Fingertip touch improves postural stability in patients with peripheral neuropathy

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

The effect of actual and imaginary handgrip on postural stability during different balance conditions

The stabilizing effect of holding an object on upright posture has been demonstrated in a variety of settings. The mechanism of this effect is unknown but could be attributed to either additional sensorimotor activity triggered by a hand contact or cognitive efforts related to performance of a supra-postural task. A potential mechanism was investigated by comparing postural stability in young healthy individuals while gripping a custom instrumented wooden stick with a 5N force and while imagining holding the same stick in the hand. Twenty subjects were tested during three standing balance conditions: on a stationary surface, on a freely moving rockerboard, and with an unexpected perturbation of 10° forward rockerboard tipping. Postural stability was evaluated as velocity of the center of mass (COM) and center of pressure (COP) compared across all experimental conditions. COM and COP velocities were equally reduced when subjects gripped the stick and imagined gripping while standing stationary and on the rockerboard. When perturbed, subjects failed to show any postural stability improvements regardless of handgrip task. Results indicate a stabilizing effect of focusing attention on motor task performance. This cognitive strategy does not appear to contribute any additional stabilization when subjects are perturbed. This study adds to the current understanding of postural stabilization strategies.     

A longitudinal investigation into the progression of dynamic postural stability performance in adolescents

Adolescent female athletes have a higher incidence of certain non-contact lower limb injuries compared to their male counterparts. Decreased postural stability is an established risk factor for lower limb injuries; however developmental-related sex differences in postural stability during adolescence have not been investigated. The objectives of this study were to longitudinally examine changes over time, and potential sex differences in dynamic postural stability performance in adolescents. One hundred and eighty four adolescent athletes participated (mean age = 13 ± 0.34 years). Participants were assessed, using the Star Excursion Balance Test (SEBT) at baseline (T1) and at 6 (T2), 12 (T3), 18 (T4) and 24 (T5) months. At each time-point, participants performed 3 trials of the anterior, posterior-medial and posterior-lateral directions of the SEBT on each limb. Reach distance for each direction was averaged across the 3 trials normalised to leg length. General linear mixed model analyses were carried out on each of the dependant variables (reach directions) with sex and time as the categorical independent variables. There was a significant sex × time interaction for the posterior-lateral reach distance scores. There were no significant sex × time interactions for any of the other reach directions. Males increased performance on the posterior-lateral reach direction from T1 to T5, while females only increased performance until T3. Young males and females demonstrate diverging postural stability profiles during adolescence.     

The effect of actual and imaginary handgrip on postural stability during different balance conditions

The stabilizing effect of holding an object on upright posture has been demonstrated in a variety of settings. The mechanism of this effect is unknown but could be attributed to either additional sensorimotor activity triggered by a hand contact or cognitive efforts related to performance of a supra-postural task. A potential mechanism was investigated by comparing postural stability in young healthy individuals while gripping a custom instrumented wooden stick with a 5N force and while imagining holding the same stick in the hand. Twenty subjects were tested during three standing balance conditions: on a stationary surface, on a freely moving rockerboard, and with an unexpected perturbation of 10° forward rockerboard tipping. Postural stability was evaluated as velocity of the center of mass (COM) and center of pressure (COP) compared across all experimental conditions. COM and COP velocities were equally reduced when subjects gripped the stick and imagined gripping while standing stationary and on the rockerboard. When perturbed, subjects failed to show any postural stability improvements regardless of handgrip task. Results indicate a stabilizing effect of focusing attention on motor task performance. This cognitive strategy does not appear to contribute any additional stabilization when subjects are perturbed. This study adds to the current understanding of postural stabilization strategies.     

