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We explored whether ankle torque variability or plantar perceptual threshold explains human balance control more effectively. We hypothesized that ankle torque variance is a better indicator of center of pressure (COP) velocity variance than plantar perceptual sensitivity. Two conditions were tested: loaded (23-kg vest added) and unloaded, as loading should diminish plantar sensitivity and increase COP velocity variability. We created a linear feedback model to assess the noise change in the sensorimotor loop induced by loading. Plantar sensitivity was quantified using a psychophysical approach while participants stood barefoot. A linear motor applied a force impulse on the participant's heel. A "yes-no" method of limits was selected to identify plantar sole sensory thresholds in both conditions. We observed reduced plantar sensitivity in loaded compared with unloaded conditions. In the loaded condition, participants exhibited greater COP velocity variance, with significant positive Pearson's correlations confirming a substantial association between ankle torque and COP velocity variances for both loaded [variance accounted for (VAF): r2 = 44.56%, P = 0.018] and unloaded conditions (VAF: r2 = 58.83%, P = 0.004). No significant correlation existed between COP velocity variance and plantar sensitivity threshold for both loaded (VAF: r2 = 0.002%, P = 0.99) and unloaded conditions (VAF: r2 = 21.81%, P = 0.35). The model confirmed an ∼88% rise in sensorimotor loop noise in the loaded condition. Ankle torque variance assesses the precision of nonperceptual and perceptual detection mechanisms in evaluating whole body motions and the accuracy in converting sensory cues into ankle torque. NEW & NOTEWORTHY: Plantar cutaneous information contributes to balance control by modulating motor commands, but plantar perceptual sensitivity is a suboptimal indicator of balance performance. Multiple sensory cues encode whole body dynamics, guiding sensorimotor mechanisms to minimize body sway variability. Ankle torque variance is proposed as a superior measure for explaining balance control performance and evaluating the sensorimotor loop's functioning in balance control. [ABSTRACT FROM AUTHOR]

This work identifies, among adolescents with idiopathic scoliosis, those demonstrating impaired sensorimotor control through a classification procedure comparing the amplitude of their vestibular-evoked postural responses. The sensorimotor control of healthy adolescents (n=17) and adolescents with idiopathic scoliosis (n=52) with either mild (Cobb angle≥15° and ≤30°) or severe (Cobb angle >30°) spine deformation was assessed through galvanic vestibular stimulation. A classification procedure sorted out adolescents with idiopathic scoliosis whether the amplitude of their vestibular-evoked postural response was dissimilar or similar to controls. Compared to controls, galvanic vestibular stimulation evoked larger postural response in adolescents with idiopathic scoliosis. Nonetheless, the classification procedure revealed that only 42.5% of all patients showed impaired sensorimotor control. Consequently, identifying patients with sensorimotor control impairment would allow to apply personalized treatments, help clinicians to establish prognosis and hopefully improve the condition of patients with adolescent idiopathic scoliosis. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to investigate the change in the fingertip forces and balance control of young adults and older adults. The subjects lifted an object of constant weight (i.e., 1500g) using their right hand, first in a seated position and then in a standing position. We quantified the ability of the participants to adjust their fingertip forces across trials by comparing the percentage of change in the peak grip force, peak load force and the ratio between peak grip force and peak load force. Moreover, we quantified their ability to stabilize their balance following the lifting of the object in the standing condition. The results showed that in both conditions young adults reduced their peak grip force much more than older adults across trials. In the seated condition, young adults increased slightly their peak load force, across trials, while older adults reduced it. In the standing condition, both groups showed similar change in peak load force across trials. Remarkably, older adults improved their balance stability similarly to young adults in the standing condition. This observation suggests that the ability of the older adults to modulate grip force applied to an object while standing is diminished probably to dedicate more attention to the balance control task rather than fine-tuning the grip force. Reducing balance instability following repetitive lifting is certainly more beneficial as the consequences of a fall could be more dramatic than dropping a cup of coffee. [Copyright &y& Elsevier]

Abstract: Proper balance control is a key aspect of acitivities of daily living. The aim of this study was to determine the contribution of body weight to predict balance stability. The balance stability of 59 male subjects with BMI ranging from 17.4 to 63.8kg/m2 was assessed using a force platform. The subjects were tested with and without vision. A stepwise multiple regression analysis was used to determine the independent effect of body weight, age, body height and foot length on balance stability (i.e., mean speed of the center of foot pressure). With vision, the stepwise multiple regression revealed that body weight accounted for 52% of the variance of balance stability. The addition of age contributed a further 3% to explain balance control. Without vision, body weight accounted for 54% of the variance and the addition of age and body height added a further 8% and 1% to explain the total variance, respectively. The final model explained 63% of the variance. A decrease in balance stability is strongly correlated to an increase in body weight. This suggests that body weight may be an important risk factor for falling. Future studies should examine more closely the combined effect of aging and obesity on falling and injuries and the impact of obesity on the diverse range of activities of daily living. [Copyright &y& Elsevier]

