Movement adjustments in preparation for single-leg jumps in individuals with functional ankle instability

There is some evidence showing that people with functional ankle instability (FAI) can present changes in postural control during the landing phase of a jump. These studies also show preliminary results indicating possible changes during phases prior to landing. Therefore, the objective of this study was to investigate whether movement adjustments prior to a jump are different between people with and without FAI. Sixty participants with (n = 30) and without (n = 30) FAI participated in this study. The main outcome measures were the variability of range of motion in ankle inversion/eversion and dorsiflexion/plantarflexion; and variability of center of pressure for the directions anterior-posterior and medio-lateral during the pre-jump period for drop jump, vertical jump and during single-leg stance. The group with instability showed more variability of center of pressure in anterior-posterior direction (p = 0.04) and variability of range of motion in ankle dorsiflexion/plantar flexion (p = 0.04) compared to control in the single-leg stance test. For the within-group comparisons, the group with instability showed more variability of center of pressure in anterior-posterior direction in the drop jump higher than single-leg stance and vertical jump. The same pattern was seen for the control group. Thus, this study suggests that people with FAI have greater ankle range of motion variability and center of pressure variability in the anterior-posterior axis when compared to healthy individuals during single-leg stance. For those same two variables, preparation for a drop jump causes more postural instability when compared to the preparation for a vertical jump and to single-leg stance.     

Effects of Visual Manipulation in Sit-to-Stand Movement in Children With Cerebral Palsy

The authors sought to verify the effects of vision on sit-to-stand (STS) movement performance by means of postural sway in children with cerebral palsy (CP) and typical children (TC). Participants were 42 TC and 21 children with CP. STS movement was assessed with eyes open and with eyes closed. Area and velocity of center of pressure sway were analyzed in each of the 3 STS phases. We observed greater postural sway during STS movement with eyes closed. Children with CP presented greater postural sway than TC did. Both groups exhibited greater postural instability with absence of vision expressing the role of vision to keep postural stability. Moreover, the greater postural instability was observed in children with CP.     

Dynamics of postural control during bilateral stance – Effect of support area,visual input and age

The present study investigated the effect of support area, visual input and aging of the dynamics of postural control during bilateral stance. Fifteen young (22.1 ± 1.7 years) and fifteen older (68.3 ± 2.7 years) individuals completed four different 90 s bilateral stance trials: 1) shoulder wide feet distance with eyes open, 2) shoulder wide feet distance with eyes closed, 3) narrow feet distance with eyes open, and 4) narrow feet distance with eyes closed on a force plate form. The anterior (AP) and mediolateral (ML) center of pressure (COP) trajectories were calculated from the middle 60 s of the ground reaction forces and moments. Sample entropy (SaEn), correlation dimension (CoD), the largest Lyapunov exponent (LyE) and entropic half-life (ENT½) were calculated for the COP in both directions. In young individuals, a narrower support area resulted in a restricted movement solution space with lower SaEn, lower LyE and longer ENT½ in the executed motor control strategy, whereas it increased the CoD in the older individuals. During the eyes closed trials, SaEn, CoD and LyE increased and decreased ENT½ for both groups in the AP direction and increased SaEn and LyE in the ML direction for the older individuals alone. This indicates that aging is associated with direction- and task-dependent changes in the dynamics of the executed COP movements during postural stance tasks.     

Diminished plantar cutaneous sensation and postural control

The purpose of this study was to assess the effect of diminished plantar cutaneous sensation induced by cooling on postural control during double- and single-limb quiet standing. 32 healthy adults were tested on an intervention day and control day. The intervention consisted of 10 min. of ice immersion of the plantar aspect of the feet prior to balance testing. Dependent variables were center of pressure velocity and area during double- and single-limb stance with eyes open and closed. Significant interactions were found between sensation and vision for double-limb center of pressure area, with a significant reduction in area of center of pressure excursions after reducing sensation with eyes closed but not with eyes open. The area of center of pressure excursions may have been reduced in an effort to curtail exploratory postural behavior given the altered afferent input from plantar receptors. There were no significant differences for plantar hypoesthesia in single-limb stance.     

Four Weeks of Neuromuscular Training Improve Static and Dynamic Postural Control in Overweight and Obese Children: A Randomized Controlled Trial

Abstract

Thirty-two children with overweight or obesity were randomly divided into a neuromuscular training group (NTG) (n = 16) and a control group (CG) (n = 16). All individuals participated in the measurement of static postural control under two conditions: the double-leg stance with eyes open (EO) and eyes closed (EC). The center of pressure variables was obtained. mSEBT was used for dynamic postural control. Neuromuscular training was performed twice per week and lasted 4 weeks. The results of this study indicate that 4 weeks of neuromuscular training improve static and dynamic postural control in children with excess body weight.     

