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The present study was designed to assess time-of-day effects on postural balance and symptoms of rheumatoid arthritis (RA) patients. A total of 15 American College of Rheumatology functional class I and II RA patients and 15 healthy controls aged between 45 and 55 (mean age: 50  ±  3) years of age voluntarily participated. We conducted a case-control, repeated-measures in design study. Postural balance, axillary temperature, pain intensity, fatigue, and sleepiness were measured during five test sessions at 06:00, 10:00, 14:00, 18:00, and 22:00 h. Participants were randomized to the order of test sessions, and each session was separated by >36 hours to minimize/eliminate learning effects. Center of pressure area (CoP area) ( p < .001), pain ( p < .01), and sleepiness ( p < .05) values were significantly higher at 06:00 and 22:00 h compared to 10:00, 14:00, and 18:00 h in the RA group. Fatigue significantly increased ( p < .05) at 22:00 h in comparison to 10:00, 14:00, and 18:00 h in the RA group. Axillary temperature was significantly ( p < .001) lower at 06:00 and at 22:00 h compared to 10:00, 14:00, and 18:00 h in the RA group. In the control group, there were no significant time-of-day difference in fatigue, but axillary temperature was significantly lower ( p < .01) at 06:00 h compared to 10:00 h, 14:00, 18:00, and 22:00 h, sleepiness values were significantly higher ( p < .05) at 06:00 and 22:00 h compared to 10:00, 14:00, and 18:00 h, and revealed CoP area values were significantly ( p < .05) higher at 06:00 h compared to 14:00 h. Finally, in the RA group, significant correlations were found between values of CoP area and pain (r = 0.47; p < .001), sleepiness (r = 0.39; p < .01), fatigue (r = -0.46; p < .001), and also axillary temperature (r = -0.35; p < .001). Multiple linear regression analysis further indicated that in the RA group, time-of-day variation in postural balance was predicted collectively by that in pain and fatigue (30.7%) (R2 = 0.307; F = 11.53; p < .001). Our results first suggest that time-of-day significantly affects postural balance, axillary temperature, pain intensity, fatigue, and sleepiness in RA patients and second that the temporal variation observed in pain, fatigue, and somnolence are concomitant with that observed in postural balance. Abbreviations : RA: Rheumatoid arthritis; H&O questionnaire: Horne and Ostberg questionnaire; PSQI: Pittsburgh sleep quality index; HAQ: Health assessment questionnaire; SF-36: the short form-36; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index; CoP: The Center of foot Pressure; CoP area : The Center of foot Pressure area; VAS: The Visual Analogue Scale; KSS: Karolinska Sleepiness Scale.

Walking while using a mobile phone has been shown to affect the walking dynamics of young adults. However, this has only been investigated using treadmill walking at a fixed walking speed. In this study, the dynamics of over ground walking were investigated using lower trunk acceleration measured over 12 consecutive trials, following differing walking speed and mobile phone use instructions. Higher walking speed significantly increased the proportion of acceleration along the vertical measurement axis, while decreasing the proportion of acceleration along the anteroposterior axis (p < 0.001). Moreover, higher walking speed also resulted in increased sample entropy along all measurement axes (p < 0.05). When walking while texting, the maximum Lyapunov exponent increased along the anteroposterior and vertical measurement axes (p < 0.05), while sample entropy decreased significantly along the vertical axis (p < 0.001). Walking speed and mobile phone use both affect the walking dynamics of young adults. Walking while texting appears to produce a reduction in local dynamic stability and an increase in regularity, however, caution is required when interpreting the extent of this task effect, since walking speed also affected walking dynamics.

Introduction: The ability to adapt dynamic balance to perturbations during gait deteriorates with age. To prevent age-related decline in adaptive control of dynamic balance, we must first understand how adaptive control of dynamic balance changes across the adult lifespan. We examined how adaptive control of the margin of stability (MoS) changes across the lifespan during perturbed and unperturbed walking on the split-belt treadmill., Methods: Seventy-five healthy adults (age range, 18-80 yr) walked on an instrumented split-belt treadmill with and without split-belts. Linear regression analyses were performed for the mediolateral (ML) and anteroposterior (AP) MoS, step length, single support time, step width, double support time, and cadence during unperturbed and perturbed walking (split-belt perturbation), with age as predictor., Results: Age did not significantly affect dynamic balance during unperturbed walking. However, during perturbed walking, the ML MoS of the leg on the slow belt increased across the lifespan due to a decrease in bilateral single support time. The AP MoS did not change with aging despite a decrease in step length. Double support time decreased and cadence increased across the lifespan when adapting to split-belt walking. Age did not affect step width., Conclusions: Aging affects the adaptive control of dynamic balance during perturbed but not unperturbed treadmill walking with controlled walking speed. The ML MoS increased across the lifespan, whereas bilateral single support times decreased. The lack of aging effects on unperturbed walking suggests that participants' balance should be challenged to assess aging effects during gait. The decrease in double support time and increase in cadence suggests that older adults use the increased cadence as a balance control strategy during challenging locomotor tasks.

