Postural control processes during standing and step initiation in autism spectrum disorder

Background

Individuals with autism spectrum disorder (ASD) show a reduced ability to maintain postural stability, though motor control mechanisms contributing to these issues and the extent to which they are associated with other gross motor activities (e.g., stepping) are not yet known.

Methods

Seventeen individuals with ASD and 20 typically developing (TD) controls (ages 6–19 years) completed three tests of postural control during standing. During the neutral stance, individuals stood with their feet shoulder width apart. During the Romberg one stance, they stood with feet close together. During the circular sway, participants stood with feet shoulder width apart and swayed in a circular motion. The standard deviation (SD) of their center of pressure (COP) in the mediolateral (ML) and anteroposterior (AP) directions and the COP trajectory length were examined for each stance. We also assessed mutual information (MI), or the shared dependencies between COP in the ML and AP directions. Participants also completed a stepping task in which they stepped forward from one force platform to an adjacent platform. The amplitude and duration of anticipatory postural adjustments (APAs) were examined, as were the maximum lateral sway, duration, and velocity of COP adjustments following the initial step. We examined stepping variables using separate one-way ANCOVAs with height as a covariate. The relationships between postural control and stepping measures and ASD symptom severity were assessed using Spearman correlations with scores on the Autism Diagnostic Observation Schedule–Second Edition (ADOS-2) and the Autism Diagnostic Interview-Revised (ADI-R).

Results

Individuals with ASD showed increased COP trajectory length across stance conditions (p = 0.05) and reduced MI during circular sway relative to TD controls (p = 0.02). During stepping, groups did not differ on APA amplitude (p = 0.97) or duration (p = 0.41), but during their initial step, individuals with ASD showed reduced ML sway (p = 0.06), reduced body transfer duration (p < 0.01), and increased body transfer velocity (p = 0.02) compared to controls. Greater neutral stance COP_ML variability (r = 0.55, p = 0.02) and decreased lateral sway (r = − 0.55, p = 0.02) when stepping were associated with more severe restricted and repetitive behaviors in participants with ASD.

Conclusions

We found that individuals with ASD showed reduced MI during circular sway suggesting a reduced ability to effectively coordinate joint movements during dynamic postural adjustments. Additionally, individuals with ASD showed reduced lateral sway when stepping indicating that motor rigidity may interfere with balance and gait. Postural control and stepping deficits were related to repetitive behaviors in individuals with ASD indicating that motor rigidity and key clinical issues in ASD may represent overlapping pathological processes.

Effect of investigator observation on gait parameters in individuals with stroke

Improvements in gait speed following various training paradigms applied to patients post-stroke does not always lead to changes in walking performance, defined as gains in daily stepping activity. We hypothesized that testing conditions, specifically the presence of an observer, influences patient behaviors and resultant outcomes may overestimate their true walking capacity. This potential Hawthorne effect on spatiotemporal and biomechanical measures of locomotor function in individuals post-stroke has not been assessed previously. Fifteen ambulatory individuals with chronic stroke wore instrumented insoles and performed two separate normal-pace walking assessments, including unobserved conditions during which participants were unattended and unaware of data collection, and observed conditions with an investigator present. Gait analysis was conducted outside of a laboratory setting using instrumented insoles equipped with a 3D accelerometer and pressure sensors which captured the spatiotemporal kinematics, vertical ground reaction forces and foot acceleration. Data were compared using paired comparisons, with subsequent correlation and stepwise regression analyses to explore potential associations between Hawthorne-induced changes in walking strategies, gait speed and locomotor performance (daily stepping). Except for cadence, other measures of spatiotemporal parameters and swing kinematics (acceleration) were not significantly different between observed vs unobserved conditions. However, analyses of ground reaction forces revealed significantly greater paretic limb loading (Δ1^st peak = 1.5 ± 1.6 N/kg Δ2^nd peak = 1.4 ± 1.8 N/kg; p < 0.01) and increases in weight bearing symmetry (11-24%, p < 0.01) during observed vs unobserved conditions. This potential Hawthorne effect was greater in those with slower walking speeds and shorter stride lengths but was not related to daily stepping. The present findings suggest that biomechanical parameters of walking function may be related to the presence of an observer and highlight the need to separately measure locomotor capacity (gait speed) and performance (daily stepping).

