Direction-specific postural instability in subjects with Parkinson's disease

What Is Wrong with Balance in Parkinson's Disease?

Postural instability and resulting falls are major factors determining quality of life, morbidity, and mortality in individuals with Parkinson’s disease (PD). A better understanding of balance impairments would improve management of balance dysfunction and prevent falls in patients with PD. The effects of bradykinesia, rigidity, impaired proprioception, freezing of gait and attention on postural stability in patients with idiopathic PD have been well characterized in laboratory studies. The purpose of this review is to systematically summarize the types of balance impairments contributing to postural instability in people with PD.

Postural instability in Parkinson Disease: to step or not to step

Postural instability is a key feature of Parkinson Disease that is associated with falls and morbidity. We designed a pull apparatus to quantitatively measure the force needed to pull subjects off-balance. Thirteen Controls and eight individuals with Parkinson Disease (PD) were evaluated. All individuals with PD reported subjective symptoms of postural instability and were symptomatic for approximately 9.4years when tested. No significant differences were found between Controls and PD subjects in the magnitude of force required to pull them off-balance. None of the Controls fell and all took a step into the direction of pull to maintain their balance. 59% of the time PD subjects fell because they did not take a step in the direction of pull to maintain their center of mass (COM) over their feet, thus indicating a deficiency in postural reflexes. If they fell on the first pull, PD subjects did not show a learning effect when pulled multiple times in the same direction. The utility of the Pull Test to detect postural instability is related to the subject's behavioral response, not the force needed to pull them off balance. Our findings may also help explain certain features of the PD gait as an attempt by subjects to avoid postural instability by not placing their COM in gravitationally unstable positions.

Compensatory stepping in Parkinson's disease is still a problem after deep brain stimulation randomized to STN or GPi

The effects of deep brain stimulation (DBS) on balance in people with Parkinson's disease (PD) are not well established. This study examined whether DBS randomized to the subthalamic nucleus (STN; n = 11) or globus pallidus interna (GPi; n = 10) improved compensatory stepping to recover balance after a perturbation. The standing surface translated backward, forcing subjects to take compensatory steps forward. Kinematic and kinetic responses were recorded. PD-DBS subjects were tested off and on their levodopa medication before bilateral DBS surgery and retested 6 mo later off and on DBS, combined with off and on levodopa medication. Responses were compared with PD-control subjects (n = 8) tested over the same timescale and 17 healthy control subjects. Neither DBS nor levodopa improved the stepping response. Compensatory stepping in the best-treated state after surgery (DBS+DOPA) was similar to the best-treated state before surgery (DOPA) for the PD-GPi group and the PD-control group. For the PD-STN group, there were more lateral weight shifts, a delayed foot-off, and a greater number of steps required to recover balance in DBS+DOPA after surgery compared with DOPA before surgery. Within the STN group five subjects who did not fall during the experiment before surgery fell at least once after surgery, whereas the number of falls in the GPi and PD-control groups were unchanged. DBS did not improve the compensatory step response needed to recover from balance perturbations in the GPi group and caused delays in the preparation phase of the step in the STN group.

Effects of amplitude cueing on postural responses and preparatory cortical activity of people with Parkinson disease

BACKGROUND AND PURPOSE

Persons with Parkinson disease (PD) are unable to modify their postural responses, and show an associated increase in cortical preparatory activity for anticipated postural perturbations. In this study we asked whether participants with PD could modify their postural responses and cortical preparatory activity when cued to focus on increasing movement amplitude before a series of predictable postural perturbations.

METHODS

Twelve participants with PD performed postural responses to 30 identical backward surface translations. We cued participants to focus on increasing movement amplitude, and examined the effects of cueing by measuring postural responses (center-of-pressure initial rate of change, automatic postural response stability, peak trunk flexion, peak ankle extension) and preparatory cortical activity (electroencephalographic measures of contingent negative variation, alpha and beta event-related desynchronization).

RESULTS

Participants with PD modified their postural responses during the amplitude trials by increasing trunk flexion, slowing center-of-pressure initial rate of change, and decreasing automatic postural response stability. However, no significant differences in contingent negative variation amplitude or alpha or beta event-related desynchronization were observed with versus without amplitude cueing.

DISCUSSION AND CONCLUSIONS

Persons with PD were able to modify their feet-in-place postural responses with amplitude cueing. These changes were not associated with changes in cortical preparation during amplitude cue trials, suggesting that other regions or measures of brain function were responsible for changes in postural responses. Future studies are needed to determine the effects of long-term amplitude-cueing practice on cortical preparation and postural stability.Video Abstract available. See Video (Supplemental Digital Content 1, http://links.lww.com/JNPT/A78) for more insights from the authors.

Early postural changes in individuals with idiopathic Parkinson's disease

Background and Objectives. Postural changes are frequent and disabling complications of Parkinson's disease (PD). Many contributing factors have been evident either related to disease pathology or to adaptive changes. This study aimed at studying the postural changes in subjects with Parkinson's disease and its relation to duration of illness and disease severity. Methods. Eighteen patients with PD and 18 healthy matched volunteers represented the sample of the study. The patients were at stage 1 or 1.5 according to the Modified Hoehn and Yahr Staging with duration of illness between 18 and 36 months. Three-dimensional analysis of the back surface was conducted to explore the postural changes in the sagittal and frontal planes in both the patients and the healthy subjects. Results. Kyphotic angle, lordotic angle, fleche cervicale, fleche lombaire, scoliotic angle, and associated vertebral rotation and pelvic obliquity were significantly increased in patients with PD compared to the healthy subjects (P ≤ 0.05). There was no association between the measured postural changes and duration of illness as well as the severity of the IPD (P ≤ 0.05). Conclusion. Postural changes start in the early stages of idiopathic PD and they have no relationship to the duration of illness and disease severity.

Using Accelerometer and Gyroscopic Measures to Quantify Postural Stability

CONTEXT

Force platforms and 3-dimensional motion-capture systems provide an accurate method of quantifying postural stability. Substantial cost, space, time to administer, and need for trained personnel limit widespread use of biomechanical techniques in the assessment of postural stability in clinical or field environments.

OBJECTIVE

To determine whether accelerometer and gyroscope data sampled from a consumer electronics device (iPad2) provide sufficient resolution of center-of-gravity (COG) movements to accurately quantify postural stability in healthy young people.

DESIGN

Controlled laboratory study.

SETTING

Research laboratory in an academic medical center.

PATIENTS OR OTHER PARTICIPANTS

A total of 49 healthy individuals (age = 19.5 ± 3.1 years, height = 167.7 ± 13.2 cm, mass = 68.5 ± 17.5 kg).

INTERVENTION(S)

Participants completed the NeuroCom Sensory Organization Test (SOT) with an iPad2 affixed at the sacral level.