Purpose: To quantify how postural stability is modified during experimental pain while performing different cognitively demanding tasks., Methods: Sixteen healthy young adults participated in the experiment. Pain was induced by intramuscular injection of hypertonic saline solution (1 mL, 6%) in both vastus medialis and vastus lateralis muscles (0.9% isotonic saline was used as control). The participants stood barefoot in tandem position for 1 min on a force plate. Center of pressure (CoP) was recorded before and immediately after injections, while performing two cognitive tasks: (i) counting forwards by adding one; (ii) counting backwards by subtracting three. CoP variables-total area of displacement, velocity in anterior-posterior (AP-velocity) and medial-lateral (ML-velocity) directions, and CoP sample entropy in anterior-posterior and medial-lateral directions were displayed as the difference between the values obtained after and before each injection and compared between tasks and injections., Results: CoP total area ( - 84.5 ± 145.5 vs. 28.9 ± 78.5 cm 2 ) and ML-velocity ( - 1.71 ± 2.61 vs. 0.98 ± 1.93 cm/s) decreased after the painful injection vs. Control injection while counting forward (P < 0.05). CoP total area (12.8 ± 53.9 vs. - 84.5 ± 145.5 cm 2 ), ML-velocity ( - 0.34 ± 1.92 vs. - 1.71 ± 2.61 cm/s) and AP-velocity (1.07 ± 2.35 vs. - 0.39 ± 1.82 cm/s) increased while counting backwards vs. forwards after the painful injection (P < 0.05)., Conclusion: Pain interfered with postural stability according to the type of cognitive task performed, suggesting that pain may occupy cognitive resources, potentially resulting in poorer balance performance.

Horseback riding requires the ability to adapt to changes in balance conditions, to maintain equilibrium on the horse and to prevent falls. Postural adaptation involves specific sensorimotor processes integrating visual information and somesthesic information. The objective of this study was to examine this multisensorial integration on postural control, especially the use of visual and plantar information in static (stable) and dynamic (unstable) postures, among a group of expert horse rider women (n = 10) and a group of non-athlete women (n = 12). Postural control was evaluated through the center of pressure measured with a force platform on stable and unstable supports, with the eyes open and the eyes closed, and with the presence of foam on the support or not. Results showed that expert horse rider women had a better postural stability with unstable support in the mediolateral axis compared to non-athletes. Moreover, on the anteroposterior axis, expert horse riders were less visual dependent and more stable in the presence of foam. Results suggested that horseback riding could help developing particular proprioceptive abilities on standing posture as well as better postural muscle tone during particular bipodal dynamic perturbations. These outcomes provide new insights into horseback riding assets and methodological clues to assess the impact of sport practice., Competing Interests: The ‘Groupe Voltaire - Forestier sellier’ employed AO in October, 2017. However this company did not play any role in this study as it was conducted during AO’s post-doctorate at CIAMS laboratory from Université Paris-Sud (October, 2012, to October, 2017). This affiliation does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Assessing the amount of attention invested in the control of balance is crucial when evaluating balance abilities. The purpose of the present study was to examine the relevance of applying entropy to human center of foot pressure data to assess attention investment in balance control. To achieve this goal, young healthy adults were tested in a static postural task consisting in standing as immobile as possible with their eyes closed under normal, altered (foam) and improved (ankle-foot orthosis). The center of foot pressure displacements were recorded using a force platform. Three dependent variables were computed. Results showed decreased values of velocity and displacement of Center of Pressure (CoP), indicating a less important amount of postural sway, and increased values of Sample Entropy of CoP, suggesting a less amount of attention invested in the control of bipedal posture than when the somatosensation from the foot and the ankle was normal.

Many tests can crudely quantify age-related mobility decrease but instrumented versions of mobility tests could increase their specificity and sensitivity. The Timed-up-and-Go (TUG) test includes several elements that people use in daily life. The test has different transition phases: rise from a chair, walk, 180° turn, walk back, turn, and sit-down on a chair. For this reason the TUG is an often used test to evaluate in a standardized way possible decline in balance and walking ability due to age and or pathology. Using inertial sensors, qualitative information about the performance of the sub-phases can provide more specific information about a decline in balance and walking ability. The first aim of our study was to identify variables extracted from the instrumented timed-up-and-go (iTUG) that most effectively distinguished performance differences across age (age 18-75). Second, we determined the discriminative ability of those identified variables to classify a younger (age 18-45) and older age group (age 46-75). From healthy adults (n = 59), trunk accelerations and angular velocities were recorded during iTUG performance. iTUG phases were detected with wavelet-analysis. Using a Partial Least Square (PLS) model, from the 72-iTUG variables calculated across phases, those that explained most of the covariance between variables and age were extracted. Subsequently, a PLS-discriminant analysis (DA) assessed classification power of the identified iTUG variables to discriminate the age groups. 27 variables, related to turning, walking and the stand-to-sit movement explained 71% of the variation in age. The PLS-DA with these 27 variables showed a sensitivity and specificity of 90% and 85%. Based on this model, the iTUG can accurately distinguish young and older adults. Such data can serve as a reference for pathological aging with respect to a widely used mobility test. Mobility tests like the TUG supplemented with smart technology could be used in clinical practice.