Comparison of Spontaneous Motor Tempo during Finger Tapping, Toe Tapping and Stepping on the Spot in People with and without Parkinson's Disease

OBJECTIVE

Spontaneous motor tempo (SMT), observed in walking, tapping and clapping, tends to occur around 2 Hz. Initiating and controlling movement can be difficult for people with Parkinson's (PWP), but studies have not identified whether PWP differ from controls in SMT. For community-based interventions, e.g. dancing, it would be helpful to know a baseline SMT to optimize the tempi of cued activities. Therefore, this study compared finger tapping (FT), toe tapping (TT) and stepping 'on the spot' (SS) in PWP and two groups of healthy controls [age-matched controls (AMC) and young healthy controls (YHC)], as SMT is known to change with age.

METHODS

Participants (PWP; n = 30, AMC; n = 23, YHC; n = 35) were asked to tap or step on the spot at a natural pace for two trials lasting 40 seconds. The central 30 seconds were averaged for analyses using mean inter-onset intervals (IOI) and coefficient of variation (CoV) to measure rate and variability respectively.

RESULTS

PWP had faster SMT than both control groups, depending on the movement modality: FT, F(2, 87) = 7.92, p < 0.01 (PWP faster than YHC); TT, F(2, 87) = 4.89, p = 0.01 (PWP faster than AMC); and SS, F(2, 77) = 3.26, p = 0.04 (PWP faster than AMC). PWP had higher CoV (more variable tapping) than AMC in FT only, F(2, 87) = 4.10, p = 0.02.

CONCLUSION

This study provides the first direct comparison of SMT between PWP and two control groups for different types of movements.

RESULTS

suggest SMT is generally faster in PWP than control groups, and more variable when measured with finger tapping compared to stepping on the spot.

Functional motor control deficits in older FMR1 premutation carriers

Individuals with fragile X mental retardation 1 (FMR1) gene premutations are at increased risk for fragile X-associated tremor/ataxia syndrome (FXTAS) during aging. However, it is unknown whether older FMR1 premutation carriers, with or without FXTAS, exhibit functional motor control deficits compared with healthy individuals. The purpose of this study, therefore, was to determine whether older FMR1 premutation carriers exhibit impaired ability to perform functional motor tasks. Eight FMR1 premutation carriers (age: 58.88 ± 8.36 years) and eight age- and sex-matched healthy individuals (60.13 ± 9.25 years) performed (1) a steady isometric force control task with the index finger at 20% of their maximum voluntary contraction (MVC) and; (2) a single-step task. During the finger abduction task, firing rate of multiple motor units of the first dorsal interosseous (FDI) muscle was recorded. Compared with healthy controls, FMR1 premutation carriers exhibited (1) greater force variability (coefficient of variation of force) during isometric force (1.48 ± 1.02 vs. 0.63 ± 0.37%; P = 0.04); (2) reduced firing rate of multiple motor units during steady force, and; (3) reduced velocity of their weight transfer during stepping (156.62 ± 26.24 vs. 191.86 ± 18.83 cm/s; P = 0.01). These findings suggest that older FMR1 premutation carriers exhibit functional motor control deficits that reflect either subclinical issues associated with premutations independent of FXTAS, or prodromal markers of the development of FXTAS.

The development of visually guided stepping

Adults use vision during stepping and walking to fine-tune foot placement. However, the developmental profile of visually guided stepping is unclear. We asked (1) whether children use online vision to fine-tune precise steps and (2) whether precision stepping develops as part of broader visuomotor development, alongside other fundamental motor skills like reaching. With 6-(N = 11), 7-(N = 11), 8-(N = 11)-year-olds and adults (N = 15), we manipulated visual input during steps and reaches. Using motion capture, we measured step and reach error, and postural stability. We expected (1) both steps and reaches would be visually guided (2) with similar developmental profiles (3) foot placement biases that promote stability, and (4) correlations between postural stability and step error. Children used vision to fine-tune both steps and reaches. At all ages, foot placement was biased (albeit not in the predicted directions). Contrary to our predictions, step error was not correlated with postural stability. By 8 years, children’s step and reach error were adult-like. Despite similar visual control mechanisms, stepping and reaching had different developmental profiles: step error reduced with age whilst reach error was lower and stable with age. We argue that the development of both visually guided and non-visually guided action is limb-specific.

Stepping characteristics during externally induced lateral reactive and voluntary steps in chronic stroke

BACKGROUND

Stepping is critical for responding to perturbations, whether externally induced or self-initiated. Falls post-stroke is equally likely to happen from either mechanism. The objective of the study was, to examine lateral stepping performance during waist-pull induced reactive steps and voluntary choice reaction time steps in chronic stroke and controls.

