Coordination of axial rotation and step execution: deficits in Parkinson's disease

Acute effects of lumbosacral mobilization on balance and functional activities in idiopathic Parkinson's disease:A randomised controlled trial

BACKGROUND

Decreased axial rotation, impaired coordination between axial segments and axial tone contribute to gait, balance and postural disorders in Parkinson's Disease.

AIMS

The aim of our study was to examine the acute effects of lumbosacral mobilization on balance and functional activities in patients with idiopathic Parkinson's Disease.

METHODS

This study was a randomized controlled clinical trial conducted at Hacettepe University. The study included 28 patients with Parkinson's Disease who were between stage 2-3 according to the Modified Hoehn&Yahr Staging Scale. Participants were randomised to the study group, including 10 minutes of lumbosacral mobilization, or the control group, including no intervention. The Unified Parkinson's Disease Rating Scale (UPDRS), Modified Parkinson's Activity Scale (MPAS), Dynamic Gait Index (DGI), and static posturography test (Modified Clinical Test of Sensory Interaction and Balance - mCTSIB) were all examined twice.

RESULTS

The UPDRS, MPAS, DGI values and the composite score with the soft ground eyes open condition in the mCTSIB were improved in the study group (p < 0.05). DGI and MPAS values reached the level of significance between the groups (p < 0.05).

CONCLUSION

This study is the first to examine the effect of lumbosacral mobilization on balance and functional activities in patients with Parkinson's disease. Lumbosacral mobilization is an effective method in PwPD. Lumbosacral mobilization may be an alternative way for these patients to improve their balance and functional activities.

Startle-induced rapid release of a gait initiation sequence in Parkinson's disease with freezing of gait

OBJECTIVE

Freezing of gait (FOG) in Parkinson's disease (PD) is characterized by the inability to initiate stepping, despite the intention to do so. This study used a startling acoustic stimulus paradigm to examine if the capacity to select, prepare and initiate gait under simple and choice reaction time conditions are impaired in people with PD and FOG.

METHODS

Thirty individuals (10 PD with FOG, 10 PD without FOG, and 10 controls) performed an instructed-delay gait initiation task under simple and choice reaction time conditions. In a subset of trials, a startle stimulus (124 dB) was presented 500 ms before the time of the imperative go-cue. Anticipatory postural adjustments preceding and accompanying gait initiation were quantified.

RESULTS

The presentation of a startling acoustic stimulus resulted in the rapid initiation of an anticipatory postural adjustment sequence during both the simple and choice reaction time tasks in all groups.

CONCLUSIONS

The neural capacity to prepare the spatial and temporal components of gait initiation remains intact in PD individuals with and without FOG.

SIGNIFICANCE

The retained capacity to prepare anticipatory postural adjustments in advance may explain why external sensory cues are effective in the facilitation of gait initiation in people with PD with FOG.

The Effects of Constraining Head Rotation on Eye and Whole-Body Coordination During Standing Turns at Different Speeds

A limitation of the ability to rotate the head with respect to the upper body has been associated with turning problems; however, the extent of head constraints on whole-body coordination has not been fully determined. The aim of this study was to limit head on body rotation and observe the effects on whole-body coordination during standing turns at various speeds. Twelve participants completed standing turns at 180°. A Vicon motion system and a BlueGain Electrooculography system were used to record movement kinematics and measure horizontal eye movements, respectively. All participants were tested at 3 randomized speeds, and under 2 conditions with or without their head constrained using a head, neck, and chest brace which restricted neck movement. A repeated-measures analysis of variance found a significant main effect of turning speed on the onset latency of all segments, peak head-thorax angular separation, and step characteristics. Constraining the head rotation had multiple significant effects including delayed onset latency and decreased intersegmental coordination defined as peak head segmental angular separations, increased total step and step duration, and decreased step size. This indicates the contribution of speed, head, and neck constraints, which have been associated with falls during turning and whole-body coordination.

Characterization of Anticipatory Postural Adjustments in Lateral Stepping: Impact of Footwear and Lower Limb Preference

Lateral stepping is a motor task that is widely used in everyday life to modify the base of support, change direction, and avoid obstacles. Anticipatory Postural Adjustments (APAs) are often analyzed to describe postural preparation prior to forward stepping, however, little is known about lateral stepping. The aim of the study is to characterize APAs preceding lateral steps and to investigate how these are affected by footwear and lower limb preference. Twenty-two healthy young participants performed a lateral step using both their preferred and non-preferred leg in both barefoot and shod conditions. APA spatiotemporal parameters (size, duration, and speed) along both the anteroposterior and mediolateral axes were obtained through force plate data. APAs preceding lateral stepping showed typical patterns both along the anteroposterior and mediolateral axis. RM-ANOVA highlighted a significant effect of footwear only on medio-lateral APAs amplitude (p = 0.008) and velocity (p = 0.037). No differences were found for the limb preference. APAs in lateral stepping presented consistent features in the sagittal component, regardless of limb/shoe factors. Interestingly, the study observed that footwear induced an increase in the medio-lateral APAs size and velocity, highlighting the importance of including this factor when studying lateral stepping.

Gait parameters of Parkinson's disease compared with healthy controls: a systematic review and meta-analysis

We systematically reviewed observational and clinical trials (baseline) studies examining differences in gait parameters between Parkinson’s disease (PD) in on-medication state and healthy control. Four electronic databases were searched (November-2018 and updated in October-2020). Independent researchers identified studies that evaluated gait parameters measured quantitatively during self-selected walking speed. Risk of bias was assessed using an instrument proposed by Downs and Black (1998). Pooled effects were reported as standardized mean differences and 95% confidence intervals using a random-effects model. A total of 72 studies involving 3027 participants (1510 with PD and 1517 health control) met the inclusion criteria. The self-selected walking speed, stride length, swing time and hip excursion were reduced in people with PD compared with healthy control. Additionally, PD subjects presented higher cadence and double support time. Although with a smaller difference for treadmill, walking speed is reduced both on treadmill (.13 m s⁻¹) and on overground (.17 m s⁻¹) in PD. The self-select walking speed, stride length, cadence, double support, swing time and sagittal hip angle were altered in people with PD compared with healthy control. The precise determination of these modifications will be beneficial in determining which intervention elements are most critical in bringing about positive, clinically meaningful changes in individuals with PD (PROSPERO protocol CRD42018113042).