Accelerometer-based assessments can identify elderly with an increased fall risk and monitor interventions. Smart devices, like the iPod Touch, with built-in accelerometers are promising for clinical gait and posture assessments due to easy use and cost-effectiveness. The aim of the present study was to establish the validity and reliability of the iPod Touch for gait and posture assessment. Sixty healthy participants (aged 18-75 years) were measured with an iPod Touch and stand-alone accelerometer while they walked under single- and dual-task conditions, and while standing in parallel and semi-tandem stance with eyes open, eyes closed and when performing a dual task. Cross-correlation values (CCV) showed high correspondence of anterior-posterior and medio-lateral signal patterns (CCV's ≥ 0.88). Validity of gait parameters (foot contacts, index of harmonicity, and amplitude variability) and standing posture parameters [root mean square of accelerations, median power frequency (MPF) and sway area] as indicated by intra-class correlation (ICC) was high (ICC = 0.85-0.99) and test-retest reliability was good (ICC = 0.81-0.97), except for MPF (ICC = 0.59-0.87). Overall, the iPod Touch obtained valid and reliable measures of gait and postural control in healthy adults of all ages under different conditions. Additionally, smart devices have the potential to be used for clinical gait and posture assessments.

Postural control is essential for most activities of daily living. The impairment of this function can be extremely disabling. This work was stimulated by the testimony of a bilateral partial foot amputee who describes his difficulty in maintaining balance while washing his hair in the shower. We postulated that if the postural control system could not rely on accurate and reliable somatosensory inputs from the foot and ankle, as is probably the case following bilateral foot amputation due to the loss of the foot afferents and efferents, the weight of visual and vestibular cues would increase. We therefore assessed if a vestibular-to-tactile sensory substitution device could compensate for this impairment. Two separate experiments were conducted. Experiment 1: The effect of a vestibular-to-tongue tactile biofeedback balance system on the postural stability of this amputee was tested (on a force platform) and compared with a non-amputated, matched control group. The results showed that use of the biofeedback reduced centre of foot (CoP) displacement in all subjects but more spectacularly in the amputee. Experiment 2: The effect of the biofeedback was tested in 16 young healthy adults following a protocol of ankle muscle fatigue (known to alter ankle neuromuscular function and to perturb the control of bipedal posture). The results showed a significant decrease in CoP displacement compared with the control, non-biofeedback condition and a significantly greater effect of the biofeedback in the fatigue than the non-fatigue condition. Taken together, the results of these two studies suggest that an individual with double partial foot amputation was able to improve his balance control thanks to the use of a vestibular-to-tongue tactile biofeedback balance system and that young healthy individuals were able to take advantage of it to reduce the postural destabilisation induced by plantar-flexor muscle fatigue. Further studies are however necessary to confirm this in larger numbers of impaired persons as well as to assess the effectiveness in dynamic situations.

The present study was designed to assess the effects of experimentally-induced plantar pain on the displacement of centre of foot pressure during unperturbed upright stance in different sensory conditions of availability and/or reliability of visual input and somatosensory input from the vestibular system and neck. To achieve this goal, fourteen young healthy adults were asked to stand as still as possible in three sensory conditions: (1) No-vision, (2) Vision, and (3) No-vision - Head tilted backward, during two experimental conditions: (1) a No-pain condition, and (2) a condition when a painful stimulation was applied to the plantar surfaces of both feet (Plantar-pain condition). Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) experimentally-induced plantar pain increased CoP displacements in the absence of vision (No-vision condition), (2) this deleterious effect was more accentuated when somatosensory information from the vestibular and neck was altered (No-vision - Head tilted backward condition) and (3) this deleterious effect was suppressed when visual information was available (Vision condition). From a fundamental point of view, these results lend support to the sensory re-weighting hypothesis whereby the central nervous system dynamically and selectively adjusts the relative contributions of sensory inputs (i.e. the sensory weightings) in order to maintain balance when one or more sensory channels are altered by the task (novel or challenging), environmental or individual conditions. From a clinical point of view, the present findings further suggest that prevention and treatment of plantar pain may be relevant for the preservation or improvement of balance control, particularly in situations (or individuals) in which information provided by the visual, neck proprioceptive and vestibular systems is unavailable or disrupted.

The present study investigated the effects of somatosensory conditions at the foot and ankle on postural responses to plantar-flexor muscle fatigue during bipedal quiet stance. Twenty-two young healthy adults were asked to stand upright as still as possible with their eyes closed in three somatosensory conditions (normal, altered and improved) both prior to and after exercises inducing plantar-flexor muscle fatigue. In the normal condition, the postural task was executed on a firm support surface constituted by the force platform. In the altered condition, a 2-cm thick foam support surface was placed under the subjects' feet. In the improved condition, increased cutaneous feedback at the foot and ankle was provided by strips of athletic tape applied across both their ankle joints. Muscle fatigue was induced in the plantar-flexor muscles of both legs through the execution of a repeated standing heel raise exercise. Centre of foot pressure displacements were recorded using a force platform. Results showed that plantar-flexor muscle fatigue yielded increased centre of foot pressure displacements under normal foot and ankle sensory conditions. Furthermore, this effect was exacerbated under altered foot and ankle sensory conditions and mitigated under improved foot and ankle sensory conditions. Altogether, the present findings suggested an increased reliance on somatosensory information from the foot and ankle for controlling upright posture in the presence of plantar-flexor muscle fatigue., (Copyright © 2011 Elsevier B.V. All rights reserved.)

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.