METHODS

In this cross-sectional study participants with chronic stroke (N = 10) and age- and gender-matched controls (N = 10) performed reactive and voluntary lateral steps. Step initiation time, global step length, step clearance, and step velocity were calculated. Other measures for reactive step included, Balance tolerance limit (perturbation magnitude when recovery transitioned from single to multiple steps), and step type. The Community Balance & Mobility Scale, and hip abductor and adductor isokinetic asymmetry torque ratio were assessed.

RESULTS

The paretic and non-paretic leg were combined since step characteristics did not differ. Step (voluntary vs. reactive) by group (stroke vs. controls) was significant for step initiation time. The stroke group took longer initiating a voluntary step (P = 0.004). Reactive and voluntary steps were executed slower (P = 0.041), with a reduced step length (P = 0.028) by the stroke group. The stroke group had a lower balance tolerance limit (P = 0.01) and took reactive medial steps more frequently (P = 0.001). The Community Balance & Mobility Scale (P > 0.001), and hip abductor and adductor asymmetry torque ratio (P > 0.001; P = 0.015) was reduced in the stroke group.

SIGNIFICANCE

Our findings indicate individuals post-stroke are slower initiating and executing reactive and voluntary steps. Though the reactive step timing is less impaired, this may be a method for enhancing faster voluntary movements and training reactive balance.

Reliability of measures of dynamic stability for the assessment of balance recovery after a forward loss of balance

BACKGROUND

Falls are common and serious events, which mostly occur during locomotion, that are associated with deficient dynamic balance. An experimental approach that simulates falling forward has become increasing popular to investigate dynamic balance. However, research has not been conducted to examine the test-retest reliability of this experimental approach.

RESEARCH QUESTION

What is the reliability of dynamic stability measures that are used for the assessment of balance recovery after forward loss of balance?

METHODS

Nineteen healthy young adults (24.3 ± 2.8 yrs; nine females) volunteered for this study. They reported twice to the laboratory to perform two tests: (i) a stepping task, in which they were instructed to recover balance by taking a step after being suddenly released from an inclined forward position; and (ii) a standing task, in which we aimed to identify the maximum forward leaning angle they were able to compensate for without taking a step. Intra-class correlation coefficients (ICC) were calculated for the margin of stability (MoS) and spatiotemporal parameters for both tests.

RESULTS

The reliability of the stepping task variables ranged from poor to excellent, with ICCs tending to increase with the number of trials included in the analysis. Intra-session analysis (one-way rm ANOVA) revealed a significant trial effect for the MoS, indicating that stepping responses changed across repeated trials. With respect to the standing task, test-retest reliability was only fair for the maximal initial leaning angle.

SIGNIFICANCE

In essence, these results indicate that the inter-session reliability of the stepping task is acceptable, depending on the measures used and the number of trials conducted. However, one must be aware that behavioral adaptations arise with repeated exposure to simulated forward falls. Finally, this study's results suggest that the reproducibility of the standing task is limited.

Effect of body configuration at step contact on balance recovery from sideways perturbations

Compensatory stepping is an important protective mechanism to prevent falling. To recover from sideways perturbations side steps are generally more advantageous than cross-over steps. However, there is lack of understanding of the characteristics of compensatory side steps following sideways perturbations that separate successful recoveries (i.e., no falls) from falls, the most clinically relevant outcome following a balance perturbation. We aimed to identify the critical determinants for successful side stepping after large sideways balance perturbations. Twelve healthy young adults were subjected to large leftward perturbations at varying intensities on a translating sheet. For recovery attempts started with a side step, we determined body configuration variables (frontal-plane leg and trunk angle) at first step contact, as well as spatiotemporal step variables (onset, length, duration, velocity). A logistic regression analysis was conducted to determine the predictive ability of body configuration and spatiotemporal variables on the probability of success (no fall vs. fall); perturbation intensity (peak jerk of translating sheet) and a random effect for individual were also included in the model. In the final model, leg angle and peak jerk were retained as predictors of successful balance recovery and these variables correctly classified the recovery outcome in 86% of the trials. This final 'body configuration' model yielded a -2 log likelihood of -36.3, whereas the best fitting model with only spatiotemporal variables yielded a -2 log likelihood of -45.8 (indicating a poorer fit). The leg angle at a given perturbation intensity appears to be a valid measure of reactive side step quality. The relative ease of measuring this leg angle at step contact makes it a candidate outcome for reactive stepping assessments in clinical practice.