MAIN OUTCOME MEASURE(S)

Primary outcomes were equilibrium scores from both systems and the time series of the angular displacement of the anteroposterior COG sway during each trial. A Bland-Altman assessment for agreement was used to compare equilibrium scores produced by the NeuroCom and iPad2 devices. Limits of agreement was defined as the mean bias (NeuroCom - iPad) ± 2 standard deviations. Mean absolute percentage error and median difference between the NeuroCom and iPad2 measurements were used to evaluate how closely the real-time COG sway measured by the 2 systems tracked each other.

RESULTS

The limits between the 2 devices ranged from -0.5° to 0.5° in SOT condition 1 to -2.9° to 1.3° in SOT condition 5. The largest absolute value of the measurement error within the 95% confidence intervals for all conditions was 2.9°. The mean absolute percentage error analysis indicated that the iPad2 tracked NeuroCom COG with an average error ranging from 5.87% to 10.42% of the NeuroCom measurement across SOT conditions.

CONCLUSIONS

The iPad2 hardware provided data of sufficient precision and accuracy to quantify postural stability. Accuracy, portability, and affordability make using the iPad2 a reasonable approach for assessing postural stability in clinical and field environments.

Recovery performance and factors that classify young fallers and non-fallers in Parkinson's disease

Postural instability is a major problem for Parkinson's disease patients (PDs). Identifying the causes of postural instability at a young age would contribute to the development of adequate training interventions aiming to reduce falls. The purpose of this study was to investigate the effect of muscle strength and balance ability on dynamic stability control after simulated disturbances and to develop an applicable tool able to classify young PDs into fallers and non-fallers. Twenty-five young PDs (12 fallers, 13 non-fallers, 48±5 yrs.) and 14 healthy controls participated in the study. Dynamic stability was examined during simulated forward falls. Muscle strength was assessed by isometric maximal plantarflexion and knee extension contractions. Balance ability was evaluated by measuring the anterior and posterior limits of stability (LoS). The fallers showed lower recovery performance in forward falls and lower muscle strength compared to controls. Muscle strength and anterior LoS were significantly associated to stability performance. These two factors could correctly classify 90% of PD fallers, establishing an accurate assessment tool to predict the falling risk in young PDs. Furthermore, muscle strength partly explained recovery performance; therefore, we can argue that young PDs with an increased falling risk may benefit from leg-extensors strengthening and stability training.

The effect of levodopa on postural stability evaluated by wearable inertial measurement units for idiopathic and vascular Parkinson's disease

BACKGROUND

Postural stability analysis has shown that postural control is impaired in untreated idiopathic Parkinson's disease (IPD), even in the early stages of the disease. Vascular Parkinson's disease (VPD) lacks consensus clinical criteria or diagnostic tests. Moreover, the levodopa effect on postural balance remains undefined for IPD and even less so for VPD.

OBJECTIVE

To characterize postural stability, using kinematic analysis with wearable inertial measurement units, in IPD and VPD patients without clinical PI, and to subsequently analyze the response to levodopa.

METHODS

Ten patients with akinetic-rigid IPD and five patients with VPD were included. Clinical and postural stability kinematic analysis was performed before and after levodopa challenge, on different standing tasks: normal stance (NS), Romberg eyes open (REO) and Romberg eyes closed.

RESULTS

In the "off state", VPD patients had higher mean distances and higher maximal distance of p ostural sway on NS and REO tasks, respectively. VPD patients maintained a higher range of anterior-posterior (AP) postural sway after levodopa. In the absence of PI and non-significant differences in UPDRS-III, a higher mPIGD score in the VPD patients was mainly due to gait disturbance. Gait disturbance, and not UPDRS-III, influenced the degree of postural sway response to levodopa for VPD patients.

CONCLUSION

Quantitative postural sway evaluation is useful in the investigation of Parkinsonian syndromes. VPD patients have higher AP postural sway that is correlated with their gait disturbance burden and also not responsive to levodopa. These observations corroborate the interconnection of postural control and locomotor networks.

Prediction of falls and/or near falls in people with mild Parkinson's disease

OBJECTIVE

To determine factors associated with future falls and/or near falls in people with mild PD.

METHODS

The study included 141 participants with PD. Mean (SD) age and PD-duration were 68 (9.7) and 4 years (3.9), respectively. Their median (q1-q3) UPDRS III score was 13 (8-18). Those >80 years of age, requiring support in standing or unable to understand instructions were excluded. Self-administered questionnaires targeted freezing of gait, turning hesitations, walking difficulties in daily life, fatigue, fear of falling, independence in activities of daily living, dyskinesia, demographics, falls/near falls history, balance problems while dual tasking and pain. Clinical assessments addressed functional balance performance, retropulsion, comfortable gait speed, motor symptoms and cognition. All falls and near falls were subsequently registered in a diary during a six-month period. Risk factors for prospective falls and/or near falls were determined using logistic regression.

RESULTS

Sixty-three participants (45%) experienced ≥ 1 fall and/or near fall. Three factors were independent predictors of falls and/or near falls: fear of falling (OR = 1.032, p<0.001) history of near falls (OR = 3.475, p = 0.009) and retropulsion (OR = 2.813, p = 0.035). The strongest contributing factor was fear of falling, followed by a history of near falls and retropulsion.

CONCLUSIONS

Fear of falling seems to be an important issue to address already in mild PD as well as asking about prior near falls.

Rethinking energy in parkinsonian motor symptoms: a potential role for neural metabolic deficits

Parkinson’s disease (PD) is characterized as a chronic and progressive neurodegenerative disorder that results in a variety of debilitating symptoms, including bradykinesia, resting tremor, rigidity, and postural instability. Research spanning several decades has emphasized basal ganglia dysfunction, predominantly resulting from dopaminergic (DA) cell loss, as the primarily cause of the aforementioned parkinsonian features. But, why those particular features manifest themselves remains an enigma. The goal of this paper is to develop a theoretical framework that parkinsonian motor features are behavioral consequence of a long-term adaptation to their inability (inflexibility or lack of capacity) to meet energetic demands, due to neural metabolic deficits arising from mitochondrial dysfunction associated with PD. Here, we discuss neurophysiological changes that are generally associated with PD, such as selective degeneration of DA neurons in the substantia nigra pars compacta (SNc), in conjunction with metabolic and mitochondrial dysfunction. We then characterize the cardinal motor symptoms of PD, bradykinesia, resting tremor, rigidity and gait disturbance, reviewing literature to demonstrate how these motor patterns are actually energy efficient from a metabolic perspective. We will also develop three testable hypotheses: (1) neural metabolic deficits precede the increased rate of neurodegeneration and onset of behavioral symptoms in PD; (2) motor behavior of persons with PD are more sensitive to changes in metabolic/bioenergetic state; and (3) improvement of metabolic function could lead to better motor performance in persons with PD. These hypotheses are designed to introduce a novel viewpoint that can elucidate the connections between metabolic, neural and motor function in PD.