The Effect of a Secondary Task on Kinematics during Turning in Parkinson’s Disease with Mild to Moderate Impairment

Patients with Parkinson’s disease (PD) show typical gait asymmetries. These peculiar motor impairments are exacerbated by added cognitive and/or mechanical loading. However, there is scarce literature that chains these two stimuli. The aim of this study was to investigate the combined effects of a dual task (cognitive task) and turning (mechanical task) on the spatiotemporal parameters in mild to moderate PD. Participants (nine patients with PD and nine controls (CRs)) were evaluated while walking at their self-selected pace without a secondary task (single task), and while repeating the days of the week backwards (dual task) along a straight direction and a 60° and 120° turn. As speculated, in single tasking, PD patients preferred to walk with a shorter stride length (p < 0.05) but similar timing parameters, compared to the CR group; in dual tasking, both groups walked slower with shorter strides. As the turn angle increased, the speed will be reduced (p < 0.001), whereas the ground–foot contact will become greater (p < 0.001) in all the participants. We showed that the combination of a simple cognitive task and a mechanical task (especially at larger angles) could represent an important training stimulus in PD at the early stages of the pathology.

Characteristics of medial-lateral postural control while exposed to the external perturbation in step initiation

Controllability of posture in the medial-lateral direction is critical for balance maintenance, particularly in step initiation. The objective of the current study was to examine  the effects of external perturbation and landing orientation on medial-lateral control stability in step initiation. Eleven young healthy participants stood on the force platform and waited for the instruction of taking a step while experiencing a pendulum perturbation applied at the lateral side of the right shoulder. Eight experimental conditions were conducted by two levels of step side (right or left), two levels of perturbation (with or without), and two levels of landing orientation (forward or diagonal). The center of pressure (COP), pelvic movements, and muscle activities were recorded and analyzed as the onset of COP and pelvic movement, the COP displacement, and cocontraction and reciprocal muscle activation pattern. The temporal events of COP and pelvic movement were not significantly different in all experimental conditions. However, COP and pelvic movement were significantly later in the diagonal condition. Most of the segments showed reciprocal muscle activation patterns in relation to the perturbation released time. Subsequently, all segments showed cocontraction muscle activation patterns, which was significantly affected by step side, perturbation, and orientation. The results suggest that how the CNS initiated a step was identical with the COP then pelvic movement. The outcome highlights the importance of external perturbation and foot landing orientation effects on postural adjustments, which may provide a different approach to help step initiation.

Exercise for Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease with a prevalence rate of 1-2 per 1000 of the population worldwide. Pharmacological management is the mainstay of treatment. Despite optimal medication, motor impairment particularly balance and gait impairment persist leading to various degree of disability and reduced quality-of-life. The present review describes motor impairment including postural impairment, gait dysfunction, reduced muscle strength and aerobic capacity and falls. Physical therapy and complementary exercises have been proven to improve motor performance and functional mobility. Evidence on the efficacy of physical therapy and complementary exercises is presented in this review. These exercises include gait training with cues, gait training with treadmill, Nordic walking, brisk walking, balance training, virtual reality interventions, Tai Chi and dance. All these treatment interventions produce short-term beneficial effects and some interventions demonstrate long-term benefit. Gait training with treadmill enhance walking performance and the effects sustain for 3-6 months. Balance training improves balance, function and reduces fall rate, and these effects carry over to at least 12 months after training ended. Sustained Tai Chi for 6 months, dance therapy for 12 months, progressive resistive training for 24 months alleviates the PD motor symptoms, suggesting that they could slow down PD progression. Based on this evidence, individuals with PD are encouraged to sustain their training in order to improve/maintain their physical ability and to combat the progression of PD.

Data-Driven Based Approach to Aid Parkinson's Disease Diagnosis

This article presents a machine learning methodology for diagnosing Parkinson's disease (PD) based on the use of vertical Ground Reaction Forces (vGRFs) data collected from the gait cycle. A classification engine assigns subjects to healthy or Parkinsonian classes. The diagnosis process involves four steps: data pre-processing, feature extraction and selection, data classification and performance evaluation. The selected features are used as inputs of each classifier. Feature selection is achieved through a wrapper approach established using the random forest algorithm. The proposed methodology uses both supervised classification methods including K-nearest neighbour (K-NN), decision tree (DT), random forest (RF), Naïve Bayes (NB), support vector machine (SVM) and unsupervised classification methods such as K-means and the Gaussian mixture model (GMM). To evaluate the effectiveness of the proposed methodology, an online dataset collected within three different studies is used. This data set includes vGRF measurements collected from eight force sensors placed under each foot of the subjects. Ninety-three patients suffering from Parkinson's disease and 72 healthy subjects participated in the experiments. The obtained performances are compared with respect to various metrics including accuracy, precision, recall and F-measure. The classification performance evaluation is performed using the leave-one-out cross validation. The results demonstrate the ability of the proposed methodology to accurately differentiate between PD subjects and healthy subjects. For the purpose of validation, the proposed methodology is also evaluated with an additional dataset including subjects with neurodegenerative diseases (Amyotrophic Lateral Sclerosis (ALS) and Huntington's disease (HD)). The obtained results show the effectiveness of the proposed methodology to discriminate PD subjects from subjects with other neurodegenerative diseases with a relatively high accuracy.

Abnormal gait pattern emerges during curved trajectories in high-functioning Parkinsonian patients walking in line at normal speed

Background

Several patients with Parkinson´s disease (PD) can walk normally along straight trajectories, and impairment in their stride length and cadence may not be easily discernible. Do obvious abnormalities occur in these high-functioning patients when more challenging trajectories are travelled, such as circular paths, which normally implicate a graded modulation in the duration of the interlimb gait cycle phases?