Perturbation-evoked lateral steps in older adults: Why take two steps when one will do?

BACKGROUND

Hip fractures in older adults often result from a fall in the lateral direction. While younger adults tend to recover balance from a lateral perturbation with a single lateral sidestep, older adults are prone to multistep responses which are associated with an increased fall risk. This study compared the stepping characteristics and stability of single and multistep responses to lateral perturbation in healthy older adults.

METHODS

Eighty-four older adults received lateral waist-pull perturbations to either side. Spatio-temporal stepping characteristics and balance stability were quantified.

FINDINGS

Fewer steps were taken to recover balance when the first step was a lateral sidestep. The stability margin of single lateral sidesteps was greater than medial sidesteps and cross-over steps to the back but not significantly different from single cross-over steps to the front at step termination. Single step responses were more stable than multistep responses at step termination and at step initiation for lateral sidesteps and cross-over steps to the front. The decreased stability of multistep responses was attributed to an increased center of mass velocity and a smaller distance between the center of mass and base-of-support at step termination.

INTERPRETATION

Although lateral sidesteps result in fewer steps than cross-over steps to the front, the stability margin was not significantly different at step termination. These results suggest difficulty terminating center of mass motion and/or inefficient center of mass control differentiates single and multistep responses. Future studies should investigate perturbation training and/or hip abductor muscle conditioning as a means of improving compensatory stepping reactions.

The iFST: An instrumented version of the Fukuda Stepping Test for balance assessment

The maintenance of the upright posture during dynamic balance requires the integration of sensory inputs regulated by the brain. After a neurological event, the assessment of balance control impairments is crucial for supporting health professionals in the design of personalized rehabilitation protocols. A commonly used test to assess balance ability is the Fukuda Stepping Test (FST). However, the clinical parameters traditionally considered are not fully representative of the patient's motor ability. The purpose of this study was to devise an instrumented version of the FST (iFST) that embodies inertial sensors and allows to obtain individual motor strategy information. Twenty-seven sub-acute stroke patients and 18 healthy adults performed a repeated stepping task with closed eyes wearing five inertial sensors located on both distal tibiae and at pelvis, sternum, and head levels. From final foot position, body rotation and linear displacements were measured. A set of indices related to upper-body stability were estimated from pelvis, sternum, and head accelerations: Root Mean Square, Attenuation Coefficients, and improved Harmonic Ratio. Two additional parameters based on upper-body angular velocities were devised to assess step-by-step repeatability and inter-segment velocity variations. The results suggest that the clinical parameters do not provide enough information about the two groups' motor strategies. Conversely, five iFST parameters were identified as predictors of patients' motor ability, discriminating not only between healthy and pathological subjects, but also between different motor deficit levels within the same pathology. The iFST could be included in the clinical routine assessment of balance impairments, supporting the design of personalized treatments.

Bilateral early activity in the hip flexors associated with falls in stroke survivors: Preliminary evidence from laboratory-induced falls

OBJECTIVE

Falls are the most common and expensive medical complication following stroke. Hypermetric reflexes have been suggested to impact post-stroke balance but no study has evaluated reflex amplitudes under real conditions of falls in this population. Our objective was to quantify the early reflexive responses during falls induced in the laboratory.

METHODS

Sixteen stroke survivors were exposed to posteriorly directed treadmill perturbations that required a forward step to maintain a balance. Perturbations differed in terms of treadmill translation displacement, velocity, and acceleration. EMG amplitudes were compared between Fall/Recovery trials, as well as Fallers/Non-Fallers at two different time windows: 50-75 and 75-100 ms.

RESULTS

Sixteen of 86 trials resulted in falls by nine subjects (Fallers). While no differences were found between 50 and 75 ms, EMG amplitude in the paretic rectus femoris muscle was larger between 75 and 100 ms during Fall trials. Further, a bilateral increase in RF activity was seen in Fallers but not Non-Fallers. Interestingly, the bilateral increase was related to perturbation intensity (larger EMG activity with larger perturbations) in Fallers, but again not in Non-Fallers.

CONCLUSIONS

Heightened early recovery hip flexor activity between 75 and 100 ms is associated with falls and Fallers post-stroke.

SIGNIFICANCE

Though requiring replication and expanded subject pools, these preliminary results reflect a possible clinically meaningful relationship between heightened reflexive responses and fall risk. Future work should evaluate the underlying mechanisms driving these heightened reflexes (e.g. stretch, startle) such that future rehabilitation techniques can address this abnormal response.

