Postural Task Difficulty Research Articles

Does Alteration of Balance Control After Ankle Muscle Fatigue in National Judo Athletes Depend on Postural Task Difficulty?

Background: The purpose of the present study was to assess the impacts of plantar-flexors and dorsi-flexors fatigue following isokinetic contractions on postural control in nine young healthy national level judo athletes. Methods: Participants were required to stand still on a force plate with opened and closed eyes in feet together (FT) and single leg (SL) stance before (PRE) and after (POST) an isokinetic fatigue protocol. Mediolateral sway (ML sway), anteroposterior sway (AP sway), and velocity sway were calculated and used to assess the postural control. Results: Velocity sway POST was significantly (P < 0.001) higher than PRE in FT stance and SL stance. Velocity sway POST was significantly higher in the SL stance than the FT stance (P = 0.01). During eyes closed, a significant interaction postural task by fatigue for all parameters was found. All parameters increased significantly after fatigue compared to PRE. After fatigue, ML sway, AP sway, and velocity sway were significantly higher for the SL stance than the FT stance. Conclusions: Ankle muscle fatigue led to reduced postural stability during different stances in young healthy judo athletes. This effect was more accentuated when vision was removed and the base of support was reduced. Alteration of postural control depended on the difficulty of the postural stance.

Cortical Correlates of Increased Postural Task Difficulty in Young Adults: A Combined Pupillometry and EEG Study.

HighlightsIncreased postural task difficulty was associated with greater responses for pupillary response, posterior alpha power, and fronto-central theta/beta power ratio.Greater pupillary response correlated with lower posterior EEG alpha power during eyes occluded standing with and without dual-task.Lastly, a greater pupillary response was associated with lower CoP displacement in the anterior-posterior direction during dual-task eyes occluded.The pupillary response reflects mental effort (or cognitive workload) during cognitive and/or motor tasks including standing postural control. EEG has been shown to be a non-invasive measure to assess the cortical involvement of postural control. The purpose of this study was to understand the effect of increasing postural task difficulty on the pupillary response and EEG outcomes and their relationship in young adults. Fifteen adults completed multiple trials of standing: eyes open, eyes open while performing a dual-task (auditory two-back), eyes occluded, and eyes occluded with a dual-task. Participants stood on a force plate and wore an eye tracker and 256-channel EEG cap during the conditions. The power spectrum was analyzed for absolute theta (4–7 Hz), alpha (8–13 Hz), and beta (13–30 Hz) frequency bands. Increased postural task difficulty was associated with greater pupillary response (p < 0.001) and increased posterior region alpha power (p = 0.001) and fronto-central region theta/beta power ratio (p = 0.01). Greater pupillary response correlated with lower posterior EEG alpha power during eyes-occluded standing with (r = −0.67, p = 0.01) and without (r = −0.69, p = 0.01) dual-task. A greater pupillary response was associated with lower CoP displacement in the anterior–posterior direction during dual-task eyes-occluded standing (r = −0.60, p = 0.04). The pupillary response and EEG alpha power appear to capture similar cortical processes that are increasingly utilized during progressively more challenging postural task conditions. As the pupillary response also correlated with task performance, this measurement may serve as a valuable stand-alone or adjunct tool to understand the underlying neurophysiological mechanisms of postural control.

Effect of individualized cognitive and postural task difficulty levels on postural control during dual task condition

BackgroundPrevious dual task studies suggested that the difficulty of the concurrent cognitive and motor tasks may not be challenging to the same degree for each person. This study approaches this problem by setting individualized difficulty levels for tasks to examine the dual task interference. Research questionDo the features of postural sway depend on increased individualized difficulty levels of concurrent cognitive and postural activities? Methods20 young healthy participants (10 male, 10 female) took part in the study. Before the experiments, cognitive task difficulty (No-, Medium-, High) has been set individually. Subjects performed postural tasks (quiet stance, voluntary sway) concurrently with or without a cognitive task which based on simple arithmetic calculations. Postural sway features were examined. ResultsPostural sway features were affected by individualized difficulty level of concurrent cognitive and postural activities. In voluntary sway, as a more challenging postural task, higher reductions were observed for such sway features as COP velocity and range in AP direction. SignificanceThis study signaled task-specific changes in postural sway features. When the difficulty levels were set individually, the effect of motor and cognitive dual task was more apparent when the balance requirement of the primary motor task increased.

