Controlling posture using a plantar pressure-based,tongue-placed tactile biofeedback system

The present paper introduces an original biofeedback system for improving human balance control, whose underlying principle consists in providing additional sensory information related to foot sole pressure distribution to the user through a tongue-placed tactile output device. To assess the effect of this biofeedback system on postural control during quiet standing, ten 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. Results showed reduced CoP displacements in the Biofeedback relative to the No-biofeedback condition. The present findings evidenced the ability of the central nervous system to efficiently integrate an artificial plantar-based, tongue-placed tactile biofeedback for controlling control posture during quiet standing.     

Can a plantar pressure–based tongue-placed electrotactile biofeedback improve postural control under altered vestibular and neck proprioceptive conditions?

We investigated the effects of a plantar pressure-based tongue-placed electrotactile biofeedback on postural control during quiet standing under normal and altered vestibular and neck proprioceptive conditions. To achieve this goal, 14 young healthy adults were asked to stand upright as immobile as possible with their eyes closed in two Neutral and Extended head postures and two conditions of No-biofeedback and Biofeedback. The underlying principle of the biofeedback consisted of providing supplementary information related to foot sole pressure distribution through a wireless embedded tongue-placed tactile output device. Center of foot pressure (CoP) displacements were recorded using a plantar pressure data acquisition system. Results showed that (1) the Extended head posture yielded increased CoP displacements relative to the Neutral head posture in the No-biofeedback condition, with a greater effect along the anteroposterior than mediolateral axis, whereas (2) no significant difference between the two Neutral and Extended head postures was observed in the Biofeedback condition. The present findings suggested that the availability of the plantar pressure-based tongue-placed electrotactile biofeedback allowed the subjects to suppress the destabilizing effect induced by the disruption of vestibular and neck proprioceptive inputs associated with the head extended posture. These results are discussed according to the sensory re-weighting hypothesis, whereby the CNS would dynamically and selectively adjust the relative contributions of sensory inputs (i.e. the sensory weights) to maintain upright stance depending on the sensory contexts and the neuromuscular constraints acting on the subject.     

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 (CoG _v ) and those of the difference between the CoP and the vertical projection of the CoG (CoP-CoG _v ). Analysis of the CoP-CoG _v 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-CoG _v displacements over the short-term region. Analysis of the CoG _v 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 CoG _v displacements is initiated and an increased anti-persistent behaviour of the CoG _v 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 CoG _v displacements.     

Sensory supplementation system based on electrotactile tongue biofeedback of head position for balance control

The present study aimed at investigating the effects of an artificial head position-based tongue-placed electrotactile biofeedback on postural control during quiet standing under different somatosensory conditions from the support surface. Eight young healthy adults were asked to stand as immobile as possible with their eyes closed on two Firm and Foam support surface conditions executed in two conditions of No-biofeedback and Biofeedback. In the Foam condition, a 6-cm thick foam support surface was placed under the subjects’ feet to alter the quality and/or quantity of somatosensory information at the plantar sole and the ankle. The underlying principle of the biofeedback consisted of providing supplementary information about the head orientation with respect to gravitational vertical through electrical stimulation of the tongue. Centre of foot pressure (CoP) displacements were recorded using a force platform. Larger CoP displacements were observed in the Foam than Firm conditions in the two conditions of No-biofeedback and Biofeedback. Interestingly, this destabilizing effect was less accentuated in the Biofeedback than No-biofeedback condition. In accordance with the sensory re-weighting hypothesis for balance control, the present findings evidence that the availability of the central nervous system to integrate an artificial head orientation information delivered through electrical stimulation of the tongue to limit the postural perturbation induced by alteration of somatosensory input from the support surface.     