A standing wave ultrasonic stepping motor using open-loop control system

We propose a standing wave ultrasonic stepping motor with blades and grooves for positioning. The step-by-step movements are achieved by applying the square wave driving voltage and the high-voltage pulse in turn. The prototype with a diameter of 30mm, a height of 10mm is experimentally characterized. The motor is superior to those previously reported due to the positioning mechanism for eliminating displacement cumulative error when using an open-loop control system. Also, the operating mode and the metal-to-metal friction drive ensure a stall torque of 0.055Nm under a relatively low operating voltage of 100V_pp at a resonance frequency of 74kHz.

Examination of reactive motor responses to Achilles tendon vibrations during an inhibitory stepping reaction time task

Inhibition is known to influence balance, step initiation and gait control. A specific subcomponent of inhibition, the perceptual inhibition process, has been suggested to be specifically involved in the integration of proprioceptive information that is necessary for efficient postural responses. This study aimed to investigate the inhibition requirements of planning and executing a choice step initiation task in young adults following experimental perturbation of proprioceptive information using Achilles tendon vibrations. We developed an inhibitory stepping reaction time task in which participants had to step in response to visual arrows that manipulated specific perceptual or motor inhibition according to two proprioceptive configurations: without or with application of vibrations. Performance of twenty-eight participants (mean age 21 years) showed that Achilles tendon vibrations induced an increase in attentional demands (higher reaction time and longer motor responses). Further, this increase in attentional demands did not affect specifically the different inhibitory processes tested in this reactive stepping task. It suggests that attentional demands associated with the vibratory perturbation to postural control do not lead to a shift from automatic to more attentional inhibition processes, at least in young adults.

Spatial constraints evoke increased number of steps during turning in Parkinson's disease

OBJECTIVE

Turning and limitations to step length were shown to trigger progressive shortening of steps, which can lead to freezing of gait. By reducing the base area in which the turn had to take place, we aimed to evaluate the contribution of spatial constraints on 360° axial turns in people with Parkinson's disease with and without freezing.

METHODS

We evaluated 40 patients with and without freezing and 16 age-matched healthy subjects. We assessed clinical data, and used body-worn inertial sensors to describe stepping and turn duration of 360° in quadratic squares of different sizes marked on the floor.

RESULTS

We found that, when subjects had to perform turns in smaller as compared to larger squares, this spatial constraint strongly affected the turning behavior, i.e. increased the number of steps, and the duration of turns. However, turning was significantly more impaired in patients as compared to controls, and patients with freezing were significantly worse as patients without freezing.

CONCLUSION

Our data show that spatial constraint during axial turning has the potential to deteriorate stepping performance, especially in patients reporting freezing of gait.

SIGNIFICANCE

The size of the base area needs to be defined in any item or scale that makes diagnostic use of turning.

Increased gait variability may not imply impaired stride-to-stride control of walking in healthy older adults: Winner: 2013 Gait and Clinical Movement Analysis Society Best Paper Award

Older adults exhibit increased gait variability that is associated with fall history and predicts future falls. It is not known to what extent this increased variability results from increased physiological noise versus a decreased ability to regulate walking movements. To "walk", a person must move a finite distance in finite time, making stride length (L_n) and time (T_n) the fundamental stride variables to define forward walking. Multiple age-related physiological changes increase neuromotor noise, increasing gait variability. If older adults also alter how they regulate their stride variables, this could further exacerbate that variability. We previously developed a Goal Equivalent Manifold (GEM) computational framework specifically to separate these causes of variability. Here, we apply this framework to identify how both young and high-functioning healthy older adults regulate stepping from each stride to the next. Healthy older adults exhibited increased gait variability, independent of walking speed. However, despite this, these healthy older adults also concurrently exhibited no differences (all p>0.50) from young adults either in how their stride variability was distributed relative to the GEM or in how they regulated, from stride to stride, either their basic stepping variables or deviations relative to the GEM. Using a validated computational model, we found these experimental findings were consistent with increased gait variability arising solely from increased neuromotor noise, and not from changes in stride-to-stride control. Thus, age-related increased gait variability likely precedes impaired stepping control. This suggests these changes may in turn precede increased fall risk.

