Effect of light finger touch in balance control of individuals with multiple sclerosis

Deficit in balance control is a common and often an initial disabling symptom of multiple sclerosis (MS). The purpose of this study was to investigate if a light finger touch contact with a stationary surface is effective in improving upright postural stability in MS. Eleven individuals with relapsing–remitting MS were standing on a force platform with eyes open and closed, feet shoulder width apart and together, and with a light touch contact of the right index finger with a stable surface and without any contact. Balance was evaluated using center of pressure measures. Individuals with MS demonstrated significant postural instability in the absence of visual inputs and with reduced base of support (p < 0.05). The availability of a light finger touch contact with a stable surface was effective in reducing postural sway in both, the sagittal and frontal planes, in all experimental conditions (p < 0.05). Light finger touch contact is effective in improving postural control in people with MS and can be considered as a useful balance rehabilitative strategy.     

Impaired postural control in children with developmental coordination disorder is related to less efficient central as well as peripheral control

BackgroundDevelopmental coordination disorder (DCD) is a neurodevelopmental impairment that affects approximately 6% of children in primary school age. Children with DCD are characterized by impaired postural control. It has yet to be determined what effect peripheral and central neuromuscular control has on their balance control.ObjectiveThe aim of this study was to investigate the underlying mechanisms to impaired postural control in children with DCD using the rambling-trembling decomposition of the center of pressure (CoP).MethodNine children with DCD (9.0 ± 0.5 years, 7 boys, 2 girls) and 10 age- and gender-matched typically developing children (TD) with normal motor proficiency (9.1 ± 0.4 years, 7 boys and 3 girls) performed 3 × 30 s bipedal standing on a force plate in six sensory conditions following the sensory organization procedure. Sway length was measured and rambling-trembling decomposition of CoP was calculated in medio-lateral (ML) and anterior-posterior (AP) direction.ResultsBoth rambling and trembling were larger for the children with DCD in AP (p = 0.031; p = 0.050) and ML direction (p = 0.025; p = 0.007), respectively.ML rambling trajectories did not differ in any conditions with fixed support surface. In ML direction children with DCD had a lower relative contribution of rambling to total sway (p = 0.013).ConclusionThis study showed that impaired postural control in children with DCD is associated with less efficient supraspinal control represented by increased rambling, but also by reduced spinal feedback control or peripheral control manifested as increased trembling.     

Altered postural sway persists after anterior cruciate ligament reconstruction and return to sport

Postural sway is defined as the movement of a body's center of mass within the base of support to maintain postural equilibrium. Deficits in postural sway are present after ACL injury; however, current evidence linking it to future injury risk is unclear. The purpose of this study was to determine if postural sway deficits persist after ACL reconstruction (ACLR). The hypothesis tested was that after ACLR, patients who return to sport (RTS) would demonstrate differences in postural sway compared to control (CTRL) subjects. Fifty-six subjects with unilateral ACLR released to RTS, and 42 uninjured CTRL subjects participated. Dynamic postural sway was assessed and 3-way (2 × 2 × 2) ANOVA was used to analyze the variables. A side × group × sex (p = 0.044) interaction in postural sway was observed. A side × group analysis also revealed an interaction (p = 0.04) however, no effect of sex was observed (p = 0.23). Analysis within the ACLR cohort showed less (p = 0.001) postural sway on the involved side (1.82 ± 0.84°) versus the uninvolved side (2.07 ± 0.96°). No side-to-side differences (p = 0.73) were observed in the CTRL group. The involved limb of subjects after ACLR demonstrated the least postural sway. In conclusion, these findings indicate that dynamic postural sway may be significantly altered in a population of athletes after ACLR and RTS compared to CTRL subjects. Further investigation is needed to determine if deficits in postural sway can be used as an effective criterion to assist in the decision to safely RTS after ACLR.     

The effects of localized muscle and whole-body fatigue on single-leg balance between healthy men and women

The purpose was to examine the effects of localized muscle and whole-body fatigue on indices of single-leg balance between healthy young men (n = 10) and women (n = 10). Subjects performed 10, 10-s single-leg balance trials on a force platform prior to performing each of three conditions (local, whole-body, and control), in a randomized order, on separate days. Localized muscle and whole-body fatigue consisted of single-leg, weight-bearing heel raises on an inclined platform, and exercise on a rowing ergometer, respectively, to the point of volitional failure. During the control condition, subjects remained in a seated position for 5 min. Immediately following each condition, five, 10-s, single-leg balance trials were performed. The localized muscle and whole-body fatigue protocols produced significant (p < 0.05) increases in medial/lateral (M/L) and total sway (TS). Men experienced a greater (p < 0.05) increase in anterior/posterior (A/P) sway following the localized muscle, than whole-body, fatigue protocol, whereas A/P sway increased more following the whole-body, than localized muscle, fatigue protocol for the women. Total sway variability increased significantly (p < 0.05) more following the localized muscle fatigue protocol than the whole-body fatigue protocol for both men and women. The major findings of the present investigation demonstrated that measures of postural control, namely M/L, A/P sway and total sway, were adversely affected following fatiguing exercise, with differential effects between men and women.     