Methods

We compared a cohort of well-treated mildly to moderately affected PD patients to a group of age-matched healthy subjects (HS), by deliberately including HS spontaneously walking at the same speed of the patients with PD. All participants performed, in random order: linear and circular walking (clockwise and counter-clockwise) at self-selected speed. By means of pressure-sensitive insoles, we recorded walking speed, cadence, duration of single support, double support, swing phase, and stride time. Stride length-cadence relationships were built for linear and curved walking. Stride-to-stride variability of temporal gait parameters was also estimated.

Results

Walking speed, cadence or stride length were not different between PD and HS during linear walking. Speed, cadence and stride length diminished during curved walking in both groups, stride length more in PD than HS. In PD compared to HS, the stride length-cadence relationship was altered during curved walking. Duration of the double-support phase was also increased during curved walking, as was variability of the single support, swing phase and double support phase.

Conclusion

The spatio-temporal gait pattern and variability are significantly modified in well-treated, high-functioning patients with PD walking along circular trajectories, even when they exhibit no changes in speed in straight-line walking. The increased variability of the gait phases during curved walking is an identifying characteristic of PD. We discuss our findings in term of interplay between control of balance and of locomotor progression: the former is challenged by curved trajectories even in high-functioning patients, while the latter may not be critically affected.

Variability of Anticipatory Postural Adjustments During Gait Initiation in Individuals With Parkinson Disease

BACKGROUND AND PURPOSE

In people with Parkinson disease (PD), difficulties with initiating stepping may be related to impairments of anticipatory postural adjustments (APAs). Increased variability in step length and step time has been observed in gait initiation in individuals with PD. In this study, we investigated whether the ability to generate consistent APAs during gait initiation is compromised in these individuals.

METHODS

Fifteen subjects with PD and 8 healthy control subjects were instructed to take rapid forward steps after a verbal cue. The changes in vertical force and ankle marker position were recorded via force platforms and a 3-dimensional motion capture system, respectively. Means, standard deviations, and coefficients of variation of both timing and magnitude of vertical force, as well as stepping variables, were calculated.

RESULTS

During the postural phase of gait initiation the interval was longer and the force modulation was smaller in subjects with PD. Both the variability of timing and force modulation were larger in subjects with PD. Individuals with PD also had a longer time to complete the first step, but no significant differences were found for the variability of step time, length, and speed between groups.

DISCUSSION AND CONCLUSIONS

The increased variability of APAs during gait initiation in subjects with PD could affect posture-locomotion coupling, and lead to start hesitation, and even falls. Future studies are needed to investigate the effect of rehabilitation interventions on the variability of APAs during gait initiation in individuals with PD.Video abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A119).

Conflicting and non-conflicting visual cues lead to error in gait initiation and gait inhibition in individuals with freezing of gait

INTRODUCTION

We asked whether conflicting visual cues influences gait initiation, gait inhibition and postural control in Parkinson's disease (PD) between freezers, non-freezers and healthy older adults.

METHODS

Twenty-five PD participants on dopaminergic medication and 17 healthy older adults were asked to initiate or refrain gait depending on visual cues: green GO (GG), green STOP (GS), red GO (RG), red STOP (RS). Center of pressure (CoP) displacement, variability and mean velocity (VCoP) in the anterior-posterior (AP) and medial-lateral (ML) directions and movement time (MT) were measured.

RESULTS

Gait initiation: Both freezers and non-freezers were different from controls in GG and GS. In GS, freezers had smaller CoP displacement and velocity in both directions (p<0.01), while non-freezers had smaller VCoP in AP and ML (p<0.01). AP CoP displacement in GS was smaller in freezers compared to non-freezers (p<0.05). Freezers had longer MT compared to controls in GG and compared to both groups in GS (p<0.01). Gait inhibition: Controls and freezers had larger CoP displacement variability (p<0.05) and velocity (p<0.01) in both directions in RG compared to RS. No differences were seen in non-freezers. Three freezers initiated walking during the RG or RS conditions.

CONCLUSION

Freezers were in general slower at initiating gait, displayed a more restrictive postural strategy and were more affected by the conflicting conditions compared to both controls and non-freezers. In freezers, the conflicting visual cues may have increased the cognitive load enough to provoke delays in processing the visual information and implementing the appropriate motor program.

Correlation between midline gait function performance and verbal fluency in patients with Parkinson's disease

BACKGROUND

Verbal fluency impairments are among the earliest and most common cognitive deficits in Parkinson's disease (PD), yet more than one study has shown that as a group, verbal fluency performance is not always different between patients with PD and age-matched controls. Here we examined whether PD-related deficits in speech and language capabilities are detectable in patients who exhibit poor midline motor function, such as control of gait. We postulated that if phonemic verbal fluency (PVF) performance in PD is dissociable from other factors such as age in this patient subgroup, a low PVF will likely reflect a general cognitive-motor deficit attributable to Parkinsonian pathology.

METHODS

Thirty-one PD and thirteen controls were evaluated on PVF and the Metronome-Paced Square Step Test (MPSST), a complex sensorimotor task that challenges axial and midline function. The MPSST requires a patient to initiate and maintain a consecutive series of diagonal and midline cross-over steps during the test.

RESULTS

We found that despite similar PVF performance between groups, the vast majority of controls but not patients completed the MPSST without any errors, and the odds of completing the MPSST without any errors was 15 times greater among control. More importantly, a significant amount of PVF variability was explained by MPSST performance in PD but not controls even after controlling for age and disease duration.

CONCLUSION

Together, these results provide evidence that PVF performance in PD likely reflects a PD-specific process and suggests that the MPSST may be a more sensitive test of PD-specific pathology than PVF.

Deficits in coordinated motor behavior and in nigrostriatal dopaminergic system ameliorated and VMAT2 expression up-regulated in aged male rats by administration of testosterone propionate

The effects of testosterone propionate (TP) supplements on the coordinated motor behavior and nigrostriatal dopaminergic (NSDA) system were analyzed in aged male rats. The present study showed the coordinated motor behavioral deficits, the reduced activity of NSDA system and the decreased expression of vesicular monoamine transporter 2 (VMAT2) in 24 month-old male rats. Long term TP treatment improved the motor coordination dysfunction with aging. Increased tyrosine hydroxylase and dopamine transporter, as well as dopamine and its metabolites were found in the NSDA system of TP-treated 24 month-old male rats, indicative of the amelioratory effects of TP supplements on NSDA system of aged male rats. The enhancement of dopaminergic (DAergic) activity of NSDA system by TP supplements might underlie the amelioration of the coordinated motor dysfunction in aged male rats. TP supplements up-regulated VMAT2 expression in NSDA system of aged male rats. Up-regulation of VMAT2 expression in aged male rats following chronic TP treatment might be involved in the maintenance of DAergic function of NSDA system in aged male rats.