Single and multiple step balance recovery responses can be different at first step lift-off following lateral waist-pull perturbations in older adults

An inability to recover lateral balance with a single step is predictive of future falls in older adults. This study investigated if balance stability at first step lift-off (FSLO) would be different between multiple and single stepping responses to lateral perturbations. 54 healthy older adults received left and right waist-pulls at 5 different intensities (levels 1-5). Crossover stepping responses at and above intensity level 3 that induced both single and multiple steps were analyzed. Whole-body center of mass (COM) and center of pressure (COP) positions in the medio-lateral direction with respect to the base of support were calculated. An inverted pendulum model was used to define the lateral stability boundary, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were detected in the COP positions between the responses at FSLO (p≥0.075), indicating no difference in the functional boundaries between the responses. Significantly smaller stability margins were observed at first step landing for multiple steps at all levels (p≤0.024), while stability margins were also significantly smaller at FSLO for level 3 and 4 (p≤0.048). These findings indicate that although reduced stability at first foot contact would be associated with taking additional steps, stepping responses could also be attributable to the COM motion state as early as first step lift-off, preceding foot contact. Perturbation-based training interventions aimed at improving the reactive control of stability would reduce initial balance instability at first step lift-off and possibly the consequent need for multiple steps in response to balance perturbations.

Aging effect on muscle synergies in stepping forth during a forward perturbation

PURPOSE

We explored changes in muscle interactions during healthy aging as a window into neural control strategies of postural preparation to action/perturbation. In particular, we quantified the strength of multi-muscle synergies stabilizing the center of pressure (COP) displacement during the preparation for making a step associated with support surface translations.

METHODS

Young and elderly subjects were required to make a step in response to support surface perturbations. Surface muscle activity of 11 leg and trunk muscles was analyzed to identify sets of 4 muscle modes (M-modes). Linear combinations of M-modes and their relationship to changes in the COP displacement in the anterior-posterior direction were then determined. Uncontrolled manifold analysis was performed to determine variance components in the M-mode space and indices of M-mode synergy stabilizing COP displacement.

RESULTS

Prior to the step initiation, the older subjects showed strong synergies that stabilized COP displacement to forward perturbation of the support surface. However, the synergy indices were significantly lower than those of the young subjects during preparation for making a step. The timings of early postural adjustment (EPA) and anticipatory postural adjustment (APA) were consistently earlier in the young subjects as compared to the older subjects. For both groups, the timing of EPA did not change across tasks, while APA showed delayed timing in response to the support surface translations.

CONCLUSIONS

We infer that changes in the indices of synergies with age may present challenges for the control of postural preparation to external perturbation in older adults. They may lead to excessive muscle co-contractions and low stability of COP displacement. The results reported here could have clinical relevance when identifying the risk of making a step, which has been linked to an increased risk of falls among the elderly.

Step-and-Repeat Nanoimprint-, Photo- and Laser Lithography from One Customised CNC Machine

The conversion of a computer numerical control machine into a nanoimprint step-and-repeat tool with additional laser- and photolithography capacity is documented here. All three processes, each demonstrated on a variety of photoresists, are performed successfully and analysed so as to enable the reader to relate their known lithography process(es) to the findings. Using the converted tool, 1 cm(2) of nanopattern may be exposed in 6 s, over 3300 times faster than the electron beam equivalent. Nanoimprint tools are commercially available, but these can cost around 1000 times more than this customised computer numerical control (CNC) machine. The converted equipment facilitates rapid production and large area micro- and nanoscale research on small grants, ultimately enabling faster and more diverse growth in this field of science. In comparison to commercial tools, this converted CNC also boasts capacity to handle larger substrates, temperature control and active force control, up to ten times more curing dose and compactness. Actual devices are fabricated using the machine including an expanded nanotopographic array and microfluidic PDMS Y-channel mixers.

Executive function is necessary for the regulation of the stepping activity when stepping in place in older adults

To determine the effect of age on stepping performance and to compare the cognitive demand required to regulate repetitive stepping between older and younger adults while performing a stepping in place task (SIP). Fourteen younger (25.4 ± 6.5) and 15 older adults (71.0 ± 9.0) participated in this study. They performed a seated category fluency task and Stroop test, followed by a 60 s SIP task. Following this, both the cognitive and motor tasks were performed simultaneously. We assessed cognitive performance, SIP cycle duration, asymmetry, and arrhythmicity. Compared to younger adults, older adults had larger SIP arrhythmicity both as a single task and when combined with the Category (p < 0.001) and Stroop (p < 0.01) tasks. Older adults also had larger arrhythmicity when dual tasking compared to SIP alone (p < 0.001). Older adults showed greater SIP asymmetry when combined with Category (p = 0.006) and Stroop (p = 0.06) tasks. Finally, they had lower cognitive performance than younger adults in both single and dual tasks (p < 0.01). Age and type of cognitive task performed with the motor task affected different components of stepping. While SIP arrhythmicity was larger for all conditions in older compared to younger adults, cycle duration was not different, and asymmetry tended to be larger during SIP when paired with a verbal fluency task. SIP does not require a high level of control for dynamic stability, therefore demonstrating that higher-level executive function is necessary for the regulation of stepping activity independently of the regulation of postural balance. Furthermore, older adults may lack the cognitive resources needed to adequately regulate stepping activity while performing a cognitive task relying on the executive function.