Investigation of treadmill and overground running: Implications for the measurement of oxygen cost in children with developmental coordination disorder

Differences in the kinematics and kinetics of overground running have been reported between boys with and without developmental coordination disorder (DCD). This study compared the kinematics of overground and treadmill running in children with and without DCD to determine whether any differences in technique are maintained, as this may influence the outcome of laboratory treadmill studies of running economy in this population. Nine boys with DCD (10.3 ± 1.1 year) and 10 typically developing (TD) controls (9.7 ± 1 year) ran on a treadmill and overground at a matched velocity (8.8 ± 0.9 km/h). Kinematic data of the trunk and lower limb were obtained for both conditions using a 12-camera Vicon MX system. Both groups displayed an increase in stance time (p < 0.001), shorter stride length (p < 0.001), higher cadence (p < 0.001) and reduced ankle plantar flexion immediately after toe-off (p < 0.05) when running on the treadmill compared with overground. The DCD group had longer stance time (p < 0.009) and decreased knee flexion at mid-swing (p = 0.04) while running overground compared to their peers, but these differences were maintained when running on the treadmill. Treadmill running improved ankle joint symmetry in the DCD group compared with running overground (p = 0.019). Overall, these findings suggest that there are limited differences in joint kinematics and lower limb symmetry between overground and treadmill running in this population. Accordingly, laboratory studies of treadmill running in children with DCD are likely representative of the energy demands of running.     

Using a dual-task protocol to investigate motor and cognitive performance in healthy children and youth

ObjectivesMild traumatic brain injury (or concussion) is a prevalent yet understudied health concern in children and youth. This injury can cause dysfunction in both motor and cognitive domains; however, most literature focuses on single-task neuropsychological tests which only assess cognition. Although dual-task research on concussed children and youth is needed as many daily activities require both motor and cognitive domains, we must first investigate whether performing simultaneous motor and cognitive tasks of varied complexity impact these domains in healthy children and youth.Participants and designData collected from 106 healthy children and youth (5–18 years) created a normative dataset. Participants performed motor (postural stability) and cognitive (visual attention) tasks under single- and dual-task conditions. The cognitive task difficulty remained constant while the motor task had four conditions of increasing difficulty. The relationship between the number of correct responses (cognitive performance) and sway index (motor performance) was determined using two repeated measures ANOVAs (p < 0.05).ResultsDual-task conditions resulted in reduced postural stability, with greater differences on the foam surface (F_2,206 = 16.070, p < 0.0005). No statistically significant differences were observed in attention (F_4,101 = 0.713, p = 0.584).ConclusionsPostural stability decreased under dual-task conditions, but attention was maintained or improved. Consequently, attention took precedence over postural control when performing tasks concurrently, demonstrating the ability for dual-task methodology to isolate specific processes. This study provides a normative dataset to be used during clinical management to identify functional deficits following concussion and acts as a starting point to explore dual-task protocols in children and youth following concussion.     

Altered postural control strategies in quiet standing more than 20 years after rupture of the anterior cruciate ligament

AimTo explore long-term consequences of anterior cruciate ligament (ACL) rupture on postural sway and control strategies during bilateral quiet standing, in subjects treated with or without reconstructive surgery compared to uninjured controls.Method70 individuals who had unilateral ACL rupture 23 ± 2.4 years ago (33 received ACL reconstructive surgery, ACL_R, and 37 had physiotherapy only, ACL_PT) and 33 uninjured matched controls (CTRL) (mean age 46 ± 5.3) stood quietly with eyes closed for 3 min on a firm and on a compliant surface, respectively. Center of pressure (CoP) was registered with a force plate and postural sway was calculated from center of mass (CoM) derived from 3D kinematics. Sway density (SD) analyses of CoP assessed distance and duration of stable phases. The torque controlling postural sway was estimated from CoP-CoM.ResultsComparisons across conditions to CTRL revealed larger CoP-CoM-area in ACL_R (p = 0.017, CI: 10.95, 143.10), but not in ACL_PT. Mean distance between SD-peaks was greater for ACL_R (p < 0.001, CI: 1.73, 5.31) than for ACL_PT (p = 0.006, CI: 0.56, 4.12) relative to CTRL. Duration of SD-peaks was smaller for both ACL_R and ACL_PT (p < 0.001, CI: −4.04, −1.23 and −3.82, −1.03, respectively) compared to CTRL. CoM-area in the ACL-groups did not differ from CTRL.ConclusionsACL-injured subjects demonstrated greater postural control efforts than CTRL but without significant differences in postural sway. Control efforts were thus not directly associated with sway and further research should be focused on variance in postural control strategies.     