Sensory supplementation system based on electrotactile tongue biofeedback of head position for balance control

The present study aimed at investigating the effects of an artificial head position-based tongue-placed electrotactile biofeedback on postural control during quiet standing under different somatosensory conditions from the support surface. Eight young healthy adults were asked to stand as immobile as possible with their eyes closed on two Firm and Foam support surface conditions executed in two conditions of No-biofeedback and Biofeedback. In the Foam condition, a 6-cm thick foam support surface was placed under the subjects' feet to alter the quality and/or quantity of somatosensory information at the plantar sole and the ankle. The underlying principle of the biofeedback consisted of providing supplementary information about the head orientation with respect to gravitational vertical through electrical stimulation of the tongue. Centre of foot pressure (CoP) displacements were recorded using a force platform. Larger CoP displacements were observed in the Foam than Firm conditions in the two conditions of No-biofeedback and Biofeedback. Interestingly, this destabilizing effect was less accentuated in the Biofeedback than No-biofeedback condition. In accordance with the sensory re-weighting hypothesis for balance control, the present findings evidence that the availability of the central nervous system to integrate an artificial head orientation information delivered through electrical stimulation of the tongue to limit the postural perturbation induced by alteration of somatosensory input from the support surface.     

Head position-based electrotactile tongue biofeedback affects postural responses to Achilles tendon vibration in humans

The purpose of the present experiment was to investigate whether postural responses to ankle proprioceptive perturbation Achilles tendon vibration were affected by the availability of augmented sensory information about head orientation/motion with respect to gravitational vertical, i.e., normally provided by the vestibular system. To achieve this goal, ten standing subjects were exposed to Achilles tendon vibration in two No Biofeedback and Biofeedback conditions. The No Biofeedback condition served as a control condition. In the Biofeedback condition, subjects performed the postural task using a head position-based electrotactile tongue-placed biofeedback system. Center of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) Achilles tendon vibration increased CoP displacements in the No Biofeedback condition and (2) this destabilizing effect was less accentuated in the Biofeedback condition. These results are consistent with and discussed in terms of sensory re-weighting mechanisms involved in postural control. In the condition of Achilles tendon vibration, which renders ankle proprioceptive information less reliable for controlling posture, the central nervous system was able to integrate alternatively available augmented sensory information suitable and usable in upright postural control to reduce the destabilizing effect of the ankle proprioceptive perturbation.     

Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle

Whereas the acuity of the position sense at the ankle can be disturbed by muscle fatigue, it recently also has been shown to be improved, under normal ankle neuromuscular state, through the use of an artificial tongue-placed tactile biofeedback. The underlying principle of this biofeedback consisted of supplying individuals with supplementary information about the position of their matching ankle position relative to their reference ankle position through electrotactile stimulation of the tongue. Within this context, the purpose of the present experiment was to investigate whether this biofeedback could mitigate the deleterious effect of muscle fatigue on joint position sense at the ankle. To address this objective, sixteen young healthy university students were asked to perform an active ankle-matching task in two conditions of No-fatigue and Fatigue of the ankle muscles and two conditions of No-biofeedback and Biofeedback. Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed that the availability of the biofeedback allowed the subjects to suppress the deleterious effects of muscle fatigue on joint position sense at the ankle. In the context of sensory re-weighting process, these findings suggested that the central nervous system was able to integrate and increase the relative contribution of the artificial tongue-placed tactile biofeedback to compensate for a proprioceptive degradation at the ankle.     

Reduced postural sway during quiet standing by light touch is due to finger tactile feedback but not mechanical support

It is well known that a light and voluntary touch with a fingertip on a fixed surface improves postural stability during quiet standing. To determine whether the effect of the light touch is due to the tactile sensory input, as opposed to mechanical support, we investigated the light touch effect on postural stability during quiet standing with and without somatosensory input from the fingertip. Seven young subjects maintained quiet standing on a force platform with (LT) and without (NT) lightly touching a fixed surface, and with (TIS) and without (CON) the application of tourniquet ischemia, which removed the tactile sensation from the fingertip. The mean velocity of centre of pressure (CoP) was calculated to assess the postural sway in each condition. The mean velocity of CoP was significantly smaller in the LT condition compared to the NT condition only under the CON condition, whereas the light touch effect was not significant under the TIS condition. We found that the reduction of the horizontal ground reaction force due to the light touch was about 20%, which was approximately equivalent to the reduction of mean velocity of CoP in the LT condition compared to the NT condition. Since the fingertip contact force was relatively large compared to the horizontal ground reaction force, one could say that the light touch effect might be due to the mechanical support provided by the contact itself. However, we demonstrated experimentally that light touch effects were diminished due to loss of finger tactile feedback induced by the tourniquet ischemia, but not due to the mechanical support provided by the light touch. One possible reason is the lack of feedback information in controlling posture, and the other is the altered control of the arm induced by the loss of tactile feedback.     