The impact of vision loss on postural stability and balance strategies in individuals with profound vision loss

Individuals with vision loss are at an increased risk of falls. Understanding what factors contribute to postural instability within this population is a necessary step towards the development of physiotherapeutic programs targeted at reduction of falls within this population. Forty-six age-matched participants were evaluated with the sensory organization test (SOT) on a NeuroCom Equitest. The conditions provided accurate and inaccurate sensory information to test the participants' ability to utilize the correct information to maintain postural stability. A one-way analysis of variance was performed on composite balance scores between groups. Based on the data analysis, significant differences were apparent in equilibrium composite scores (P<.05) and strategy utilized to maintain postural stability between the visually impaired and sighted sample. Results indicate that restricted vision has a negative impact on overall postural stability and visually impaired individuals utilize greater use of hip strategy to maintain postural stability.     

Effects and after-effects of voluntary intermittent light finger touch on body sway

Effects of light touch on body sway have usually been investigated with some form of constant contact. Only two studies investigated transient sway dynamics following the addition or withdrawal of light touch. This study adopted a paradigm of intermittent touch and assessed body sway during as well as following short periods of touch of varying durations to investigate whether effects and after-effects of touch differ as a function of touch duration. In a modified heel-to-toe posture, 15 blindfolded participants alternated their index finger position between no-touching and touching on a strain gauge in response to low- and high-pitched auditory cues. Five trials of 46 s duration were segmented into 11 sections: a 6-s no-touching period was followed by five pseudo-randomly ordered touching periods of 0.5-, 1-, 1.5-, 2-, and 5-s duration, each of which was followed by another 6-s no-touching interval. Consistent with previous research, compared to no-touching intervals sway was reduced during touch periods with touch durations greater than 2 s. Progressive reductions in sway were evident after touch onset. After touch withdrawal in the 2-s touch condition, postural sway increased and returned to baseline level nearly immediately. Interestingly, in the 5-s touch condition, reductions in sway persisted even after touch withdrawal in the medio-lateral and antero-posterior plane for around 2.5 s and 5.5 s, respectively. Our intermittent touch paradigm resulted in duration-dependent touch effects and after-effects; the latter is a novel finding and may result from a more persistent postural set involved in proactive sway control.     

Effects and after-effects of voluntary intermittent light finger touch on body sway

Effects of light touch on body sway have usually been investigated with some form of constant contact. Only two studies investigated transient sway dynamics following the addition or withdrawal of light touch. This study adopted a paradigm of intermittent touch and assessed body sway during as well as following short periods of touch of varying durations to investigate whether effects and after-effects of touch differ as a function of touch duration. In a modified heel-to-toe posture, 15 blindfolded participants alternated their index finger position between no-touching and touching on a strain gauge in response to low- and high-pitched auditory cues. Five trials of 46 s duration were segmented into 11 sections: a 6-s no-touching period was followed by five pseudo-randomly ordered touching periods of 0.5-, 1-, 1.5-, 2-, and 5-s duration, each of which was followed by another 6-s no-touching interval. Consistent with previous research, compared to no-touching intervals sway was reduced during touch periods with touch durations greater than 2 s. Progressive reductions in sway were evident after touch onset. After touch withdrawal in the 2-s touch condition, postural sway increased and returned to baseline level nearly immediately. Interestingly, in the 5-s touch condition, reductions in sway persisted even after touch withdrawal in the medio-lateral and antero-posterior plane for around 2.5 s and 5.5 s, respectively. Our intermittent touch paradigm resulted in duration-dependent touch effects and after-effects; the latter is a novel finding and may result from a more persistent postural set involved in proactive sway control.     

Frontal plane margin of stability is increased during texting while walking

Injurious falls associated with cell phone use during ambulation are increasingly common. Studies examining texting while walking suggest this task alters the attentional component of walking to the extent that safety may be compromised. Here, we quantified the extent to which frontal plane dynamic stability while walking was affected by the cognitive and physical demands of texting. Twenty experienced texters performed four, 10-min treadmill walking tasks at a self-selected velocity in random order: (1) normal walk (control), (2) walking while verbally performing mathematical calculations (cognitive demand), (3) walking while bimanually holding and looking directly at a phone (physical demand), and (4) walking while texting continuous mathematical calculations (cognitive and physical). We quantified the frontal plane minimum margin of stability (MOS_min), a measure that considers the position and normalized velocity of the center of mass with respect to the lateral border of the base of support was calculated over each 10-min walking period. Compared to the normal walking condition, the texting and phone holding conditions resulted in a small but significant (6%) increase in MOS_min (p = 0.005 and 0.026, respectively). Compared to normal walking, the effect of performing mathematical calculations on MOS_min was not significant (p = 0.80). These results suggest that frontal plane stability of experienced texters during controlled treadmill walking conditions can be affected by the physical, but not the cognitive demand of texting. This may represent a compensatory mechanism by the CNS to ensure stability in the event of an unexpected disturbance.     

