The effect of a contralateral foot touch on stability of one-leg stance in young adults: an exploratory study.

PURPOSE: Previous studies demonstrated that providing light finger touch to a stationary object leads to reduced body sway. The focus of the current exploratory study was on the investigation of postural sway during one-leg stance when light touch is provided by the contralateral foot. METHODS: Eleven healthy young adults participated in the study. They stood on the top of the force platform with eyes open and on their dominant leg with no touch and with a touch from the contralateral foot applied to the stance leg. Medial arch, heel, and big toe of the contralateral foot were used to touch the medial malleolus or mid shank of the stance leg. The excursion, velocity, and sway area of the centre of pressure were obtained and analysed. RESULTS: Standing with light touch from the contralateral foot to the medial malleolus resulted in significantly smaller postural sway as compared to standing with no touch (p < 0.05). There was no difference in the study outcomes between conditions of standing with a touch applied by the medial arch, heel, or big toe to the stance leg. CONCLUSIONS: The results of the study suggest that the application of light touch provided by a contralateral foot could be an effective strategy for enhancing body stability when no external support is available. The study outcome provides a foundation for future studies exploring ways to enhance balance control during one-leg stance.

The Effect of Additional Leg Supports in Control of Posture in Sitting.

The objective of the study was to investigate the effect of leg supports on the anticipatory and compensatory postural adjustments of sitting subjects exposed to external perturbations in the anterior-posterior direction. Ten young participants received perturbations applied to the upper body while sitting on a stool with an anterior or posterior leg support and when using a footrest. Electromyographic activities of the trunk and leg muscles and center of pressure displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Anticipatory activities were observed in the tibialis anterior, biceps femoris, and erector spinae muscles in the anterior leg support condition. Early onset of muscle activity was observed in the tibialis anterior, biceps femoris, rectus femoris, and erector spinae muscles in the posterior leg support condition compared to the feet support condition. Moreover, to maintain balance participants utilized co-contraction of muscles as the main mechanism of balance control in sitting regardless of the availability of the anterior or posterior leg support. There was no effect of a leg support on center of pressure displacements. The outcome of the study provides a background for future investigations of the effect of leg supports on control of balance in sitting when perturbed.

The feasibility of using an auditory cue to elicit anticipatory postural adjustments for a posterior perturbation.

When humans are exposed to a predictable external perturbation, they usually generate anticipatory postural adjustments (APAs), which reduce the effect of potential body disturbance. However, when an external perturbation comes from behind and as such unpredicted, no APAs are generated, which challenges postural control. The aim of this study was to examine whether humans exposed to unpredictable perturbations could generate APAs using an auditory cue. Ten young adults were exposed to external perturbations hitting their shoulders from behind with or without an auditory cue prior to the physical impact. Electromyography (EMG) activities of eight trunk and leg muscles and center-of-pressure (COP) displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results showed that young adults were able to rely on an auditory cue to generate APAs prior to external perturbations coming from behind, and they demonstrated stronger APAs with training. Moreover, they utilized co-contraction of ventral and dorsal muscles as their APA response. The outcome provides a foundation for future studies aiming at using auditory cues to facilitate the generation of APAs and improve postural control in people with impaired balance while exposed to perturbations.

Older adults utilize less efficient postural adaptations when they are uncertain about the magnitude of a perturbation.

People frequently experience perturbations while standing or walking in crowded areas or when interacting with external objects. Balance maintenance in response to a perturbation is affected by the predictability of the magnitude of a body disturbance. The aim of this quasi-experimental study was to investigate the role of aging in maintenance of standing balance in response to perturbations of varying magnitudes. Twelve older adults and twelve young adults received a series of frontal perturbations of small or large magnitudes induced to their upper body by a pendulum impact while standing. The perturbation sequence included 10 trials of small, 15 trials of large, and 10 more trials of small magnitudes. The participants were exposed to either repetitive perturbations of known (predictable) magnitude or perturbations of unknown (unpredictable) magnitude as they were not told which of the perturbation magnitude (small, large) to expect. Electromyographic activity of six leg and trunk muscles and displacements of the center of pressure were recorded and analyzed during anticipatory (APAs) and compensatory (CPAs) phases of postural control. When exposed to both, repetitive perturbations of known magnitude and perturbations of unpredictable magnitude, older adults, compared to young adults, demonstrated delayed and smaller anticipatory and compensatory postural adaptations. Older adults also required more trials to modify postural adjustments, as compared to young adults. The findings imply that the ability to predict magnitudes of frontal perturbations is declined in older adults.