Differential integration of kinaesthetic signals to postural control

The purpose of the present experiment was to identify whether non-visual sensory cues involved in the maintenance of balance control could be weighted differently from one subject to another in condition during which kinaesthetic signals, stemming from the ankle proprioceptors and plantar pressure somatosensory sensors, were altered. A large population of blindfolded healthy young university students (n = 140) were asked to sway as little as possible on: (1) a firm support (Firm condition) and (2) an unstable support used to impair the exploitation of the kinematic ankle proprioceptive and plantar pressure somatosensation (Foam condition). Centre of foot pressure (CoP) displacements were recorded using a force platform. Analyses of the surface area, range, and mean velocity of the CoP displacements showed significant negative correlations between the postural sway observed in the Firm condition and the increase in postural sway observed in the Foam condition. In other words, the alteration of ankle proprioception had a greater destabilising effect in subjects exhibiting the smallest CoP displacements when standing in a normal proprioception condition. The present findings suggest that the exploitation of the kinaesthetic relationships to postural control varied from one subject to another, hence evidencing the need to introduce differential approach to assess the general impact of preferential modes of spatial referencing in postural control.     

Re-weighting of somatosensory inputs from the foot and the ankle for controlling posture during quiet standing following trunk extensor muscles fatigue

The present study focused on the effects of trunk extensor muscles fatigue on postural control during quiet standing under different somatosensory conditions from the foot and the ankle. With this aim, 20 young healthy adults were asked to stand as immobile as possible in two conditions of No fatigue and Fatigue of trunk extensor muscles. In Experiment 1 (n = 10), somatosensation from the foot and the ankle was degraded by standing on a foam surface. In Experiment 2 (n = 10), somatosensation from the foot and ankle was facilitated through the increased cutaneous feedback at the foot and ankle provided by strips of athletic tape applied across both ankle joints. The centre of foot pressure displacements (CoP) were recorded using a force platform. The results showed that (1) trunk extensor muscles fatigue increased CoP displacements under normal somatosensatory conditions (Experiment 1 and Experiment 2), (2) this destabilizing effect was exacerbated when somatosensation from the foot and the ankle was degraded (Experiment 1), and (3) this destabilizing effect was mitigated when somatosensation from the foot and the ankle was facilitated (Experiment 2). Altogether, the present findings evidenced re-weighting of sensory cues for controlling posture during quiet standing following trunk extensor muscles fatigue by increasing the reliance on the somatosensory inputs from the foot and the ankle. This could have implications in clinical and rehabilitative areas.     

Improving human ankle joint position sense using an artificial tongue-placed tactile biofeedback

Proprioception is comprised of sensory input from several sources including muscle spindles, joint capsule, ligaments and skin. The purpose of the present experiment was to investigate whether the central nervous system was able to integrate an artificial biofeedback delivered through electrotactile stimulation of the tongue to improve proprioceptive acuity at the ankle joint. To address this objective, nine young healthy adults were asked to perform an active ankle-matching task with and without biofeedback. The underlying principle of the biofeedback consisted of supplying subjects with supplementary information about the position of their matching ankle position relative to their reference ankle position through a tongue-placed tactile output device (Tongue Display Unit). Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed more accurate and more consistent matching performances with than without biofeedback, as indicated by decreased absolute and variable errors, respectively. These findings suggested that the central nervous system was able to take advantage of an artificial tongue-placed tactile biofeedback to improve the position sense at the ankle joint.     