• Alpha peak frequency (APF) is increased in adolescents with idiopathic scoliosis. • Higher APF may indicate increased cortical processing to maintain balance control. • Increased APF may be a compensatory strategy to overcome sensorimotor dysfunction. Adolescent idiopathic scoliosis (AIS) is a multifactorial disorder characterized by a tridimensional deformation of the spine. AIS pathophysiology is still unclear and its aetiology is unknown. Results from several studies revealed balance control alterations in adolescents with AIS suggesting cortical sensorimotor processing impairments. Studies assessing cortical activity involved in balance control revealed an increase in alpha peak frequency (APF), which is a neurophysiological marker of thalamo-cortical transmission, related to a more challenging balance task. The objective of this study is to assess APF of adolescents with AIS during balance control in upright standing posture using electroencephalography (EEG). EEG was recorded in 16 girls with AIS and 15 control girls in normal standing posture on a force platform. The participants stood upright for 2 min with eyes open and 2 min with eyes closed. Fast Fourier transformations of EEG data were calculated to obtain APF. Balance performances were assessed through the area of an ellipse covering the center of pressure (COP) displacement and the root mean square value of the COP velocity. Compared to the control group, APF was higher in the AIS group at central, frontal, parietal and occipital regions. Further, COP analyses did not reveal any difference between AIS and control groups. A higher APF may indicate the need for increased cortical processing to maintain balance control in normal upright standing in adolescents with AIS compared to healthy controls. We suggest that this may be a compensatory strategy to overcome balance control challenges. [ABSTRACT FROM AUTHOR]

• Adolescent idiopathic scoliosis (AIS) shows altered electrocortical dynamics during balance control. • Cortical dynamics assessment seems sensitive to detect sensorimotor dysfunction. • Participants with AIS adapt their electrocortical dynamics to maintain balance control. This study aims at examining the cortical dynamics of sensorimotor information processing related to balance control in participants with adolescent idiopathic scoliosis (AIS) and in age-matched controls (CTL). Cortical dynamics during standing balance control were assessed in 13 girls with AIS and 13 age-matched controls using electroencephalography. Time-frequency analysis were used to determine frequency power during ankle proprioception alteration (ankle tendons co-vibration interval) or reintegration of ankle proprioception (post-vibration interval) with or without vision. Balance control did not differ between groups. In the co-vibration interval, a significant suppression in alpha (8–12 Hz) and beta (13–30 Hz) band power and a significant increase in theta (4–7 Hz) band power were found respectively in the vision and non-vision condition in the AIS group compared to the CTL group. In the post-vibration interval, significant suppressions in beta (13–30 Hz) and gamma (30–50 Hz) band power were observed in the AIS group in the non-vision condition. Participants with AIS showed brain oscillations differences compared to CTL in the sensorimotor cortex while controlling their balance in various sensory conditions. Future study using evaluation of cortical dynamics could serve documenting whether rehabilitation programs have an effect on sensorimotor function in AIS. [ABSTRACT FROM AUTHOR]

Idiopathic scoliosis is the most frequent spinal deformity in adolescence. While its aetiology remains unclear, impairments in balance control suggest a dysfunction of the sensorimotor control mechanisms. The objective of this paper is to evaluate the ability of patients with idiopathic scoliosis to reweigh sensory information. Using a neuromechanical model, the relative sensory weighting of vestibular and proprioceptive information was assessed. Sixteen healthy adolescents and respectively 20 and 16 adolescents with mild or severe scoliosis were recruited. Binaural bipolar galvanic vestibular stimulation was delivered to elicit postural movement along the coronal plane. The kinematics of the upper body, using normalized horizontal displacement of the 7th cervical vertebra, was recorded 1s before, 2s during, and 1s following vestibular stimulation. The neuromechanical model included active feedback mechanisms that generated corrective torque from the vestibular and proprioceptive error signals. The model successfully predicted the normalized horizontal displacement of the 7th cervical vertebra. All groups showed similar balance control before vestibular stimulation; however, the amplitude (i.e., peak horizontal displacement) of the body sway during and immediately following vestibular stimulation was approximately 3 times larger in patients compared to control adolescents. The outcome of the model revealed that patients assigned a larger weight to vestibular information compared to controls; vestibular weight was 6.03% for controls, whereas it was 13.09% and 13.26% for the mild and severe scoliosis groups, respectively. These results suggest that despite the amplitude of spine deformation, the sensory reweighting mechanism is altered similarly in adolescent patients with scoliosis. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Obesity affects postural sway during normal quiet standing; however, the reasons for the increased postural sway are unknown. Improving muscular strength is regarded as a potential way to improve postural control, particularly for obese and overweight subjects. The purpose of this investigation is to evaluate the role of muscular strength on postural sway in obese and overweight individuals. Methods: Fifteen healthy weight (control group), seventeen obese (obese group) subjects and nine football players (heavy athletic group) participated in this investigation. Isometric knee extension force and postural sway were measured. Muscular strength was calculated in absolute measures as well as relative to body mass (muscular strength to body mass). Results: The heavy athletic group demonstrated significantly stronger (absolute) lower limb strength (1593.9N (95% CI 1425.5, 1762.3)) than both the obese (796.2N (95% CI 673.8, 824.5)) and control (694.1N (95% CI 563.7, 824.5)) groups. As well, when muscular strength was expressed as a ratio to body mass the heavy athletic group had significantly higher values (1.27 (95% CI 1.11, 1.43)) than obese (0.78 (95% CI 0.66, 0.89) and control (1.00 (95% CI (0.88, 1.12)) individuals. Despite this, they swayed similarly to the obese (mean center of pressure speed of 0.83cms−1 (95% CI 0.72, 0.93) vs. 0.87cms−1 (95% CI 0.80, 0.95)), that is, significantly more than the controls (0.60cms−1 (95% CI 0.52, 0.68)). Conclusion: Isometric knee extensor strength has a minimal effect on postural sway in heavier athletic individuals during normal quiet stance. [Copyright &y& Elsevier]