The effect of the predictability of perturbation magnitudes in older adults with mild cognitive impairment.

Balance impairment is common in older adults with mild cognitive impairment (MCI). The ability to predict the magnitude of the body disturbance is essential to balance maintenance. The purpose of the study was to investigate the effect of the predictability of the perturbation magnitudes on anticipatory (APAs) and compensatory (CPAs) postural adjustments in older adults with MCI and healthy older adults. Fifteen individuals with MCI and fourteen age-matched control participants stood on the force platform and received the pendulum perturbations of small or large magnitudes applied to their upper body. Electromyographic activity of eight leg and trunk muscles and displacements of the center of pressure (COP) were recorded and analyzed during the APA and CPA phases of postural control. Individuals with MCI demonstrated smaller APAs in the conditions of the perturbation of unpredictable magnitude and required more trials to optimize their postural adjustments, as compared to healthy older adults. Moreover, individuals with MCI had reduced postural stability in the conditions of unpredictable magnitude of the perturbation. The findings suggest that cognitive decline adversely affects the ability to predict the magnitude of the perturbations.

Older adults can rely on an auditory cue to generate anticipatory postural adjustments prior to an external perturbation.

To minimize the potential postural disturbance induced by predictable external perturbations, humans generate anticipatory postural adjustments (APAs) using visual information about a perturbation. However, it is unknown whether older adults can generate APAs relying on auditory information. Ten older adults received external perturbations (a) with visual information but no auditory information available, (b) without neither visual nor auditory information, (c) with both visual and auditory information available, and (d) participated in training with only auditory information available. In addition, they were tested again after 1 week of washout period. Electromyography activities of eight leg and trunk muscles and ground reaction forces were recorded and analyzed during the anticipatory and compensatory phases. Outcome measures included the latencies and integrals of muscle activities, and center-of-pressure displacements. After a short period of training, participants were able to rely on the auditory cue only to generate APAs close to that when the visual information was available. In addition, after 1 week of washout period, they were able to partially retain the skill to rely on auditory cues to generate APAs. The outcome provides a foundation for future studies focusing on utilizing auditory cues to optimize postural control in individuals who have balance or vision deficit.

Perturbation-based training enhances anticipatory postural control in individuals with chronic stroke: a pilot study.

Individuals with stroke commonly have impaired balance control. The aim of this study was to investigate the effect of targeted intervention on anticipatory postural adjustments (APAs) and postural control in people with stroke. Six participants with unilateral hemiparesis due to a stroke (5.0-8.4 years post stroke) participated in a two-phase random crossover study. The participants received in counterbalanced order (a) 2 weeks of experimental, targeted intervention (pushing a medicine ball attached to the ceiling using their unaffected upper extremity) and (b) 2 weeks of control, self-guided general mobility exercise program with a 1-week washout period in between. All study participants were assessed with laboratory tests before and after each intervention. Lab tests included predictable external perturbations induced by a pendulum impact and clinical assessments of balance. Bilateral electromyographic activity of eight trunk and leg muscles and center of pressure (COP) displacements were recorded, and data during the anticipatory and compensatory phases of postural control were analyzed. After the experimental intervention, as compared to control intervention, the participants showed earlier APA onsets (P < 0.05), smaller COP displacements (P < 0.05), and improved [although not significantly (P >0.05)] scores of clinical tests of balance. The results of this feasibility study provide a foundation for developing balance rehabilitation protocols focused on improving APAs in individuals with neurological disorders.

The Effect of Predictability of the Perturbation Magnitude on Anticipatory and Compensatory Postural Adjustments during a Bimanual Load-Lifting Task.