Does Alteration of Balance Control After Ankle Muscle Fatigue in National Judo Athletes Depend on Postural Task Difficulty?

ackground: The purpose of the present study was to assess the impacts of plantar-flexors and dorsi-flexors fatigue following isokinetic contractions on postural control in nine young healthy national level judo athletes. Methods: Participants were required to stand still on a force plate with opened and closed eyes in feet together (FT) and single leg (SL) stance before (PRE) and after (POST) an isokinetic fatigue protocol. Mediolateral sway (ML sway), anteroposterior sway (AP sway), and velocity sway were calculated and used to assess the postural control. Results: Velocity sway POST was significantly (P &lt; 0.001) higher than PRE in FT stance and SL stance. Velocity sway POST was significantly higher in the SL stance than the FT stance (P = 0.01). During eyes closed, a significant interaction postural task by fatigue for all parameters was found. All parameters increased significantly after fatigue compared to PRE. After fatigue, ML sway, AP sway, and velocity sway were significantly higher for the SL stance than the FT stance. Conclusions: Ankle muscle fatigue led to reduced postural stability during different stances in young healthy judo athletes. This effect was more accentuated when vision was removed and the base of support was reduced. Alteration of postural control depended on the difficulty of the postural stance.

Intracortical Inhibition Increases during Postural Task Execution in Response to Balance Training

Intracortical inhibitory modulation seems crucial for an intact motor control and motor learning. However, the influence of long(er) term training on short-interval intracortical inhibition (SICI) is scarcely investigated. With respect to balance, it was previously shown that with increasing postural task difficulty, SICI decreased but the effect of balance training (BT) is unknown. The present study tested whether improvements in postural control due to BT are accompanied by changes in SICI. SICI was measured in the tibialis anterior by applying paired-pulse magnetic stimuli to the motor cortex in a BT group (n = 13) training 2 weeks on an unstable platform and a control (CON) group (n = 13) while performing three progressively demanding postural tasks: stable stance (‘Stable’), standing on a movable platform partly secured with elastic straps (‘Straps’) or freely moving (‘Free’). The BT group improved postural control significantly more than the CON-group (‘Free’ condition: +80% vs. + 21%; p < 0.001). For SICI, there was a main effect of POSTURAL TASK (F2, 48 = 24.6; p < 0.001) with decreasing SICI when task difficulty increased and a TIME × GROUP interaction (F1, 24 = 5.9; p = 0.02) caused by significantly enhanced SICI in the BT group in all three postural tasks after the training. The increases in SICI were significantly correlated with improvements in balance performance (r = 0.56; p = 0.047). The present study confirms previous findings of task-specific modulation of SICI when balancing. More importantly, training was shown to increase SICI and this increase was correlated with changes in balance performance. Thus, changes in SICI seem to be involved not only for the control but also when adapting upright posture with training.

Alterations in the cortical control of standing posture during varying levels of postural threat and task difficulty.

Cortical excitability increases during the performance of more difficult postural tasks. However, it is possible that changes in postural threat associated with more difficult tasks may in themselves lead to alterations in the neural strategies underlying postural control. Therefore, the purpose of this study was to examine whether changes in postural threat are responsible for the alterations in corticospinal excitability and short-interval intracortical inhibition (SICI) that occur with increasing postural task difficulty. Fourteen adults completed three postural tasks (supported standing, free standing, or standing on an unstable board) at two surface heights (ground level or 3 m above ground). Single- and paired-pulse magnetic stimuli were applied to the motor cortex to compare soleus (SOL) and tibialis anterior (TA) test motor-evoked potentials (MEPs) and SICI between conditions. SOL and TA test MEPs increased from 0.35 ± 0.29 to 0.82 ± 0.41 mV (SOL) and from 0.64 ± 0.51 to 1.96 ± 1.45 mV (TA), respectively, whereas SICI decreased from 52.4 ± 17.2% to 39.6 ± 15.4% (SOL) and from 71.3 ± 17.7% to 50.3 ± 19.9% (TA) with increasing task difficulty. In contrast to the effects of task difficulty, only SOL test MEPs were smaller when participants stood at high (0.49 ± 0.29 mV) compared with low height (0.61 ± 0.40 mV). Because the presence of postural threat did not lead to any additional changes in the excitability of the motor corticospinal pathway and intracortical inhibition with increasing task difficulty, it seems unlikely that alterations in perceived threat are primarily responsible for the neurophysiological changes that are observed with increasing postural task difficulty. NEW & NOTEWORTHY We examined how task difficulty and postural threat influence the cortical control of posture. Results indicated that the motor corticospinal pathway and intracortical inhibition were modulated more by task difficulty than postural threat. Furthermore, because the presence of postural threat during the performance of various postural tasks did not lead to summative changes in motor-evoked potentials, alterations in perceived threat are not responsible for the neurophysiological changes that occur with increasing postural task difficulty.