The effects of visual input on postural control of the lumbar spine in unstable sitting

Postural control of the lumbar spine in unstable sitting was quantified through the analysis of the center of pressure (CoP) movement recorded by a force plate situated underneath a seat that incorporated a hemisphere. Thirteen healthy subjects were tested under conditions of increasing seat instability and elimination of visual input. The purpose of this study was to determine the relative effects of visual input and support surface instability on open and closed loop postural control mechanisms in sitting and to determine the association between traditional summary statistics and random walk analysis of CoP movement. The effects of the seat instability level and visual input on the CoP movement parameters were tested with a two-factor, repeated measures ANOVA (p<0.01). In all summary statistics CoP movement parameters increased significantly due to the seat instability level and lack of visual input. The random walk analysis identified two regions, short- and long-term, which has been postulated to represent open and closed loop control mechanism, respectively. While short-term scaling exponents were independent from visual input, CoP displacement in the short-term region was significantly increased in the eyes closed condition. Summary statistic of CoP total path length per second correlated highly with critical point coordinates and short-term diffusion coefficients. The CoP movement in the long-term region was consistent with a closed loop control mechanisms. The findings of visual influence on what is assumed as an open-loop control mechanism does not, at face value, support the hypothesis that two separate mechanisms are working to achieve postural control.     

Development of postural stability limits: Anteroposterior and mediolateral postural adjustment mechanisms do not follow the same maturation process

There is increasing evidence that indicates a critical transition period for the maturation of postural control from the ages of 6–7 years. Some studies suggest that this transitional period may be explained by a change from a ballistic toward a sensory strategy, but the cause remains unknown. The purpose of this study was to investigate the influence of the transition period on dynamic postural control in a natural self-initiated leaning task under different sensory conditions. We evaluated the center of pressure (COP) displacement during maximum leaning in four directions (forward, backward, rightward, leftward) under three sensory conditions (eyes open, eyes closed and eyes closed standing on a foam). Three groups were tested: young children (4 years old), older children (8–10 years old) and adults (21–42 years old). The maximum COP excursion along the anteroposterior and mediolateral axes and the COP amplitude were analyzed. Young children showed smaller maximum anteroposterior and mediolateral COP excursion than other groups. Older children also exhibited a significantly smaller maximum excursion along the mediolateral direction but performed similar to adults along the anteroposterior direction. In a similar manner, the analysis of the COP amplitude did not indicate any differences between the groups along the anteroposterior axis. In contrast, along the mediolateral axis, the results showed developmental differences. Furthermore, the effect of sensory conditions was similar across the children's groups. Our results suggest an important plasticity period for the maturation of postural control mechanisms. Notably, our findings support the idea that the postural mechanisms controlling the anteroposterior axis reach maturity before the mechanisms involved in controlling the mediolateral axis.     

Older adults exhibit altered motor coordination during an upper limb object transport task requiring a lateral change in support

Investigating an ecologically relevant upper limb task, such as manually transporting an object with a concurrent lateral change in support (sidestepping alongside a kitchen counter), may provide greater insight into potential deficits in postural stability, variability and motor coordination in older adults. Nine healthy young and eleven older, community dwelling adults executed an upper limb object transport task requiring a lateral change in support in two directions at two self-selected speeds, self-paced and fast-paced. Dynamic postural stability and movement variability was quantified via whole-body center of mass motion. The onset of lead lower limb movement in relation to object movement onset was quantified as a measure of motor coordination. Older adults demonstrated similar levels of stability and variability as their younger counterparts, but at slower peak movement velocity and increased task duration. Furthermore, older adults demonstrated asymmetrical motor coordination between left and right task directions, while younger adults remained consistent regardless of task direction. Thus, older adults significantly modulated movement speed and motor coordination to maintain similar levels of stability and variability compared to their younger counterparts.     

