Is postural control affected by expertise in alpine skiing?

Objectives: This study examined the postural performance of two groups of male skiers competing at different levels and the consequences on postural control of the suppression of visual afferences by eye closure. Methods: Seven national level (NAT) skiers and 7 regional level (REG) skiers were asked to stand as still as possible on a force platform with eyes opened and closed and while wearing or not wearing their ski boots in a stable posture and in two unstable postures (in the sagittal or frontal plane). Postural performance was assessed with centre of foot pressure measurements. Results: REG and NAT skiers were similarly influenced by the absence of visual information and presented similar postural performance when tests were performed with ski boots. However, without ski boots, REG skiers displayed better postural performance than NAT skiers. Conclusions: The inferior postural performance of NAT skiers without ski boots could be a long term effect of repetitive wearing of ski boots, which impairs postural performance by restricting the range of motion of the ankle-foot complex. Since individuals with decreased postural performance are believed to be more susceptible to ankle injury than those with finer postural control, NAT skiers should benefit from specific training aimed at improving postural ability and preventing ankle injury.     

Test–retest reliability of muscle vibration effects on postural sway

The effect of alterations in the processing of proprioceptive signals, on postural control, has been studied using muscle vibration effects. However, reliability and agreement of muscle vibration have still to be addressed.This study aimed to assess intra- and interday reliability and agreement of vibration effects of lumbar paraspinal and triceps surae muscles in a non-selected sample of 20 subjects, standing on solid surface and on foam. We used mean position and velocity of Centre of Pressure (CoP), during and after vibration to quantify the effect of muscle vibration. We also calculated the ratio of vibration effects on the lumbar paraspinal and triceps surae muscles (proprioceptive weighting).Displacement of the CoP during vibration showed good reliability (ICCs > 0.6), and proprioceptive weighting of displacement fair to good reliability (0.52–0.73). Agreement measures were poor, with most CV's ranging between 18% and 36%. Change in CoP velocity appeared not to be reliable. Balance recovery, when based on CoP position and calculated a short period after cessation of vibration, showed good reliability. According to this study, displacement during vibration, proprioceptive weighting and selected recovery variables are the most reliable indicators of the response to muscle vibration.     

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.     

Do sensorial manipulations affect subjects differently depending on their postural abilities?

Objectives

To examine whether sensorial manipulation affects subjects differently according to their postural performance and the strategies used. The literature showed that the level of competition of soccer players influences their postural performance and strategy.

Methods

Eight high‐level (HL) professional soccer players and nine regional‐level (RL) soccer players were tested (1) in a reference condition and (2) in a manipulated sensorial condition (MAN). The MAN condition consisted of perturbing the proprioceptive and exteroceptive information. For each postural condition, balance was assessed by measuring the centre of foot pressure using a force platform during a test of bipedal standing posture.

Results

The postural control was less perturbed in the HL than in the RL players in the two postural conditions. Moreover, the group–condition interaction showed that the postural control was less disturbed in the HL than in the RL players when the sensory information was manipulated.

Conclusions

The HL soccer players probably possessed a better internal model of verticality than the RL players. Subjects who had a better postural control level were less disturbed by sensorial manipulation than the others in postural regulation.Postural regulation requires the integration of proprioceptive and exteroceptive information. When this information is perturbed or manipulated, postural control is altered. Indeed, cutaneous sensory disturbance by hypothermic anaesthesia,¹ myotendinous interference by muscle vibration,² pain by stimulation of skin thermoreceptors,³ electromyostimulation,⁴ galvanic vestibular stimulation⁵ or visual manipulation by stroboscopic light⁶ affects postural stability in healthy subjects. Keshner et al⁷ showed that combined disturbances (ie, visual, proprioceptive, vestibular) caused greater disturbance than any one presented alone. However, combined perturbations might not disturb all subjects in the same way. We do not know whether subjects who present a better postural performance level counteract differently to the effects of manipulating proprioceptive and exteroceptive information in postural regulation than the others. Moreover, the postural strategy—that is, preferential involvement of short (visuovestibular contribution) or long (myotatic participation) neuronal loops in postural regulation—can also influence the effects of sensorial perturbation. To study this, sportsmen at different levels of competition should be studied.Indeed, the level of competition influences the postural performance: the higher the level of competition, the more stable the posture.^8,9 The level of competition also influences the preferential use of the different neuronal loops involved in balance regulation as Paillard et al⁹ showed with soccer players. Hence, one can wonder (1) whether high‐level soccer players can preserve better postural control than players at a lower level when their proprioceptive and exteroceptive informations are disturbed and (2) whether these two categories of players are differently affected by sensorial manipulation.The aim of this work was to compare the postural behaviour between high‐level soccer players and players at a lower level in two different postural conditions. The first condition was the reference (no sensorial perturbation), whereas in the second condition proprioceptive and exteroceptive information was disturbed.     

