Nicolas Pinsault

Experimental neck muscle pain impairs standing balance in humans

Impaired postural control has been reported in patients with chronic neck pain of both traumatic and non-traumatic etiologies, but whether painful stimulation of neck muscle per se can affect balance control during quiet standing in humans remains unclear. The purpose of the present experiment was thus to investigate the effect of experimental neck muscle pain on standing balance in young healthy adults. To achieve this goal, 16 male university students were asked to stand upright as still as possible on a force platform with their eyes closed in two conditions of No pain and Pain of the neck muscles elicited by experimental painful electrical stimulation. Postural control and postural performance were assessed by the displacements of the center of foot pressure (CoP) and of the center of mass (CoM), respectively. The results showed increased CoP and CoM displacements variance, range, mean velocity, and mean and median frequencies in the Pain relative to the No pain condition. The present findings emphasize the destabilizing effect of experimental neck muscle pain per se, and more largely stress the importance of intact neck neuromuscular function on standing balance.

Cervicocephalic Relocation Test to the Neutral Head Position: Assessment in Bilateral Labyrinthine-Defective and Chronic, Nontraumatic Neck Pain Patients

OBJECTIVE To determine whether vestibular or cervical proprioceptive information influence the cervicocephalic relocation test to the neutral head position, by comparing head repositioning errors obtained in asymptomatic, unimpaired control subjects with those obtained in bilateral labyrinthine-defective patients and chronic, nontraumatic neck pain patients. DESIGN A group-comparison study. SETTING University medical bioengineering laboratory. PARTICIPANTS Labyrinthine-defective patients (n=7; mean age+/-SD, 67+/-15 y), nontraumatic neck pain patients (n=7; 56+/-9 y), and asymptomatic, unimpaired control subjects (n=7; 64+/-12 y). INTERVENTIONS Participants were asked to relocate the head on the trunk, as accurately as possible, after full active cervical rotation to the left and right sides. Ten trials were performed for each rotation side. MAIN OUTCOME MEASURES Absolute and variable errors were used to assess accuracy and consistency of the repositioning, respectively. RESULTS No significant difference in repositioning errors was observed between labyrinthine-defective patients and control subjects, whereas nontraumatic neck pain patients demonstrated significantly increased absolute errors in horizontal and global components and higher variable errors in horizontal component. CONCLUSIONS These findings suggest that the vestibular system is not involved in the performance of the cervicocephalic relocation test to neutral head position, and further support this test as a measure of cervical proprioceptive acuity.

Inter-individual variability in sensory weighting of a plantar pressure-based, tongue-placed tactile biofeedback for controlling posture.

The purpose of the present experiment was to investigate whether the sensory weighting of a plantar pressure-based, tongue-placed tactile biofeedback for controlling posture could be subject to inter-individual variability. To achieve this goal, 60 young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Overall, results showed reduced CoP displacements in the Biofeedback relative to the No-biofeedback condition, evidencing the ability of the central nervous system to efficiently integrate an artificial plantar-based, tongue-placed tactile biofeedback for controlling posture during quiet standing. Results further showed a significant positive correlation between the CoP displacements measured in the No-biofeedback condition and the decrease in the CoP displacements induced by the use of the biofeedback. In other words, the degree of postural stabilization appeared to depend on each subjects balance control capabilities, the biofeedback yielding a greater stabilizing effect in subjects exhibiting the largest CoP displacements when standing in the No-biofeedback condition. On the whole, by evidencing a significant inter-individual variability in sensory weighting of an additional tactile information related to foot sole pressure distribution for controlling posture, the present findings underscore the need and the necessity to address the issue of inter-individual variability in the field of neuroscience.

A wireless embedded tongue tactile biofeedback system for balance control

We describe the architecture of an original biofeedback system for balance improvement for fall prevention and present results of a feasibility study. The underlying principle of this biofeedback consists of providing supplementary information related to foot sole pressure distribution through a wireless embedded tongue-placed tactile output device. Twelve young healthy adults voluntarily participated in this experiment. They were asked to stand as immobile as possible with their eyes closed in two conditions of no-biofeedback and biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed reduced CoP displacements in the biofeedback relative to the no-biofeedback condition. On the whole, the present findings evidence the effectiveness of this system in improving postural control on young healthy adults. Further investigations are needed to strengthen the potential clinical value of this device.

Degradation of cervical joint position sense following muscular fatigue in humans.

Study Design. Before and after intervention trials. Objective. To investigate the effect of cervical muscular fatigue on joint position sense. Summary of Background Data. Although fatigue-related degradation of proprioceptive acuity at lower and upper limbs is well documented, to date no study has investigated whether muscular fatigue induced at the neck could modify joint position sense. Methods. A total of 9 young healthy adults were asked to perform the cervicocephalic relocation test to the neutral head position, that is, to relocate the head on the trunk, as accurately as possible, after full active cervical rotation to the left and right sides. This experimental task was executed in 2 conditions of No fatigue and Fatigue of the scapula elevator muscles. Absolute and variable errors were used to assess the cervical joint repositioning accuracy and consistency, respectively. Results. Less accurate and less consistent repositioning performances were observed in Fatigue relative to No fatigue condition, as indicated by increased absolute and variable errors, respectively. Conclusion. Results of the present experiment evidence that cervical joint position sense, assessed through the cervicocephalic relocation test to the neutral head position, is degraded by muscular fatigue.