A new instrumented method for the evaluation of gait initiation and step climbing based on inertial sensors: a pilot application in Parkinson's disease

Background

Step climbing is a demanding task required for personal autonomy in daily living. Anticipatory Postural Adjustments (APAs) preceding gait initiation have been widely investigated revealing to be hypometric in Parkinson’s disease (PD) with consequences in movement initiation. However, only few studies focused on APAs prior to step climbing. In this work, a novel method based on wearable inertial sensors for the analysis of APAs preceding gait initiation and step climbing was developed to further understand dynamic balance control. Validity and sensitivity of the method have been evaluated.

Methods

Eleven PD and 20 healthy subjects were asked to perform two transitional tasks from quiet standing to level walking, and to step climbing respectively. All the participants wore two inertial sensors, placed on the trunk (L2-L4) and laterally on the shank. In addition, a validation group composed of healthy subjects and 5 PD patients performed the tasks on two force platforms. Correlation between parameters from wearable sensors and force platforms was evaluated. Temporal parameters and trunk acceleration from PD and healthy subjects were analyzed.

Results

Significant correlation was found for the validation group between temporal parameters extracted from wearable sensors and force platforms and between medio-lateral component of trunk acceleration and correspondent COP displacement. These results support the validity of the method for evaluating APAs prior to both gait initiation and step climbing. Comparison between PD subjects and a subgroup of healthy controls confirms a reduction in PD of the medio-lateral acceleration of the trunk during the imbalance phase in the gait initiation task and shows similar trends during the imbalance and unloading phase of the step climbing task. Interestingly, PD subjects presented difficulties in adapting the medio-lateral amplitude of the imbalance phase to the specific task needs.

Conclusions

Validity of the method was confirmed by the significant correlation between parameters extracted from wearable sensors and force platforms. Sensitivity was proved by the capability to discriminate PD subjects from healthy controls. Our findings support the applicability of the method to subjects of different age. This method could be a possible valid instrument for a better understanding of feed-forward anticipatory strategies.

Postural strategies assessed with inertial sensors in healthy and parkinsonian subjects

The present study introduces a novel instrumented method to characterize postural movement strategies to maintain balance during stance (ankle and hip strategy), by means of inertial sensors, positioned on the legs and on the trunk. We evaluated postural strategies in subjects with 2 types of Parkinsonism: idiopathic Parkinson's disease (PD) and Progressive Supranuclear Palsy (PSP), and in age-matched control subjects standing under perturbed conditions implemented by the Sensory Organization Test (SOT). Coordination between the upper and lower segments of the body during postural sway was measured using a covariance index over time, by a sliding-window algorithm. Afterwards, a postural strategy index was computed. We also measured the amount of postural sway, as adjunctive information to characterize balance, by the root mean square of the horizontal trunk acceleration signal (RMS).

RESULTS

showed that control subjects were able to change their postural strategy, whilst PSP and PD subjects persisted in use of an ankle strategy in all conditions. PD subjects had RMS values similar to control subjects even without changing postural strategy appropriately, whereas PSP subjects showed much larger RMS values than controls, resulting in several falls during the most challenging SOT conditions (5 and 6). Results are in accordance with the corresponding clinical literature describing postural behavior in the same kind of subjects. The proposed strategy index, based on the use of inertial sensors on the upper and lower body segments, is a promising and unobtrusive tool to characterize postural strategies performed to attain balance.

Why we should study gait initiation in Parkinson's disease

The gait initiation process is of particular interest in Parkinson's disease because it combines motor and cognitive components of movement preparation (referred to as anticipatory postural adjustments) and movement execution (the step by itself). Moreover, gait initiation in Parkinson's disease is often affected by motor blocks (a subtype of the "freezing of gait" phenomenon). Gait initiation disturbances in Parkinson's disease include delayed release of anticipatory postural adjustments, hypokinetic anticipatory postural adjustments (reduced scaling) and bradykinetic anticipatory postural adjustments (abnormal timing). The most extreme form is freezing of gait with sometimes the absence of anticipatory postural adjustments. Other phenomena can be also described in some freezing patients (such as multiple anticipatory postural adjustments, described clinically as "knee trembling"). The fact that emotion, attention, external triggers and dopaminergic drugs can all modify this motor program suggests the existence of a complex pathophysiological mechanism that involves not only locomotor networks but also cortical areas and the basal ganglia system. Abnormal coupling between standing posture and anticipatory postural adjustments and between the latter and step execution appears to be a crucial part of the pathophysiological mechanism. Although external cueing appears to be of interest, few studies have provided evidence of the efficacy of various rehabilitation methods in routine care.

Age and Parkinson's disease related kinematic alterations during multi-directional gait initiation

Previous literature suggests that older adults and persons with Parkinson's disease (PWP) exhibit impaired performance during gait initiation (GI) and turning while walking. While researchers have identified specific impairments during GI and turning separately in these populations, little is known about when these two tasks occur concurrently. Our objective was to determine how multi-directional GI kinematics are affected by aging and Parkinson's disease. Kinematic data were collected on 12 healthy young adults (HYA), 11 healthy older adults (HOA) and 11 PWP during GI in four conditions: forward, medial 45°, lateral 45°, and lateral 90°. Spatiotemporal characteristics and segmental angles were analyzed using separate 3 (group)×4 (condition) mixed ANOVA. Combined across all the conditions, HOA took a smaller (P=0.009) and slower (P=0.023) first step, and slower second step (P=0.021) compared to HYA. PWP took a slower first step (P=0.009), and longer time to initiate the second step (P=0.017) compared to HOA. Also, PWP had greater head rotation at the start of GI during the medial 45° condition (P=0.043) and reduced overall segmental rotation before toe-off of the second step during the lateral 45° condition (P=0.035), and at heel-strike of first step (P=0.031) and before toe-off of second step during lateral 90° condition (P=0.035). For HOA, their general slowness of movement could be attributed to aging effects. For PWP, rigidity and bradykinesia could impair activities of daily living like multi-directional GI and may be associated with an increased risk of falls.