Is postural control restored following anterior cruciate ligament reconstruction? A systematic review

Purpose

The aim of this systematic review was to determine whether lower limb postural control is restored in patients following anterior cruciate ligament (ACL) reconstruction surgery when compared to healthy controls.

Methods

A systematic review was conducted. Electronic databases including Medline, Embase, SPORTDiscus and CINAHL were searched from the earliest possible entry to April 2010. Studies that evaluated postural control in patients following ACL reconstruction surgery with a control group using a force platform were included.

Results

Ten studies evaluating 644 participants at a mean 29?months follow-up were included in this review. In static balance tasks, there was a trend towards improved postural control in the control group for eyes-open but not eyes-closed conditions. Only four studies evaluated dynamic balance, and the results from these were somewhat mixed. Nonetheless, there was evidence to suggest impaired postural control in patients following ACL reconstruction surgery when compared to controls, particularly for more challenging tasks.

Conclusion

Although there appears to be a trend towards impaired static and dynamic postural control in patients following ACL reconstruction surgery, the limited number of studies and differing methodologies makes conclusions tentative. Deficits in dynamic tasks may be more relevant to people intending to return to sport following surgery due to the inherently dynamic nature of sport and should perhaps be the focus of future research.

Level of evidence

III.     

What is the most effective type of audio-biofeedback for postural motor learning?

Biofeedback is known to improve postural control and reduce postural sway. However, the effects that different biofeedback modes (coding for more or less complex movement information) may have on postural control improvement are still poorly investigated. In addition, most studies do not take into account the effects of spontaneous motor learning from repetition of a task when investigating biofeedback-induced improvement in postural control. In this study, we compared the effects of four different modes of audio-biofeedback (ABF), including direction and/or magnitude of sway information or just a non-specific-direction alarm, on the postural sway of 13 young healthy adults standing on a continuously rotating surface. Compared to the non-specific-direction alarm, ABF of continuous postural sway direction and/or amplitude resulted in larger postural sway reduction in the beginning of the experiment. However, over time, spontaneous postural motor learning flattened the effects of the different modes of ABF so that the alarm was as effective as more complex information about body sway. Nevertheless, motor learning did not make ABF useless, since all modes of ABF further reduced postural sway, even after subjects learned the task. All modes of ABF resulted in improved multi-segmental control of posture and stabilized the trunk-in-space. Spontaneous motor learning also improved multi-segmental control of posture but not trunk-in-space stabilization as much as ABF. In conclusion, although practice standing on a perturbing surface improved postural stability, the more body sway information provided to subjects using ABF, the greater the additional improvement in postural stability.     

Vibration-induced post-effects: a means to improve postural asymmetry in lower leg amputees?

Muscle vibration has been shown to induce long-lasting and oriented alteration of standing posture in healthy individuals. The postural alterations can last several minutes following the end of vibration and are called post-effects. The goal of this study was to determine whether persons with lower leg amputation that show persistent postural asymmetry after usual rehabilitation experience these postural post-effects and if this could improve their weight bearing on the prosthesis. Centre of pressure (CP) position during stance was recorded prior to and up to 13 min after a 30 s unilateral vibration applied during sitting to lateral neck (trapezius) or hip (gluteus medius) muscles in 14 individuals with unilateral lower leg amputation and 18 controls. The amputees’ postural asymmetry was confirmed prior to the vibration intervention. A CP displacement, without an increase in CP velocity, was observed in both groups of participants over the 13 min post-vibration. For both the neck or hip vibration sites, the CP shifts were directed in the medio-lateral plane and were oriented either towards the vibrated side or the opposite side across subjects. This led to a decrease of postural asymmetry in half of the group of amputees. Within subject, the orientation of the post-effect was constant and changed to the opposite direction with vibration of the opposite body side. It is suggested that the post-effects are produced by a change of the postural reference consequent to the sustained proprioceptive message induced during the muscle vibration period. The orientation of the post-effects is discussed in relation to the notion of reference frame preference. All in all, because post-effect orientation is constant within subject and adaptive, future studies should investigate if individuals with lower leg amputation could benefit from postural post-effects induced by muscle vibration to improve function.     