Few clinical studies have evaluated physiotherapeutic interventions in patients with degenerative cerebellar ataxia. Investigations on the effectiveness of biofeedback-based interventions for training postural control in these patients have not been conducted yet. The aim of the present study was to assess the effectiveness of a 2-week intensive tongue-placed electrotactile biofeedback program for patients with progressive cerebellar ataxia. Subjects were seven adult patients suffering from cerebellar degeneration. Postural control was assessed with static posturography in two sensory conditions eyes open/closed on firm surface. For quantification of postural behavior, we used area, sway path and mean velocity of the centre of foot pressure (CoP). Effects of treatment were determined by comparing Pre, Post and one month follow-up (Retention) experimental sessions. Analysis of measured CoP parameters for tests on firm surface showed a significant main effect of visual condition and no difference across test sessions under open eyes condition. Under eyes closed condition, there were significant differences between Pre versus Post and Pre versus Retention, while the difference Post versus Retention was not significant. Our results suggest that a balance rehabilitation program with postural exercise performed with a head position-based tongue-placed biofeedback system could significantly improve bipedal postural control in patients suffering from degenerative cerebellar ataxia.

This experiment was designed to investigate whether and how decreasing the amount of attentional focus invested in postural control could affect bipedal postural control. Twelve participants were asked to stand upright as immobile as possible on a force platform in one control condition and one cognitive condition. In the latter condition, they performed a short-term digit-span memory task. Decreased center-of-gravity displacements and decreased center-of-foot-pressure displacements minus center-of-gravity displacements were observed in the cognitive condition relative to the control condition. These results suggest that shifting the attentional focus away from postural control by executing a concurrent attention-demanding task could increase postural performance and postural efficiency.

The proprioceptive cues in the control of movement is recognized as playing a major role in postural control. However, little is known about its possible increased contribution to postural control consecutive to repetitive muscular activations. To test this, the short-term effects induced by a 1-legged exercise on 2-legged postural control with the eyes closed were assessed in healthy subjects. The center-of-pressure (CP) displacements obtained using a force platform were split into 2 elementary movements: center-of-gravity vertical projection (CGv) and the difference (CP - CGv). These movements assessed the net postural performance and the level of neuromuscular activity, respectively, and were processed afterward (a) through variances, mean velocity, and the average surface covered by the trajectories and (b) a fractional Brownian motion (fBm) modeling. The latter provides further information about how much the subject controls the movements and the spatiotemporal relation between the successive control mechanisms. No difference was found using the classical parameters. In contrast, fBm parameters showed statistically significant changes in postural control after 1-legged exercises: The spatial and temporal coordinates of the transition points for the CG movements along the anteroposterior axis are decreased. Because the body movement control does not rely on visual or vestibular cues, this ability to trigger the corrective process of the CG movements more quickly in the postexercise condition and once a more reduced distance has been covered emphasizes how prior muscular activation improves body movement detection. As a general rule, these data show that the motor systems control body motions better after repetitive stimulation of the sensory cues. These insights should be of interest in physical activities based on a precise muscular length control.

The present experiment was designed to assess the effect of active (deliberate) maintenance of a small forward (FL) or backward body lean (BL) (about 2° ankle flexion) with respect to the spontaneous direction of balance (or neutral posture, N) on postural balance. We questioned whether BL and FL stances, which impose a volitional proprioceptive control of the body-on-support angle, could efficiently reduce mediolateral displacements of the centre of pressure (CoP) induced by the visual motion of a room and darkness. Subjects (n = 15) were asked to stand upright quietly feet together while confronted to a large visual scene rolling to 10° on either side in peripheral vision (and surrounding vertical visual references in central vision) at 0.05 Hz. CoP displacements were recorded using a force platform. Analysis of medio-lateral CoP root-mean square showed that the effect of the moving room depends on the subject's postural stability performance in the eyes open N stance condition. Two significant postural behaviours emerged. (1) The most stable subjects (G1) were not affected by the conditions of altered vision, but swayed more in BL stance than in the N stance. (2) The unstable subjects (G2) exhibited (i) larger CoP displacements in altered visual conditions and a greater coupling of the CoP with the motion of the visual scene, (ii) enhanced visual dependency with postural leaning, and (iii) decreased CoP displacements when leaning forward in the eyes open motionless scene. Interestingly, the visual quotient positively correlated with the proprioceptive quotient, indicating that the more the subjects relied heavily on the visual frame of reference (FOR) the more they were influenced by body leaning. This result suggested hence a lesser ability to use efficiently body-ground proprioceptive cues. On the whole, the present findings indicate that body leaning could provide a useful mean to assess the subject's ability to use body-ground proprioceptive cues not only to improve postural stability during eyes opening (especially during forward leaning), but also as a mean to disclose subjects' visual dependency and their associated difficulties to shift from visual to proprioceptive-based FOR.