The contribution of proprioceptive information to postural control in elderly and patients with Parkinson's disease with a history of falls

Proprioceptive deficits negatively affect postural control but their precise contribution to postural instability in Parkinson’s disease (PD) is unclear. We investigated if proprioceptive manipulations differentially affect balance, measured by force plates, during quiet standing in 13 PD patients and 13 age-matched controls with a history of falls. Perceived limits of stability (LoS) were derived from the differences between maximal center of pressure (CoP) displacement in anterior–posterior (AP) and medio-lateral (ML) direction during a maximal leaning task. Task conditions comprised standing with eyes open (EO) and eyes closed (EC): (1) on a stable surface; (2) an unstable surface; and (3) with Achilles tendon vibration. CoP displacements were calculated as a percentage of their respective LoS. Perceived LoS did not differ between groups. PD patients showed greater ML CoP displacement than elderly fallers (EF) across all conditions (p = 0.043) and tended to have higher postural sway in relation to the LoS (p = 0.050). Both groups performed worse on an unstable surface and during tendon vibration compared to standing on a stable surface with EO and even more so with EC. Both PD and EF had more AP sway in all conditions with EC compared to EO (p < 0.001) and showed increased CoP displacements when relying on proprioception only compared to standing with normal sensory input. This implies a similar role of the proprioceptive system in postural control in fallers with and without PD. PD fallers showed higher ML sway after sensory manipulations, as a result of which these values approached their perceived LoS more closely than in EF. We conclude that despite a similar fall history, PD patients showed more ML instability than EF, irrespective of sensory manipulation, but had a similar reliance on ankle proprioception. Hence, we recommend that rehabilitation and fall prevention for PD should focus on motor rather than on sensory aspects.

Recurrent Falls in People with Parkinson's Disease without Cognitive Impairment: Focusing on Modifiable Risk Factors

Falls can be considered a disabling feature in Parkinson's disease. We aimed to identify risk factors for falling, testing simultaneously the ability of disease-specific and balance-related measures. We evaluated 171 patients, collecting demographic and clinical data, including standardized assessments with the Unified Parkinson's Disease Rating Scale (UPDRS), activities of daily living (ADL) and motor sections, modified Hoehn and Yahr Scale, Schwab and England, eight-item Parkinson's Disease Questionnaire, Activities-specific Balance Confidence Scale, Falls Efficacy Scale-International (FES-I), Berg Balance Scale, Dynamic Gait Index, Functional Reach, and Timed Up and Go. ROC curves were constructed to determine the cutoff scores for all measures. Variables with P < 0.1 entered a logistic regression model. The prevalence of recurrent falls was 30% (95% CI 24%–38%). In multivariate analysis, independent risk factors for recurrent falls were (P < 0.05) levodopa equivalent dose (OR = 1.283 per 100 mg increase; 95% CI = 1.092–1.507), UPDRS-ADL > 16 points (OR = 10.0; 95% CI = 3.6–28.3), FES-I > 30 points (OR = 6.0; 95% CI = 1.6–22.6), and Berg ≤ 48 points (OR = 3.9; 95% CI = 1.2–12.7).We encourage the utilization of these modifiable risk factors in the screening of fall risk.

Motor Switching and Motor Adaptation Deficits Contribute to Freezing of Gait in Parkinson’s Disease

Background. Patients with freezing of gait (FOG) have more difficulty with switching tasks as well as controlling the spatiotemporal parameters of gait than patients without FOG. Objective. To compare the ability of patients with and without FOG to adjust their gait to sudden speed switching and to prolonged walking in asymmetrical conditions. Methods. Gait characteristics of 10 freezers, 12 non-freezers, and 12 controls were collected during tied-belt conditions (3 and 4 km/h), motor switching and reswitching (increase of speed in one belt from 3 to 4 km/h and vice versa), and adaptation (adjustment to asymmetrical gait) and re-adaptation (returning to symmetrical gait) on a split-belt treadmill. Results. Following switching, freezers showed the largest increase of step length asymmetry ( P = .001). All groups gradually adapted their gait to asymmetrical conditions, but freezers were slower and demonstrated larger final asymmetry than the other 2 groups ( P = .001). After reswitching, freezers again showed the largest step length asymmetry ( P = .01). During re-adaptation, both controls and non-freezers reached symmetrical levels, but freezers did not. Interestingly, only immediately after switching did one episode of FOG and one episode of festination occur in 2 different patients. Conclusions. Freezers have more difficulties adapting their gait during both suddenly triggered and continued gait speed asymmetry. The impaired ability of freezers during both switching and reswitching would suggest that they have an adaptive deficit rather than difficulties with asymmetry per se. Future work needs to address whether these adaptation problems can be ameliorated with rehabilitation.

Individuals with transtibial limb loss use interlimb force asymmetries to maintain multi-directional reactive balance control

BACKGROUND

Deficits in balance control are one of the most common and serious mobility challenges facing individuals with lower limb loss. Yet, dynamic postural balance control among individuals with lower limb loss remains poorly understood. Here we examined the kinematics and kinetics of dynamic balance in individuals with unilateral transtibial limb loss.

METHODS

Five individuals with unilateral transtibial limb loss, and five age- and gender-matched controls completed a series of randomly applied multi-directional support surface translations. Whole-body metrics, e.g. peak center-of-mass displacement and net center-of-pressure displacement were compared across cohorts. Stability margin was computed as the difference between peak center-of-pressure and center-of-mass displacement. Additionally, center-of-pressure and ground reaction force magnitude and direction were compared between the prosthetic, intact, and control legs.

FINDINGS

Peak center-of-mass displacement and stability margin did not differ between individuals with transtibial limb loss and controls for all perturbation directions except those loading only the prosthetic leg; in such cases the stability margin was actually larger than controls. Despite similar center-of-mass displacement, greater center-of-pressure displacement was observed in the intact leg during anterior-posterior perturbations, and under the prosthetic leg in medial-lateral perturbations. Further, in the prosthetic leg, ground reaction forces were smaller and spanned fewer directions.

INTERPRETATION

Deficits in balance control among individuals with transtibial limb loss may be due to their inability to use their prosthetic leg to generate forces that are equal in magnitude and direction to those of unimpaired adults. Targeting this force-generating deficit through technological or rehabilitation innovations may improve balance control.