Transient Effects of Gaze Stability Exercises on Postural Stability in Patients With Posterior Circulation Stroke

The authors sought to investigate if short-term gaze stability exercises have an effect on postural stability of dynamic standing during neck movement in patients with posterior circulation stroke (PCS). Patients in both PCS and non-PCS groups were assigned to either an intervention or control group. The intervention group performed the gaze stability exercises for 10 min while the control group was merely resting. The center of pressure velocity was calculated to evaluate the postural stability. After intervention, PCS and non-PCS showed a significant reduction in center of pressure velocity during dynamic standing with eyes closed condition, and the PCS group showed a significant improvement in eye-opened condition. This study indicated that gaze stability exercises improve PCS patients' postural control, especially during dynamic standing.     

Effects of vision and cognitive load on anticipatory and compensatory postural control

This study assessed the effects of vision and cognitive load on anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) in response to an externally triggered postural perturbation. A ball-hitting test was repeated under different visual conditions (eyes open, EO; eyes closed, EC) and cognitive loads (no load, 3-subtraction task, time-limited 3-subtraction task). Data were collected separately for I) surface electromyography from the right side of the biceps brachii (BIC) and erector spinae (ES) to detect the latency and response intensity (RI); and II) displacement of the centre of pressure (ΔCOP) to detect the standard deviation (ΔCOP_SD) and maximum value (ΔCOP_max) in the anterior-posterior direction. Compared with the results under the EC condition, the ES latency was shorter and the RI of the BIC was lower under the EO condition. Accordingly, the ΔCOP_SD and ΔCOP_max were increased in the APAs phase and decreased in the CPAs phase. Cognitive load had no effect on APAs and CPAs or on ΔCOP in the APAs phase. However, ΔCOP_max was decreased in the CPAs phase during the EC condition. In conclusion, vision played an important role in APAs and CPAs for muscle activation and ΔCOP. Cognitive load had no effect on neuromuscular APAs or CPAs except when the postural perturbation occurred when visually unexpected.     

Postural sway and joint kinematics during quiet standing are affected by lumbar extensor fatigue

The purpose of this study was to investigate changes in postural sway and strategy elicited by lumbar extensor muscle fatigue. Specifically, changes in center of mass (COM), center of pressure (COP), and joint kinematics during quiet standing were determined, as well as selected cross correlations between these variables that are indicative of movement strategy. Twelve healthy male participants stood quietly both before and after exercises that fatigued the lumbar extensors. Whole-body movement and ground reaction force data were recorded and used to calculate mean body posture and variability of COM, COP, and joint kinematics during quiet standing. Three main findings emerged. First, participants adopted a slight forward lean post-fatigue as evidenced by an anterior shift of the COM and COP. Second, post-fatigue increases in joint angle variability were observed at multiple joints including joints distal to the fatigued musculature. Despite these increases, anterior-posterior (AP) ankle angle correlated well with AP COM position, suggesting the body still behaved similar to an inverted pendulum. Third, global measures of sway based on COM and COP were not necessarily indicative of changes in individual joint kinematics. Thus, in trying to advance our understanding of how localized fatigue affects movement patterns and the postural control system, it appears that joint kinematics and/or multivariate measures of postural sway are necessary.     

Velocity discrimination: reliability and construct validity in older adults

The aim of this study was to determine whether a test of velocity discrimination is a reliable and valid measure of proprioception in healthy older adults. Results revealed excellent test-retest reliability over a 2-week period. Velocity discrimination also indicated good construct validity with modest correlations with center of pressure sway outcomes in eyes open and closed conditions as well as stair climbing time. Good construct validity was identified by velocity discrimination sensitivity to age with a higher mean value for the older participants than for the younger participants. These findings suggest velocity discrimination is a valid and reliable measure of velocity sense, which may be included with measures of position and movement sense to enhance the proprioceptive testing repertoire among researchers. Implications of these results are discussed in terms of evaluation of proprioceptive training programs aimed to enhance postural control.     

Age-related differences in postural reaction time and coordination during voluntary sway movements

The elderly are known to exhibit declines in postural control during standing and walking, however little is known about how the elderly react under time-critical and challenging postural situations. The purpose of this study was to examine age-related differences in reaction time (RT) and the pattern of temporal coordination between center of pressure (COP), trunk and head motion during voluntary postural sway movements. Healthy young (n=10; mean=24 years; SD=5 years) and elderly men (n=8; mean=75 years; SD=2 years) stood on a force plate with tri-axial accelerometers attached to the head and lower trunk. Participants were required to generate sway in the anterior-posterior (AP) or medial-lateral (ML) direction in response to an auditory cue during two different testing conditions called Static reaction and Dynamic reaction. Static reactions involved the initiation of voluntary sway in either the AP or ML direction from quiet stance. Dynamic reactions involved an orthogonal switch of voluntary sway between the AP and ML directions. Compared to the young, elderly individuals exhibited slower RT during both Static and Dynamic reaction, and smaller differences in RT and phasing between COP, trunk, and head motion. The results of this study suggest that the elderly adopted more rigid coordination strategies compared to the young when executing a rapid change in direction of whole body motion. The rigid movement strategy of the elderly was presumably generated in an effort to compensate for increased challenge to the maintenance of stability.     