Postural motor learning in people with Parkinson's disease

Protective postural responses to external perturbations are hypokinetic in people with Parkinson's disease (PD), and improving these responses may reduce falls. However, the ability of people with PD to improve postural responses with practice is poorly understood. Our objective was to determine whether people with PD can improve protective postural responses similarly to healthy adults through repeated perturbations, and whether improvements are retained or generalize to untrained perturbations. Twelve healthy adults and 15 people with PD underwent 25 forward and 25 backward translations of the support surface, eliciting backward, and forward protective steps, respectively. We assessed whether: (1) performance improved over one day of practice, (2) changes were retained 24 h later, and (3) improvements generalized to untrained (lateral) postural responses. People with PD and healthy adults improved postural response characteristics, including center of mass displacement after perturbations (p < 0.001), margin of stability at first footfall (p = 0.001), step latency (p = 0.044), and number of steps (p = 0.001). However, unlike controls, improvements in people with PD occurred primarily in the first block of trials. Improvements were more pronounced during backward protective stepping than forward, and with the exception of step latency, were retained 24 h later. Improvements in forward-backward stepping did not generalize to lateral protective stepping. People with PD can improve protective stepping over the course of 1 day of perturbation practice. Improvements were generally similar to healthy adults, and were retained in both groups. Perturbation practice may represent a promising approach to improving protective postural responses in people with PD; however, additional research is needed to understand how to enhance generalization.

Kinect-based choice reaching and stepping reaction time tests for clinical and in-home assessment of fall risk in older people: a prospective study

Background

Quick protective reactions such as reaching or stepping are important to avoid a fall or minimize injuries. We developed Kinect-based choice reaching and stepping reaction time tests (Kinect-based CRTs) and evaluated their ability to differentiate between older fallers and non-fallers and the feasibility of administering them at home.

Methods

A total of 94 community-dwelling older people were assessed on the Kinect-based CRTs in the laboratory and were followed-up for falls for 6 months. Additionally, a subgroup (n = 20) conducted the Kinect-based CRTs at home. Signal processing algorithms were developed to extract features for reaction, movement and the total time from the Kinect skeleton data.

Results

Nineteen participants (20.2 %) reported a fall in the 6 months following the assessment. The reaction time (fallers: 797 ± 136 ms, non-fallers: 714 ± 89 ms), movement time (fallers: 392 ± 50 ms, non-fallers: 358 ± 51 ms) and total time (fallers: 1189 ± 170 ms, non-fallers: 1072 ± 109 ms) of the reaching reaction time test differentiated well between the fallers and non-fallers. The stepping reaction time test did not significantly discriminate between the two groups in the prospective study. The correlations between the laboratory and in-home assessments were 0.689 for the reaching reaction time and 0.860 for stepping reaction time.

Conclusion

The study findings indicate that the Kinect-based CRT tests are feasible to administer in clinical and in-home settings, and thus represents an important step towards the development of sensor-based fall risk self-assessments. With further validation, the assessments may prove useful as a fall risk screen and home-based assessment measures for monitoring changes over time and effects of fall prevention interventions.

Serotonergic activation of locomotor behavior and posture in one-day old rats

The purpose of this study was to determine what dose of quipazine, a serotonergic agonist, facilitates air-stepping and induces postural control and patterns of locomotion in newborn rats. Subjects in both experiments were 1-day-old rat pups. In Experiment 1, pups were restrained and tested for air-stepping in a 35-min test session. Immediately following a 5-min baseline, pups were treated with quipazine (1.0, 3.0, or 10.0 mg/kg) or saline (vehicle control), administered intraperitoneally in a 50 μL injection. Bilateral alternating stepping occurred most frequently following treatment with 10.0 mg/kg quipazine, however the percentage of alternating steps, interlimb phase, and step period were very similar between the 3.0 and 10.0 mg/kg doses. For interlimb phase, the forelimbs and hindlimbs maintained a near perfect anti-phase pattern of coordination, with step period averaging about 1s. In Experiment 2, pups were treated with 3.0 or 10.0 mg/kg quipazine or saline, and then were placed on a surface (open field, unrestrained). Both doses of quipazine resulted in developmentally advanced postural control and locomotor patterns, including head elevation, postural stances, pivoting, crawling, and a few instances of quadrupedal walking. The 3.0 mg/kg dose of quipazine was the most effective at evoking sustained locomotion. Between the 2 experiments, behavior exhibited by the rat pup varied based on testing environment, emphasizing the role that environment and sensory cues exert over motor behavior. Overall, quipazine administered at a dose of 3.0 mg/kg was highly effective at promoting alternating limb coordination and inducing locomotor activity in both testing environments.