Adolescence idiopathic scoliosis (AIS) is a 3D deformity of the spine that occurs during growth. It affects 2–3 % of adolescents, and the prevalence is ∼10 times higher in girls compared to boys. There is growing evidence that alteration in the processing of vestibular signals results in asymmetrical activity in the vestibulospinal pathway. Since the latest modulates back muscles activity, an asymmetrical functioning of the vestibulospinal pathway could be related to AIS. To assess the symmetry of the vestibular pathway, we calculated coherence between vestibular evoked activity and postural response. Nineteen adolescent girls (4 with AIS and 15 with no AIS) participated in this study. Participants received stochastic electrical vestibular stimulation (EVS; frequency spectrum: 0–25 Hz, amplitude ± 3 mA, DS5 stimulator, Digitimer Ltd) while standing upright on a force platform (model OPTIMA, Advanced Mechanical Technology, Inc.), arms alongside, eyes closed, and head immobilized ∼18° tilted upward (Laerdal Medical). Binaural or monaural (left and right) EVS induced changes in ground reaction forces along the anteroposterior (AP) and medio-lateral (ML) axis. Vestibulomotor coherence between EVS and ML or AP forces was calculated. Compared to controls, adolescents with AIS showed a greater asymmetry in vestibulomotor coherence along the ML axis when comparing right and left monaural EVS. Although the EVS should mainly evoke changes in ML axis, vestibulomotor coherence was observed between EVS and forces along the AP axis only in the AIS group. The results suggest An asymmetrical vestibulomotor transformation in the adolescents with idiopathic scoliosis is suggested. [ABSTRACT FROM AUTHOR]

Several studies revealed balance control alterations in adolescents with idiopathic scoliosis (AIS) suggesting cortical sensorimotor processing impairments. This study aims at examining the cortical dynamics of sensorimotor information processing related to balance control in different sensory tasks in participants with AIS and in age-matched controls (CTL) using electroencephalography (EEG). Cortical dynamics during normal standing balance and during ankle tendons co-vibration (proprioception alteration) and post-vibration (proprioception reintegration) were assessed in 16 girls with AIS and 15 CTL using EEG. The participants stood on a force platform. Fourier transform and time-frequency analysis were used to determine alpha peak frequency (APF) and band power synchronization/desynchronization in all conditions with and without vision. Balance performances were assessed through the distance covered by the center of pressure (COP). COP did not differ between groups in all conditions. APF was larger in the AIS group at central, frontal and parietal regions. In the co-vibration condition, a significant desynchronization in alpha (8–12 Hz) and beta (13–30 Hz) band power and a significant increase in theta (4–7 Hz) band power were found respectively in the vision and non-vision condition in AIS compared to CTL. In the post-vibration condition, significant desynchronization in beta and gamma (30–50 Hz) band power were observed in the AIS group in the non-vision condition. Differences in APF and frequency band power in AIS compared to CTL may indicate the need for increased cortical processing to maintain balance control. Future investigations may help understand the pathomechanism of progressive scoliosis. [ABSTRACT FROM AUTHOR]

Important for balance control, the activation of the cutaneous foot receptors largely depends on the speed and amplitude of the body oscillations during standing. Here, we tested the hypothesis that the transmission of cutaneous inputs to the cortex is reduced during prolonged intervals of small body sways due to continued local skin compression and that under such circumstances, central mechanisms trigger large sways to reactivate the cutaneous receptors. We compared the amplitude of the somatosensory cortical potentials (P50-N90) evoked by electric stimulations of the foot sole during either small or large sways in 16 adults that were standing still with the eyes closed. We found greater P50-N90 amplitude when the stimulation occurred during large body sways, consistent with an increased sensory transmission. Importantly, body oscillations computed 200 ms prior to large sways had smaller amplitude than intervals that were not followed by large sways. The hypothesis of a depressed sensory transmission during continued skin compression was supported by our microneurographic recordings showing adaptation/suppression of tactile fibres discharge during continuous pressure applied to the mechanoreceptors. Finally, the hypothesis that large sways during standing correspond to a self-generated functional behaviour to release skin compression is supported by cortical source and EMG analyses showing respectively that large sways were preceded by activation of cortical areas known to be engaged in motor planning (supplementary motor area and dorsolateral prefrontal cortex) and by ankle muscle activations. Together, the present findings provide evidence for an important sensory function of large body sways for balance control. [ABSTRACT FROM AUTHOR]