Assessment of the postural control strategies used to play two Wii Fit™ videogames

The Nintendo Wii Fit? may provide an affordable alternative to traditional biofeedback or virtual reality systems for retraining or improving motor function in populations with impaired balance. The purpose of this study was to evaluate postural control strategies healthy individuals use to play Wii Fit? videogames. Sixteen young adults played 10 trials of Ski Slalom and Soccer Heading respectively. Centre of pressure (COP) excursion and three-dimensional movement data were acquired to determine variability in medial–lateral COP sway and shoulder–pelvic movement. While there was no difference in medial–lateral COP variability between games during trial 1, there was a significant difference after 10 trials. COP sway increased (59–75 mm) for Soccer Heading while it decreased (67–33 mm) for Ski Slalom from trial 1 to trial 10. During Ski Slalom participants demonstrated decreased shoulder and pelvic movement combined with increased pelvic–shoulder coupling. Conversely, participants demonstrated greater initial shoulder tilt when playing Soccer Heading, with no reduction in pelvic rotation and tilt. Participants decreased pelvic and trunk movements when skiing, suggesting a greater contribution of lower extremity control while they primarily used a trunk strategy to play Soccer Heading.     

Is postural asymmetry associated with emotional stability in healthy subjects? A preliminary study

Purpose

Considering that musculo-skeletal system and nervous system reciprocally are connected by the presence of proprioceptors and interoceptors, the aim of this study was to investigate the relationship between emotional stability and posture.

Methods

We recruited 100 healthy volunteers (age 30.2 ± 9.8 years) who regularly practiced physical activity, and we evaluated posture (vertical line of Barrè) and emotional stability (a specific component of the Big Five Questionnaire—BFQ). Chi-square test was used to evaluate the distribution of the postural evaluation by sex. ANOVA with Bonferroni correction was used to evaluate the differences of the BFQ in the groups of Barrè (ascending, descending, mixed, and disharmonic). A multiple regression models was set to assess the factors related to gender, age, and posture. P < 0.05 was considered significant.

Results

In 86 subjects, we found asymmetric posture expressed by malalignment of the Barrè line with respect to the median line. Control of Emotion did not differ between the different groups in Barrè assessment test (p = 0.07), but for Impulse Control, there were significant differences between mixed and descending and between mixed and neutral posture (p = 0.03). In emotional stability, we observed significant differences between mixed and descending and mixed and neutral (p = 0.02). The subjects who had greater control of emotions and impulses had a mixed or a descending-type posture of the vertical evaluation in the Barrè test (p < 0.01).

Conclusions

Emotional stability was associated with postural adjustment, affecting, in particular, the cervical spine and legs. We could hypothesize that symmetrical posture is not necessarily related to psychological balance, while asymmetric posture may represent a sign of good control of emotions and impulses.

     

The effect of instructions on postural–suprapostural interactions in three working memory tasks

Examining postural control while simultaneously performing a cognitive, or suprapostural task, has shown a fairly consistent trend of improving postural control in young healthy adults and provides insight into postural control mechanisms used in everyday life. However, the role of attention driven by explicit verbal instructions while dual-tasking is less understood. Therefore, the purpose of this investigation is to determine the effects of explicit verbal instructions on the postural–suprapostural interactions among various domains of working memory. A total of 22 healthy young adults with a heterogeneous history of ankle sprains volunteered to participate (age: 22.2 ± 5.1 years; n = 10 history of ankle sprains, n = 12 no history). Participants were asked to perform single-limb balance trials while performing three suprapostural tasks: backwards counting, random number generation, and the manikin test. In addition, each suprapostural task was completed under three conditions of instruction: no instructions, focus on the postural control task, focus on the suprapostural task. The results indicate a significant effect of instructions on postural control outcomes, with postural performance improving in the presence of instructions across all three cognitive tasks which each stress different aspects of working memory. Further, postural–suprapostural interactions appear to be related to the direction or focus of an individual’s attention as instructions to focus on the suprapostural task resulted in the greatest postural control improvements.Thus, attention driven by explicit verbal instructions influence postural–suprapostural interactions as measured by a temporal–spatial postural control outcome, time-to-boundary, regardless of the suprapostural task performed.     