Self-triggered assistive stimulus training improves step initiation in persons with Parkinson's disease

BACKGROUND

Prior studies demonstrated that hesitation-prone persons with Parkinson's disease (PDs) acutely improve step initiation using a novel self-triggered stimulus that enhances lateral weight shift prior to step onset. PDs showed reduced anticipatory postural adjustment (APA) durations, earlier step onsets, and faster 1st step speed immediately following stimulus exposure.

OBJECTIVE

This study investigated the effects of long-term stimulus exposure.

METHODS

Two groups of hesitation-prone subjects with Parkinson's disease (PD) participated in a 6-week step-initiation training program involving one of two stimulus conditions: 1) Drop. The stance-side support surface was lowered quickly (1.5 cm); 2) Vibration. A short vibration (100 ms) was applied beneath the stance-side support surface. Stimuli were self-triggered by a 5% reduction in vertical force under the stance foot during the APA. Testing was at baseline, immediately post-training, and 6 weeks post-training. Measurements included timing and magnitude of ground reaction forces, and step speed and length.

RESULTS

Both groups improved their APA force modulation after training. Contrary to previous results, neither group showed reduced APA durations or earlier step onset times. The vibration group showed 55% increase in step speed and a 39% increase in step length which were retained 6 weeks post-training. The drop group showed no stepping-performance improvements.

CONCLUSIONS

The acute sensitivity to the quickness-enhancing effects of stimulus exposure demonstrated in previous studies was supplanted by improved force modulation following prolonged stimulus exposure. The results suggest a potential approach to reduce the severity of start hesitation in PDs, but further study is needed to understand the relationship between short- and long-term effects of stimulus exposure.

Initial motor symptoms of Parkinson disease

Parkinson disease (PD) is characterized by a wide variety of motor and nonmotor symptoms. Although recently nonmotor symptoms have gained considerable relevance and interest, especially in advanced stages, motor symptoms define the main core of PD and are essential for clinical diagnosis. In this article, we review the characteristics, presentation, and evolution of motor symptoms in early PD.

Posture and locomotion coupling: a target for rehabilitation interventions in persons with Parkinson's disease

Disorders of posture, balance, and gait are debilitating motor manifestations of advancing Parkinson's disease requiring rehabilitation intervention. These problems often reflect difficulties with coupling or sequencing posture and locomotion during complex whole body movements linked with falls. Considerable progress has been made with demonstrating the effectiveness of exercise interventions for individuals with Parkinson's disease. However, gaps remain in the evidence base for specific interventions and the optimal content of exercise interventions. Using a conceptual theoretical framework and experimental findings, this perspective and review advances the viewpoint that rehabilitation interventions focused on separate or isolated components of posture, balance, or gait may limit the effectiveness of current clinical practices. It is argued that treatment effectiveness may be improved by directly targeting posture and locomotion coupling problems as causal factors contributing to balance and gait dysfunction. This approach may help advance current clinical practice and improve outcomes in rehabilitation for persons with Parkinson's disease.". . .postural activity should be regarded as a function in its own right and not merely as a component of movement. . ."James Purdon Martin.

Postural preparation prior to stepping in patients with Parkinson's disease

People with Parkinson's disease (PD) frequently have difficulties with generating anticipatory postural adjustments (APAs) for forward propulsion and lateral weight transfer when initiating gait. This impairment has been attributed to deficits in motor planning and preparation. This study examined the preparation of APAs prior to an imperative cue to initiate forward stepping. A startling acoustic stimulus (SAS) was used to probe the state of preparation of the APA in eight PD (off medication) and seven matched control subjects. Subjects performed visually cued trials involving a pre-cue light instructing them to prepare to step, followed 3.5 s later by a go-cue light to rapidly initiate stepping. In random trials, a SAS (124 dB) was presented at −1,500, −1,000, −500, −250, −100, or 0 ms before the go-cue. Subjects also performed self-initiated steps. Ground reaction forces (GRFs), center of pressure (CoP) changes, and electromyographic (EMG) signals were recorded. The SAS triggered APAs in 94 ± 11% (PD) and 96 ± 8% (control) of trials at latencies 89 ± 4 ms (PD) and 97 ± 3 ms (control) earlier than Control trials. The temporal profile of APA preparation was similar between groups. However, peak EMG, GRF, and mediolateral CoP amplitudes were reduced in PD. SAS-evoked APAs at 0 ms matched Control trial APAs and were enhanced compared with self-initiated stepping. These results demonstrate that people with mild to moderate PD can plan and prepare the appropriate APA sequence prior to the expected cue to initiate gait; however, the prepared APAs are underscaled in magnitude.

Perturbations of ground support alter posture and locomotion coupling during step initiation in Parkinson's disease

During the initiation of stepping, anticipatory postural adjustments (APAs) for lateral weight transfer and propulsion normally precede the onset of locomotion. In Parkinson's disease (PD), impaired step initiation typically involves altered APA ground force production with delayed step onset and deficits in stepping performance. If, as in stance and gait, sensory information about lower limb load is important for the control of stepping, then perturbations influencing loading conditions could affect the step initiation process. This study investigated the influence of changes in lower limb loading during step initiation in patients with PD and healthy control subjects. Participants performed rapid self-triggered step initiation with the impending single stance limb positioned over a pneumatically actuated platform. In perturbation trials, the stance limb ground support surface was either moved vertically downward (DROP) or upward (ELEVATE) by 1.5 cm shortly after the onset of the APA phase. Overall, PD patients demonstrated a longer APA duration, longer time to first step onset, and slower step speed than controls. In both groups, the DROP perturbation reinforced the intended APA kinetic changes for lateral weight transfer and resulted in a significant reduction in APA duration, increase in peak amplitude, and earlier time to first step onset compared with other conditions. During ELEVATE trials that opposed the intended weight transfer forces both groups rapidly adapted their stepping to preserve standing stability by decreasing step length and duration, and increasing step height and foot placement laterally. The findings suggested that sensory information associated with limb load and/or foot pressure modulates the spatial and temporal parameters of posture and locomotion components of step initiation in interaction with a centrally generated feedforward mode of neural control. Moreover, impaired step initiation in PD may at least acutely be enhanced by augmenting the coupling between posture and locomotion.

