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.     

Light finger contact concurrently reduces postural sway and enhances signal detection performance in children with developmental coordination disorder

The current study examined the effects of light finger touch on postural sway and signal detection performance in children with developmental coordination disorder (DCD). Children with DCD (n = 30; 18 boys, 12 girls; age = 11.87 ± 0.48 years) and typically developing children (n = 30; 14 boys, 16 girls; age = 11.73 ± 0.52 years) were recruited from schools in Pintung County, Taiwan. Participants completed a signal detection task under no finger touch (NT) and light finger touch (LT) conditions, while postural sway in both anteroposterior (AP) and mediolateral (ML) axes was recorded. In both conditions, children with DCD exhibited significantly higher levels of postural sway (p < 0.05) and lower signal detection performances (p < 0.05) than TDC. Additionally, both groups significantly reduced postural sway (p < 0.05) and enhanced signal detection performance (p < 0.05) when engaged in light finger touch compared with no finger touch. While the effect of LT on postural sway was greater among TDC relative to children with DCD (p < 0.05), the effect of LT on signal detection was greater in children with DCD compared with TDC (p < 0.05). These results suggest that light finger touch is effective in concurrently reducing postural sway and enhancing signal detection in both groups.     

Development of adaptive sensorimotor control in infant sitting posture

A reliable and adaptive relationship between action and perception is necessary for postural control. Our understanding of how this adaptive sensorimotor control develops during infancy is very limited. This study examines the dynamic visual–postural relationship during early development. Twenty healthy infants were divided into 4 developmental groups (each n = 5): sitting onset, standing alone, walking onset, and 1-year post-walking. During the experiment, the infant sat independently in a virtual moving-room in which anterior-posterior oscillations of visual motion were presented using a sum-of-sines technique with five input frequencies (from 0.12 to 1.24 Hz). Infants were tested in five conditions that varied in the amplitude of visual motion (from 0 to 8.64 cm). Gain and phase responses of infants’ postural sway were analyzed. Our results showed that infants, from a few months post-sitting to 1 year post-walking, were able to control their sitting posture in response to various frequency and amplitude properties of the visual motion. Infants showed an adult-like inverted-U pattern for the frequency response to visual inputs with the highest gain at 0.52 and 0.76 Hz. As the visual motion amplitude increased, the gain response decreased. For the phase response, an adult-like frequency-dependent pattern was observed in all amplitude conditions for the experienced walkers. Newly sitting infants, however, showed variable postural behavior and did not systemically respond to the visual stimulus. Our results suggest that visual–postural entrainment and sensory re-weighting are fundamental processes that are present after a few months post sitting. Sensorimotor refinement during early postural development may result from the interactions of improved self-motion control and enhanced perceptual abilities.     

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.     

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.     

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.     

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.     

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.     

Time dependent structure of postural sway in individuals with multiple sclerosis

Non-linear analyses, which examine the time dependent structure of physiological output have been found to be able to detect subtle differences in postural control between pathological groups and healthy controls while traditional linear parameters do not. This investigation examines whether a specific non-linear metric, approximate entropy, may provide a novel biomarker for balance impairment in individuals with multiple sclerosis (MS) who have normal sway. This analysis included a sample of 30 individuals with MS with normal postural sway and 36 controls. Participants stood on a force platform for two trials of 30 s with eyes open. Postural control was indexed by sway area, mean velocity along the antero-posterior (AP) and mediolateral (ML) axis. The time dependent structure of the COP along the AP and ML axes was indexed with approximate entropy (ApEn_AP; ApEn_ML). T-tests and Mann–Whitney U tests were utilized to analyze differences between groups. Per design there were no differences in sway area between the MS and control groups. Additionally, there were no differences in sway velocity. The MS group had lower ApEn_ML values compared to the control group (U = 376, p = .026). The results indicate that individuals with MS who have normal sway area had greater time dependent structure in ML sway. This investigation highlights the utility of non-linear analyses when assessing balance impairment in MS samples that present with minimal sway area.     

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.     

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.     

Immediate effects of perturbation treadmill training on gait and postural control in patients with Parkinson’s disease

The study investigates immediate adaptations of gait and balance to a single session of perturbed treadmill walking in patients with Parkinson’s disease. 39 Parkinson’s patients in stage 1–3.5 of the Hoehn and Yahr Scale were randomized into one of two groups, stratified by disease severity: The experimental group (n = 19) walked on a treadmill prototype which constantly applied perturbation by small three-dimensional tilting movements of the walking surface. The control group (n = 20) trained on the identical treadmill without perturbations. Patients walked on the treadmill for 20 min. Primary outcome measure was overground walking speed. Secondary outcomes were postural sway during quiet standing and spatiotemporal gait parameters during treadmill walking. Outcomes were measured repeatedly throughout the training session and after 10 min retention. The experimental group significantly increased overground walking speed after intervention compared to the control group (p = 0.014; ES = +0.41). Gait variability during treadmill walking significantly decreased after walking with perturbation. Sway area increased with treadmill walking only in the control group (p = 0.009; ES = +0.49). No other postural sway measures changed over time. Subgroup analyses revealed that in the experimental group patients with more pronounced motor impairment demonstrated larger increases in overground walking speed (p = 0.016; ES = +0.40) and stance phase symmetry (p = 0.011; ES = −0.42). In conclusion, a single session of perturbation treadmill training led to gait improvements, which were more pronounced compared to unperturbed treadmill walking. Effects on static postural sway were less pronounced.     