Instrumented functional reach test differentiates individuals at high risk for Parkinson's disease from controls

The functional reach (FR) test as a complex measure of balance including limits of stability has been proven to differentiate between patients with Parkinson’s disease (PD) and controls (CO). Recently, it has been shown that the instrumentation of the FR (iFR) with a wearable sensor may increase this diagnostic accuracy. This cross-sectional study aimed at investigating whether the iFR has the potential to differentiate individuals with high risk for PD (HRPD) from CO, as the delineation of such individuals would allow for, e.g., early neuromodulation. Thirteen PD patients, 13 CO, and 31 HRPD were investigated. HRPD was defined by presence of an enlarged area of hyperechogenicity in the mesencephalon on transcranial sonography and either one motor sign or two risk and prodromal markers of PD. All participants were asked to reach with their right arm forward as far as possible and hold this position for 10 s. During this period, sway parameters were assessed with an accelerometer (Dynaport, McRoberts) worn at the lower back. Extracted parameters that differed significantly between PD patients and CO in our cohort [FR distance (shorter in PD), anterior–posterior and mediolateral acceleration (both lower in PD)] as well as JERK, which has been shown to differentiate HRPD from CO and PD in a previous study, were included in a model, which was then used to differentiate HRPD from CO. The model yielded an area under the curve of 0.77, with a specificity of 85%, and a sensitivity of 74%. These results suggest that the iFR can contribute to an assessment panel focusing on the definition of HRPD individuals.

Postural instability detection: aging and the complexity of spatial-temporal distributional patterns for virtually contacting the stability boundary in human stance

Falls among the older population can severely restrict their functional mobility and even cause death. Therefore, it is crucial to understand the mechanisms and conditions that cause falls, for which it is important to develop a predictive model of falls. One critical quantity for postural instability detection and prediction is the instantaneous stability of quiet upright stance based on motion data. However, well-established measures in the field of motor control that quantify overall postural stability using center-of-pressure (COP) or center-of-mass (COM) fluctuations are inadequate predictors of instantaneous stability. For this reason, 2D COP/COM virtual-time-to-contact (VTC) is investigated to detect the postural stability deficits of healthy older people compared to young adults. VTC predicts the temporal safety margin to the functional stability boundary ( =  limits of the region of feasible COP or COM displacement) and, therefore, provides an index of the risk of losing postural stability. The spatial directions with increased instability were also determined using quantities of VTC that have not previously been considered. Further, Lempel-Ziv-Complexity (LZC), a measure suitable for on-line monitoring of stability/instability, was applied to explore the temporal structure or complexity of VTC and the predictability of future postural instability based on previous behavior. These features were examined as a function of age, vision and different load weighting on the legs. The primary findings showed that for old adults the stability boundary was contracted and VTC reduced. Furthermore, the complexity decreased with aging and the direction with highest postural instability also changed in aging compared to the young adults. The findings reveal the sensitivity of the time dependent properties of 2D VTC to the detection of postural instability in aging, availability of visual information and postural stance and potential applicability as a predictive model of postural instability during upright stance.

Deception effects on standing center of pressure

Accurate deception detection is a desirable goal with many applications including credibility assessment, security screening, counter-terrorism, and homeland security. However, many deception detection methodologies involve intrusive sensors or other limitations that preclude their use in a covert manner. Posturography may overcome these limitations by using minimally invasive force platform technology. In this study, we tested the hypothesis that posturography would reveal deception-related increases in postural rigidity similar to those observed with previous methodologies. Participants were randomly assigned to a control (CG) or experimental group (EG), and interviewed about the contents of a backpack in their possession while standing on a force platform. EG participants were asked to conceal the presence of several "prohibited" items in the backpack from the interviewer. Center of pressure (COP) measures from the force platform were used to characterize postural sway during participants' verbal responses. We observed a significant deception-related increase in sway frequency, an effect primarily occurring during longer responses that is likely related to increased cognitive load. These findings suggest deception-related increases in postural rigidity as reported in previous work, and demonstrate the feasibility of using posturography as a deception detection tool.

Postural mechanisms to control body displacements in the performance of lateral gaze shifts

Medialateral postural control mechanisms (bodyweight distribution and center of pressure location) have been studied in static conditions. Our objective was to determine how these mechanisms are adjusted to perform voluntary movements, in our case 80° lateral gaze shifts at 0.125 Hz and 0.25 Hz. In healthy, young adults, we expected body marker (neck, lower back) and center of pressure displacements to be significantly greater in gaze shift conditions than in the stationary gaze condition. To explain these changes in center of pressure displacement, the amplitude contribution of both mechanisms was expected to increase significantly. All these results were found accordingly. Unexpectedly, the active contribution of the bodyweight distribution mechanism was negatively related to body marker displacements in the gaze shift conditions (ns in stationary condition). Moreover, changes in the contribution of the mechanisms were statistically weaker in effect size than changes in body displacement. However, the participants were not unstable because they performed the visual tasks as requested. We propose that the strength of medialateral postural control mechanisms may not only be strengthened to control challenging ML stance conditions but also slightly weakened to allow the performance of adequate body motions in ongoing tasks.

The influence of instruction on arm reactions in individuals with Parkinson's disease

The purpose of this study was to examine whether explicit instruction would facilitate arm reactions in individuals with Parkinson's disease (PD). Individuals with (n = 10) and without (n = 15) PD responded to unexpected support-surface translations. To recover their balance, participants were required to either respond naturally (react natural) or to reach toward a nearby handrail (explicit instruction). Arm reactions were quantified from electromyographic (EMG) and arm kinematic recordings. Results showed that while explicit instruction led to earlier and larger arm reactions, the benefits were not different between individuals with and without PD. Specifically, when explicitly instructed to reach toward a handrail, shoulder EMG responses were 4% earlier (p = .005) and 32% larger (p < .001) compared to when instructed to react naturally. A 44% greater peak wrist medio-lateral velocity (p < .001) and a 29% greater peak shoulder abduction angular velocity (p < .001) were also observed when participants were instructed to direct their arms toward a handrail after an unexpected support-surface translation. Explicit instruction also led to a higher frequency of handrail contact and a 49 ms earlier time to handrail contact compared to the react natural condition (p = .015). These results suggest that providing instruction to promote arm movement may help reduce falls in older adults with and without PD.