Haptic feedback from manual contact improves balance control in people with Parkinson's disease

Parkinson's disease (PD) degrades balance control. Haptic (touch and proprioception) feedback from light contact with a stationary surface inadequate to mechanically stabilize balance improves balance control in healthy people. In this study we tested whether PD impairs use of haptic cues independent of mechanical support to control balance. We measured postural sway in thirteen individuals with PD (H&Y 1–3, median = 2, Q₁ = 2, Q₃ = 2) and thirteen age-matched controls balancing in a widened, sharpened Romberg stance in four conditions: eyes-closed, no manual contact; eyes-closed light-touch contact (<1 N), eyes-closed, unrestricted contact; and eyes-open, no contact. To determine whether PD-severity affects any of these balance strategies, PD participants were tested on- and off-medication, and using the more- and less-affected body side in the stance and manual contact.Individuals with PD simultaneously maintained non-supportive fingertip contact and balance in this task without practice. PD participants swayed more than control participants (ML CP p = 0.010; shoulder p < 0.001), but manual contact reduced sway. Non-supportive manual contact stabilized balance more than vision (p < 0.05). PD-severity factors had no significant effect (p > 0.05).We conclude the effect of PD on balance is not specific to vision or haptic feedback. Nevertheless, haptic cues from manual contact, independent of mechanical support, improve balance control in individuals with PD. We discuss the implication that PD or associated dopaminergic pathways do not directly affect haptic feedback balance control mechanisms, including arm/posture coordination and proprioceptive integration.     

A comparison of running kinematics and kinetics in children with and without developmental coordination disorder

The aim of this study was to compare running gait in children with and without developmental coordination disorder (DCD). Fourteen boys with DCD (9.5 ± 1 yr) and 14 typically developing (TD) controls (9.6 ± 1 yr) ran at a velocity of 2.44 ± 0.25 m/s along a 15 m track, with kinematic and kinetic data of the trunk and lower limb obtained for three cycles of each limb using a 12-camera Vicon MX system and AMTI force plate. Although features of the kinematic and kinetic trajectories were similar between groups, the DCD group displayed decreased peak knee extension compared with the TD group prior to initial foot contact (p = 0.016). Furthermore, the DCD group displayed increased variability in sagittal plane kinematics at the hip and ankle during toe off compared with the TD group. Kinetic analysis revealed that children with DCD displayed significantly reduced knee extensor moments during the stance phase of the running cycle (p = 0.033). Consequently, peak knee power absorption and ankle power generation was significantly lower in the DCD group (p = 0.041; p = 0.017). Furthermore, there was a trend for children with DCD to have shorter strides (p = 0.052, ES = 0.499) and a longer stance period than the TD controls (p = 0.06, ES = 0.729). These differences may have implications for the economy of running and subsequently the planning of targeted intervention programs to improve running gait in children with DCD.     

Circadian amplitude and homeostatic buildup rate in postural control

Postural control during quiet stance is a common everyday physical activity. Sleepiness is increasingly prevalent in our 24-h society. Yet, little research exists that quantitatively links the fluctuations in sleepiness and postural control. This study quantifies the circadian amplitude and homeostatic buildup rate in postural control. With a force plate we assessed postural control in 12 participants (21–38 years) every 2 h during 24 h of sustained wakefulness. The sway area was 1.39 ± 0.71 mm² at the circadian high around noon, and 4.02 ± 0.67 mm² at the circadian low around 6 am (a 189% change, p = 0.02). The circadian amplitude of the sway area was therefore 2.63 mm². The sway area was 1.92 ± 0.64 mm² at the start of the 24-h period and 4.42 ± 0.69 mm² at the end of the period (a 130% change, p < 0.001). The homeostatic buildup rate of sway area was 0.04 h^?1. The circadian- and homeostatic effects on sway variability, sway velocity, sway frequency and fractal dimension were smaller but still significant. This study found that the circadian amplitude and homeostatic buildup rate are quantifiable from posturographic data, and that they have significant impact on postural control. This finding is important because it means that one could apply the framework of the famous two-process model of sleep regulation (published by Borbély in 1982) to explain the previously reported sleepiness-related changes in postural control.     