The Effect of Vision and Surface Compliance on Balance in Untrained and Strength Athletes

The purpose of this investigation was to evaluate the effect of the removal of vision and/or surface compliance on postural stability in strength athletes who habitually use free-weights and compound movements in their training (i.e., powerlifters, Olympic weightlifters), and untrained individuals. Static and dynamic balance testing was performed with eyes open or closed on stable and memory foam surfaces. Both groups had similar increases in postural sway area and velocity during quiet standing testing; whereas group main effects and interactions for dynamic testing revealed that untrained participants experienced greater relative declines in postural performance when voluntary limits of stability are stressed, especially when both vision and surface compliance were deterred. These results demonstrate that in comparison to untrained young adults, postural control variables may be reduced to a lesser extent in strength athletes when sensory constraints are altered; however this appears to be specific to the type of postural task performed.     

Effect of altered surfaces on postural sway characteristics in elderly subjects

Mobility is essentially based on successful balance control. The evaluation of functional strategies for postural stability is requisite for effective balance rehabilitation and fall prevention in elderly subjects. Our objective was to clarify control mechanisms of different standing positions reflecting challenges of typical everyday life situations. For this purpose, elderly subjects stood on different surfaces resulting in a change of the biomechanical constraints. Sway parameters out of time and frequency domain were calculated from center-of-pressure (COP) excursions. Besides the classic quantification of the amount of sway variability, we investigated the temporal organization of postural sway by means of nonlinear time series analysis. Limb load symmetry was quantified via foot pressure insoles. We found task dependent motor outputs: (1) asymmetrical loading in all conditions; (2) altered amount and structure of COP movements with dissimilar changes in medio-lateral and anterior–posterior direction; (3) changes of the motor output affect several time scales especially when standing on a balance board or with one foot on a step. Our results indicate that elderly subjects preferred forcefully one limb which supports a step-initiation strategy. Modifications of the postural sway structure refer to the interaction of multiple control mechanisms to cope with the altered demands. The identification of postural strategies employed in daily activities augments the ecological validity of postural control studies.     

The functional role of central and peripheral vision in the control of posture

Three experiments were conducted to investigate the role of central and peripheral vision (CV and PV) in postural control. In Experiment 1, either the central or peripheral visual field were selectively stimulated using a circular random dot pattern that was either static or alternated at 5 Hz. Center of foot pressure (CoP) was used to examine postural sway during quiet standing under both CV and PV conditions. The results showed that, when the visual stimulus was presented in the periphery, the CoP area decreased and more so in the anterior-posterior (AP) than in the medio-lateral (ML) direction, indicating a characteristic directional specificity. There was no significant difference between the static and dynamic (alternating) conditions. Experiment 2 investigated the directional specificity of body sway found in Experiment 1 by having the trunk either be faced toward the stimulus display or perpendicularly to it, with the head always facing the display. The results showed that the stabilizing effect of peripheral vision was present in the direction of stimulus observation (i.e., the head/gaze direction), irrespective of trunk orientation. This suggested that head/gaze direction toward the stimulus presentation, rather than a biomechanical factor like greater mobility of the ankle joint in AP direction than in ML direction, was essential to postural stability. Experiment 3 further examined whether the stabilizing effect of peripheral vision found in Experiments 1 and 2 was caused because more dots (500) were presented as visual cues to the peripheral visual field than to the central visual field (20 dots) by presenting the same number of dots (20) in both conditions. It was found that, in spite of the equal number of dots, the postural sway amplitudes were larger for the central vision conditions than for the peripheral vision conditions. In conclusion, the present study showed that peripheral rather than central vision contributes to maintaining a stable standing posture, with postural sway being influenced more in the direction of stimulus observation, or head/gaze direction, than in the direction of trunk orientation, which suggests that peripheral vision operates primarily in a viewer-centered frame of reference characterized by the head/gaze direction rather than in a body-centered frame of reference characterized by the anatomical planes of the body.     