Interest of active posturography to detect age-related and early Parkinson's disease-related impairments in mediolateral postural control

Patients with Parkinson's disease display impairments of postural control most particularly in active, challenging conditions. The objective of the present study was to analyze early signs of disease-related and also age-related impairments in mediolateral body extension and postural control. Fifty-five participants (18 Hoehn and Yahr stage 2 patients in the off-drug condition, 18 healthy elderly control subjects, and 19 young adults) were included in the study. The participants performed a quiet stance task and two active tasks that analyzed the performance in mediolateral body motion: a limit of stability and a rhythmic weight shift task. As expected, the patients displayed significantly lower and slower body displacement (head, neck, lower back, center of pressure) than elderly control subjects when performing the two body excursion tasks. However, the behavioral variability in both tasks was similar between the groups. Under these active conditions, the patients showed significantly lower contribution of the hip postural control mechanisms compared with the elderly control subjects. Overall, the patients seemed to lower their performance in order to prevent a mediolateral postural instability. However, these patients, at an early stage of their disease, were not unstable in quiet stance. Complementarily, elderly control subjects displayed slower body performance than young adults, which therefore showed an additional age-related impairment in mediolateral postural control. Overall, the study illustrated markers of age-related and Parkinson's disease impairments in mediolateral postural control that may constrain everyday activities in elderly adults and even more in patients with Parkinson's disease.

Relationships between balance and cognition in patients with subjective cognitive impairment, mild cognitive impairment, and Alzheimer disease

BACKGROUND

Balance impairments are common in patients with Alzheimer disease (AD), but which aspects of balance are affected, at which stage of cognitive impairment, and their associations with cognitive domains remain unexplored.

OBJECTIVES

The aims of this study were: (1) to explore differences in balance abilities among patients with subjective cognitive impairment (SCI) or mild cognitive impairment (MCI), mild AD, and moderate AD and (2) to examine the relationship between the various aspects of balance and cognitive domains.

DESIGN

This was a cross-sectional study.

METHODS

Home-dwelling patients with SCI or MCI (n=33), mild AD (n=99), and moderate AD (n=38) participated in this study. The Balance Evaluation Systems Test (BESTest), comprising 6 subscales-"Biomechanical Constraints," "Stability Limits/Verticality," "Anticipatory Postural Adjustments," "Postural Responses," "Sensory Orientation," and "Stability in Gait"-was used to assess balance. Cognitive domains were assessed using the following measures: Mini-Mental Status Examination, Word-List Learning Test from the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), Verbal Fluency Test, Clock Drawing Test, and Trail Making Test, parts A and B (TMT-A and TMT-B, respectively). Two-way between-group analyses of variance, adjusted for age, were used to analyze differences among the groups. Multiple linear regression analysis was used to explore the associations between balance and cognition.

RESULTS

Differences were found between the groups on all BESTest subscales; the moderate AD group had the worst scores. The TMT-B (measuring executive function) was associated with all of the BESTest subscales after controlling for demographic factors.

LIMITATIONS

The cross-sectional design hampered interpretation of the development of balance impairments.

CONCLUSIONS

The study findings indicate that all aspects of balance control deteriorate with increasing severity of cognitive impairment and that executive function plays an important role in balance control. Physical therapists should pay attention to these findings both in clinical practice and in future research.

Technology-Assisted Balance and Gait Training Reduces Falls in Patients With Parkinson’s Disease

Objective. To examine the effects of technology-assisted balance and gait training on reducing falls in patients with Parkinson’s disease (PD). Methods. Eligible subjects were randomly allocated to an experimental group given technology-assisted balance and gait training (BAL, n = 26) and an active control group undertaking strengthening exercises (CON, n = 25). The training in each group lasted for 3 months. The number of fallers and fall rate were used as primary outcomes, and single-leg-stance-time, latency of postural response to perturbation, self-selected gait velocity, and stride length as secondary outcomes. Fall incidence was recorded over 15 months after the baseline assessment (Pre). Other tests were performed at Pre, after 3-month intervention (Post3m), at 3 months (Post6m), and 12 months (Post15m) after treatment completion. Results. Forty-five subjects who completed the 3-month training were included in the data analysis. There were fewer fallers in the BAL than in the CON group at Post3m, Post6m, and Post15m ( P < .05). In addition, the BAL group had lower fall rate than the CON group at Post3m and Post6m (incidence rate ratio: 0.111-0.188, P < .05), and marginally so at Post15m (incidence rate ratio: 0.407, P = .057). Compared with the CON subjects, the BAL subjects demonstrated greater reduction in the postural response latency and increase in the stride length against baseline at each assessment interval ( P < .05), and marginally more increases of single-leg-stance-time at Post3m ( P = .064), Post6m ( P = .041) and Post15m ( P = .087). Conclusions. Our positive findings provide evidence for the clinical use of technology-assisted balance and gait training in reducing falls in people with PD.

Brain activity during complex imagined gait tasks in Parkinson disease

OBJECTIVE

Motor imagery during functional magnetic resonance imaging (fMRI) allows assessment of brain activity during tasks, like walking, that cannot be completed in an MRI scanner. We used gait imagery to assess the neural pathophysiology of locomotion in Parkinson disease (PD).

METHODS

Brain activity was measured in five locomotor regions (supplementary motor area (SMA), globus pallidus (GP), putamen, mesencephalic locomotor region, cerebellar locomotor region) during simple (forward) and complex (backward, turning) gait imagery. Brain activity was correlated to overground walking velocity.

RESULTS

Across tasks, PD exhibited reduced activity in the globus pallidus compared to controls. People with PD, but not controls, exhibited more activity in the SMA during imagined turning compared to forward or backward walking. In PD, walking speed was correlated to brain activity in several regions.

CONCLUSIONS

Altered SMA activity in PD during imagined turning may represent compensatory neural adaptations during complex gait. The lowered activity and positive correlation to locomotor function in GP suggests reduced activity in this region may relate to locomotor dysfunction.

SIGNIFICANCE

This study elucidates changes in neural activity during gait in PD, underscoring the importance of testing simple and complex tasks. Results support a positive relationship between activity in locomotor regions and walking ability.

Stance width changes how sensory feedback is used for multisegmental balance control

A multilink sensorimotor integration model of frontal plane balance control was developed to determine how stance width influences the use of sensory feedback in healthy adults. Data used to estimate model parameters came from seven human participants who stood on a continuously rotating surface with three different stimulus amplitudes, with eyes open and closed, and at four different stance widths. Dependent variables included lower body (LB) and upper body (UB) sway quantified by frequency-response functions. Results showed that stance width had a major influence on how parameters varied across stimulus amplitude and between visual conditions. Active mechanisms dominated LB control. At narrower stances, with increasing stimulus amplitude, subjects used sensory reweighting to shift reliance from proprioceptive cues to vestibular and/or visual cues that oriented the LB more toward upright. When vision was available, subjects reduced reliance on proprioception and increased reliance on vision. At wider stances, LB control did not exhibit sensory reweighting. In the UB system, both active and passive mechanisms contributed and were dependent on stance width. UB control changed across stimulus amplitude most in wide stance (opposite of the pattern found in LB control). The strong influence of stance width on sensory integration and neural feedback control implies that rehabilitative therapies for balance disorders can target different aspects of balance control by using different stance widths. Rehabilitative strategies designed to assess or modify sensory reweighting will be most effective with the use of narrower stances, whereas wider stances present greater challenges to UB control.