Evidence of sensorimotor deficits in functional ankle instability: A systematic review with meta-analysis

Functional ankle instability (FAI) has been associated with impaired sensorimotor function; however individual studies have produced conflicting results. In an attempt to reduce this ambiguity, a systematic review with meta-analysis was undertaken to determine which sensorimotor deficits exist with FAI. Fifty-three studies assessing sensorimotor factors in subjects with FAI were included from 465 identified articles. Studies were rated for methodological quality and data were pooled for peroneal reaction time, joint position sense, and postural sway during single-leg stance and time to stabilisation from a single-leg jump. Data on joint movement sense were unable to be pooled. When subjects with unstable ankles were compared to healthy controls, sensorimotor impairments were demonstrated for passive joint position sense (mean difference (MD) = 0.7°, 95% confidence interval (CI): 0.2–1.2°, p = 0.004), active joint position sense (MD = 0.6°, 95% CI: 0.2–1.0°, p = 0.002), postural sway in single-leg stance (standardised MD (SMD) = 0.6, 95% CI: 0.2–1.0, p = 0.002), the star excursion balance test (SMD = 0.4, 95% CI: 0.1–0.7, p = 0.009), and time to stabilisation from a single-leg jump in a medio-lateral (MD = 0.6 ms, 95% CI: 0.4–0.8, p < 0.0001) and an antero-posterior direction (MD = 0.7 ms, 95% CI: 0.4–1.0, p < 0.0001). Peroneal reaction time was not affected. Sensorimotor deficits occur for joint position sense and postural control in subjects with FAI. Deficits in peroneal muscle reaction time following perturbation are not evident.     

Effects of singular and dual task constraints on motor skill variability in childhood

We examined the effects of singular versus dual task constraints involving upper and lower extremities in typically developing children in young (4–6 years old), middle (7–9 years old), and old (10–13 years old) age groups. The purposes of this study were: 1) to investigate the effects of singular upper and lower extremity and dual upper and lower extremity conditions on motor variability and 2) to examine if variability in children’s motor actions would differ according to age (i.e., young, middle, or old). Twenty-four children (M age = 8.7; SD = 3.7) completed three tasks: finger rotation (upper extremity singular task constraint), obstacle crossing (lower extremity singular task constraint), and box carrying while walking (upper and lower extremity dual task constraint). Compared to the old age group, the young age group displayed more variable rotation strategies during clockwise (χ²(8, N = 24) = 12.4, p = 0.046) and counterclockwise finger rotation (χ²(8, N = 24) = 12.8, p = 0.047). During box carrying, children in the young age group had the most motor variability in their stride length, velocity, the vertical positioning of the box, and minimum and maximum joint excursion (all ps < 0.05). Crossing leg frontal plane hip angles were more variable on low versus high obstacles (all ps < 0.05). Our results suggest that four- to six-year-old children may still be developing the ability to produce consistent motor actions, especially under dual-task constraints. Examining children in the context of completing tasks with a variety of constraints may be useful in assessing the development of children's motor variability.     

The influence of Mulligan ankle taping during balance performance in subjects with unilateral chronic ankle instability

Objective: To determine whether Mulligan ankle tape influenced the performance in subjects with unilateral chronic ankle instability (CAI) during static balance; postural sway recovery patterns after hopping and dynamic tracking balance tasks.Design: A cross-sectional, within-subjects experimental study design between 4 ankle conditions (taped; untaped: injured and uninjured).Participants: 20 volunteer recreational athletes with unilateral CAI were recruited. Means and standard deviations highlighted the athletes' characteristics: age = 23 ± 1 years; height = 173.1 ± 2.4 cm; weight = 69.3±3 kg; Functional Ankle Disability Index (FADI) = 93.5 ± 5.1% and FADI Sport = 84.2 ± 9.4%.Interventions: Mulligan ankle taping.Main Outcome Measurements: Static balance (10 s); postural sway recovery patterns after a 30 s functional hop test (immediately, 30 and 60 s); dynamic tracking balance tasks (wandering, target overshoot and reaction-time).Results: Between the four conditions, static balance showed no significant differences (p = 0.792); significant changes occurred in postural sway over time (p < 0.001); no significant changes were reported for the dynamic tracking tasks. Wandering was highly correlated with reaction-time and overshooting (p < 0.01).Conclusion: Under resting and fatigued conditions, Mulligan ankle taping did not impact on the neuromuscular control during static and dynamic balance in subjects with healthy and unstable ankles.     