Background: Although impaired balance control during quiet standing has repeatedly been reported in persons suffering from foot pain, a better understanding of the effect of foot pain on unperturbed postural control is needed in order to propose and implement efficient podiatry treatments/interventions into clinical practice. The present study was hence designed to address this issue., Methods: Ten young healthy adults were asked to stand upright, eyes closed, as still as possible in three experimental conditions: (1) a no-pain condition, (2) a condition when a painful stimulation was applied to the plantar surfaces of both feet, and (3) a condition in which painful stimulation was applied to another body part, the palms of both hands. The centre of foot pressure displacements was recorded using a force platform., Findings: For the same perceived intensity of the pain, the severe painful stimulation applied to the plantar surfaces of both feet increased centre of foot pressure displacements, whereas the severe painful stimulation applied to the palms of both hands did not., Interpretation: These results reveal the deleterious effect of experimentally induced pain on the plantar soles on unperturbed bipedal postural control. At this point, it is conceivable that these effects of experimental pain could generalise to the effects of pain in patients. Accordingly, the present findings suggest that clinical and/or instrumental interventions designed to mitigate pain in patients suffering from plantar foot pain (e.g., podiatry treatments/interventions) could improve postural control., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Neck muscle vibration (NMV) during upright standing is known to induce forward leaning, which has been explained as a global response to the (illusory) perception of a lengthening of the dorsal neck muscles. However, the effects of NMV both at the level of individual joints and on whole-body postural coordination, and its potential modulation by vision, have not yet been analyzed in detail. Eight healthy young adult participants completed a total of ten trials each, with a 10-s period of unperturbed standing followed by a 10-s period of NMV. Participants were instructed to stand "as still as possible". This postural task was executed under two visual conditions: eyes open (EO) and eyes closed (EC). Postural responses were measured in terms of center of pressure (CoP) and center of mass (CoM) profiles, and whole-body kinematics. Responses to NMV at the level of individual body segments and joints were assessed by decomposing the time series into linear trends and residual fluctuations. Inter-segmental coordination was analyzed using a decorrelation technique, assessing motor-equivalent stabilization of four task-related variables: CoM position, trunk orientation, as well as head position and orientation. NMV induced a general forward leaning response under both visual conditions, visible in CoP, CoM, segment positions and orientations. Locally, NMV induced a pronounced extension of the atlanto-occipital joint. Residual fluctuations were higher with EC and unaffected by NMV. Coordination analysis showed that stabilization of different body parts was differentially affected by NMV. Head orientation was consistently stabilized across all conditions, with weaker coordination in the EC condition. In contrast, motor-equivalent stabilization of CoM and head position, and trunk orientation was only observed during no-vibration periods. Taken together, our results demonstrate specific effects of vision and proprioception on different aspects of local and global postural control. While perturbed neck proprioception seemed to affect the postural "set point" (inducing forward leaning), vision appeared to mainly serve in noise reduction (residual fluctuations) and control of head orientation.

Postural control is a highly automatized basic activity that requires limited attentional investments. These investments have been shown to increase from balancing experts to controls, and from controls to persons with impaired postural control. Such between-subject comparisons led to a proposed direct relation between the regularity of center-of-pressure (COP) fluctuations and the amount of attention invested in posture. This study aims to expand this relation to a within-subject comparison of conditions that differ in balance demands. Specifically, more regular COP fluctuations were expected for standing than sitting, as stimulus-response reaction-time studies showed that the required attentional demands are lower for sitting than standing. COP registrations were made for fifteen healthy young adults in seated and standing postures. COP regularity was quantified with sample entropy. As expected, COP fluctuations were found to be more regular for standing than sitting, as evidenced by significantly lower sample entropy values. These findings expand the relation between COP regularity and the amount of attention invested in posture to postural tasks that vary in balance demands. An assessment of COP regularity may thus not only be instrumental in the examination of attentional investment in posture in between-subject designs, but also for different postures in within-subjects designs., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The present study was designed to assess the relative contribution of each leg to unperturbed bipedal posture in lower limb amputees. To achieve this goal, eight unilateral traumatic trans-femoral amputees (TFA) were asked to stand as still as possible on a plantar pressure data acquisition system with their eyes closed. Four dependent variables were computed to describe the subject's postural behavior: (1) body weight distribution, (2) amplitude, (3) velocity and (4) regularity of centre of foot pressure (CoP) trajectories under the amputated (A) leg and the non-amputated (NA) leg. Results showed a larger body weight distribution applied to the NA leg than to the A leg and a more regular CoP profiles (lower sample entropy values) with greater amplitude and velocity under the NA leg than under the A leg. Taken together, these findings suggest that the NA leg and the A leg do not equally contribute to the control of unperturbed bipedal posture in TFA. The observation that TFA do actively control unperturbed bipedal posture with their NA leg could be viewed as an adaptive process to the loss of the lower leg afferents and efferents because of the unilateral lower-limb amputation. From a methodological point of view, these results demonstrate the suitability of computing bilateral CoP trajectories regularity for the assessment of lateralized postural control under pathological conditions.

We used unilateral plantar-flexor muscles fatigue to assess the capacity of the central nervous system to adapt quiet two-legged stance control to a unilateral ankle neuromuscular perturbation. Eighteen young healthy adults stood barefoot with their eyes closed and were asked to sway as little as possible. The Experimental group (n = 9) executed this postural task in two conditions, before (pre-test) and following the completion of a fatiguing exercise designed to induce a muscular fatigue in the plantar-flexor muscles of their dominant leg (post-test). For the Control group (n = 9), this fatiguing exercise was replaced with a standing rest period corresponding to the fatiguing exercise. Results of the Experimental group showed no significant difference between the weightbearing index measured in the pre-test condition and that observed in the post-test condition. Results further revealed that unilateral plantar-flexor muscles fatigue yielded different effects on the centre of foot pressure (CoP) displacements under the non-fatigued leg and under the fatigued leg: a wider surface area of the CoP displacements was observed under the non-fatigued than under the fatigued leg, and a higher mean speed of the CoP displacements was observed under the non-fatigued leg only in the post-test relative to the pre-test condition. These findings evidenced that the contribution of each leg to the control of quiet two-legged stance is modified as a result of muscle fatigue of unilateral plantar-flexor muscles. The greater contribution of the non-fatigued leg could be viewed as a fatigue-induced adaptive change in the control of quiet two-legged stance in response to an alteration of the unilateral ankle neuromuscular function induced by unilateral plantar-flexor muscles fatigue.

