS was applied to the skin overlying the mastoid processes of 10 subjects while they stood on a force plate with eyes closed. The position of the center of pressure (COP) at the feet was recorded from a forceplate, while the head displacement was measured with a magnetic position tracking system. The stimulus conditions included four frequencies (0.1, 0.25, 0.45, and 1.1 Hz) and five peak amplitudes (0.05, 0.1, 0.25, 0.5, and 1.0 mA). Each subject experienced one trial at each amplitude-frequency pair. Additionally, each subject underwent three trials in which a dual-frequency stimulus (0.1 plus 0.45 Hz at a peak of 0.5 mA each) was presented. The stimuli elicited sway in the frontal plane in all subjects, as evidenced by changes in the displacement of the COP and head. Sway magnitude decreased with increasing stimulus frequency and increased with increasing stimulus amplitude. However, the response magnitude saturated at higher stimulus amplitudes. Phase lag increased with increasing stimulus frequency. The response to the dual-frequency stimulus was reduced at 0.1 Hz and nearly equal at 0.45 Hz in comparison with the single-frequency responses. This study suggests that the postural sway response is nonlinear due to saturation and violation of the principle of superposition.

Adult↗

PubMed2003

Perturbation of the postural control system induced by muscular fatigue.

In this experiment, we induced muscular fatigue of ankle plantar-flexors to examine how it deteriorates the regulation of bipedal quiet upright standing. Postural stability was assessed in conditions with and without vision over 60 s period to examine not only classical postural variables (time- and frequency-domain analyses), but also structural variables (stabilogram-diffusion analysis). Muscular fatigue was induced with repeated plantar-flexion of both legs. With muscular fatigue, subjects exhibited an increased postural sway (faster center of pressure (CP) velocity, and greater CP mean and median frequency) and a decreased long-term scaling exponent compared with the control conditions. The fatigue conditions, however, did not modify the range of oscillations and the variability of the postural oscillations around the mean position of CP. The effects of muscular fatigue were similar with eyes open and eyes closed. These results suggest that fatigue did induce some changes in the control mode of postural stability, but the detection/action capabilities of the sensorimotor system remained partly efficient when the ankle plantar-flexors were fatigued. Furthermore, the decreased long-term scaling exponent observed with fatigue suggests that the control of upright stance operates in a less stochastic and more antipersistent manner when fatigue is present (i.e. past and future behaviors were more negatively correlated and thus more tightly regulated). Altogether, the present results suggest that, compared with the no-fatigue conditions, fatigue places higher demands on the postural control system by increasing the frequency of actions needed to regulate the upright stance.

Adult↗