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.     

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.     

Effect of hearing aids on static balance function in elderly with hearing loss

While a few studies have investigated the relationship between hearing acuity and postural control, little is known about the effect of hearing aids on postural stability in elderly with hearing loss. The aim was to compare static balance function between elderly with hearing loss who used hearing aids and those who did not use. The subjects asked to stand with (A) open eyes on rigid surface (force platform), (B) closed eyes on rigid surface, (C) open eyes on a foam pad, and (D) closed eyes on a foam pad. Subjects in the aided group (n = 22) were tested with their hearing aids turned on and hearing aids turned off in each experimental condition. Subjects in the unaided group (n = 25) were tested under the same experimental conditions as the aided group. Indicators for postural stability were center of pressure (COP) parameters including; mean velocity, standard deviation (SD) velocity in anteroposterior (AP) and mediolateral (ML) directions, and sway area (95% confidence ellipse). The results showed that within open eyes–foam surface condition, there was greater SD velocity in the off-aided than the on-aided and the unaided than the on-aided (p < 0.0001 for SD velocity in AP and ML). Also, no significant differences were found between the off-aided and unaided group (p = 0.56 and p = 0.77 for SD velocity in AP and ML, respectively). Hearing aids improve static balance function by reducing the SD velocity. Clinical implications may include improving hearing inputs in order to increase postural stability in older adults with hearing loss.     

Reflex ankle stiffness is inversely correlated with natural body sway

We aimed to determine whether effective ankle stiffness (EAS), measured during slow unperceived perturbations of stance, is related to natural anterior–posterior body sway. Because the perturbations are not perceived, any neural component of the response to perturbation is assumed to be “reflex”, in the broad sense of an involuntary response to a stimulus. Subjects stood on a force platform for three 10-min trials. EAS was obtained from the average slope (Δτ/Δα) of the relation between ankle torque (τ) and ankle angle (α), recorded during repeated perturbations delivered at the waist by a weak spring. EAS was normalised using the subject's “load stiffness” (LS), calculated from mass (m) and height (h) above the ankle joint (m·g·h). Sway was obtained from fluctuations in ankle angle prior to perturbation. Variation in EAS and sway between subjects provided spread of data for correlation. There were no significant changes in EAS or sway across trials. All subjects had higher EAS than LS and mean EAS (1124 N m/rad) was significantly greater (p < 0.01) than mean LS (531 N m/rad). There was a strong significant inverse correlation between mean sway and mean normalised EAS (r = −0.68, p = 0.03). We conclude that the body, in response to slow unperceived perturbations, simulates an inverted pendulum with a stiffness of about twice LS and that EAS is largely generated by neural modulation of postural muscles. The inverse correlation between EAS and body sway suggests that the reflex mechanisms responding to perturbation also influence the extent of natural sway.     

Neuroimaging of an attention demanding dual-task during dynamic postural control

Cognitive tasks impact postural control when performed concurrently as dual-tasks. This is presumed to result from capacity limitations in relevant brain regions. We used functional near-infrared spectroscopy (fNIRS) to measure brain activation of the left motor, temporal, and dorsal-lateral prefrontal brain regions of younger (n = 6) and older (n = 10) adults. Brain activation was measured during an auditory choice reaction task (CRT) and standing on a dynamic posturography platform, both as single-tasks and concurrently as dual-task. Body sway was assessed by median absolute deviation (MAD) of anterior-posterior translation of the center of mass (COM). Brain activation was measured as changes in oxy-hemoglobin by fNIRS. During both single- and dual-task conditions, we found that older adults had greater brain activation relative to younger adults. During dual task performance, the total activation was less than expected from the sum of individual conditions for both age groups, indicating a dual-task interference (reduction in younger adults = 53% [p = 0.02]; in older adults = 53%; [p = 0.008]). This reduction was greater for the activation attributable to the postural task (reduction younger adults = 75% [p = 0.03]; older adults = 59% [p = 0.005]) compared to the CRT task (reduction younger adults = 10%, [p = 0.6]; older adults = 7.3%, [p = 0.5]) in both age groups. Activation reduction was not accompanied by any significant changes in body sway in either group (older adults: single-task MAD = 0.94 cm, dual-task MAD = 1.10 cm, p = 0.20; younger adults: single-task RMS = 0.95 cm, dual-task MAD = 1.08 cm, p = 0.14). Our results indicate that neural resources devoted to postural control are reduced under dual-task conditions that engage attention.     

Does forward head posture affect postural control in human healthy volunteers?

Proprioceptive afferent input from neck muscles plays an important role in postural control. Forward head posture has the potential to impair proprioceptive information from neck muscles and contribute to postural control deficits in patients with neck pain. This study investigated whether induced forward head posture affects postural control in healthy participants when compared to natural head posture. Centre of pressure sway area, distance covered and mean velocity were measured during 30 s of static standing using a force platform with 25 healthy individuals (mean age ± SD = 20.76 ± 2.19 years) in 8 different conditions. Base of support, eyes open or closed and natural or forward head posture varied within these testing conditions. The majority of comparisons between natural and forward head posture were not statistically significant (p > 0.05). This suggests that induced forward head posture in young healthy adults does not challenge them enough to impair postural control. Future studies should evaluate whether forward head posture affects postural control of individuals with chronic neck pain.