Vestibular and neck somatosensory weighting changes with trunk extensor muscle fatigue during quiet standing

The purpose of this study was to investigate whether vestibular and neck somatosensory weighting could change in conditions of trunk extensor muscle fatigue during quiet standing. To achieve this goal, 20 young healthy adults were asked to stand as still as possible in two conditions of No fatigue and Fatigue of trunk extensor muscles. In Experiment 1 (n = 10), the postural task was executed in two head conditions: Neutral and Head tilted backwards, recognised to degrade vestibular and neck somatosensory information. In Experiment 2 (n = 10), the postural task was executed in two stimulation conditions: No tactile stimulation and Tactile stimulation of the neck provided by the application of strips of adhesive bandage to the skin over and around the neck. The centre of foot pressure displacements (CoP) were recorded using a force platform. Results showed that (1) trunk extensor muscles fatigue increased CoP displacements under normal vestibular and neck somatosensatory conditions (Experiments 1 and 2), (2) this destabilizing effect of fatigue was exacerbated when vestibular and neck somatosensory information was altered (Experiment 1) and (3) this destabilizing effect of fatigue was suppressed when neck somatosensory information was neck was facilitated (Experiment 2). Taken together, results of Experiments 1 and 2 could be interpreted as an up-weighting of vestibular and neck somatosensory information for controlling posture during quiet standing following trunk extensor muscles fatigue.     

Postural destabilization induced by trunk extensor muscles fatigue is suppressed by use of a plantar pressure-based electro-tactile biofeedback

Separate studies have reported that postural control during quiet standing could be (1) impaired with muscle fatigue localized at the lower back, and (2) improved through the use of plantar pressure-based electro-tactile biofeedback, under normal neuromuscular state. The aim of this experiment was to investigate whether this biofeedback could reduce postural destabilization induced by trunk extensor muscles. Ten healthy adults were asked to stand as immobile as possible in four experimental conditions: (1) no fatigue/no biofeedback, (2) no fatigue/biofeedback, (3) fatigue/no biofeedback and (4) fatigue/biofeedback. Muscular fatigue was achieved by performing trunk repetitive extensions until maximal exhaustion. The underlying principle of the biofeedback consisted of providing supplementary information related to foot sole pressure distribution through electro-tactile stimulation of the tongue. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed (1) increased CoP displacements along the antero-posterior axis in the fatigue than no fatigue condition in the absence of biofeedback and (2) no significant difference between the no fatigue and fatigue conditions in the presence of biofeedback. This suggests that subjects were able to efficiently integrate an artificial plantar pressure information delivered through electro-tactile stimulation of the tongue that allowed them to suppress the destabilizing effect induced by trunk extensor muscles fatigue.     

Attentional demands associated with the use of a light fingertip touch for postural control during quiet standing

The purpose of the present experiment was to investigate whether and how using a light fingertip touch for postural control during quiet standing requires additional attentional demands. Nine young healthy university students were asked to respond as rapidly as possible to an unpredictable auditory stimulus while maintaining stable seated and upright postures in three sensory conditions: vision, no-vision and no-vision/touch. Touch condition involved a gentle light touch with the right index finger on a nearby surface at waist height. Center of foot pressure (CoP) displacements were recorded using a force platform. Reaction times (RTs) values were used as an index of the attentional demand necessary for calibrating the postural system. Results showed decreased CoP displacements in both the vision and no-vision/touch conditions relative to the no-vision condition. More interestingly, a longer RT in the no-vision/touch than in the vision and no-vision conditions was observed. The present findings suggest that the ability to use a light fingertip touch as a source of sensory information to improve postural control during quiet standing is attention demanding.     

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.     

The effects of unilateral medial arch support stimulation on plantar pressure and center of pressure adjustment in young gymnasts

The purpose of this study was to examine the contribution of tactile afferents from the medial arch of the foot on postural control. The center of pressure (CoP) position and right/left plantar pressure distributions of 13 gymnasts, with and without a medial arch support, were recorded by a force platform coupled with a baropedometry analysis. Stimulation of the subject's plantar sole was accomplished using a 3 mm thick medial arch insert. Right arch stimulation induced an ipsilateral increase of plantar pressure and a contralateral displacement of the CoP to the left. Left arch support also resulted in an ipsilateral increase in plantar pressure and displacement of the CoP to the right. Stimulation of the plantar arch may induce a perception that the body's center of mass has shifted toward the stimulated foot. To maintain stability, individuals may then shift their CoP in the opposite direction. This response may involve compensatory muscle activation strategies to adjust posture. Clinicians may apply these results in their use of foot orthoses to address postural anomalies in patients.     