Evaluation of postural stability in youth athletes: the relationship between two rating systems

Objectives: The Balance Error Scoring System (BESS) has been documented as a useful way to evaluate postural control following sport-related concussions sustained by youth athletes. However, limitations have been reported with its use due to the reliance on visual observation as the primary measurement outcome. The primary purpose of this study was to examine the correlation between the modified BESS (mBESS) as rated by a clinician and a simultaneous analysis performed by an integrated video-force plate system. The secondary purpose was to assess if a history of prior concussion affected postural control.

Methods: A group of healthy youth athletes (n = 398; mean age 13.7 ± 2.4 years) completed the mBESS while simultaneously undergoing an integrated video-force plate evaluation to measure postural stability. Spearman rank-order correlations were used to determine the strength of correlation between the 2 rating systems. In addition, performance on the mBESS between those with and without a history of concussion was compared using univariate ANCOVAs.

Results: A moderately high correlation was found during single-leg stance (ρ = -0.64, p < .001), while a weak correlation was found during tandem stance (ρ = -0.30, p < .001). No postural control differences were found between groups with and without a concussion history.

Conclusion: The video-force plate rating system correlates well with the clinician rating during the single-leg stance of the mBESS, but not during double-leg or tandem stances. A history of concussion did not affect mBESS scores.     

Dynamic postural stability,is associated with competitive level,in youth league soccer players

ObjectivesTo assess the effect of competitive level on dynamic postural stability in young elite and sub-elite soccer players.DesignCross-sectional study.SettingLaboratory.ParticipantsFifty-four male soccer players of Under 16 and Under 17 categories (mean age 15.9 ± 0.6), divided into two groups who regularly compete at national (n = 28) and regional (n = 26) levels.Main outcome measuresDynamic Postural Stability Index (DPSI) and vertical Time to Stabilization (vTTS) for a forward-jump landing. Static postural sway was calculated on the basis of center-of-pressure trajectories for a 20 s one-legged stance.ResultsPlayers at national level exhibit better dynamic postural control than those at regional level, as indicated by the significantly lower DPSI (0.327 vs. 0.373, p < 0.001) and vTTS (0.887 vs. 1.158 s, p = 0.003). In contrast, no differences between groups were found in any of the postural sway parameters for the static test.ConclusionsYoung soccer players at national level are characterized by better balance performance in terms of faster and more efficient stabilization after a forward jump, while one-leg static standing tests appear not challenging enough to reveal differences in balance abilities associated with the combination of superior technical and physical features.     

Influence of dance training on challenging postural control task

BackgroundPrevious studies have shown that dance training affects postural control, particularly during challenging tasks. However, it is still unknown whether dance training also affects the ability to use vestibular, somatosensory, and visual cues, thus leading to postural control differences.ObjectiveThe main goal of the present study was to evaluate the influence of dance training on sensory weighting during static postural control.MethodThe center of pressure of 24 participants was recorded (12 dancers and 12 control non-dancers) using a force platform as well as the modified Clinical Test of Sensory Organization in Balance (mCTISB).ResultsThe results suggest that dancers perform significantly better than controls in conditions where somatosensory cues are disturbed. Moreover, a significant negative correlation between vestibular frequency band and training intensity was observed, along with, a significant positive correlation between visual frequency band and training intensity.SignificanceThis research outlines dancers’ increased ability to modulate sensory weighting differently than non-dancers during postural task where somatosensory cues are reduced.     