Background: To minimize the potential postural disturbance induced by external or self-initiated perturbations, humans generate anticipatory postural adjustments based on their perceived consequences of the body disturbance. Lifting is a common activity that induces a self-initiated perturbation that can compromise balance control. Aim: To assess anticipatory (APAs) and compensatory (CPAs) postural adjustments generated in response to a self-initiated perturbation induced by lifting objects of uncertain mass. Methods: Ten young adults lifted the tray with either light or heavy object placed in it. Electromyographic activity of eight trunk and leg muscles, and center-of-pressure (COP) displacements were recorded and analyzed during the APAs and CPAs phases. Results: When the object mass changed unpredictably, the participants generated APAs based on the most recent experience of lifting and needed three trials of lifting to generate optimal APAs and CPAs. Conclusions: Young adults were able to predict the perturbation magnitude during self-initiated perturbations induced by lifting objects. The outcome provides a foundation for future studies focusing on the role of predictability of perturbation consequences in postural control of older adults and individuals with balance deficit.

Perceptual distortion in virtual reality and its impact on dynamic postural control.

BACKGROUND: Voluntary movement such as lifting a foot in preparation to stepping acts as a self-initiated perturbation that disturbs postural equilibrium. To maintain and restore equilibrium, humans utilize early, anticipatory, and compensatory postural adjustments. Despite technological progress in accessible virtual reality (VR) devices, little is known on the usage of VR in control and maintenance of balance while standing. RESEARCH QUESTION: How does VR modulate early, anticipatory, and compensatory postural adjustments during a dynamic task of leg lifting while avoiding an obstacle? METHODS: First, the postural adjustments in a single-leg obstacle avoidance were compared between real and VR settings, where a statistical reanalysis was performed with data subsets that minimize the difference of foot elevation speed. Second, the effect of simple foot elevation was examined to identify the fundamental nature of leg lifting motion as a self-initiated perturbation. Lastly, perceptual distortion in VR was assessed by evaluating how the spatial scale of the virtual scene used in the single-leg obstacle avoidance experiment was recognized by participants. RESULTS: The VR setting reduced the activities of lower leg muscles on the supporting side not only in the compensatory phase but also in the preparatory early and anticipatory phases. On the other hand, simple foot elevation resulted in a significant increase of muscle activities with lifting height only found in the compensatory phase. Furthermore, it is suggested that the VR induced perceptual distortion in estimating the sizes of the virtual objects. SIGNIFICANCE: The findings provide more definitive evidence that VR presentation modulates the components of postural adjustments for maintaining upright stance while being perturbed. One of the potential psychophysical factors is perceptual distortion in VR, and this provides critical information for further development of VR based training system.

Role of angular position of the seat in control of posture in response to external perturbation.

Ability of the human body to regain balance after being externally perturbed is important in the maintenance of vertical posture. The goal of this study was to investigate trunk and leg muscle response to external perturbation while sitting on a stool with varying seat inclinations. Ten healthy subjects were required to receive a perturbation applied to the upper body while sitting on an adjustable stool with 0°, 10° forward or 10° backward inclination of the seat and without footrest and leg support. Electromyographic activities of the trunk and leg muscles and center of pressure displacements were recorded and analyzed during the anticipatory (APA) and compensatory (CPA) phases of postural control. APAs and CPAs were generated in response to an external perturbation. Delays in the onset of anticipatory muscle activity were seen when seated on the inclined seat compared to sitting on the horizontal seat (p < 0.05). To maintain balance after a perturbation, participants activated the trunk and thigh muscles, the activity of which was modulated to a greater degree than that of leg muscles. Moreover, they utilized co-contraction of muscles as the main mechanism of balance control in sitting. Furthermore, there was no effect of a seat inclination on COP displacements. The outcome provides a background for future investigations of the effect of seat inclination on control of balance in sitting.

The Role of Predictability of Perturbation in Control of Posture: A Scoping Review.

Efficient maintenance of posture depends on the ability of humans to predict consequences of a perturbation applied to their body. The purpose of this scoping review was to map the literature on the role of predictability of a body perturbation in control of posture. A comprehensive search of MEDLINE, EMBASE, and CINAHL databases was conducted. Inclusion criteria were studies of adults participating in experiments involving body perturbations, reported outcomes of posture and balance control, and studies published in English. Sixty-three studies were selected. The reviewed information resources included the availability of sensory information and the exposure to perturbations in different sequences of perturbation magnitudes or directions. This review revealed that people use explicit and implicit information resources for the prediction of perturbations. Explicit information consists of sensory information related to perturbation properties and timing, whereas implicit information involves learning from repetitive exposures to perturbations of the same properties.

Reaching in sitting: The effect of seat design and body manipulations.