Effects of age on listening and postural control during realistic multi-tasking conditions

Successful performance of balance-related activities requires the effective integration of sensory, cognitive, and motor processes that can be affected by age-related changes. Of these age-related sensory changes, the effects of declines in hearing on balance have not been well-studied despite the fact that hearing loss has now been acknowledged as a significant risk factor for falls. The goal of this study was to evaluate age-related differences in a “standing while listening” task within increasingly challenging conditions resembling those that are often encountered in realistic, everyday situations.This study used a dual-task paradigm in an immersive Virtual Reality street scene setting in which postural load (firm, compliant), listening load (number of talkers), and visual load (eyes open/closed) were manipulated. A multi-talker divided attention listening task was used. Postural performance was assessed using center of pressure (COP) path length, while listening performance was assessed using spoken word recognition accuracy.Results demonstrated that age-related differences were observed in postural performance when postural demands were the highest and in listening performance when listening demands were the highest. Proportional dual-task costs were more pronounced for postural task performance compared to listening task performance and were more pronounced for older compared to younger adults. Postural dual-task costs increased as a function of increasing listening loads. Removal of visual information improved listening task performance across both groups and reduced the dual-task costs to listening in older adults when listening demands were highest (resulting in dual-task benefits).Taken together, the findings support previously documented age-related declines in postural control and auditory processing, demonstrate that increasing listening demands may result in poorer balance, particularly in older adults, and provide additional insights into the interactive effects of age-related declines when sensory, motor, and cognitive challenges are incremented factorially.     

Effects of sensory manipulations on the dynamical structure of center-of-pressure trajectories of children with cerebral palsy during sitting

Aim: To investigate the effects of manipulating visual information and the compliance of the support surface on the area of sway and dynamical trajectories of center-of-pressure (CoP) in children with CP and children with typical development during static sitting. Methods: 32 typical children, 14 children with mild CP and 12 with moderate-to-severe CP were tested for CoP sway during static sitting under four sensory conditions: (1) eyes open on a rigid surface; (2) eyes closed on a rigid surface; (3) eyes open on foam; (4) eyes closed on foam. Results: Children with moderate-to-severe CP showed greater regularity and local stability of dynamical CoP trajectories and lower complexity in their motor patterns than typical children and children with mild CP. Moreover, removing vision and sitting on a compliant surface reduced the regularity of CoP trajectories. Conclusion: Children with CP were able to adjust the structure and complexity of their postural control responses to sensory challenges, although the structure of their postural responses was poorer than in typical children.     

Static balance in children with developmental coordination disorder

The purpose of this study was to compare the postural sway profiles of 9/10-year-old children with developmental coordination disorder and balance problems (DCD-BP, n=64) with those of non-DCD children (n=71). We measured center of pressure excursions in conditions with and without vision for 30s while standing still on the dominant leg, the non-dominant leg, or both legs. Sway area, total path length, and Romberg's quotient were analyzed. Most measures differed significantly between groups, except sway area when the children stood with vision on either the dominant leg or both legs. When standing on the dominant leg or both legs, DCD-BP children demonstrated greater total path length in all conditions and a greater sway area in without-vision conditions. DCD-BP children showed more difficulty standing on the non-dominant leg with eyes both open and closed. While boys showed results similar to the total group, the girls with DCD-BP only exhibited significant differences in three conditions with eyes closed, but not with eyes open. Analysis of Romberg's coefficient also indicated that children with DCD-BP did not over-rely on visual information.     

The precision demands of viewing distance modulate postural coordination and control

There are contrasting views on the role of vision in modifying postural organization (information-driven and postural facilitation) and limited direct tests of the underlying postural mechanisms. Here, we examined whether the distinction between the two views is appropriate given that both are interrelated parts of task constraints modulating postural coordination and control. The study investigated whether changes in the organization of the postural system are a function of the visual precision demands of a task and, in addition, whether such organization could be described as reflecting an intermittent controller. Sixteen participants were instructed to maintain quiet postural stance while fixating a point at different viewing distances (25, 50, 135, 220, 305 cm) or standing with eyes closed. The 25-cm condition showed the lowest standard deviation of the center of pressure (COP) and the highest correlation dimension (CD) in the anterior posterior direction. Analyses revealed that, contrary to the intermittent controller hypothesis, adaptations in the continuous COP and center of mass (COM) coupling characterized the observed changes in CD. The findings show that the natural act of looking to the same feature in the environment as a function of visual viewing distance can lead to quantitative and qualitative changes in the dynamics of posture. This is consistent with the view that postural facilitation and information availability are integrated in the perceptual-motor dynamics.