Using motor imagery to study the neural substrates of dynamic balance

This study examines the cerebral structures involved in dynamic balance using a motor imagery (MI) protocol. We recorded cerebral activity with functional magnetic resonance imaging while subjects imagined swaying on a balance board along the sagittal plane to point a laser at target pairs of different sizes (small, large). We used a matched visual imagery (VI) control task and recorded imagery durations during scanning. MI and VI durations were differentially influenced by the sway accuracy requirement, indicating that MI of balance is sensitive to the increased motor control necessary to point at a smaller target. Compared to VI, MI of dynamic balance recruited additional cortical and subcortical portions of the motor system, including frontal cortex, basal ganglia, cerebellum and mesencephalic locomotor region, the latter showing increased effective connectivity with the supplementary motor area. The regions involved in MI of dynamic balance were spatially distinct but contiguous to those involved in MI of gait (Bakker et al., 2008; Snijders et al., 2011; Crémers et al., 2012), in a pattern consistent with existing somatotopic maps of the trunk (for balance) and legs (for gait). These findings validate a novel, quantitative approach for studying the neural control of balance in humans. This approach extends previous reports on MI of static stance (Jahn et al., 2004, 2008), and opens the way for studying gait and balance impairments in patients with neurodegenerative disorders.

Factors associated with fear of falling in people with Parkinson's disease

Background

This study aimed to comprehensibly investigate potential contributing factors to fear of falling (FOF) among people with idiopathic Parkinson’s disease (PD).

Methods

The study included 104 people with PD. Mean (SD) age and PD-duration were 68 (9.4) and 5 (4.2) years, respectively, and the participants’ PD-symptoms were relatively mild. FOF (the dependent variable) was investigated with the Swedish version of the Falls Efficacy Scale, i.e. FES(S). The first multiple linear regression model replicated a previous study and independent variables targeted: walking difficulties in daily life; freezing of gait; dyskinesia; fatigue; need of help in daily activities; age; PD-duration; history of falls/near falls and pain. Model II included also the following clinically assessed variables: motor symptoms, cognitive functions, gait speed, dual-task difficulties and functional balance performance as well as reactive postural responses.

Results

Both regression models showed that the strongest contributing factor to FOF was walking difficulties, i.e. explaining 60% and 64% of the variance in FOF-scores, respectively. Other significant independent variables in both models were needing help from others in daily activities and fatigue. Functional balance was the only clinical variable contributing additional significant information to model I, increasing the explained variance from 66% to 73%.

Conclusions

The results imply that one should primarily target walking difficulties in daily life in order to reduce FOF in people mildly affected by PD. This finding applies even when considering a broad variety of aspects not previously considered in PD-studies targeting FOF. Functional balance performance, dependence in daily activities, and fatigue were also independently associated with FOF, but to a lesser extent. Longitudinal studies are warranted to gain an increased understanding of predictors of FOF in PD and who is at risk of developing a FOF.

The degrees of freedom problem in human standing posture: collective and component dynamics

The experiment was setup to investigate the coordination and control of the degrees of freedom (DFs) of human standing posture with particular reference to the identification of the collective and component variables. Subjects stood in 3 postural tasks: feet side by side, single left foot quiet stance and single left foot stance with body rocking at the ankle joint in the sagittal plane. All three postural tasks showed very high coherence (∼ 1) of center of pressure (COP)--center of mass (COM) in the low frequency range. The ankle and hip coherence was mid range (∼.5) with the tasks having different ankle/hip compensatory cophase patterns. The findings support the view that the in-phase relation of the low frequency components of the COP-COM dynamic is the collective variable in the postural tasks investigated. The motions of the individual joints (ankle, knee, hip, neck) and couplings of pair wise joint synergies (e.g., ankle-hip) provide a supporting cooperative role to the preservation of the collective variable in maintaining the COM within the stability region of the base of support (BOS) and minimizing the amount of body motion consistent with the task constraint.

Increasing speed to improve arm movement and standing postural control in Parkinson's disease patients when catching virtual moving balls

Research has shown that moving targets help Parkinson's disease (PD) patients improve their arm movement while sitting. We examined whether increasing the speed of a moving ball would also improve standing postural control in PD patients during a virtual reality (VR) ball-catching task. Twenty-one PD patients and 21 controls bilaterally reached to catch slow-moving and then fast-moving virtual balls while standing. A projection-based VR system connected to a motion-tracking system and a force platform was used. Dependent measures included the kinematics of arm movement (movement time, peak velocity), duration of anticipatory postural adjustments (APA), and center of pressure (COP) movement (movement time, maximum amplitude, and average velocity). When catching a fast ball, both PD and control groups made arm movements with shorter movement time and higher peak velocity, longer APA, as well as COP movements with shorter movement time and smaller amplitude than when catching a slow ball. The change in performance from slow- to fast-ball conditions was not different between the PD and control groups. The results suggest that raising the speed of virtual moving targets should increase the speed of arm and COP movements for PD patients. Therapists, however, should also be aware that a fast virtual moving target causes the patient to confine the COP excursion to a smaller amplitude. Future research should examine the effect of other task parameters (e.g., target distance, direction) on COP movement and examine the long-term effect of VR training.

Effect of muscle vibration on postural balance of Parkinson's diseases patients in bipedal quiet standing

[Purpose] The purpose of this study was to investigate the effect of muscle vibration applied to the lower extremities on static postural balance of patients with Parkinson’s disease (PD). [Subjects] Seven subjects with Parkinson’s disease participated in this study. [Methods] The oscillators of vibration were attached to the muscle bellies of the tibialis anterior, gastrocnemius, biceps femoris, and rectus femoris on both sides of the lower extremities with adhesive tape. A vibration frequency of 60 Hz was used to induce static postural reactions. Subjects’ center of pressure (COP) sway and peak ground reaction force (GRF) were measured with their eyes open with and without vibration. COP sway and peak GRF (Fx, Fy, Fz) were measured using a force plate (AMTI, Newton, USA), which provides x, y and z coordinates of body movement. [Results] The area of COP sway with vibration was significantly smaller than that with no vibration, but the length of COP sway showed no difference between two conditions. Peak medial-lateral maximum force (Fy) with vibration was significantly higher than that with no vibration, but peak anterior-posterior force (Fx) and peak vertical force (Fz) showed no differences. [Conclusion] These results suggest that vibration applied to the lower extremities can help PD patients control postural balance during quiet standing.