Effects of support surface and optic flow on step-like movements in pre-crawling and crawling infants

Step-like movements were examined in pre-crawling (n=9) and crawling (n=9) 6-13 month-old infants in the air and on a surface in response to a static pattern or optic flows that moved toward or away from the infant. Infants completed six 60-s trials. A significant interaction between locomotor status and support condition revealed that pre-crawling infants made more step-like movements in the air than on a rigid surface. In contrast, crawling infants made an equivalent number of step-like movements in the air and on the surface. Optic flow did not influence the number of step-like movements made by infants. The pre-crawling infant finding is consistent with a finding in a previous study in which two month-old infants were shown to step more in the air than on the ground. This finding is discussed relative to the idea that the infant stepping pattern disappears because the legs become too heavy to lift.

The effect of sensor-based exercise at home on functional performance associated with fall risk in older people - a comparison of two exergame interventions

Background

There is good evidence that balance challenging exercises can reduce falls in older people. However, older people often find it difficult to incorporate such programs in their daily life. Videogame technology has been proposed to promote enjoyable, balance-challenging exercise. As part of a larger analysis, we compared feasibility and efficacy of two exergame interventions: step-mat-training (SMT) and Microsoft-Kinect® (KIN) exergames.

Methods

148 community-dwelling people, aged 65+ years participated in two exergame studies in Sydney, Australia (KIN: n = 57, SMT: n = 91). Both interventions were delivered as unsupervised exercise programs in participants’ homes for 16 weeks. Assessment measures included overall physiological fall risk, muscle strength, finger-press reaction time, proprioception, vision, balance and executive functioning.

Results

For participants allocated to the intervention arms, the median time played each week was 17 min (IQR 32) for KIN and 48 min (IQR 94) for SMT. Compared to the control group, SMT participants improved their fall risk score (p = 0.036), proprioception (p = 0.015), reaction time (p = 0.003), sit-to-stand performance (p = 0.011) and executive functioning (p = 0.001), while KIN participants improved their muscle strength (p = 0.032) and vision (p = 0.010), and showed a trend towards improved fall risk scores (p = 0.057).

Conclusions

The findings suggest that it is feasible for older people to conduct an unsupervised exercise program at home using exergames. Both interventions reduced fall risk and SMT additionally improved specific cognitive functions. However, further refinement of the systems is required to improve adherence and maximise the benefits of exergames to deliver fall prevention programs in older people’s homes.

Trial registrations

ACTRN12613000671763 (Step Mat Training RCT)

ACTRN12614000096651 (MS Kinect RCT)

Patterns of muscle coordination during stepping responses post-stroke

This study compared self-induced stepping reactions of seventeen participants after stroke and seventeen controls. Surface electromyographic (EMG) signals were recorded bilaterally from the soleus (SOL), tibialis anterior (TA), biceps femoris (BF) and rectus femoris (RF) muscles. Principal component analysis (PCA) was used to reduce the data into muscle activation patterns and examine group differences (paretic, non-paretic, control leg). The first principal component (PC1) explained 46.7% of the EMG signal of the stepping leg. Two PCs revealed distinct activation features for the stepping paretic leg: earlier TA onset at step initiation and earlier BF and SOL onset at mid-step. For the stance leg, PC1 explained 44.4% of the EMG signal and significant differences were found in the non-paretic leg compared to paretic (p < 0.001) and control (p < 0.001). In PC1, at step onset the BF and SOL EMG and the RF and TA EMG were increased over the latter half of the step. No PC loadings were distinct for the paretic leg during stance, however differences were found in the non-paretic leg: earlier TA burst and increased BF and SOL EMG at step initiation. The results suggest impairments in the paretic leg when stepping and compensatory strategies in the non-paretic stance leg.