Are there differences in postural regulation according to the level of competition in judoists?

The aim of this work was to study the posturokinetic capacities and use of visual information by judoists according to their level of competition. Twenty male judoists aged between 16 and 19 took part. They were separated into two groups: those that competed at regional level and those that competed at national and international level. Static balance was measured on a force platform. No difference was seen between the two groups. However, it seems that visual information is more important to the higher level judoists. Perhaps the level of competition influences the sensory canals involved in balance.     

What is the influence of surgical treatment of adolescent idiopathic scoliosis on postural control?

PurposeTo evaluate the effect of surgical treatment on the control of upright balance in adolescent idiopathic scoliosis (AIS).MethodsThirty adolescents were divided into two groups: Group C (n = 15) consisted of individuals without scoliosis (control), and Group S (n = 15) consisted of individuals with scoliosis. The mean amplitude and velocity of the center of pressure (COP) evaluations in the anterior-posterior and medial-lateral directions were obtained before surgery and at 7, 30, 60 and 90-days after surgery, in an upright position, using a force platform.ResultsGroup S showed larger oscillation than Group C before surgery. The COP oscillation in Group S after surgery was larger than that in the pre-surgery period. The oscillation diminished over the post-surgery period, but individuals in the 90-day post-surgery period still had larger oscillation compared with the oscillation in the pre-surgery period.ConclusionGroup S had larger AP and ML mean amplitude and mean velocity before and after surgery compared with Group C, which suggests that a sensorimotor impairment or sensory integration problem could explain the balance control alterations more than biomechanical factors in the AIS.     

Intermittent use of an “anchor system” improves postural control in healthy older adults

Haptic information, provided by a non-rigid tool (i.e., an “anchor system”), can reduce body sway in individuals who perform a standing postural task. However, it was not known whether or not continuous use of the anchor system would improve postural control after its removal. Additionally, it was unclear as to whether or not frequency of use of the anchor system is related to improved control in older adults. The present study evaluated the effect of the prolonged use of the anchor system on postural control in healthy older individuals, at different frequencies of use, while they performed a postural control task (semi-tandem position). Participants were divided into three groups according to the frequency of the anchor system's use (0%, 50%, and 100%). Pre-practice phase (without anchor) was followed by a practice phase (they used the anchor system at the predefined frequency), and a post-practice phase (immediate and late-without anchor). All three groups showed a persistent effect 15 min after the end of the practice phase (immediate post-practice phase). However, only the 50% group showed a persistent effect in the late post-practice phase (24 h after finishing the practice phase). Older adults can improve their postural control by practicing the standing postural task, and use of the anchor system limited to half of their practice time can provide additional improvement in their postural control.     

Does calf muscle spasticity contribute to postural imbalance? A study in persons with pure hereditary spastic paraparesis

ObjectivesThe contribution of spasticity to postural imbalance in patients with upper motor neuron syndrome is still unclear. This study aimed to evaluate the responses to support-surface perturbations in patients with hereditary spastic paraparesis (HSP). These patients typically suffer from bilateral spasticity with relatively preserved muscle strength of the lower limbs. Particularly toes-up rotations were expected to be destabilizing due to insufficient suppression of calf muscle stretch reflexes.MethodsParticipants were seventeen symptomatic community-dwelling patients with autosomal dominant pure HSP and seventeen healthy controls. All patients had increased muscle tone of the triceps surae (TS) but no muscle contractures. Perturbations were applied by rotating or translating a platform with increasing intensity in four sagittal-plane directions. The primary outcome was maximum intensity (‘limit of stability’) sustained without stepping or grabbing in each type of perturbation. Leg muscle tone and strength were assessed with the Modified Ashworth Scale and Medical Research Council (MRC) scale, respectively.ResultsFor toes-up perturbations, limits of stability in patients were substantially lower than in controls, which were related to TS muscle tone but not to tibialis anterior (TA) strength. Toes-down rotations were indiscriminative. For backward perturbations, patients also had lower limits of stability, unrelated to TA strength or TS muscle tone. In forward perturbations, patients with TS strength MRC 4 were less stable than patients with normal TS strength and controls.ConclusionCalf muscle spasticity and weakness differently contribute to postural imbalance in patients with HSP. This notion could have implications for the clinical management of spasticity.     

Gathering your ‘sea legs’: Extended durations in an offshore environment increases postural sway excursions

BackgroundMal de debarquement (MdD), or often called ‘sea legs’, is the perception of self-motion after exposure to passive movement such as being on a boat at sea. Previous studies highlight sensory re-organization difficulties and postural control impairments after disembarking from sea travel in experienced crew members. However, the impact of MdD in individuals with minimal offshore experience, defined as participating in less than 2 offshore excursions per year, has not been investigated.Research questionDoes exposure to boat motion while at sea alter static postural control after disembarking in individuals with minimal offshore experience?MethodsHealthy adults (n = 24) with minimal offshore experience had their static balance assessed on a force platform before (PRE) and after (POST) a 7-h deep sea fishing excursion. Static balance was tested in eyes open (EO), eyes closed (EC), eyes open on a foam surface (EOF), and eyes closed on a foam surface (ECF) conditions. Sway excursions, sway velocity and sway variability in the medial-lateral (ML) and anterior-posterior (AP) directions were computed and then compared PRE/POST using a paired t-test (p < 0.05).ResultsSignificant increases in ML sway excursion (p = 0.004), ML sway range (p < 0.001), ML sway variability (p < 0.001), AP sway excursion (p = 0.045), AP sway range (p = 0.020), and AP sway variability (p = 0.030) were observed at POST during EOF. Significant increases in ML sway excursion (p = 0.027), AP sway excursion (p = 0.020), and AP sway variability (p = 0.014) at POST were also observed during ECF. No differences were found in the EO condition (p > 0.05).SignificanceIncreases in postural sway excursion and variability were observed in individuals with minimal offshore experience after disembarking. Our findings suggest sensory re-organization difficulties in order to maintain an upright posture in challenging sensory conditions are dependent on vestibular and somatosensory inputs following exposure to boat motion at sea.     

Does head extension and flexion increase postural instability in elderly subjects when visual information is kept constant?

The present study determined the effects of flexing and extending the head on the postural stability and mean anterior-posterior (A-P) center of mass (CM) position during upright stance in the elderly. To ensure visual input to stability was not a confounding variable, visual information was kept as constant as possible for all head positions. Twelve healthy elderly subjects (72.3 +/- 4.7 years) were asked to stand stationary on a single force-platform. Postural stability (assessed using the rms A-P excursion of the center of pressure (CP)) was determined for standing with the head erect, and with the head flexed and extended. The vestibular contribution to postural stability becomes increasingly important under challenging conditions, so to highlight the effects of vestibular system input, measurements of postural stability under conditions where visual and somatosensory inputs were disrupted were included. Changes in the mean A-P CM position when tilting the head were assessed by determining changes in the mean A-P location of the CP from standing with the head erect. Compared to standing with the head erect and looking straight ahead, postural stability was reduced when the head was flexed or extended (P < 0.01). Changes in mean A-P CM position were only significant when standing with the head flexed (P < 0.05). This suggests that increases in postural instability with the head tilted from the erect position may be in part due to mechanical perturbation rather than solely vestibular disruption.     

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.     

Are there specific conditions for which expertise in gymnastics could have an effect on postural control and performance?

The first aim of this study was to analyse the effect of elite training, linked to expertise, in gymnastics on postural performance and control. For this purpose, body sway of expert gymnasts was compared to other sportsmen, non-experts and non-gymnasts, in two different postures: bipedal (easy and unspecific to gymnasts) and unipedal (difficult and fairly specific). The second aim was to compare the groups in the same tasks but in a visual condition for which they were not trained, i.e. with eyes closed. Postural performance was assessed by centre of gravity motion, which was computed from centre of pressure motion, estimating postural control. A significant difference between the two groups was observed for postural performance in the unipedal posture and with eyes open only. Regardless of their posture, the groups were similarly affected by removal of vision. Expertise in gymnastics seemed to improve postural performances only in situations for which their practise is related to, i.e. unipedal with eyes open. These reveal the importance of choosing a relevant postural configuration and visual condition according to the people's training or by extension experience.