Classification of body movements based on posturographic data

The human body, standing on two feet, produces a continuous sway pattern. Intended movements, sensory cues, emotional states, and illnesses can all lead to subtle changes in sway appearing as alterations in ground reaction forces and the body's center of pressure (COP). The purpose of this study is to demonstrate that carefully selected COP parameters and classification methods can differentiate among specific body movements while standing, providing new prospects in camera-free motion identification. Force platform data were collected from participants performing 11 choreographed postural and gestural movements. Twenty-three different displacement- and frequency-based features were extracted from COP time series, and supplied to classification-guided feature extraction modules. For identification of movement type, several linear and nonlinear classifiers were explored; including linear discriminants, nearest neighbor classifiers, and support vector machines. The average classification rates on previously unseen test sets ranged from 67% to 100%. Within the context of this experiment, no single method was able to uniformly outperform the others for all movement types, and therefore a set of movement-specific features and classifiers is recommended.

Parkinson disease and exercise

Parkinson disease (PD) is a progressive, neurodegenerative movement disorder. PD was originally attributed to neuronal loss within the substantia nigra pars compacta, and a concomitant loss of dopamine. PD is now thought to be a multisystem disorder that involves not only the dopaminergic system, but other neurotransmitter systems whose role may become more prominent as the disease progresses (189). PD is characterized by four cardinal symptoms, resting tremor, rigidity, bradykinesia, and postural instability, all of which are motor. However, PD also may include any combination of a myriad of nonmotor symptoms (195). Both motor and nonmotor symptoms may impact the ability of those with PD to participate in exercise and/or impact the effects of that exercise on those with PD. This article provides a comprehensive overview of PD, its symptoms and progression, and current treatments for PD. Among these treatments, exercise is currently at the forefront. People with PD retain the ability to participate in many forms of exercise and generally respond to exercise interventions similarly to age-matched subjects without PD. As such, exercise is currently an area receiving substantial research attention as investigators seek interventions that may modify the progression of the disease, perhaps through neuroprotective mechanisms.

Effect of partial weight-supported treadmill gait training on balance in patients with Parkinson disease

OBJECTIVE

To investigate the role of conventional gait training and partial weight-supported treadmill gait training (PWSTT) in improving the balance of patients with Parkinson disease (PD).

DESIGN

Prospective randomized controlled design.

SETTING

National-level university tertiary hospital for mental health and neurosciences.

PATIENTS

Sixty patients with PD fulfilling the United Kingdom Brain Bank PD diagnostic criteria were recruited from the neurology outpatient department and movement disorder clinic.

METHODOLOGY

The patients were randomly assigned into 3 equal groups: (1) a control group that only received a stable dosage of dopaminomimetic drugs; (2) a conventional gait training (CGT) group that received a stable dosage of dopaminomimetic drugs and conventional gait training; and (3) a PWSTT group that received a stable dosage of dopaminomimetic drugs and PWSTT with unloading of 20% of body weight. The sessions for the CGT and PWSTT groups were provided for 30 minutes per day, 4 days per week, for 4 weeks (16 sessions).

OUTCOME MEASURES

The Unified Parkinson Disease Rating Scale (UPDRS) motor score, dynamic posturography, Berg Balance Scale, and Tinetti performance-oriented mobility assessment (POMA) were used as main outcome measures.

RESULTS

A significant interaction effect was observed in the UPDRS motor score, mediolateral index, Berg Balance Scale, limits of stability (LOS) total score, POMA gait score, and balance score. Post-hoc analysis showed that in comparison with the control group, the PWSTT group had a significantly better UPDRS motor score, balance indices, LOS in 8 directions, POMA gait, and balance score. The CGT group had a significantly better POMA gait score compared with control subjects. Compared with the CGT group, the PWSTT group had a significantly better UPDRS motor score, mediolateral index, POMA gait score, and LOS total score.

CONCLUSION

PWSTT may be a better interventional choice than CGT for gait and balance rehabilitation in patients with PD.

Obstacle crossing in Parkinson's disease: mediolateral sway of the centre of mass during level-ground walking and obstacle crossing

BACKGROUND

Falls are common in idiopathic Parkinson's disease (PD) and frequently occur when walking and crossing obstacles.

OBJECTIVE

To determine whether people with mild to moderately severe PD have abnormal centre of mass (CoM) motion in response to the perturbations of level-ground walking and obstacle crossing.

METHOD

Mediolateral excursion and velocity of the CoM were measured using three-dimensional motion analysis and force platforms in 20 people with mild to moderately severe PD at the peak dose of their PD medication, and 20 age and sex matched healthy control participants.

RESULTS

People with PD had greater sideways sway than healthy older adults when walking, particularly when walking over obstacles. People with PD also maintained their CoM more medial to their stance foot throughout the swing phase of gait compared to controls. The severity of motor symptoms in people with PD, measured using the UPDRS-III, was associated with faster sideways CoM motion but not increased CoM excursions.

CONCLUSIONS

Environmental hazards, such as ground-based obstacles, may accentuate postural instability in people with PD. Increased mediolateral sway might be due to impaired postural responses or kinematic compensations to increase foot clearance. Fall prevention programs could benefit from inclusion of components educating people with PD about the risks associated with obstacle crossing when walking.

The effect of moderate Parkinson's disease on compensatory backwards stepping

Postural instability is a major unmet need in the treatment of Parkinson's disease (PD) and its progression is not well understood. This study examined compensatory stepping taken in response to a backwards waist pull in participants with moderate PD (H&Y III) compared to age-range matched healthy controls (HC). The first step in the response was quantified in terms of strategy, temporal, kinematic, and center of pressure (COP) parameters previously observed to be significantly different in mild PD (H&Y II) compared to HC. Patients with moderate PD, compared to HC, utilized more steps to regain balance, had a longer weight-shift-time, and utilized a base-width neutral step to regain balance. However, there were no differences in ankle angle or COP location at landing as observed in mild PD, possibly due to the use of the base-width neutral step. These results suggest that moderate PD significantly impairs the compensatory response to a backwards pull. Further study should examine the progression of impairment in compensatory responses across PD severity levels, and the correlation with fall risk.

Clinical and posturographic correlates of falling in Parkinson's disease

Various clinical tests and balance scales have been used to assess postural stability and the risk of falling in patients with idiopathic Parkinson's disease (IPD). Quantitative posturography allows a more objective assessment but the findings in previous studies have been inconsistent and few studies have investigated which posturographic measures correlate best with a history of falling. The purpose of this study was to determine the efficacy of clinical tests, balance scales, and stable-platform posturography in detecting postural instability and discriminating between fallers and non-fallers in a home-dwelling PD cohort. Forty-eight PD subjects (Hoehn & Yahr stage 1-3) and 17 age-matched controls had the following assessments: Activities-specific Balance Confidence scale, Berg Balance Scale, Unified Parkinson's Disease Rating Scale (UPDRS) (motor), pull-test, timed up-and-go, static posturography, and dynamic posturography to assess multidirectional leaning balance. Of the clinical assessments, all but the pull-test were closely correlated with a history of falling. Static posturography discriminated between PD fallers and controls but not between PD fallers and non-fallers, whereas dynamic posturography (reaction time, velocity, and target hit-time) also discriminated between fallers and non-fallers. Our findings suggest that this combination of clinical and posturographic measures would be useful in the prospective assessment of falls risk in PD patients. A further prospective study is now required to assess their predictive value. © 2013 Movement Disorder Society.