Axial kinesthesia is impaired in Parkinson's disease: effects of levodopa

Integration of sensory and motor inputs has been shown to be impaired in appendicular muscles and joints of Parkinson's disease (PD) patients. As PD advances, axial symptoms such as gait and balance impairments appear, which often progresses to complete inability stand or walk unaided. The current study evaluates kinesthesia in the axial musculature of PD patients during active postural control to determine whether impairments similar to those found in the appendages are also present in the hip and trunk. Using axial twisting, we quantified the detection threshold and directional accuracy of the hip relative to the feet (i.e. Hip Kinesthesia) and the hip relative to the shoulders (i.e. Trunk Kinesthesia). The relation of kinesthetic threshold to disease progression as measured by UPDRS and the effect of levodopa treatment on kinesthesia were assessed in 12 PD compared to age-matched controls. Subjects stood unaided while passively twisted at a very low constant rotational velocity (1 degrees /s). The results showed that accuracy in determining the direction of axial twisting was reduced in PD relative to healthy control subjects in the hip (PD-ON: 81%; PD-OFF: 91%; CTL=96%) and trunk (PD-ON: 81%; PD-OFF: 88%; CTL=95%). Thresholds for perception of axial twisting were increased when PD subjects were ON levodopa versus OFF in both the hip (p<0.01) and the trunk (p<0.05). The magnitude of decrease in sensitivity due to being ON levodopa was significantly correlated with the increase in UPDRS motor scores (Hip: r=0.90, p<0.01 and Trunk: r=0.60, p<0.05). This effect was not significantly correlated with equivalent levodopa dosage. PD subjects with disease onset on the left side of their body showed significantly higher axial thresholds than subjects with right PD onset (p<0.05). In conclusion, deficits in axial kinesthesia seem to contribute to the functional impairments of posture and locomotion in PD. Although levodopa has been shown to improve appendicular kinesthesia, we observed the opposite in the body axis. These findings underscore the dissociable neurophysiological circuits and dopaminergic pathways that are known to innervate these functionally distinct muscle groups.

Short-term effects of posture-assisted step training on rapid step initiation in Parkinson's disease

BACKGROUND AND PURPOSE

Anticipatory postural adjustments (APAs) for lateral weight transfer and stability precede and accompany gait initiation. Individuals with Parkinson's disease (PD) show altered APA characteristics with delays in initiating stepping that may reflect impaired interactions between posture and locomotion. The purpose of this study was to determine the short-term effects of a single session of repetitive robotic assistance training with the APA on rapid step initiation in individuals with PD in the medications "on" state and healthy control individuals. Ground reaction forces and step kinematics were recorded.

METHODS

Subjects first performed baseline trials of unassisted self-paced rapid forward stepping. Next, a training acquisition series involved 50 trials with a lateral pull applied to the pelvis by a robotic system to assist with the early phase of the APA during stepping. To assess potential retention effects of training, unassisted stepping trials were evaluated immediately after acquisition trials (immediate retention) and one week later (one-week retention).

RESULTS

Overall, the subjects with PD had a longer APA duration (P < 0.03), and longer first step duration (P < 0.04) than the healthy control individuals. Compared with baseline, APA duration was shorter (P < 0.001) and step onset time became earlier (P < 0.001) for acquisition trials but these effects were not retained. Step duration, which became shorter (P < 0.001) during the late acquisition trials (P = 0.002), demonstrated immediate retention (P < 0.001) and one-week retention (P < 0.001).

CONCLUSION

Posture-assisted training, affecting the interaction between posture and locomotion, may have therapeutic potential for improving movement performance in individuals with PD.

Anticipatory postural adjustments prior to step initiation are hypometric in untreated Parkinson's disease: an accelerometer-based approach

BACKGROUND AND PURPOSE

Anticipatory postural adjustments (APAs), prior to step initiation, are bradykinetic in advanced Parkinson's disease (PD) and may be one of the factors associated with 'start hesitation'. However, little is known about APAs in the early stage of PD. In this study, we determined whether body-worn accelerometers could be used to characterize step initiation deficits in subjects with early-to-moderate, untreated PD.

METHODS

Eleven PD and 12 healthy control subjects were asked to take two steps. Postural adjustments were compared from center of pressure (COP) and from acceleration of the trunk at the center of mass level (L5).

RESULTS

Our findings show that APAs measured from the peak COP displacement toward the swing leg and the peak trunk acceleration toward the stance leg were smaller in untreated PD compared with control subjects. The magnitude of APAs measured from peak COP displacements and accelerations were correlated.

CONCLUSION

These results suggest that quantitative analysis of step initiation from one accelerometer on the trunk could provide useful information for the characterization of patients in early stages of PD, when clinical evidence of start hesitation may not be detectable. Ambulatory monitoring of step initiation is also promising for monitoring patient progression in the home environment, and eventually providing feedback for preventing freezing of gait episodes.

Postural disorders in Parkinson's disease

Posture is often affected in Parkinson's disease. Postural abnormalities belong to the motor axial involvement. Generally, postural dysfunction induces clinical impairment at the latest stages of the disease, except in late-onset idiopathic Parkinson's disease and in atypical parkinsonian syndromes. Posture may be affected in its orientation component (stooped posture, camptocormia, Pisa syndrome) or in its balance component (loss of postural reflexes). Overall, postural impairment is poorly improved by levodopa, which implies that it is unlikely due to the nigrostriatal dopaminergic denervation. Several methods of investigation have been proposed but are generally not available in clinical practice. Medical treatment and deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus pars interna are less efficient on axial than on distal motor signs. The pedonculopontine nucleus seems promising as a new target for DBS in combination with the subthalamic nucleus. Physical therapy is, in most cases, the best way to improve postural dysfunction.