Center of pressure and the projection of the time-course of sitting skill acquisition

A normal time-course for the acquisition of sitting is essential. A delay in sitting may affect other developmental milestones, resulting in deficiencies in overall skill. Therefore, our aim was to identify variables whose measures at the very beginning of sitting would allow for the projection of the evolution of the sitting skill. Center of pressure data were collected from the postural sway of twenty-six typically developing infants while sitting on a force platform with a beginning ability to sit upright. Spatial, temporal and frequency variables of postural sway were obtained from both the medial/lateral and anterior/posterior directions of sway. Discriminant function analysis was conducted to identify potential predictors of the duration between onset and fully independent sitting. Gender (p = 0.025), median frequency (p = 0.006), and correlation dimension (p = 0.002) were identified to be predictive of grouping with 73.1% correct classification of the participating infants into short, mid, and long delay groups. In conclusion, measures taken at the earliest stage of sitting may allow the projection of the time-course to achieve independent sitting for typical infants. This approach may be useful for monitoring typical development.     

Effects of emotional videos on postural control in children

The link between emotions and postural control has been rather unexplored in children. The objective of the present study was to establish whether the projection of pleasant and unpleasant videos with similar arousal would lead to specific postural responses such as postural freezing, aversive or appetitive behaviours as a function of age. We hypothesized that postural sway would similarly increase with the viewing of high arousal videos in children and adults, whatever the emotional context. 40 children participated in the study and were divided into two groups of age: group 7–9 years (n = 23; mean age = 8 years ± 0.7) and group 10–12 years (n = 17; mean age = 11 years ± 0.7). 19 adults (mean age = 25.8 years ± 4.4) also took part in the experiment. They viewed emotional videos while standing still on a force platform. Centre of foot pressure (CoP) displacements were analysed. Antero-posterior, medio-lateral mean speed and sway path length increased similarly with the viewing of high arousal movies in the younger, older children, and adults. Our findings suggest that the development of postural control is not influenced by the maturation of the emotional processing.     

Balance dysfunction in hereditary and spontaneous spastic paraparesis

ObjectiveTo determine how postural sway is affected in people with spastic paraparesis (pwSP) and the impact of different impairments.MethodsIn 20 pwSP and 18 matched healthy controls standing postural sway was measured with eyes open and closed. Vibration threshold, isometric ankle and hip muscle strength and ankle stiffness with the participant at rest or preactivating the muscle was measured.ResultsAntero-posterior (AP) and medio-lateral (ML) sway was higher in pwSP. Muscle strength was reduced and ankle stiffness increased in pwSP. Increased vibratory threshold was seen in 35% of participants. Higher total ankle stiffness (R² = 0.44) was associated with lower AP sway with eyes open whilst hip abductor weakness was associated with increased ML sway with eyes open (R² = 0.36) or closed (R² = 0.47) or AP sway with the eyes closed (R² = 0.48).ConclusionsThe degree of postural sway was related to muscle paresis of the hip abductors particularly in the ML direction and under conditions of reduced sensory input. People with higher total ankle stiffness have less AP sway suggesting that this may help to stabilise the body.     

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.     

Cognitive loading-induced sway alterations are similar in those with chronic ankle instability and uninjured controls

Performing a cognitive task while balancing can result in either increased or decreased sway depending on the nature of the cognitive task, and is commonly used in pathologic populations to evaluate postural performance. A total of 39 participants were recruited into two groups: uninjured controls (n = 20, age: 21.9 ± 2.1 years, height: 175.0 ± 11.2 cm, mass: 71.3 ± 14.9 kg) and chronic ankle instability (n = 19, age: 22.1 ± 5.6 years, height: 169.7 ± 7.7 cm, mass: 72.9 ± 17.3 kg). Participants were asked to perform one of three cognitive tasks while maintaining single limb balance. Cognitive tasks included backwards counting by 3 (BC), the manikin test (MAN), and random number generation (RNG). Time-to-boundary minima, mean, and standard deviations were calculated and compared between groups as pre to post change scores. Effect sizes and 95% confidence intervals were also calculated to test for group differences and the effect of task performance on sway. No significant main effects of Group or Group by Task interactions were identified (p > 0.05). However, a significant multivariate main effect of Task was identified in BC (p = 0.001, F(6, 32) = 4.804) and RNG (p < 0.001, F(6, 32) = 6.233) but not for MAN (p = 0.117). The results suggest that those with chronic ankle instability and uninjured controls have similar postural–suprapostural interactions across multiple cognitive task domains. Both the BC and RNG tasks resulted in less sway for all participants. Our results suggest that dual-task interference in the CAI population may not be present as previous research would suggest.     

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.