Increasing mediolateral standing sway is associated with increasing corticospinal excitability, and decreasing M1 inhibition and facilitation

In standing, corticospinal excitability increases and primary motor cortex (M1) inhibition decreases in response to anterior posterior or direction unspecific manipulations that increase task difficulty. However, mediolateral (ML) sway control requires greater active neural involvement. Therefore, the primary purpose of this study was to determine the pattern of change in neural excitability when ML postural task difficulty is manipulated and to test whether the neural excitability is proportional to ML sway magnitude across conditions. Tibialis anterior corticospinal excitability was quantified using motor evoked potential (MEP) and postural sway was indexed using ML center of pressure (COP) velocity. Additionally, we examined inhibition and facilitation processes in the primary motor cortex using the paired pulse short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) techniques respectively. Measurements were repeated in four conditions with quiet stance as a control. Differences between conditions were tested using one-way repeated measures ANOVAs, on log transformed data. Associations were quantified using Spearman’s Rank Correlation Coefficient. There was a significant main effect of condition on all the neural excitability measures with MEP (p<0.001) being highest in the most difficult condition, and SICI (p=0.01), ICF (p<0.001) being lowest in the most difficult condition. Increasing ML COP velocity was significantly associated with increasing MEP amplitude (r=0.68, p<0.001), but decreasing SICI (r=0.24, p=0.03) and ICF (r=−0.54, p<0.001). Our results show that both corticospinal and M1 excitability in standing are scaled in proportion to ML task difficulty.

Normal subjects with different sagittal spino-pelvic morphotypes may walk differently

, M. Salavati, A.M. ArablooUniversity of Social Welfare and RehabilitationSciences, Tehran, Islamic Republic of IranResearch question: To clarify the relation between attentionand balance in patients with nonspecific low back pain (NSLBP), byassessing feet-in-place balance recovery reactions under differentconditions of cognitive and postural difficulty.Introduction: Patients with LBP demonstrate altered posturalresponses following perturbations [1]. Deficits in sensory/motorsystemshavebeenproposedtoberelatedtothesealterations[2,3].Aswellassensory/motorsystems,higher-cognitiveprocesseshavecontribution in the process of regaining balance and interactionbetween posture and cognition depends on factors such as diffi-culty of postural task [4,5]. However, little is known about the roleof cognitive processes in postural control of LBP.Materials and methods: 20 patients with NSLBP and 20matched controls between the ages of 18 and 45, stood on a move-ableplatformwitheachfootonaseparateforceplateandmaintaintheir balance (a) while expecting a series of forward/backwardtranslations of the support surface at two different sizes (b) with(DT)andwithout(ST-Balance)performingacognitivetask.Thecog-nitive (Auditory Stroop) task was also performed while standing(ST-cognition). Perturbation magnitude was scaled to the sub-ject’s height, while maintaining the translation duration across allsubjects. Resultant sway had 6 and 8?/s angular momentum formediumandlargesizesofperturbation,respectively.Faceplatesig-nals were used to determine anteroposterior excursion of center ofpressure (CoP) to find reaction time (time from perturbation onsetto onset of subject reaction), latency (time from onset of subjectreaction to Maximum amplitude of response), Max amplitude andinitial velocity of response (mean velocity between onset of reac-tion and max amplitude). The mean of 3 trials of CoP parametersand cognitive reaction times was used for statistical analysis.Results: In LBP group CoP responses were delayed in reactiontime and latency, also reduced in velocity compared to controls. Atsmallersizeofperturbation,theadditionalcognitiveloadincreasedvelocity in LBP group but decreased this variable at larger sizeof perturbation. Reaction time of stroop task was significantlyincreasedinDTcomparedtoST-cognitionconditionsandwasover-all slower in LBP group compared to controls.Discussion: Detrimental changes in balance control of LBP suf-ferers were influenced differently by cognitive task. This finding,in combination with overall poorer performance of cognitive taskmay imply altered cognitive regulation of balance control in LBP.Because level of postural difficulty affects adaptation of posturalstrategy under cognitive loading (may be due to different posturaltreatvalue),bothcognitiveandposturalchallengingshouldbecon-sidered in rehabilitation of these patients.References

Effect of Dual-Tasking on Dynamic Postural Control in Individuals With and Without Nonspecific Low Back Pain