Gait initiation in older adults with postural instability

BACKGROUND

This study examined changes in the translation of the center of pressure during forward and lateral (90 degrees to the side) gait initiation in two populations of older adults with postural instability.

METHODS

Twenty-eight older adults transitioning to frailty and 16 persons with Parkinson's disease in the "on medication state" were evaluated during initiation trials. Displacements, velocities, and smoothness of the center of pressure trace were calculated and compared.

FINDINGS

Both groups produced movements of the center of pressure that on average were reduced compared to healthy populations. Adults transitioning to frailty were able to scale the output of the motor program so forces that propel the body in the intended direction of movement were maximized as evidenced by movements of the center of pressure. The adults transitioning to frailty produced patterns of center of pressure trajectories that were more similar to healthy adults where as individuals with Parkinson's disease produced trajectories that were counterproductive to producing efficient gait initiation in both the forward and lateral direction.

INTERPRETATION

These findings suggest that persons with Parkinson's disease even when in the medicated state exhibit inefficient postural adjustments during both forward and lateral gait initiation and that these postural adjustments are more susceptible to deterioration from the complex interaction of central and peripheral changes associated with Parkinson's disease than to aging alone.

Turning in Parkinson's disease patients and controls: The effect of auditory cues

Turning is an impaired activity in persons with Parkinson's disease (PwPD). The current study examines the turning characteristics in PwPD (9 freezers and 10 nonfreezers) and 9 controls, and explores the effect of rhythmic auditory cues while turning. Turning parameters were collected from a 180 degrees left U-turn during a noncued and a cued condition, using a 3D measuring system. Auditory cues were supplied with a metronome at a rhythm equaling the subject's comfortable step frequency during straight line walking. Results showed that in contrast to controls, PwPD used a wider turning-arc and took smaller, narrower steps. In addition, they demonstrated a higher Coefficient of Variation (CV) of step duration (6.92%) compared to controls (4.88%, P < 0.05). The "wide-arc" turning strategy of PwPD was more prominent in freezers than in nonfreezers. Auditory cues reduced the CV of step duration in PwPD (both freezers and nonfreezers) during turning (from 6.92 to 6.00%, P < 0.05). In summary: Cueing reduced the gait-timing variability during turning, but PwPD maintained a wider arc to turn compared with controls.

The association between impaired turning and normal straight walking in Parkinson's disease

Turning whilst walking was investigated by gait analysis in a group of Parkinson's Disease (PD) patients with mild clinical impairment and no significant abnormalities in stride parameters and kinematics of steady-state, linear walking. Comparison with age-matched controls demonstrated that patients approached turns with a slower step and completed turning with a greater number of steps. Moreover, the normal cranio-caudal sequence, whereby rotation of the head toward the intended direction of travel is followed by rotation of the trunk, was replaced by nearly simultaneous rotation of head and trunk and decreased relative head excursion after the second turning step. The evidence of abnormal inter-segmental coordination during turning in mildly affected, normally walking patients suggests that task-specific pathophysiological mechanisms, not necessary related to basic locomotor deficits, underlie disturbed directional changes in PD. Furthermore, turning-related neural systems may be more vulnerable to functional impairments associated with PD, as compared with linear walking. Hierarchically higher control levels involved in the turning ability may explain the observed unexpected association.

Acute effects of a lateral postural assist on voluntary step initiation in patients with Parkinson's disease

Anticipatory postural adjustments (APAs) for lateral weight transfer and stability precede and accompany voluntary stepping. Patients with Parkinson's disease (PD) show delays in step initiation with altered APA characteristics that may reflect impaired interactions between posture and locomotion. The purpose of this study was to examine the influence of a lateral postural assist on step initiation in patients with early stage PD while off medication and healthy controls. Subjects performed self-paced rapid forward steps. In one condition (ASSIST), the APA was assisted at onset with a lateral pull applied to the pelvis by a motor-driven robotic system. Ground reaction forces and whole body kinematics were recorded to characterize the APA and step characteristics. Overall, PD subjects had a longer APA duration (P < 0.01) and longer first step duration (P < 0.027) than Control subjects. With the ASSIST, the APA duration for both groups was shorter (P < 0.001), the step onset time was earlier (P < 0.001), and the speed of the first step became faster for PD subjects. Postural assistance affecting the interaction between posture and locomotion may have therapeutic potential for improving movement function in patients with PD.

Axial rotation in Parkinson's disease

AIMS

To investigate the ability of patients with Parkinson's disease to perform a rotation around the longitudinal axis of the body. Three questions were raised. Is body rotation impaired in Parkinson's disease? Is there a level of the kinematic chain from the head to the foot at which the impairment is more severe? Is the deficit related to the general slowness of movement in Parkinson's disease?

METHODS

Kinematic data were recorded. The temporal organisation of body rotation during gait initiation was analysed in 10 patients with Parkinson's disease, who were all at an advanced stage of the disease and had all experienced falls and freezing during their daily life, and in five controls. The latency of the onset of the rotation of each segment was measured by taking the onset of the postural phase of step initiation as reference value. Locomotor variables were also analysed.

RESULTS

Body rotation was found to be impaired in patients with Parkinson's disease, as the delay in the onset of the rotation of each segment is greater than that in controls. Moreover, a specific uncoupling in the onset of shoulder and pelvis segment rotation was seen in patients. This impairment of rotation is not related only to the general slowness of movements.

CONCLUSION

Patients with Parkinson's disease were found to have an impairment of posturo-kinetic coordination and impaired capacity to exert appropriate ground reaction forces to orient the pelvis in space.