The aim of this study was to evaluate the effects of a session of plantar massage and joint mobilization of the feet and ankles on clinical balance performance in elderly people. A randomized, placebo-controlled, cross-over trial was used to examine the immediate effects of manual massage and mobilization of the feet and ankles. Twenty-eight subjects, aged from 65 to 95 years (78.8+/-8.5 years - mean+/-SD) were recruited from community nursing homes. Main outcome measures were the performances in three tests: One Leg Balance (OLB) test, Timed Up and Go (TUG) test and Lateral Reach (LR) test. Results demonstrated a significant improvement after massage and mobilization compared with placebo for the OLB test (1.1+/-1.7s versus 0.4+/-1.2s, p<0.01) and the TUG test (0.9+/-2.6s versus 0.2+/-1.2s, p<0.05). Conversely, performances in the LR test did not improve significantly. These results emphasise the positive impact of a single session of manual therapy applied to the feet and ankles on balance in elderly subjects.

We examined to which extent proprioceptive information involved in the perception of subjective vertical corresponded to mechanical mass-based axes of the body. Blindfolded subjects (n=14) estimated their subjective vertical in conditions of deviation of the centre of mass (CM) of (1) the head-trunk unit or (2) the head segment alone. Verticality estimates (provided in a haptic modality) were significantly altered by the deviation of the head-trunk CM (by either 4 degrees or 7 degrees), indicating that the subjects used mass-based proprioceptive information stemming from the trunk. Modifying the perception of body orientation by shifting the trunk CM sideways while keeping the body vertical, deviates the subjective vertical towards the opposite side in a similar way to the so-called 'E-effect'. The induced deviations of head CM (9.33 degrees) did not affect the subjective vertical, suggesting that when the balance of the body is not threatened, proprioceptive or vestibular information is prioritized to estimate gravitational direction.

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.

Although previous studies have investigated the effects of bilateral muscle fatigue on bipedal postural control, whether and how the central nervous system could adapt to unilateral muscle fatigue for controlling bipedal stance remains to be investigated. The purpose of the present experiment was designed to address this issue by assessing the effect of unilateral muscle fatigue induced on the hip's abductors of the dominant leg on bipedal standing. Twenty-four young healthy adults stood barefoot, feet together, with their eyes closed and were asked to sway as little as possible. The experimental group (n=12) executed this postural task in two conditions, pre- and post-fatigue. In the post-fatigue condition, the measurements were performed immediately after a designated fatiguing exercise for the hip abductors of their dominant leg. For the control group (n=12), this fatiguing exercise was replaced by a laying rest period corresponding to the fatiguing exercise. The distribution of the body weight and plantar centre of foot pressure (CoP) displacements from the non-fatigued and fatigued leg were recorded along the mediolateral and anteroposterior axes using a plantar pressure data acquisition system. Results of the experimental group showed that unilateral muscle fatigue induced on the hip's abductors of the dominant leg had different effects on the plantar CoP displacements (1) under the non-fatigued and fatigued legs, yielding larger displacements under the non-fatigued leg only, and (2) in the anteroposterior and mediolateral axes, yielding larger displacements along the mediolateral axis only. These observations could not be accounted for by any asymmetrical distribution of the body weight on both legs which were similar for both pre- and post-fatigue conditions. The observed postural responses could be viewed as an adaptive process to cope with an unilateral alteration in the hip neuromuscular function induced by the fatiguing exercise for controlling bipedal stance. The increase in CoP displacements observed under the non-fatigued leg in the fatigue condition could reflect enhanced exploratory "testing of the ground" movements with sensors of the non-fatigued leg's feet, providing supplementary somatosensory inputs to the central nervous system to preserve/facilitate postural control in condition of altered neuromuscular function of the dominant leg's hip abductors induced by the fatiguing exercise.

Background and Aims: Complex interactions between visual, vestibular and somatosensory information and the cerebellar system are involved in the maintenance of upright posture. Previous studies have shown that normal aging and pathologies may lead to deterioration of the control of upright standing posture., Methods: In order to investigate postural control during quiet standing in the elderly, the center of pressure (CoP) was analysed on two force platforms in three different groups. The first group was composed of 13 healthy older adults (O), the second consisted of 9 older adults with plantar sole deficit (OD), and the third (control) group was composed of 8 young healthy subjects (Y). All subjects were tested with eyes closed, before and after tactile plantar stimulation lasting ten minutes. Center of pressure displacements were analyzed in terms of sway area, mean velocity, and mean root mean square (RMS) along both mediolateral and antero-posterior axes., Results: Results showed that, before tactile plantar stimulation, the sway area and mean RMS were greater in O and OD subjects compared with Y ones. After tactile plantar stimulation, a decrease in the mean RMS was observed in OD subjects, this effect being significant only for the medio-lateral axis., Conclusions: These results suggest that application of tactile plantar stimulation may compensate a loss of superficial plantar sensitivity.

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.