Adaptation of gait termination on a slippery surface in Parkinson's disease

Parkinson's disease (PD) causes instability and difficulty adapting to changing environmental and task demands. We examined the effects of PD on the adaptation of gait termination (GT) on a slippery surface under unexpected and cued circumstances. An unexpected slip perturbation during GT was followed by a slip perturbation during GT under two conditions: planned over multiple steps and cued one step prior to GT. Feed forward and feedback-based responses to the perturbation were compared to determine (1) how PD affects the ability to integrate adaptive feed forward and feedback-based GT strategies on a slippery surface, (2) if adaptations can be implemented when GT is required within one step, and (3) if behaviour changes with repeated exposure. Similar to the control group (n=10), the PD group (n=8) adapted and integrated feed forward and feedback-based components of GT under both stop conditions. Feed forward adaptations included a shorter, wider step, and appropriate stability margin modifications. Feedback-based adaptations included a longer, wider subsequent step. When cued to stop quickly, both groups maintained most of these adaptations: foot angle at contact increased in the first cued stop but adapted with practice. The group with PD differed in their ability to adapt GT with slower, wider steps and less stability.

Postural instability in patients with Parkinson's disease. Epidemiology, pathophysiology and management

Postural instability is one of the cardinal signs in Parkinson's disease (PD). It can be present even at diagnosis, but becomes more prevalent and worsens with disease progression. It represents one of the most disabling symptoms in the advanced stages of the disease, as it is associated with increased falls and loss of independence. Clinical and posturographic studies have contributed to significant advances in unravelling the complex pathophysiology of postural instability in patients with PD, but it still remains yet to be fully clarified, partly due to the difficulty in distinguishing between the disease process and the compensatory mechanisms, but also due to the fact that non-standardized techniques are used to measure balance and postural instability. There is increasing evidence that physical therapy, especially highly challenging balance exercises, can improve postural stability and reduce the risk of falls, although the long-term effects of physical therapy interventions on postural stability need to be explored given the progressive nature of PD. Pharmacotherapy with dopaminergic medications can provide significant improvements in postural instability in early- to mid-stage PD but the effects tend to wane with time consistent with spread of the disease process to non-dopaminergic pathways in advanced PD. Donepezil has been associated with a reduced risk of falls and methylphenidate has shown potential benefit against freezing of gait, but the results are yet to be replicated in large randomized studies. Surgical treatments, including lesioning and deep brain stimulation surgery targeting the subthalamic nucleus and the globus pallidus internus, tend to only provide modest benefit for postural instability. New surgical targets such as the pedunculopontine nucleus have emerged as a potential specific therapy for postural instability and gait disorder but remain experimental.

A Systems Perspective on Postural and Gait Stability: Implications for Physical Activity in Aging and Disease

Postural instability, falls, and fear of falling that accompany frailty with aging and disease form major impediments to physical activity. In this article we present a theoretical framework that may help researchers and practitioners in the development and delivery of intervention programs aimed at reducing falls and improving postural stability and locomotion in older individuals and in those with disability due to disease. Based on a review of the dynamical and complex systems perspectives of movement coordination and control, we show that 1) central to developing a movement-based intervention program aimed at fall reduction and prevention is the notion that variability can play a functional role and facilitate movement adaptability, 2) intervention programs aimed at fall reduction should focus more on coordination and stability boundary measures instead of traditional gait and posture outcome variables, and 3) noise-based intervention techniques using stochastic resonance may offer external aids to improve dynamic balance control.

A novel conceptual framework for balance training in Parkinson's disease-study protocol for a randomised controlled trial

Background

There is increasing scientific knowledge about the interaction between physiological (musculoskeletal, neuromuscular, cognitive and sensory) systems and their influence on balance and walking impairments in Parkinson’s disease. We have developed a new conceptual framework for balance training, emphasising specific components of balance control related to Parkinson’s disease symptoms by using highly challenging, progressive and varying training conditions. The primary aim of this proposed randomised controlled trial will be to investigate the short-term and long-term effects of a 10-week balance training regime in elderly with Parkinson’s disease.

Methods/Design

Eighty participants with mild to moderate idiopathic Parkinson’s disease will be recruited and randomly allocated to an intervention group receiving balance training or a control group whose participants will continue to receive their usual care. The intervention will consist of a 10-week group training regime (1-hour training, three times per week), which will be led by two physiotherapists to ensure training progression and safety. The conceptual framework will be applied by addressing specific balance components (sensory integration, anticipatory postural adjustments, motor agility, stability limits) through varying training conditions and structured progression. Assessment will be conducted through a multi-dimensional battery of outcomes, prior to and immediately after the 10-week intervention, and at 9 and 15 months’ follow-up after entering the study. Primary outcome measures will be balance performance (assessed using the Mini Balance Evaluation Systems Test), change in gait velocity (m/s) between single and dual task walking, and fear of falling (evaluated using the Fall Efficacy Scale International).

Discussion

This study has the potential to provide new insight and knowledge of the effects of specific, varied and challenging balance training on a wide health spectrum in elderly with PD. If found to be effective, this pragmatic approach with translation of theory into practice, can be implemented in existing outpatient care.

Trial registration

NCT01417598

Keeping your balance while balancing a cylinder: interaction between postural and voluntary goals

The present study investigated whether postural responses are influenced by the stability constraint of a voluntary, manual task. We also examined how task constraint and first experience (the condition with which the participants started the experiment) influence the kinematic strategies used to simultaneously accomplish a postural response and a voluntary task. Twelve healthy, older adults were perturbed during standing, while holding a tray with a cylinder placed with the flat side down (low constraint, LC) or with the rolling, round side down (high constraint, HC). Central set changed according to the task constraint, as shown by a higher magnitude of both the gastrocnemius and tibialis anterior muscle activation bursts in the HC than in the LC condition. This increase in muscle activation was not reflected, however, in changes in the center of pressure or center of mass displacement. Task constraint influenced the peak shoulder flexion for the voluntary tray task but not the peak hip flexion for the postural task. In contrast, first experience influenced the peak hip flexion but not the peak shoulder flexion. These results suggest an interaction between two separate control mechanisms for automatic postural responses and voluntary stabilization tasks.