BACKGROUND: Sitting is a common and familiar position used daily as a platform for many motor activities in the workplace, at school, or at home. OBJECTIVE: To investigate how difference in the chair design and selected sitting manipulations contribute to reach distance in sitting. METHODS: Ten healthy subjects were required to reach forward as far as possible while sitting in an adjustable chair with 0°, 10° forward or 10° backward inclination of the seat, with and without footrest and leg support, with legs crossed, and when holding the edge of the seat with the contralateral arm. RESULTS: In comparison to sitting with feet on the footrest, the maximal reaching distance decreased significantly when sitting on either forward or backward inclined seat (p < 0.05) and it increased when the subjects held the edge of the seat while seated with footrest and the posterior leg support (p < 0.05). There was no major effect of crossing the legs or the use of anterior leg support on the maximal reach distance. CONCLUSIONS: Modification of the chair design could increase or decrease reaching distance in sitting. The outcome of the study provides a background for future investigations of the effect of sitting positions on reaching distance in the workplace, at home, or at school.

The role of predictability of the magnitude of a perturbation in control of vertical posture when catching an object.

The predictability of perturbation magnitude plays an important role in control of standing posture. The aim of the study was to examine anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to catching objects of uncertain mass. Twenty adults caught the same object with either light or heavy weight placed in it. Electromyographic activity of eight trunk and leg muscles, displacements of the center of pressure, and angular displacement of the shoulder joint were recorded and analyzed during the APAs and CPAs intervals. When the subjects experienced repeated catching of the object with the same weight, they estimated the object mass beforehand and generated APAs more precisely. When the object mass changed unpredictably, they generated APAs based on the most recent catch and needed four to six trials to optimize APAs and CPAs. The muscle co-contraction was a primary pattern for catching the object of uncertain mass. The results of the study suggest that catching the object of uncertain mass is a challenging task that involves co-contraction of postural muscles to maintain balance.

Enhancement of balance, and mobility in individuals with multiple sclerosis using visual cue guided multidirectional step training - A pilot study.

BACKGROUND: Individuals with multiple sclerosis (MS) often experience limitations in mobility due to impairment of gait and balance. Rehabilitation approaches to improve balance and mobility in individuals with MS are limited. We have developed a novel visual cue guided multi-direction step (MDS) training method to improve balance and mobility in individuals with MS. OBJECTIVE: To examine the effect of MDS training on balance, gait, and mobility in individuals with MS. METHODS: Five individuals with relapsing- remitting MS participated in the 4-week training involving stepping in eight directions in response to a visual cue. Balance, gait, and mobility were assessed before and after training. RESULTS: Training related improvements were seen in the limits of stability (p< .05), spatial and temporal gait parameters (p<.05), and performance of the Tinetti Mobility Assessment (p=.001), 10-Meter Walk test (p<.001), and Four-Square Step test (p<.002). CONCLUSION: Balance, gait, and mobility in individuals with MS could be improved after 4 weeks of visual cue guided multi-direction stepping training. Outcomes from this feasibility study could help to refocus conventional rehabilitation strategies aimed at aiding individuals with MS to achieve maximal independence in mobility.

The effect of a textured insole on anticipatory postural adjustments.

PURPOSE: To obtain preliminary data on the effect of a textured insole on postural control. METHODS: Nine healthy subjects were exposed to external perturbations applied to their shoulders while standing with or without a single textured insole. Body weight distribution and bilateral electromyographic activity (EMG) of trunk and leg muscles were recorded. Onsets of EMG activity of muscles were calculated and analyzed within the interval typical for anticipatory postural adjustments. RESULTS: When a textured insole was provided under one foot, subjects shifted their body weight towards the contralateral foot. With no insole, the anticipatory onsets of EMG activity of the left and right muscles were symmetrical; when a textured insole was used, the EMG onsets of the muscles on the contralateral side of the body were seen earlier as compared to the insole side. This early activation was more pronounced in the trunk muscles (p < 0.05). CONCLUSIONS: Using a single textured insole under one-foot induced asymmetry of anticipatory onsets of EMG activity in healthy subjects. The outcome highlights the importance of investigating the role of a single textured insole in control of vertical posture and provides a foundation for future studies focussed on improvement of postural control in individuals with body asymmetry due to unilateral weakness.

Effect of Light Finger Touch, a Cognitive Task, and Vision on Standing Balance in Stroke.