Purpose: To investigate the effectiveness of a head position-based, tongue-placed biofeedback system in providing sensory supplementation to preserve head stability in space in the absence of visual information., Methods: Nine healthy young men with normal vision and no history of previous motor problems, neck injury, vertigo, neurologic disease, or vestibular impairment voluntarily participated in the experiment. They were asked to stand, their feet placed in a semitandem position, as immobile as possible in two conditions of No Vision and Vision and two conditions of No Biofeedback and Biofeedback. In the Biofeedback condition, subjects executed the postural task using a biofeedback system whose principle consisted of supplying them with additional information about their head orientation/motion with respect to gravitational vertical through electrotactile stimulation of the tongue. A system for the analysis of movement was used to record the head displacements., Results: Without the provision of the biofeedback (No Biofeedback condition), the No Vision condition yielded increased head displacements along the mediolateral axis compared with the Vision condition. Conversely, when biofeedback was available (Biofeedback condition), no significant difference between the No Vision and Vision conditions was observed., Conclusions: These results suggest that healthy young subjects were able to efficiently use head position-based, tongue-placed biofeedback to suppress the head instability induced by the suppression of vision. Hence the present findings demonstrate the effectiveness of a head position-based, tongue-placed biofeedback in providing sensory supplementation to preserve head stability in space in conditions of absent visual information.

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.

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.

Objectives: To assess the effects of the scaled display of visual foot center of pressure (COP) feedback on upright postural control under different somatosensory conditions at the foot and the ankle., Design: Before and after intervention trials., Setting: University medical bioengineering laboratory., Participants: Young healthy adults (N=8; mean age, 23+/-2.5 y; mean body weight, 76.8+/-11.2 kg; mean height, 179.8+/-6.8 cm)., Interventions: Participants were asked to stand upright, as immobile as possible, in 3 visual conditions: a stationary cross feedback (SC-FB) condition and 2 different foot COP feedback (COP-FB) conditions involving increasing scale displays of 2:1 (COP-FB2) and of 10:1 (COP-FB10). These latter conditions correspond to the ratio between the COP displacement on the screen and the actual COP displacement measured by the force platform. This postural task was executed on 2 (firm, foam) support surface conditions. In the foam condition, a 2-cm thick foam support surface was placed under the participants' feet to alter the quality and/or quantity of somatosensory information at the foot and the ankle., Main Outcome Measure: COP displacements were recorded using a force platform., Results: In the firm support surface condition, no significant difference was observed between the COP-FB2 and the SC-FB conditions, whereas the COP-FB10 condition yielded decreased COP displacements relative to the SC-FB condition. In the foam support surface condition, both the COP-FB2 and the COP-FB10 conditions yielded decreased COP displacements relative to the SC-FB condition, with a greater stabilizing effect in the COP-FB10 than COP-FB2 condition., Conclusions: The postural effects of the scale display of visual COP feedback differed depending on the somatosensory conditions at the foot and the ankle. These findings suggest that increased reliance on augmented sensory information for controlling upright posture in conditions of altered somatosensory input from the foot and ankle could have implications in clinical and rehabilitative areas.

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.

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.

The purpose of the present experiment was to investigate the effect of a therapeutic manipulation of the feet and ankles on postural control during quiet standing in elderly adults. Seventeen elderly adults stood barefeet on a force platform and were asked to sway as little as possible. Within a trial, vision was suppressed by eyes closure. The task was executed in two experimental sessions: before and after a therapeutic manipulation of the feet and ankles. Centre of feet pressure (COP) displacements along the mediolateral (ML) and anteroposterior (AP) axes were recorded. For the two experimental sessions, subjects exhibited comparable COP displacements when vision was available and were similarly affected by the suppression of vision. However, when subjects had to adapt to the absence of vision within a 10s temporal frame, postural behaviour became different in the two experimental sessions: the sum of the ML and AP COP displacements increased within the 10s temporal frame before the therapeutic manipulation of the feet and ankles, whereas it remained unchanged after it. These results suggested that the therapeutic manipulation of the feet and ankles allows the elderly adults to partially compensate for the destabilising effect induced by the suppression of vision.

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.

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.

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 subject's 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.

Background: The purpose of this study was to investigate the effects of trunk extensor muscles fatigue on undisturbed postural control in young healthy adults., Methods: Fifteen university students were asked to stand upright as immobile as possible with their eyes closed in two conditions of Fatigue and No fatigue of the trunk extensor muscles. Muscular fatigue was achieved by performing trunk repetitive extensions until maximal exhaustion. Centre of foot pressure displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity and those of the difference between the centre of pressure and those of the difference between the centre of pressure and the vertical projection of the centre of gravity. These motions were processed through space-time and frequency domain analyses., Findings: Larger centre of pressure minus centre of gravity and centre of gravity motions in the Fatigue than No fatigue condition are observed along both the medio-lateral and antero-posterior axes, this effect being more accentuated along the antero-posterior axis., Interpretation: The present findings suggest that trunk extensor muscles fatigue deteriorates undisturbed stance control, yielding, along the antero-posterior axis mainly, (1) a greater neuromuscular requirements for ensuring standing control, as indicated by the increased centre of pressure minus centre of gravity motions, and (2) a deterioration of postural performance, as indicated by the increased centre of gravity motions.

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.

Objective: To evaluate whether performing cognitive tasks while exercising influenced the effects of an exercise program designed to reduce the risk of falling in elderly women with osteoporosis., Methods: We included 68 osteoporotic women older than 70 years of age (mean age, 73.5 years+/-1.6) who followed a program of 12 sessions of balance, coordination, and ambulation exercises designed to lessen the risk of falling. The patients were divided into two groups based on proximity to the study centers. The groups were randomly allocated to the exercise program alone (N=31, single-task group) or to the same program combined with cognitive tasks performed while exercising (N=37, dual-task group). Timed up-and-go tests and one-leg balance (OLB) tests were done at baseline, at the end of the exercise program, and 3 months after the end of the exercise program., Results: In both groups, the exercise program produced significant improvements in up-and-go and OLB times. Additional improvements occurred over the first 3 months following the program. Adding cognitive exercises did not provide added efficacy., Conclusions: Balance was improved after the exercise sessions. The improvements were clinically significant and increased over time.