ObjectiveThe purpose of this study was to compare the effect of dual tasking on postural and cognitive performance between participants with and without nonspecific chronic low back pain. MethodsIn this 3-factor mixed-design study, dynamic postural stability was assessed in 15 patients with chronic nonspecific low back pain and 15 age-, sex-, and size-matched asymptomatic participants. Bilateral stance on a Biodex Balance System was investigated at 3 levels of postural task difficulty (different platform stabilities levels with eyes open and closed) and 2 levels of cognitive task difficulty (with or without auditory Stroop test). We measured anterior-posterior, medial-lateral, and overall indices for postural performance. Average reaction time and error ratio of a modified auditory Stroop test were calculated as measures of the cognitive task performance. ResultsMixed-design 3-way analyses of variance revealed significant interactions. Post hoc 2-way analyses of variance showed significant group by cognitive task difficulty for anterior-posterior (P < .001), medial-lateral (P = .003), and overall stability indices (P < .001) on a stiffness level of 5 with eyes closed. At this level, there were significant differences between single- and dual-task conditions for anterior-posterior (P < .001), medial-lateral (P = .02), and overall stability indices (P < .001) only in the chronic low back pain group. Also, at the most difficult postural conditions, participants with chronic low back pain increased their error ratio (P = .002), whereas matched asymptomatic individuals increased their reaction time (P < .01) of the auditory Stroop test. ConclusionPostural task performance is attenuated by cognitive loading at a moderate level of postural task difficulty. Therefore, to observe the effect of attentional demands of postural control, task difficulty should be considered.

Attentional focus influences postural control and reaction time performances only during challenging dual-task conditions in healthy young adults

The dual-task paradigm has previously been used to investigate the attentional demands associated with postural control. Previous studies have identified both the focus of attention and the difficulty of a postural task as potential factors influencing dual-task performance. The aim of this study was to examine how the instructed focus of attention influences dual-task performance during quiet standing tasks of various levels of difficulty. Thirteen young adults participated in two testing sessions consisting of standing as still as possible on a force platform in different postural conditions, while simultaneously performing a simple reaction time (RT) task. Postural task difficulty was manipulated by various combinations of three bases of support (feet together, tandem and single leg) and two visual conditions (eyes opened and closed). Participants were instructed to focus on either their balance or their RT performance, depending on the testing session. When comparing postural control with respect to session focus, anterior-posterior sway velocity decreased with the addition of the simple RT task when the focus was on balance, but only during the more difficult dual-task conditions. In contrast, sway area and medial-lateral sway velocity did not change between the two instructed focus sessions. Participants responded faster in all dual-task conditions when focusing on RT performance than on balance. The modified attention allocation index indicated that participants' ability to modulate their allocation of attentional resources to respond positively to instruction was more pronounced in the most challenging postural condition. The present findings could have important implications for the interpretation of dual-task performance in both clinical and research settings.

Postural performance of vestibular loss patients under increased postural threat1

The effects of increasing postural task difficulty on balance control was investigated in 9 compensated vestibular loss patients whose results were compared to 11 healthy adults. Subjects were tested in static (stable support) and dynamic (sinusoidal translation of the support) conditions, both at floor level and at height (62 cm above the floor), and with and without vision, to create an additional postural threat. Wavelet analysis of the center of foot pressure displacement and motion analysis of the body segments were used to evaluate the postural performance. Evaluation questionnaires were used to examine the compensation level of the patients (DHI test), their general anxiety level (SAST), fear of height (subjective scale), and workload (NASA TLX test). (Vestibular loss patients rely more on vision and spend more energy maintaining balance than controls, but they use the same postural strategy as normals in both static and dynamic conditions.) Questionnaire data all showed differences in behavior and perceptions between the controls and the patients. However, at height and without vision, a whole body strategy leading to rigid posture replaces the head stabilization strategy found for standing at floor level. The effects of height on postural control can be attributable to an increase in postural threat and attention changes resulting from modifications in perception.

Reliability of center of pressure measures of postural stability in healthy older adults: Effects of postural task difficulty and cognitive load

Postural instability is a major risk factor of falling in the elderly. It is well documented that postural control may decline while performing a concurrent cognitive task and this effect increases with age. Despite the extensive use of dual tasking in balance assessment protocols, a lack of sufficient reliability information is evident. This study determines the reliability of the postural stability measures in older adults, assessed under single and dual-task conditions and different levels of postural difficulty. Sixteen older adults completed quiet stance postural measurements at three levels of difficulty (rigid surface-eyes open, rigid surface-eyes closed, and foam surface-eyes closed), with or without performing a concurrent backward counting task, in two sessions 1 week apart. Force plate data was used to calculate center of pressure (COP) parameters including mean velocity, phase plane portrait, area (95% confidence ellipse), standard deviation (SD) of amplitude, and SD of velocity. Intraclass correlation coefficient (ICC), standard error of measurement (SEM), coefficient of variation (CV), and minimal metrically detectable change (MMDC) were calculated for each COP measure in all test conditions. Mean velocity, total phase plane, phase plane in ML direction, and SD of velocity in ML direction were the most reliable COP measures across all test conditions. ICC values were consistently higher in ML direction compared with AP direction. In general, velocity-related COP measures in ML direction showed to be highly reliable. Further research may explore the predictive and evaluative value of these COP parameters.