Influence of visual biofeedback and inherent stability on trunk postural control

BackgroundFor individuals who never achieve independent standing, rehabilitation is focused on trunk posture and balance control. Visual biofeedback has the potential to augment sitting balance training, however previous work in this area has been limited to standing.Research questionTo what extent do different types of visual biofeedback influence trunk sway in sitting?MethodsTwelve healthy young adults sat on an articulating bench. During ‘sway referencing’ trials, the bench tilted up and down in proportion to trunk sway in the frontal plane. This paradigm increased difficulty of the balance task and required participants to rely on visual and vestibular cues. Participants were provided different visual biofeedback through a rotating needle-gage display. Trials lasted 165 s, were ordered randomly, and included either direct feedback (needle rotated in proportion to body sway), inverted feedback (needle rotated in the opposite direction of sway), time delayed feedback (0.5 s), random feedback, eyes closed, or control (eyes open with screen off). To explore the impact of inherent stability, trials were repeated with and without external trunk support.ResultsBody sway depended on feedback type. Specifically, direct and inverted feedback reduced root-mean-squared (RMS) sway the most, time delayed feedback had a smaller effect, and random visual feedback increased participants’ RMS sway compared to control. Frequency domain analyses demonstrated direct and inverted visual feedback reduced sway amplitude at the lower frequencies while having minimal effect on (or increasing) sway amplitude at higher frequencies.SignificanceThis study extends previous work by showing that visual biofeedback can have powerful effects on sitting balance, even with external support. Results from the different types of feedback conditions further our understanding of how the brain interprets visual biofeedback. Frequency-based results were similar to previous studies using different modalities and suggest participants interpret biofeedback through sensory addition as opposed to sensory substitution.     

Improvement of dynamic postural stability by an exercise program

BackgroundCentral processing of multi-sensory feedback and motor commands responsible for force production are critical for postural control. An exercise program was developed to realign spinal curvature, but its effect on postural control is unknown.Research QuestionTo what extent would the exercise program influence on center of pressure (CoP) sway on stable and unstable surfaces?MethodsSubjects (n = 30) were randomly assigned into one of three groups: exercise on a cylinder-shaped tube (98-cm length, 15-cm diameter, n = 10), exercise on a flat surface (n = 10), and a control group that laid supine on a flat surface (n = 10). Standing posture of each subject was quantified using anterior-, posterior-, and lateral-view photography. Each subject’s CoP sway was measured while standing on a static and dynamic platform with eyes open and eyes closed. Subjects were instructed to stand still when the platform was held stationary (e.g., no tilt) during the static condition. During the dynamic condition the platform was allowed to tilt in response to changes of CoP and subjects were instructed to maintain the platform in a horizontal position.ResultsOnly when subjects performed the exercise program on the tube, the angles of neck flexion and pelvis tilt decreased, and CoP sway in the sagittal, but not frontal plane, decreased during the dynamic platform conditions with both eyes open and eyes closed (p < 0.05).SignificanceIt is speculated that performing the exercise program on the tube might enhance a) central processing of somatosensory and vestibular inputs, b) motor commands responsible for force production in postural control, and c) biomechanical advantage by the realigned posture. The exercise program can be used by a variety of populations as home-exercise to realign the neck and pelvic posture and improve dynamic postural stability.     

Influence of knee position on the postural stability index registered by the Biodex Stability System

The importance of knee position for bodily stability is described by some authors, however Biodex Stability System (BSS) trials have not been used to assess the reliability and effects of different knee positions. The purposes of this study were to test the reliability of BSS indices using two knee positions in the measurement protocol (either permitting slight knee flexion or maintaining them locked in total extension) and to compare the BSS indices between these two knee positions. The measurements were taken of the Overall Stability Index (OSI), Anterior–Posterior Stability Index (APSI) and Medial–Lateral Stability Index (MLSI) during a 30 s protocol which gradually and automatically increased in difficulty among 21 healthy female subjects (22.8 ± 1.0 years old). The subjects performed four trials which, without visual feedback, permitted knee flexion as well as four trials which did not, in a randomized order. The first two trials in each set were used for familiarization only. Permitting slight flexion yielded better reliability results (OSI Intra-class Correlation Coefficient [ICC] = 0.93, APSI ICC = 0.90, MLSI ICC = 0.89) than maintaining the knee in total extension (OSI ICC = 0.88, APSI ICC = 0.87, MLSI ICC = 0.79), with good agreement in the Bland and Altman test. Moreover, permitted knee flexion in BSS presented better balance stability values for OSI (P = 0.001) and APSI (P = 0.024), however the MLSI did not present significant difference between positions (P = 0.345).     

Higher visual reliance during single-leg balance bilaterally occurring following acute lateral ankle sprain: A potential central mechanism of bilateral sensorimotor deficits

BackgroundSingle-leg balance (SLB) impairment from eyes-open to eyes-closed trials is significantly greater in patients with chronic ankle instability than in uninjured controls, indicating higher reliance on visual information. It is of clinical interest to see if the visual adaptation occurs immediately after injury.Research questionWe aimed to investigate visual reliance in patients with acute lateral ankle sprain (ALAS) during SLB with both injured and uninjured limbs and during double-leg balance (DLB).MethodsThe study assessed visual reliance of 53 participants: 27 ALAS patients and 26 persons without a history of ALAS. All participants executed DLB with eyes open and closed, and then completed SLB with both the injured and uninjured limbs (side-matched limbs of the uninjured control group) in both visual conditions. Order of limb and visual condition for SLB was randomly selected. Visual reliance was quantified for each postural task with a percent change between the two visual conditions, with the greater change representing higher visual reliance. We performed separate group-by-limb analysis-of-variance with repeated measures for SLB percent scores and independent t-tests for DLB outcomes.ResultsFor all SLB measures there were no significant group-by-limb interactions (p > 0.05) but significant group main effects (p = 0.013–0.029). With no side-to-side differences, the ALAS group presented higher declines in SLB from the eyes-open to eyes-closed conditions than did the uninjured control group, indicating higher visual reliance. Similarly, for DLB there were significant group differences for almost all measures (p = <.001–0.037), with the ALAS group showing greater visual reliance.SignificanceModerately higher visual reliance occurs acutely and bilaterally during SLB in ALAS patients. Similar visual adaptions also occur during DLS. These findings will provide insight into a central mechanism underlying bilateral sensorimotor deficits following ALAS and allow clinicians to improve current rehabilitation strategies for acute patients.     

Subjective stability perception is related to postural anxiety in older subjects

BackgroundUnder static conditions, the objective and subjective measures of postural stability correlate well. However, age-related changes in postural control and task-related anxiety may modify the relationship between these subjective and objective measures. Ultimately, patients’ symptoms represent subjective reports, thus understanding this relationship has clinical implications.AimsThis study investigates the relationship between subjective-objective measures of postural stability in dynamic conditions and whether this relationship is influenced by age or task-related anxiety.Methods50 healthy participants (aged 18–83 years) stood on a platform oscillating at variable amplitudes, with-without a fall-preventing harness to modulate task-related anxiety. Trunk sway path, hip velocity and foot lifts (objective measures) and subjective scores of instability and task-related anxiety were recorded.ResultsThe subjective perception of stability accurately matched objective body sway, following a logarithmic function profile (r² = 0.72, p < 0.001). This function did not change significantly with age, harness or task presentation order. A strong relationship was observed between subjective measures of stability and task-related anxiety for all subjects (r = 0.81, p < 0.001). Task repetition reduced anxiety in the young, uncoupling anxiety changes from subjective instability, but not in the elderly who retained higher anxiety levels in line with subjective unsteadiness.DiscussionSubjects accurately rate their own instability during dynamic postural challenges, irrespective of age and actual fall risk. However, anxiety may selectively modulate the perception of instability in older subjects. The perception of stability relies upon the integration of sensory afferents but also recruits emotional-cognitive processes, particularly in older individuals. The use of a safety harness has no influence on subjective or objective postural stability.     

BTrackS limits of stability test is a reliable assessment of volitional dynamic postural control

BackgroundUnconstrained limits of stability assessment reveals aspects of volitional postural sway control that are inaccessible by other means. Prior versions of this assessment include instructions to sway towards predefined targets, and may not capture the full capability of the individual.Research questionThis study sought to establish the test-retest reliability of a novel limits of stability protocol.MethodsVolitional sway area was determined during unconstrained trials, where participants were instructed to explore their ability to sway towards the perimeter of their base of support. Visual feedback was provided via computer monitor. Forty healthy young adults (mean age = 20.2 ± 1.3, 15 males, 25 females) participated in this study. Trials were collected in three sessions, repeated at the same time of the same day, with one week between. Reliability was assessed using IntraClass Correlation Coefficients (ICC), considering the total area of sway as well as quadrant level area.ResultsReliability was moderate between the first and second session (0.583), and much higher 0.921) between the second and third session. The quadrant level reliability was poor to excellent (0.183−0.791), with similar trends between the three sessions.SignificanceUltimately, these results indicate that the novel limits of stability test is reliable. However, it is recommended that a practice trial be conducted prior to baseline establishment.     

Multisensory factors in postural control: Varieties of visual and haptic effects

Background Previous work on balance control in children and adults highlights the importance of multisensory information. Work in this vein has examined two principal input sources – the role of visual and haptic information on balance. Recent work has explored the impact of a different form of haptic input – object holding – on balance in young infants.Research question This experiment examined the impact of simultaneous visual input and haptic input on balance in children and adults, employing two novel forms of haptic input.Methods Static balance was measured in 3–5 year olds, 7–9 year olds, and young adults, in the presence of all possible combinations of manipulated visual input (eyes open, eyes closed) and haptic input (no touch, object hold, touch an unstable support, touch a stable support).Results Analysis of postural stability (mean velocity) indicated that stability was influenced by visual input, haptic input, and age group. For visual input stability increased in eyes open versus eyes closed conditions. For haptic input, stability systematically increased with increasing levels of fixed haptic input (e.g., no touch, object hold, unstable touch, stable touch). Stability also increased as a function of increasing age group. There were no interactions between the factors.Significance The finding that the two novel forms of haptic input – object hold and touch with an unstable support surface – increased stability relative to no touch input, but not as much as touch with a stable support, indicates that children use haptic information in a self-referential fashion for controlling posture. The failure to observe any interactions between visual and haptic inputs with age suggests that multisensory processing is generally additive across development, and has implications for the occurrence of sensory weighting across developmental epochs.     

Toe flexor strength is not related to postural stability during static upright standing in healthy young individuals

BackgroundThe human foot has adapted specifically to support body weight when standing upright. At the base of the postural control system, the unique arch structure of the foot still has an uncertain role in human upright standing. Because the toe flexor muscles help to support the foot arches, they might be an important contributor to postural stability. However, no research has identified the influence of the toe flexor strength or the foot arch height on postural stability in static upright standing.Research question: The aim of this study was to examine whether the toe flexor strength and the foot arch height were related to postural stability in static standing in healthy young individuals.MethodsFifty healthy young individuals were recruited into this cross-sectional study. Toe flexor strength was measured using a toe grip dynamometer, and it was normalised by body mass (rTFS). Foot arch height was assessed as the distance between the navicular tuberosity of the foot and the floor, and it was normalised by height (rFAH). Postural stability was evaluated using the path of the centre of pressure (COP) during double-leg standing with eyes open and single-leg standing with eyes open.ResultsrTFS and rFAH were 2.6 ± 0.8 N/kg and 2.8 ± 0.4%, respectively, and they were not significantly correlated (r = 0.094), indicating that they were independent variables. The results of Pearson’s correlation analysis revealed that any body size related variables (height, body mass, BMI) were not significantly correlated with COP variables under either double-leg or single-leg standing, rTFS was not significantly correlated with COP variables under either double-leg or single-leg standing and rFAH was not significantly correlated with COP variables under double-leg standing.SignificanceToe flexor strength has no significant role in maintaining postural stability during static upright standing.