The aim of the exploratory study was to investigate the individual and combined effects of light finger touch, a cognitive task, and vision on postural sway in individuals with stroke. Nine older adults with stroke stood on the force platform with eyes open and eyes closed, with and without a light finger touch contact with the stationary frame, and when counting backward from a randomly chosen three-digit number or without it. The center of pressure (COP) excursion, velocity, range and sway area was calculated. Participants demonstrated significantly larger postural sway when vision was not available (p < 0.05), smaller postural sway when using a finger touch contact (p < 0.05), and increased postural sway while performing the cognitive task (p < 0.05). When finger touch and a cognitive task was performed simultaneously, body sway decreased as compared to standing and performing a cognitive task in eyes open (p < 0.05) and eyes closed conditions. Results indicate that light touch in individuals with stroke mitigates the impact of cognitive load. The findings contribute to the understanding of the role of sensory integration in balance control of individuals with neurological impairments and older adults.

Effect of predictability of the magnitude of a perturbation on anticipatory and compensatory postural adjustments.

Balance maintenance in response to a perturbation could be affected by the predictability of the magnitude of the body disturbance. We investigated anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to perturbations of predictable and unpredictable magnitudes. Twenty young adults received series of perturbations of small or large magnitudes the order of which was varied. Electromyographic activity of six leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded. The muscle onset time, integrals of muscle activity, and COP displacements in the anterior-posterior direction were analyzed during the APA and CPA phases. The results indicated that when the participants were exposed to the repeated perturbation magnitude, it became predictable and they generated APAs more precisely according to the magnitudes of the perturbation. Moreover, when the magnitude of perturbation changed unpredictably, the participants overestimated or underestimated the magnitudes of the perturbation, as they generated APAs based on their prior experience of dealing with the perturbation. The optimal adjustment of APAs occurred after five trials of repeated perturbations. The findings imply that the process of APAs and CPAs generation depends on the accuracy of the predictability of perturbation magnitudes.

The role of an auditory cue in generating anticipatory postural adjustments in response to an external perturbation.

Anticipatory postural adjustments (APAs) are usually generated to minimize the potential postural disturbance induced by predictable external perturbations. Visual information about a perturbation is important for the generation of APAs, but whether people can rely on auditory information to generate APAs is unknown. The aim of this study was to investigate the role of an auditory cue in generating APAs when visual information is not available. Fifteen young adults participated in the study. They received external perturbations a) with visual information but no auditory information available, b) without neither visual nor auditory information, c) with both visual and auditory information available, and d) with only auditory information available. Electromyography (EMG) activities of eight leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded and analyzed during the anticipatory and compensatory (CPAs) phases. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results showed that after a short training, participants were able to rely only on the auditory cue to generate APAs comparable to that when the visual information was available. In addition, a training effect was found such that the participants demonstrated stronger APAs and less demands for CPAs through the training trials. The outcome provides a foundation for future studies focusing on the utilization of auditory cues for postural control in older adults and individuals who have vision deficit.

Individuals with stroke improve anticipatory postural adjustments after a single session of targeted exercises.

Impairment of anticipatory postural adjustments (APAs) is an important source of postural instability in older adults and individuals with neurological disorders. The aim of the study was to investigate whether APAs could be improved in people with stroke as a result of targeted exercise involving their unaffected upper extremity. Nine individuals with stroke and five healthy control individuals participated in the laboratory tests before and after a single session of practice consisting of pushing a medicine ball attached to the ceiling and stopping the ball with their palm when it returns. The tests included self-initiated perturbations induced by fast, discrete shoulder flexion movements and external perturbations induced by a pendulum impact. Bilateral EMG activity of eight trunk and leg muscles was recorded and analyzed during the anticipatory phase of postural control. Significantly early APAs onsets (p < .05) were seen in trunk and leg muscles after a single session of practice as compared to pre-practice in both the groups and individuals with stroke improved their ability to generate APAs more than control group. While the improvement was more pronounced on the unaffected side of the body, enhanced APAs were recorded on the affected side as well. The observed practice-related earlier activations of muscles confirm a possibility of APA enhancement in individuals with stroke. The outcome provides a background for the development of balance rehabilitation protocols focused on improvement of anticipatory postural adjustments in individuals with neurological disorders.