The Effects of Scale Display of Visual Feedback on Postural Control During Quiet Standing in Healthy Elderly Subjects

OBJECTIVE To assess the effects of scale display of visual feedback (VFB) on postural control during quiet standing in healthy elderly subjects. DESIGN Before and after intervention trials. SETTING Medical university bioengineering laboratory. PARTICIPANTS Twelve healthy elderly subjects (mean age, 70.2+/-2.8 y; mean body weight, 65.5+/-4.1 kg; mean height, 163.4+/-6.5 cm). INTERVENTION Participants were asked to stand upright as immobile as possible in an eyes-open condition and 3 VFB conditions involving increasing scale displays: 2 to 1 (VFB(2)), 5 to 1 (VFB(5)), and 10 to 1 (VFB(10)). These latter conditions correspond to the ratio between the real displacements of the center of pressure (COP), as measured by the force platform, and their visualization on the monitor screen. MAIN OUTCOME MEASURE COP displacements were recorded using a force platform. RESULTS VFB had different effects on the COP displacements depending on the scale display; no significant difference was observed between the VFB(2) and the eyes-open conditions, whereas the VFB(5) and VFB(10) conditions yielded decreased COP displacements relative to the eyes-open condition. CONCLUSIONS The effectiveness of the VFB system in improving postural control during quiet standing in elderly subjects depends on the scale display. These findings could have implications in clinical and rehabilitative areas.

Cervical joint position sense is impaired in older adults

Background and aims: Although the role of afferent input from cervical muscles on the control of posture and locomotion is recognised, it is surprising that there is an absence of data reporting whether joint position sense at the cervical level is impaired in older healthy adults. The present experiment was designed to address this issue. Methods: Eighteen young (mean age= 23 yrs) and 18 older healthy adults (mean age= 68 yrs) were asked to perform the cervicocephalic relocation test (CRT) to the neutral head position (NHP), that is, to relocate the head on the trunk, as accurately as possible, after active cervical rotation to the left and right sides. Ten trials were performed for each rotation. Absolute and variable errors were used to assess cervical joint repositioning accuracy and consistency, respectively. Results: Less accurate and less consistent repositioning performances were observed in older adults than in young adults, as indicated by increased absolute and variable errors, respectively. Conclusions: The present findings show that cervical joint position sense, assessed through the CRT to the NHP, is impaired in older adults.

Effectiveness of an electro-tactile vestibular substitution system in improving upright postural control in unilateral vestibular-defective patients.

We investigated the effects of an electro-tactile vestibular substitution system (EVSS) on upright postural control in 12 unilateral vestibular-defective patients. The underlying principle of this system consists in supplying the user with additional information about his/her head orientation/motion with respect to gravitational vertical, normally provided by the vestibular system, through electro-tactile stimulation of his/her tongue. Subjects were asked to stand as immobile as possible with their eyes closed in two No-EVSS and EVSS conditions. Reduced centre-of-foot pressure displacements were observed in the EVSS relative to the No-EVSS condition. These results, demonstrating the effectiveness of the EVSS system in improving upright postural control in unilateral vestibular-defective patients, could have implications in clinical and rehabilitative areas.

How a plantar pressure-based, tongue-placed tactile biofeedback modifies postural control mechanisms during quiet standing

The purpose of the present study was to determine the effects of a plantar pressure-based, tongue-placed tactile biofeedback on postural control mechanisms during quiet standing. To this aim, 16 young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements, recorded using a force platform, were used to compute the horizontal displacements of the vertical projection of the centre of gravity (CoGv) and those of the difference between the CoP and the vertical projection of the CoG (CoP-CoGv). Analysis of the CoP-CoGv displacements showed larger root mean square (RMS) and mean power frequencies (MPF) in the Biofeedback than in the No-biofeedback condition. Stabilogram-diffusion analysis further showed a concomitant increased spatial and reduced temporal transition point co-ordinates at which the corrective processes were initiated and an increased persistent behaviour of the CoP-CoGv displacements over the short-term region. Analysis of the CoGv displacements showed decreased RMS and increased MPF in the Biofeedback relative to the No-biofeedback condition. Stabilogram-diffusion analysis further indicated that these effects mainly stem from reduced spatio-temporal transition point co-ordinates at which the corrective process involving CoGv displacements is initiated and an increased anti-persistent behaviour of the CoGv displacements over the long-term region. Altogether, the present findings suggest that the main way the plantar pressure-based, tongue-placed tactile biofeedback improves postural control during quiet standing is via both a reduction of the correction thresholds and an increased efficiency of the corrective mechanism involving the CoGv displacements.

Effects of Mirror Feedback on Upright Stance Control in Elderly Transfemoral Amputees

OBJECTIVE To investigate the effects of mirror feedback on upright stance control in elderly transfemoral amputees. DESIGN Before and after intervention trials. SETTING University medical bioengineering laboratory. PARTICIPANTS Elderly transfemoral amputees (N=12). INTERVENTIONS Participants were asked to stand upright, as immobile as possible, in 2 Eyes-open and Mirror-feedback experimental conditions. The latter experimental condition consisted of supplying the participants with their frontal reflection by positioning a mirror in front of them. MAIN OUTCOME MEASURES Weight-bearing symmetry and the displacements of the center of foot pressure under the nonaffected limb and the prosthetic limb. RESULTS Mirror feedback did not modify weight-bearing symmetry and had different effects on the center of foot pressure displacements under the nonaffected limb and prosthetic limb: a decreased center of foot pressure surface area was observed in the Mirror-feedback condition relative to the Eyes-open condition under the nonaffected limb, whereas no significant difference between the Eyes-open condition and the Mirror-feedback condition was observed under the prosthetic limb. CONCLUSIONS Results suggest that elderly transfemoral amputees were able to integrate augmented visual biofeedback through the use of mirror-reflected body image to improve their upright stance control. The present findings could have implications for clinical practice and rehabilitation.