Locomotor disorders in patients at early stages of Parkinson's disease: a quantitative analysis

Several studies have been performed with automatic motion analysis techniques to investigated the locomotor disorders of patients with severe Parkinson's disease (PD). These are mainly related to steady-state walking. Aim of the present study was to investigate the presence and the degree of these disorders in patients at early stages of PD. For this purpose a group of patients with mild PD (H&Y < or =2) and a group of age-matched controls were assessed by means of multifactorial analysis of kinematic and kinetic variables, during the execution of the following motor tasks: steady-state walking, gait initiation and turning around an obstacle. Results showed that PD patients did not differ from controls in steady-state walking, while significant differences emerged in gait initiation and turning strategies. Main differences consisted in a limitation of the amplitude of the imbalance phase and of the first step, and, for the turning task, in a delayed initiation of the turning movement, with an altered head-trunk rotational strategy. It is concluded that patients in early stages of PD do not reveal, during steady state walking, consistent impairments of kinematic and kinetic patterns typical of severe PD patients. Nevertheless, they present significant alterations in transient conditions such as gait initiation and change of walking direction. The above results suggest that a quantitative analysis of locomotor tasks which imply the transition from one condition to another, could provide parameters useful for the characterization of early stage PD patients and, potentially, markers for a precox differential diagnosis respect other neurodegenerative diseases characterized by parkinsonisms.

Gait Initiation and Dynamic Balance Control in Parkinson’s Disease

OBJECTIVE

To determine whether the magnitude of the separation between the center of pressure (COP) and the whole-body center of mass (COM) during gait initiation can differentiate patients with varying severity of Parkinson's disease (PD) disability.

DESIGN

Cross-sectional, intact groups research design.

SETTING

Biomechanics research laboratory.

PARTICIPANTS

Forty-three patients were stratified into 2 groups based on the Hoehn and Yahr (H&Y) disability score, which heavily favors balance in determining disability. The 2 groups were: H&Y score of 2.0 or less (n=23; age, 61+/-10y) or H&Y score of 2.5 or higher (n=20; age, 70+/-9y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The peak COP-COM distance represents the maximum separation between the location of the whole-body COM and the ground reaction force's COP, and thus is an indicator of dynamic balance control. The peak COP-COM was evaluated during 3 phases of the COP trajectory during a gait initiation task.

RESULTS

The peak magnitude of the COP-COM distance was significantly greater during the end of the single-support phase in the less disabled patients (H&Y score <or=2.0) than in more balance disabled patients (H&Y score >or=2.5) (P=.004).

CONCLUSIONS

The differences in COP-COM distances between these H&Y groups suggest that patients with PD who have impaired postural control produce shorter COM-COP distances than do persons without clinically detectable balance impairment. This method of evaluation could prove a useful quantitative index to examine the impact of interventions designed to improve ambulation and balance in PD.

Falls in Parkinson's disease

PURPOSE OF REVIEW

To summarize the latest insights into the clinical significance, assessment, pathophysiology and treatment of falls in Parkinson's disease.

RECENT FINDINGS

Recent studies have shown that falls are common in Parkinson's disease, even when compared with other fall-prone populations. The clinical impact of falls is considerable, often leading to an incapacitating fear of renewed falls. The associated costs for society are substantial. Clinical assessment often includes the retropulsion test, and recent studies have offered practical recommendations regarding the execution and scoring of this test. Insights into the pathophysiology underlying falls are growing and point to an important role for the loss of inter-segmental flexibility ('stiffness'), which predisposes patients to falls in a backward or medial-lateral direction. New evidence has clarified why Parkinson's disease patients commonly fall during transfers and under 'dual tasking' circumstances. The absence of adequately directed arm movements may explain the relatively high proportion of hip fractures in Parkinson's disease. The importance of freezing of gait as a cause of falls is recognized, and we are beginning to understand the different manifestations of gait freezing. Recent work has defined the contributions of pharmacotherapy, stereotactic neurosurgery, physiotherapy and multidisciplinary interventions in the treatment of postural instability to prevent falls in Parkinson's disease.

SUMMARY

No dramatic breakthroughs have occurred during the review period, but new information in various areas may be useful for practising clinicians. Interesting new questions have been raised that should fuel studies of pathophysiological mechanisms, which could help in the development of improved treatment strategies to reduce falls in Parkinson's disease.

Electromyographic profiles of gait prior to onset of freezing episodes in patients with Parkinson's disease

Freezing in Parkinson's disease is a severe and disabling problem of unknown aetiology. The aim of this study was to analyse the temporal pattern and the magnitude of the electromyographic activity of the lower limb muscles just before freezing and to compare this with a voluntary stop and ongoing gait. We recruited 11 patients with a mean age of 64.8 years (SD 5.1) and a mean Unified Parkinson Disease Rating Scale (part III--off) score of 29 (SD 7.9). Within a standard 3D gait laboratory setting, surface electromyographic (EMG) data of the tibialis anterior (TA) and gastrocnemius (GS) muscles were collected using a portable EMG module. Patients in the off-phase of the medication cycle performed several trials of normal walking and voluntary stops or were exposed to freezing-provoking circumstances. Filtered EMG signals were rectified, smoothed and expressed as a percentage of the gait cycle. EMG onset was determined using a preset threshold, corrected after visual inspection. The magnitude of EMG was calculated by integrating EMG signals (iEMG) over (real) time. To control for the altered timing of activity, iEMG was also normalized for time (iEMGnormt). Analysis of variance of repeated measures analysis showed that significantly abnormal timing occurred in the TA and GS muscles with overall preserved reciprocity. Before freezing, TA swing activity already started prematurely during the pre-swing phase, whereas it was significantly shortened during the actual swing phase. For the GS muscle, a similar pattern of premature activation and termination was found during the stance phase before a freeze. GS activity also showed prolonged bursts of activity during the swing phase, not present during the normal and stop condition. Total iEMG activity of both TA and GS was significantly reduced during the pre-freezing gait cycles. However, when controlling for the altered duration of the bursts, the average iEMGnormt increased, as did the peak EMG in TA. In GS, iEMGnormt was not different in the three conditions. In conclusion, our data show that a consistent pattern of premature timing of TA and GS activity occurred before freezing, which was interpreted as a disturbance of central gait cycle timing. The total amount of EMG activity was reduced in both lower limb muscles due to the shortened time in which the muscles were active. In contrast to GS, activity in TA showed increased amplitudes of the EMG bursts, indicating a compensation strategy of pulling the leg into swing. The observed changes contribute to insufficient forward progression, deceleration and eventually a breakdown of movement.