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.

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.

The purpose of the present experiment was to investigate whether and how the head extended posture, commonly encountered in many routine activities, affects undisturbed upright stance control mechanisms in humans. Sixteen young healthy adults stood feet together, with their eyes closed and were asked to sway as little as possible in two Neutral and Extended head conditions. Centre of pressure (CP) displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference CP - CG(v). A time-domain analysis shows increased mean velocity and surface covered by the trajectory of both elementary motions in the Extended head condition. A frequency analysis also reveals increased root mean squares on the CP - CG(v) motions, suggesting increased muscular activity in the Extended head condition. Furthermore, similar changes occur on CG(v) motions. Finally, modelling these trajectories as a fractional Brownian motion process demonstrates increased spatial transition point co-ordinates at which the corrective process is initiated and a more deterministic control mechanism in this corrective process involving CG(v) motions in the Extended head position. Together, the present findings suggest that head extension position yields a reorganisation of the control mechanisms for maintaining undisturbed upright stance.

Objective: To investigate the effect of mirror feedback on postural control during quiet standing in elderly adults., Design: Before and after intervention trials., Setting: Pneumology center in France., Participants: Eleven elderly adults (mean age, 70.7+/-4.6 y; mean body weight, 64.5+/-15.0 kg; mean height, 161.4+/-12.0 cm)., Interventions: Participants were asked to stand upright, as immobile as possible, in 2 eyes-open and mirror-feedback conditions. The latter experimental condition consisted of supplying the subjects with their frontal reflection by positioning a mirror in front of them., Main Outcome Measures: Foot center of pressure (COP) displacements in the mediolateral (ML) and anteroposterior (AP) directions were recorded using a force platform., Results: The mirror-feedback condition had different effects on postural sway, depending on the direction: range, variability, and maximal instantaneous speed of the COP displacements decreased in the ML direction, whereas these effects remained unchanged in the AP direction., Conclusions: This study provided evidence that mirror feedback may put elderly adults at lower risk of falling.

Separate studies have demonstrated that vibration and fatigue of ankle muscles alter postural control. The purpose of the present experiment was to investigate the effect of ankle muscle vibration on the regulation of postural sway in bipedal stance following ankle muscle fatigue. Center of foot pressure displacements were recorded using a force platform. Results showed a similar increase in postural sway under muscle fatigue as well as under muscle vibration. Interestingly, under muscle fatigue muscle vibration did not induce a further increase in postural sway. Two hypotheses could, at least, account for this observation: (1). fatigued muscles are less sensitive to muscle vibration and (2). the central nervous system relies less upon proprioceptive information originating from fatigued muscles for regulating postural sway.

Objective To investigate if attention to additional sensory information from the fingertip can improve postural stability during pain, which is known to impair balance. Methods In 16 healthy volunteers, experimental pain was induced by intramuscular injection of hypertonic saline in the right vastus medialis muscle (isotonic saline used as nonpainful control, intramuscular injection in the same location). Pain intensity was assessed on an 11-point numeric rating scale (NRS; 0 representing "no pain" and 10 "maximum pain"). Subjects were asked to stand as still as possible on a force plate for 40 seconds with their eyes closed. Their postural stability was quantified by the area and velocity of center of pressure (CoP) displacement. The CoP was recorded with and without pain during two different conditions: 1) no touch and 2) the subjects were asked to lightly touch a curtain with their right index finger and focus their attention on keeping it as still as possible. Results Hypertonic injections induced higher NRS scores compared with control injections (P  < 0.05). During the hypertonic injection condition, the CoP area and velocity in both directions increased during no touch compared with the light touch condition (P  < 0.05). No differences were found during light touch between the hypertonic and isotonic injection conditions. Although experimental knee-related pain impaired postural stability, lightly touching a curtain with the fingertip decreased postural sway during painful conditions. Conclusions Providing additional sensory information while pain patients are performing balance exercises may improve postural stability and increase the quality of exercise, consequent rehabilitation protocols, and clinical outcomes. [ABSTRACT FROM AUTHOR]

Assessment of joint functional and proprioceptive abilities is essential for balance, posture, and motor control rehabilitation. Joint functional ability refers to the capacity of movement of the joint. It may be evaluated thereby measuring the joint range of motion (ROM). Proprioception can be defined as the perception of the position and of the movement of various body parts in space. Its role is essential in sensorimotor control for movement acuity, joint stability, coordination, and balance. Its clinical evaluation is commonly based on the assessment of the joint position sense (JPS). Both ROM and JPS measurements require estimating angles through goniometer, scoliometer, laser-pointer, and bubble or digital inclinometer. With the arrival of Smartphones, these costly clinical tools tend to be replaced. Beyond evaluation, maintaining and/or improving joint functional and proprioceptive abilities by training with physical therapy is important for long-term management. This review aims to report Smartphone applications used formeasuring and improving functional and proprioceptive abilities. It identifies that Smartphone applications are reliable for clinical measurements and are mainly used to assess ROM and JPS. However, there is lack of studies on Smartphone applications which can be used in an autonomous way to provide physical therapy exercises at home. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]