Light touch contribution to balance in normal bipedal stance

 It has previously been shown that light contact with the finger tip on a fixed surface reduces centre of pressure (CoP) fluctuations in the frontal plane when standing in an unstable posture with the feet in line (tandem Romberg stance). Positive cross-correlations between horizontal finger forces and CoP fluctuations with finger forces exhibiting a phase lead suggest the hand provides sensory input for postural stability. The present study investigates whether this is the case for normal posture. We report reduced CoP fluctuations in the sagittal plane when light touch is permitted during normal bipedal stance. Moreover, we find positive crosscorrelations between finger tip forces and CoP fluctuations which are of similar magnitude and phase lag to those observed in tandem Romberg stance. This shows the utility of hand touch input for regulation of normal upright posture as well as inherently unstable postures such as tandem Romberg. Received: 24 November 1997 / Accepted: 20 December 1998     

Postural control during quiet standing following cervical muscular fatigue: effects of changes in sensory inputs

The purpose of the present experiment was to investigate the effects of cervical muscular fatigue on postural control during quiet standing under different conditions of reliability and/or availability of somatosensory inputs from the plantar soles and the ankles and visual information. To this aim, 14 young healthy adults were asked to sway as little as possible in three sensory conditions (No vision, No vision-Foam support and Vision) executed in two conditions of No fatigue and Fatigue of the scapula elevator muscles. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) the cervical muscular fatigue yielded increased CoP displacements in the absence of vision, (2) this effect was more accentuated when somatosensation was degraded by standing on a foam surface and (3) the availability of vision allowed the individuals to suppress this destabilising effect. On the whole, these findings not only stress the importance of intact cervical neuromuscular function on postural control during quiet standing, but also suggest a reweigthing of sensory cues in balance control following cervical muscular fatigue by increasing the reliance on the somatosensory inputs from the plantar soles and the ankles and visual information.     

Control of bipedal posture following localised muscle fatigue of the plantar-flexors and finger-flexors

The present experiment investigated the control of bipedal posture following localised muscle fatigue of the plantar-flexors and finger-flexors. Twelve young healthy adults voluntarily participated in this study. They were asked to stand upright as still as possible with their eyes closed in two randomly ordered experimental sessions. Each session consisted of pre- and post-fatigue bipedal static postural control measurements immediately before and after a designated fatiguing protocol for plantar-flexor and finger-flexor muscles. Centre of foot pressure (CoP) displacements were recorded using a force platform. The results showed that the postural effects of localised muscle fatigue differed between the muscles targeted by the fatiguing procedures. Indeed, localised muscle fatigue of the plantar-flexors yielded increased CoP displacements, whereas localised muscle fatigue of the finger-flexors had no significant effect on the CoP displacements. In other words, fatigue localised to muscles which are involved in the performance of the postural task (plantar-flexors) degraded postural control, whereas fatigue localised to muscles which are not involved in the performance of the postural task did not. Taken together, the present findings support the recent conclusions that the effects of localised muscle fatigue on upright postural control is joint- and/or muscle-specific, and suggest that localised muscles fatigue of the plantar-flexors could mainly affect bipedal postural control via sensorimotor rather than cognitive processes.     

Posture, Place, and Mood Effects on Ambulatory Blood Pressure

Ambulatory blood pressure was studied as a function of posture, place, and mood in 131 subjects classified according to race, gender, and hypertensive status. The effect of posture was significant and explained a substantial proportion of within-subject variability. After controlling for posture, significant place and mood effects were observed when subjects were sitting but not when they were standing. Home vs. work differences in both systolic and diastolic blood pressure were significantly greater in Whites than in Blacks. Similar differences in systolic blood pressure were greater in mild hypertensive than in normotensive subjects. The results of this study underscore the need to control for effects of posture when interpreting ambulatory blood pressure readings.