Age-Related Changes in Posture Control are Differentially Affected by Postural and Cognitive Task Complexity

The simple postural task of quiet standing, which requires minimal attentional resources, is generally paired with cognitive activity. Competition for attentional resources is a consequence of simultaneously performing balance tasks and cognitive tasks, and impairment of attentional resource allocation with aging leads to increased risks of fall. We investigated age-related changes in posture control during dual task performance, using a paradigm that crossed a static (quiet standing) and a dynamic (keeping balance on a translational force plate) postural task and cognitive tasks of low demand (mental arithmetic) and high demand (spatial memory). Postural performance was analyzed through center-of-pressure displacements using both statistical (body sway area/sway velocity) and nonlinear (wavelet transform) methods in three age groups (younger, middle-aged, and older healthy participants). Results showed that 1) the nonlinear analysis method was more sensitive than the traditional approach in distinguishing performance between age groups, a result that explains discrepancies in the dual-task literature; 2) dual-tasking costs were dependent on both postural task difficulty and cognitive task complexity, corroborating previous investigations; 3) younger adults improved their postural performance during dual-tasking, but older adults lowered their performance; 4) balance recovery strategies in the dynamic postural task appeared to differ in younger versus older adults. Together, our findings on dual-tasking can be interpreted within the conceptual frame of task prioritization: shifting attention away from postural task automates posture control in the younger adults, whereas prioritization of postural task and selection of compensatory strategy are the main characteristics of posture control in the older population.

Does articulation contribute to modifications of postural control during dual-task paradigms?

Many studies have been carried out to investigate the attentional resources required for postural control, using a ‘dual-task’ methodology in which performance on mental and postural control tasks is compared when these are carried out separately and concurrently. Most mental tasks used in these dual-task studies have employed verbal responses. However, changes in respiration during speech production are known to produce changes in postural control. Hence, the goal of this study was to determine whether articulation might contribute to the changes found in postural sway when a spoken mental task is being performed and to determine if the type of postural control measurement might also have an impact on the outcome of the study. Twenty young healthy participants were asked to stand on a force platform while executing secondary tasks that were performed silently or required a verbal response, and that required high or low levels of attention. Vision and postural task difficulty were manipulated. Performance of all tasks produced an increased sway frequency and decreased sway amplitude relative to the no task baseline. However, tasks that required articulation resulted in a more pronounced increase in postural sway frequency and sway path than did the tasks that did not require any articulation. These findings could imply that the addition of a secondary task results in increased stiffness, whereas articulation results in a further increased frequency of sway, which leads to an increase in sway path. We conclude that changes in the various parameters of sway that accompany performance of secondary tasks are complex, and are not always wholly attributable to attentional load, but may also be partly due to the motor requirements of the task, such as those involved in articulation.

Attentional demands for static postural control after stroke

Brown LA, Sleik RJ, Winder TR. Attentional demands for static postural control after stroke. Arch Phys Med Rehabil 2002;83:1732-5. Objective: To assess the attentional demands associated with postural control among people who have had a stroke. Design: Nonrandomized matched case-control study. Setting: University research laboratory in Canada. Participants: Six individuals who had suffered a left or right cerebral ischemic attack in the past year and a sample of 6 age- and gender-matched controls. Participants in the stroke group had a mean age of 64.17±13.14 years; control participants had a mean age of 64.00±13.91 years. Mean National Institute of Health Stroke Scale scores for these patients were 7.67±4.92 at the time of stroke and 1.66±1.36 at the time of testing. None of the patients were taking medications that would alter cognitive status or balance abilities. Intervention: Participants performed a verbal reaction-time test while engaged in 3 postural tasks (sitting, standing, standing with feet together). Main Outcome Measure: Reaction time: latency between visual stimulus and verbal response. Results: Reaction times in the stroke group differed significantly in all conditions from the controls (410±72ms vs 320±54ms, P<.01). A significant interaction was found between group and postural task (P=.05), with reaction-time scores showing a progressive increase in postural task difficulty among participants who had suffered a stroke. Post hoc comparisons revealed that sitting reaction-time scores were significantly slower than reaction-time scores for feet together standing (P=.008) among participants in the stroke group. Conclusion: Individuals who have suffered a stroke showed increased attentional demands for tasks of static postural control compared with healthy, age-matched participants. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation