Practice and transfer effects during fast single-joint elbow movements in individuals with Down syndrome

Integrated Physiotherapeutic Intervention for Rehabilitation of a Patient With Intellectual Disabilities: A Case Report

Intellectual disabilities (ID) encompass a broad spectrum of neurodevelopmental disorders marked by impairments in cognitive functioning and adaptive behavior. Accessing and benefiting from rehabilitation services pose significant challenges for individuals within this population. In this case study, the rehabilitation journey of a 44-year-old man with ID, emphasizes the tailored approach to his rehabilitation program. The primary objectives of the program were to augment the patient's functional capabilities, foster independence, and enhance his overall quality of life. The case highlights the significance of personalized, comprehensive rehabilitation strategies intricately tailored to address the distinct requirements of individuals with ID. The case study delineates a comprehensive rehabilitation regimen integrating physical therapy to address the multifaceted needs of individuals with varying degrees of disability. This inclusive approach represents a paradigm shift toward a multidisciplinary (physiotherapy along with general medical care, special education, vocational training, and community-based interventions) person-centered model of care. Through addressing the varied needs of individuals with ID, the rehabilitation plan endeavors to empower them to lead enriching, self-directed lives within their communities, thereby unlocking their complete potential. This case study stands as evidence of the profound impact of customized rehabilitation interventions in cultivating inclusivity and optimizing the well-being of individuals with ID.

Visuomotor skill learning in young adults with Down syndrome

BACKGROUND

Individuals with Down syndrome (DS) have impaired general motor skills compared to typically developed (TD) individuals.

AIMS

To gain knowledge on how young adults with DS learn and retain new motor skills.

METHODS AND PROCEDURES

A DS-group (mean age = 23.9 ± 3 years, N = 11), and an age-matched TD-group (mean age 22.8 ± 1.8, N = 14) were recruited. The participants practiced a visuomotor accuracy tracking task (VATT) in seven blocks (10.6 min). Online and offline effects of practice were assessed based on tests of motor performance at baseline immediate and 7-day retention.

OUTCOMES AND RESULTS

The TD-group performed better than the DS-group on all blocks (all P < 0.001). Both groups improved VATT-performance online from baseline to immediate retention, (all P < 0.001) with no difference in online effect between groups. A significant between-group difference was observed in the offline effect (∆TD - ∆DS, P = 0.04), as the DS-group's performance at 7-day retention was equal to their performance at immediate retention (∆DS, P > 0.05), whereas an offline decrease in performance was found in the TD-group (∆TD, P < 0.001).

CONCLUSIONS AND IMPLICATIONS

Visuomotor pinch force accuracy is lower for adults with DS compared to TD. However, adults with DS display significant online improvements in performance with motor practice similar to changes observed for TD. Additionally, adults with DS demonstrate offline consolidation following motor learning leading to significant retention effects.

Effective Throughput Analysis of Different Task Execution Strategies for Mid-Air Fitts' Tasks in Virtual Reality

Fitts' law and throughput based on effective measures are two mathematical models frequently used to analyze human motor performance in a standardized pointing task, e.g., to compare the performance of input and output devices. Even though pointing has been deeply studied in 2D, it is not well understood how different task execution strategies affect throughput in pointing in 3D virtual environments. In this work, we examine the effective throughput measure, claimed to be invariant to task execution strategies, in Virtual Reality (VR) systems with three such strategies, "as fast, as precise, and as fast and as precise as possible" for ray casting and virtual hand interaction, by re-analyzing data from a 3D pointing ISO 9241-411 study. Results show that effective throughput is not invariant for different task execution strategies in VR, which also matches a more recent 2D result. Normalized speed vs. accuracy curves also did not fit the data. We thus suggest that practitioners, developers, and researchers who use MacKenzie's effective throughput formulation should consider our findings when analyzing 3D user pointing performance in VR systems.

The legacy of Gerald L. Gottlieb in human movement neuroscience

In this paper, we review the legacy of Gerald (Gerry) Gottlieb in various fields related to the neural control of human movement. His studies on the myotatic (stretch) reflex and postmyotatic responses to ankle joint perturbations paved the way for current explorations of long-loop reflexes and their role in the control of movement. The dual-strategy hypothesis introduced order into a large body of literature on the triphasic muscle activation patterns seen over a variety of voluntary movements in healthy persons. The dual-strategy hypothesis continues to be important for understanding the performance of subjects with disordered motor control. The principle of linear synergy (covariance of joint torques) was an attempt to solve one of the notorious problems of motor redundancy, which remains an important topic in the field. Gerry's attitude toward the equilibrium-point hypothesis varied between rejection and using it to explore patterns of hypothetical control variables and movement variability. The discovery of reciprocal excitation in healthy neonates fostered other studies of changes in spinal cord physiology as motor skills develop. In addition, studies of people with spasticity and the effects of treatment with intrathecal baclofen were crucial in demonstrating the possibility of unmasking voluntary movements after suppression of the hyperreflexia of spasticity. Gerry Gottlieb contributed a significant body of knowledge that formed a solid foundation from which to study a variety of neurological diseases and their treatments, and a more comprehensive and parsimonious foundation to describe the neural control of human movement.

Current Trends in Pediatric Physical Therapy Practice for Children With Down Syndrome

BACKGROUND

Physical therapists (PTs) have a broad range of approaches to the management of Down syndrome (DS).

PURPOSE

To examine the breadth of physical therapy practice for children with DS.

METHODS

A survey was distributed to 1000 randomly selected members of the Academy of Pediatric Physical Therapy.

DATA ANALYSIS

Responses were categorized into 13 thematic subcategories and 3 International Classification of Functioning, Disability and Health (ICF) subcategories.

RESULTS AND DISCUSSION

One hundred eight PTs participated. Joint stability and alignment were the most common physical therapy-related problem. Functional movement was the most common physical therapy intervention. Most clinicians identified and treated at the ICF level of body functions and structure. Multiple assessment tools were used and tended to include norm-referenced tests. There was diversity of interventions with varying amounts of supporting evidence.

CONCLUSIONS

PTs manage children with DS for a wide variety of needs with a variety of interventions.

Analysis of Movement Acceleration of Down's Syndrome Teenagers Playing Computer Games

OBJECTIVE

This study aimed to evaluate movement acceleration characteristics in adolescents with Down syndrome (DS) and typical development (TD), while playing bowling and golf videogames on the Nintendo^® Wii™.

MATERIALS AND METHODS

The sample comprised 21 adolescents diagnosed with DS and 33 with TD of both sexes, between 10 and 14 years of age. The arm swing accelerations of the dominant upper limb were collected as measures during the bowling and the golf games. The first valid measurement, verified by the software readings, recorded at the start of each of the games, was used in the analysis.

RESULTS

In the bowling game, the groups presented significant statistical differences, with the maximum (M) peaks of acceleration for the Male Control Group (MCG) (M = 70.37) and Female Control Group (FCG) (M = 70.51) when compared with Male Down Syndrome Group (MDSG) (M = 45.33) and Female Down Syndrome Group (FDSG) (M = 37.24). In the golf game the groups also presented significant statistical differences, the only difference being that the maximum peaks of acceleration for both male groups were superior compared with the female groups, MCG (M = 74.80) and FCG (M = 56.80), as well as in MDSG (M = 45.12) and in FDSG (M = 30.52).

CONCLUSION

It was possible to use accelerometry to evaluate the movement acceleration characteristics of teenagers diagnosed with DS during virtual bowling and golf games played on the Nintendo Wii console.

Protocol study for a randomised, controlled, double-blind, clinical trial involving virtual reality and anodal transcranial direct current stimulation for the improvement of upper limb motor function in children with Down syndrome

INTRODUCTION

Down syndrome results in neuromotor impairment that affects selective motor control, compromising the acquisition of motor skills and functional independence. The aim of the proposed study is to evaluate and compare the effects of multiple-monopolar anodal transcranial direct current stimulation and sham stimulation over the primary motor cortex during upper limb motor training involving virtual reality on motor control, muscle activity, cerebral activity and functional independence.

METHODS AND ANALYSIS

A randomised, controlled, double-blind, clinical trial is proposed. The calculation of the sample size will be defined based on the results of a pilot study involving the same methods. The participants will be randomly allocated to two groups. Evaluations will be conducted before and after the intervention as well as 1 month after the end of the intervention process. At each evaluation, three-dimensional analysis of upper limb movement muscle activity will be measured using electromyography, cerebral activity will be measured using an electroencephalogram system and intellectual capacity will be assessed using the Wechsler Intelligence Scale for Children. Virtual reality training will be performed three times a week (one 20 min session per day) for a total of 10 sessions. During the protocol, transcranial stimulation will be administered concomitantly to upper limb motor training. The results will be analysed statistically, with a p value≤0.05 considered indicative of statistical significance.

ETHICAL ASPECTS AND PUBLICITY

The present study received approval from the Institutional Review Board of Universidade Nove de Julho (Sao Paulo,Brazil) under process number 1.540.113 and is registered with the Brazilian Registry of Clinical Trials (N° RBR3PHPXB). The participating institutions have presented a declaration of participation. The volunteers will be permitted to drop out of the study at any time with no negative repercussions. The results will be published and will contribute evidence regarding the use of this type of intervention on children.

Coupling between visual information and body sway in adults with Down syndrome

BACKGROUND

Prior studies suggest that infants with Down syndrome (DS) need more experience to acquire a similar relationship between visual information and body sway than infants without DS. However, it is unclear how adults with DS deal with visual information to control posture.

AIM

To examine the coupling between visual information and body sway in adults with DS.

METHODS

Twenty adults with DS (25.8±4.0years) and twenty age- and sex-matched controls (25.6±4.0years) stood upright inside a "moving room" in two experimental conditions: continuous (room oscillated continuously at 0.1, 0.2, and 0.5Hz) and discrete (room moved forward or backward for a brief moment). Tridimensional body sway and moving room displacement data were registered.

RESULTS

Individuals with DS coupled their body sway to the imposed visual stimulus, but showed higher position variability at frequencies other than the frequency of room movement (0.48cm) and lower coherence (0.80) than controls (0.40cm and 0.90, respectively).

CONCLUSIONS

Adults with DS were able to couple to the visual cue, but with differences in terms of the scaling of postural responses to spatial parameters of the visual stimulus.

Can response time be trained with bilateral limb training in children with Down syndrome?

Aims:

Response time (RT), that is, the time taken to respond is known to be delayed in children with Down syndrome (DS). We performed a pilot study to evaluate whether bilateral limb training can be used to train RT, in children with DS.

Settings and Design:

10 children with DS (5 males) were recruited from a special school in a suburban region using convenience sampling.

Subjects and Methods:

Response time was measured using an indigenously developed RT Analyzer, before and after intervention, from right and left hand. Structured bilateral limb training was given for a period of 4 weeks, using low-cost, locally available materials, in community settings.

Statistical Analysis Used:

The Wilcoxon signed ranks test was used for statistical analysis.

Results:

Significant improvements in RT following 4 weeks of intervention were seen in the left hand (P = 0.006) but not in the right hand (P = 0.104).

Conclusions:

Response time can be trained in children with DS using 4 weeks of bilateral limb training activities using low-cost, locally available materials.

Mechanical energy assessment of adult with Down syndrome during walking with obstacle avoidance

The aim of this study is analyzing the differences between plane walking and stepping over an obstacle for two groups of healthy people and people with Down syndrome and then, evaluating the movement efficiency between the groups by comprising of their mechanical energy exchanges. 39 adults including two groups of 21 people with Down syndrome (age: 21.6 ± 7 years) and 18 healthy people (age: 25.1 ± 2.4 years) participated in this research. The test has been done in two conditions, first in plane walking and second in walking with an obstacle (10% of the subject's height). The gait data were acquired using quantitative movement analysis, composed of an optoelectronic system (Elite2002, BTS) with eight infrared cameras. Mechanical energy exchanges are computed by dedicated software and finally the data including spatiotemporal parameters, mechanical energy parameters and energy recovery of gait cycle are analyzed by statistical software to find significant differences. Regards to spatiotemporal parameters velocity and step length are lower in people with Down syndrome. Mechanical energy parameters particularly energy recovery does not change from healthy people to people with Down syndrome. However, there are some differences in inter-group through plane walking to obstacle avoidance and it means people with Down syndrome probably use their residual abilities in the most efficient way to achieve the main goal of an efficient energy recovery.

Postural stability in young adults with Down syndrome in challenging conditions

To evaluate postural control and performance in subjects with Down syndrome (SwDS), we measured postural sway (COP) in quiet stance in four 20-second tests: with eyes open or closed and on hard or foam surface. Ten SwDS and eleven healthy subjects participated, aged 29.8 (4.8) and 28.4 (3.9), respectively. The time-series recorded with the sampling rate of 100 Hz were used to evaluate postural performance (COP amplitude and mean velocity) and strategies (COP frequency, fractal dimension and entropy). There were no intergroup differences in the amplitude except the stance on foam pad with eyes open when SwDS had larger sway. The COP velocity and frequency were larger in SwDS than controls in all trials on foam pad. During stances on the foam pad SwDS increased fractal dimension showing higher complexity of their equilibrium system, while controls decreased sample entropy exhibiting more conscious control of posture in comparison to the stances on hard support surface. This indicated that each group used entirely different adjustments of postural strategies to the somatosensory challenge. It is proposed that the inferior postural control of SwDS results mainly from insufficient experience in dealing with unpredictable postural stimuli and deficit in motor learning.

Timing of muscle response to a sudden leg perturbation: comparison between adolescents and adults with Down syndrome

Movement disturbances associated with Down syndrome reduce mechanical stability, worsening the execution of important tasks such as walking and upright standing. To compensate these deficits, persons with Down syndrome increase joint stability modulating the level of activation of single muscles or producing an agonist-antagonist co-activation. Such activations are also observed when a relaxed, extended leg is suddenly released and left to oscillate passively under the influence of gravity (Wartenberg test). In this case, the Rectus femoris of adults with Down syndrome displayed peaks of activation after the onset of the first leg flexion. With the aim to verify if these muscular reactions were acquired during the development time and to find evidences useful to give them a functional explanation, we used the Wartenberg test to compare the knee joint kinematics and the surface electromyography of the Rectus femoris and Biceps femoris caput longus between adolescents and adults with Down syndrome. During the first leg flexion, adolescents and adults showed single Rectus femoris activations while, a restricted number of participants exhibited agonist-antagonist co-activations. However, regardless the pattern of activation, adults initiated the muscle activity significantly later than adolescents. Although most of the mechanical parameters and the total movement variability were similar in the two groups, the onset of the Rectus femoris activation was well correlated with the time of the minimum acceleration variability. Thus, in adolescents the maximum mechanical stability occurred short after the onset of the leg fall, while adults reached their best joint stability late during the first flexion. These results suggest that between the adolescence and adulthood, persons with Down syndrome explore a temporal window to select an appropriate timing of muscle activation to overcome their inherent mechanical instability.

Feedback reliance during an arm-tapping task with obstacle avoidance in adults with Down syndrome

Optimal movement control reflects a combination of both feedback and feedforward processes. However, as motor control evolves, feedforward mechanisms become prevailing respect to feedback-based movements, and less reliance on sensory information leads to a decreased number of corrections in the trajectory. In subjects with Down syndrome (DS), the study of the wrist's trajectory during an arm-tapping task revealed feedback-based corrections designed to reduce the degree of discrepancy between the position of the limb and the target, leading to the assumption that performers with DS have problems with movement planning and feedforward control. The present study was aimed at expanding the evidence about motor control in DS by evaluating the influence of a perturbing factor (an obstacle) on motor control strategies during an arm-tapping task and to clarify if the presence of an obstacle elicited a higher reliance on feedback control in controls and in DS. Sixteen right-handed adults with DS and 21 right-handed, age-matched control subjects (N) were evaluated by means of quantitative motion analysis. The results suggest that the presence of an obstacle elicited changes in the motor strategies of both DS and N, with a destabilizing effect that led subjects to rely more on feedback control. DS showed some aspects of movement efficiency that were in accordance with N strategies, but the prevailing factor of optimization in these subjects remained safety. A focused rehabilitation could help DS subjects to develop more efficient motor strategies in the presence of motor uncertainty and perturbations.

Indirect estimates of jaw muscle tension in children with suspected hypertonia, children with suspected hypotonia, and matched controls

PURPOSE

In this study, the authors compared indirect estimates of jaw-muscle tension in children with suspected muscle-tone abnormalities with age- and gender-matched controls.

METHOD

Jaw movement and muscle activation were measured in children (ages 3 years, 11 months, to 10 years) with suspected muscle-tone abnormalities (Down syndrome or spastic cerebral palsy; n = 10) and controls (n = 11). Two measures were used to infer jaw tension: a kinematic index of mass-normalized stiffness and electromechanical delay (EMD). The kinematic index used video-based kinematics to obtain the slope of the peak velocity-displacement relationship. The EMD was derived from the interval between the onset of suprahyoid muscle activity and the onset of jaw depression.

RESULTS

Neither measure differentiated the groups. The kinematic index revealed differences between stressed and unstressed syllables in 3-syllable productions by the participants with cerebral palsy and controls, but not in 2-syllable productions by the participants with Down syndrome and controls.

CONCLUSION

This preliminary investigation included the novel application of 2 measures to infer the jaw-muscle tension of children with suspected tone abnormalities. Although the results do not support the hypothesis that suspected muscle-tone abnormalities affect jaw movement sufficiently to influence speech production, considerations for interpreting the findings include methodological limitations and possible compensatory muscle coactivation.

Motor strategies and motor programs during an arm tapping task in adults with Down Syndrome

Slow movements and atypical patterns of muscle activation are well-known features of Down Syndrome (DS). Some studies attribute these features to a deficit in voluntary motor commands and preprogramming of actions, that lead subjects with DS to be more reliant on feedback control. In the present study, we evaluated the movement strategies of 13 adult subjects with DS and of 22 age-matched controls (N) during an arm tapping task. By means of quantitative motion analysis, our aim was to describe movement differences in DS respect to typical population and provide a means of interpreting such differences in terms of the underlying different control processes. The results highlighted distinct motor strategies for the tapping task in the two groups, with DS relying more on the trunk motion and N relying on the elbow motion to accomplish the task. Furthermore, DS corrected their wrist trajectory more than N subjects, giving shape to multi-peaked velocity profiles. Longer duration of the trials and a higher index of curvature were found in DS. The results suggest that subjects with DS rely more on feedback control, whereas they have problems with movement planning and feed-forward control. The different strategy operated by subjects with DS leads to a different task performance.

Gait parameter adjustments for walking on a treadmill at preferred, slower, and faster speeds in older adults with down syndrome

The combined effects of ligamentous laxity, hypotonia, and decrements associated with aging lead to stability-enhancing foot placement adaptations during routine overground walking at a younger age in adults with Down syndrome (DS) compared to their peers with typical development (TD). Our purpose here was to examine real-time adaptations in older adults with DS by testing their responses to walking on a treadmill at their preferred speed and at speeds slower and faster than preferred. We found that older adults with DS were able to adapt their gait to slower and faster than preferred treadmill speeds; however, they maintained their stability-enhancing foot placements at all speeds compared to their peers with TD. All adults adapted their gait patterns similarly in response to faster and slower than preferred treadmill-walking speeds. They increased stride frequency and stride length, maintained step width, and decreased percent stance as treadmill speed increased. Older adults with DS, however, adjusted their stride frequencies significantly less than their peers with TD. Our results show that older adults with DS have the capacity to adapt their gait parameters in response to different walking speeds while also supporting the need for intervention to increase gait stability.

Impaired plasticity at specific subset of striatal synapses in the Ts65Dn mouse model of Down syndrome

BACKGROUND

Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS.

METHODS

Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated.

RESULTS

The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum.

CONCLUSIONS

The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS.

“Abnormal” movements: What are they reflections of?

We agree with Latash & Anson that therapeutic approaches should be directed toward solving the underlying problem, not toward adapting the abnormal to normal behaviour. The fundamental obstacle, however, is that doing so requires a solution of the “equivalence problem” in movement control.

Defective preprogramming does not account for the clinical deficits of Parkinson's disease

Latash & Anson argue that changed motor patterns should not be viewed as pathological. Instead, they should be viewed as adaptations to a primary deficit. We argue that the evidence shows: (1) bradykinesia is not an adaptation to a different primary deficit, and (2) bradykinetic movements are not “normal” slowed movements but, to the contrary, bradykinesia is part of the pathophysiology of Parkinson's disease.

Generic mechanisms of coordination in special populations

We show that left-handers can be considered as a “special” population. We indicate that the asymmetries in performance exhibited by left-handers are due to a basic asymmetry in the underlying coordination dynamics that constrains bimanual coordination. In contrast to the claims of Latash & Anson, we argue that considerable knowledge has been gained regarding the essential equations of motion that govern biological coordination.

“Normal” is not the issue: It is “effective” goal attainment that counts

Adaptive motor patterns that emerge after a neuromusculoskeletal lesion reflect not only the primary lesion, but also the dynamic characteristics of the musculoskeletal linkage and environment in which the action is performed. Although these patterns may be optimal, they may also be ineffective as goal-directed actions; effectiveness may only be regained if training addresses primary deficits and ensures practice without gross biomechanical adaptations.

The goal of treatment for motor impairment is not to “normalize” but to “functionalize” through facilitative modulation and enabling context

Adaptations occurring in the central nervous system (CNS) in the presence of pathology are not uniformly “good” for the organism when viewed in a functional context. A functional reordering of CNS priorities can be produced by allowing restructuring of the external context or through modification of neuromuscular physiology or anatomy designed to reduce the inherent restriction of functional movement in upper motor neuron syndrome. In fact, volitional control can often be “unmasked” through such interventions. Therapeutic interventions should not be directed toward “normalization” of motor patterns but should permit a functional reordering of CNS priorities that would otherwise not be possible.

What are “normal movements” in atypical populations?

Redundancy of the motor control system is an important feature that gives the central control structures options for solving everyday motor problems. The choice of particular control patterns is based on priorities (coordinative rules) that are presently unknown. Motor patterns observed in unimpaired young adults reflect these priorities. We hypothesize that under certain atypical conditions, which may include disorders in perception of the environment and in decision making, structural or biochemical changes within the central nervous system (CNS), and/or structural changes of the effectors, the central nervous system may reconsider its priorities. A new set of priorities will reflect the current state of the system and may lead to different patterns of voluntary movement. Under such conditions, changed motor patterns should be considered not pathological but rather adaptive to a primary disorder and may even be viewed as optimal for a given state of the system of movement production. Therapeutic approaches should not be directed toward restoring the motor patterns to as close to “normal” as possible but rather toward resolving the original underlying problem. We illustrate this approach using, as examples, movements in amputees, in patients with Parkinson's disease, in patients with dystonia, and in persons with Down syndrome.

What are “normal movements” inanypopulation?

It is the contention of Latash & Anson (L&A) that in atypical populations, such as those with cognitive, central neurological, or peripheral disorders, the central nervous system (CNS) is capable of producing more effective, though often less “normal,” movement patterns ifleft to its own devices. It is the aim of this commentary to extend their argument to other populations by pointing out the many parallels with development of movement patterns in sport.

Should stereotypic movement synergies in hemiparetic patients be considered adaptive?

The motor deficits observed in patients following some lesions of the central nervous system may be viewed as falling at one extreme of the continuum of possible motor behaviours. They are usually associated with an impaired ability to select and control specific movements from the available repertoire. Such movements may not be viewed as abnormal. However, it is unlikely that the primary motor deficits can all be considered adaptive.

“Constraint” versus “choice” in preferred movement patterns

Movement patterns in impaired gait are not selected by a smart central nervous system (CNS), but arise by virtue of mutual constraints of task, limitations in personal dynamics available for the task, and optimality criteria. An oscillatory model of gait cycle is presented that exemplifies this control and coordination scheme. Preferred gait patterns may be based on physical principles rather than CNS “coordinative rules.”

Developmental “movement disorders” and problem solving

Normal infants show a wide range of “atypical” movements. These, like the movements of atypical and normal adults, are best characterized as solutions to motor problems. Motor patterns alone may not be precise indicators of neurological status.

Is motor pathology associated with setting new CNS priorities or with increased difficulty in overcoming or suppressing preexisting CNS priorities?

Whereas Latash & Anson (L&A) have underscored the rearrangement or setting of new priorities, our primary focus is on preexisting central nervous system (CNS) priorities that become even more prevalent and intrusive under pathological conditions. The adaptations observed in the disordered motor system can often be understood against the backdrop of these primary CNS constraints. Even though this perspective has not been specifically addressed in the target article, we consider it complementary and not necessarily in opposition to L&A's primary thesis.

Development of reaching and grasping skills in infants with Down syndrome

Reaching and grasping skills have been described to emerge from a dynamic interaction between intrinsic and extrinsic factors. The aims of the study were to investigate the effect of such intrinsic factors as age and Down syndrome on the development of reaching and grasping skills and on overall gross motor skill, and to test the influence of the overall level of gross motor skill on the development of reaching and grasping. Seven infants with Down syndrome (DS) and seven infants with typical development were assessed at the ages of 4, 5 and 6 months. The following variables were analyzed: straightness index, mean velocity, movement units and deceleration time (for reaching movements), grasping frequency and AIMS scores. Intrinsic factors such as age and DS were found to influence the development of reaching, grasping, and of the overall level of gross motor skill. The overall level of gross motor skill was observed to influence grasping.

Evidence for slowing as a function of index of difficulty in young adults with Down syndrome

Speed-accuracy trade-offs in persons with Down syndrome and typically developing controls were tested with a Fitts' task. Movement time scaled linearly with index of difficulty in both groups, and there were no accuracy differences. Persons with Down syndrome were slower than typically developing individuals. Regression analysis on movement time and index of difficulty showed a nearly two-fold higher regression coefficient and a nearly three-fold larger intercept value in the Down syndrome group. The dwell time on a target was much longer for Down syndrome persons but scaled with index of difficulty in about the same percentage for participants in both groups. Because of differences primarily related to scaling, we conclude that mechanisms of motor control are similar in Down syndrome and typically developing groups.

Complexity of force output during static exercise in individuals with Down syndrome

Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS (n = 29, age 26 yr), and healthy young (n = 26, age 27 yr) and older (n = 33, age 70 yr) individuals. Mean, standard deviation (SD), and coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls (P < 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls (P < 0.05). The DS group had a significantly greater proportion of spectral power within the 0-to 4-Hz bandwidth than the young and older controls (P < 0.05). The DS group had significantly lower ApEn values than the young controls (P < 0.05), but there were no differences in ApEn between the DS group and the old controls (P > 0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.

Controle postural em indivíduos portadores da síndrome de Down: revisão de literatura

Este trabalho consistiu numa revisão da literatura sobre controle postural em indivíduos portadores da síndrome de Down, por meio de consulta às bases de dados Medline, Lilacs e Web of Science. Dentre os artigos publicados nos últimos 16 anos, selecionaram-se 30, dos quais 7 focalizam a natureza dos défices no sistema de controle postural, como alterações neurobiológicas e biomecânicas, e 23 enfocam o controle postural no período de desenvolvimento (11 artigos) e em adolescentes e adultos (12 artigos) portadores da síndrome. Discutem-se os marcos teóricos que conformam a compreensão do desenvolvimento postural e seus défices, bem como as implicações dessa compreensão para a prática da fisioterapia.

Learning motor synergies by persons with Down syndrome

Persons with Down syndrome are frequently described as 'clumsy'. The recent progress in the development of quantitative approaches to motor synergies has allowed researchers to move towards an understanding of 'clumsiness' at the level of underlying control mechanisms. This progress has also offered an opportunity to quantify changes in motor synergies that accompany improvement in the performance of motor tasks. Previous studies of our group have shown, in particular, that persons both with and without Down syndrome are able to show improvements in indices of their multi-finger synergies in tasks that require accurate production of finger forces. In particular, 3 days of practice has been shown to lead to significant improvements in indices of multi-finger synergies that stabilize the time patterns of the total force produced by the fingers of a hand. Persons with Down syndrome showed a qualitative change in their synergies that failed to stabilize the total force altogether prior to practice and became able to do so after practice. In addition, the studies have also shown that variable practice is more beneficial for the improvement of motor synergies than blocked practice. I would like to draw an optimistic conclusion that persons with Down syndrome are not inherently 'clumsy', but have a vast potential for an improvement of their motor performance. The current state of the area of motor control allows researchers and practitioners to tap into these reserves, and to use quantitative indices of changes in motor synergies with practice to optimize motor performance of these individuals.

Effect of practice on a novel task--walking on a treadmill: preadolescents with and without Down syndrome

BACKGROUND AND PURPOSE

The authors propose that preadolescents with Down syndrome (DS) initially adapt to contexts that challenge their stability by increasing stiffness and impulse but, with practice, they will continue to adapt, but in the opposite direction, by decreasing stiffness and impulse. The purpose of this study was to explore changes in stiffness and impulse values of participants with DS after sufficient, task-specific practice distributed over time in a motivating environment.

SUBJECTS

Eight preadolescents with DS and 8 preadolescents with typical development (TD) participated.

METHODS

At pretest and posttest visits, participants walked over ground at their preferred speed and on a treadmill at 40%, 75%, and 110% of their over-ground speed. Practice included 4 sessions of treadmill walking at 75% of over-ground speed for 12 minutes, with approximately 800 strides per leg per session.

RESULTS

The preadolescents with DS had reduced stiffness and impulse values following walking practice while still producing kinematic patterns uniquely different from those of their peers with TD.

DISCUSSION AND CONCLUSION

Preadolescents with DS can adjust their dynamic resources, both upward and downward. With practice, they can maintain stability while improving efficiency, producing stiffness and impulse values more like those of their peers with TD.

The effect of joint instability on latency and recruitment order of the shoulder muscles

Several shoulder dysfunctions are generally characterized as Shoulder Impingement Syndrome (SIS). Specifically, glenohumeral instability (GI) has been viewed as a primary cause of SIS in young individuals, mainly in overhead athletics. Past studies have associated GI with modifications in latency, recruitment order and/or EMG activity. However, it is not clear if pain and/or joint instability can account for these observed changes. The aim of this investigation was to analyze the effect of glenohumeral instability on the latencies and recruitment order of the superficial muscles of the glenohumeral and scapulothoracic joints in swimmers without pain symptom. Eight individuals with and eight without history of Shoulder Impingement Syndrome performed bilateral and simultaneous shoulder elevations at three different distances. The shoulder kinematics and EMG activities of glenohumeral and scapulothoracic muscles were registered. Results showed that subjects of both groups performed the task with similar latencies and recruitment order of the muscle activities. We conclude that shoulder instability does not necessarily affect the latencies and recruitment order of the shoulder muscles during the elevation of the shoulder in the scapular plane. Pain and other factors may be involved in the kinematics and electromyographic alterations demonstrated in other experiments.

Coupling between muscle activities and muscle torques during horizontal-planar arm movements with direction reversal

In this study we investigated the hypothesis that the simple set of rules used to explain the modulation of muscle activities during single-joint movements could also be applied for reversal movements of the shoulder and elbow joints. The muscle torques of both joints were characterized by a triphasic impulse. The first impulse of each joint accelerated the limb to the target and was generated by an initial burst of the muscles activated first (primary mover). The second impulse decelerated the limb to the target, reversed movement direction and accelerated the limb back to the initial position, and was generated by an initial burst of the muscles activated second (secondary movers). A third impulse, in each joint, decelerated the limb to the initial position due to the generation of a second burst of the primary movers. The first burst of the primary mover decreased abruptly, and the latency between the activation of the primary and secondary movers varied in proportion with target distances for the elbow, but not for the shoulder muscles. All impulses and bursts increased with target distances and were well coupled. Therefore, as predicted, the bursts of muscle activities were modulated to generate the appropriate level of muscle torque.

Physical activity intervention for older adults with intellectual disability: report on a pilot project

A 12-week pilot project on physical activity was introduced in a day habilitation setting to a group of 12 older adults with intellectual disability and a variety of physical and behavioral conditions. Our purpose was to determine whether (a) this intervention would positively impact physical function in this population, (b) consumers would choose to participate in physical activity sessions, and (c) day habilitation staff could sustain this program beyond the intervention period. Findings indicate that 92% of participants experienced improvement in at least one domain of physical function, physical activity sessions remained a popular activity choice for consumers, and many participants sustained functional gains 1 year after habilitation staff assumed responsibility for sessions.

Modeling dynamic resource utilization in populations with unique constraints: Preadolescents with and without Down syndrome

In this study we used a damped inverted pendulum and spring with an escapement function model to compare the global levels of stiffness and forcing used by 12 preadolescents with Down syndrome (DS) and 12 with typical development (TD). Participants walked overground at their self-selected speed and on a treadmill at speeds slower and faster than overground. Children with DS, who are characterized as hypotonic with reduced capacity for producing muscle force, exhibited significantly higher levels of stiffness and forcing (angular impulse) when walking on the treadmill and higher forcing but not stiffness overground, than children with TD. Both groups adapted to imposed speed increases similarly by increasing their global stiffness and angular impulse. We propose children with DS increased stiffness in order to overcome their hypotonia and joint laxity, thus, optimizing on stability, rather than metabolic efficiency. Higher angular impulse values for children with DS may reflect higher energy cost associated with increasing stiffness and their inherent biomechanical and physiological characteristics that reduce efficiency. We conclude that the inverted pendulum and spring with escapement function model is a useful tool for uncovering solutions to movement problems-solutions that reflect the dynamic resources of the individual and ones that are discovered, rather than prescribed.

Postural control in children: implications for pediatric practice

Based on a systems theory of motor control, reactive postural control (RPA) and anticipatory postural control (APA) in children are reviewed from several perspectives in order to develop an evidence-based intervention strategy for improving postural control in children with limitations in motor function. Research on development of postural control, postural control in children with specific motor disabilities, and interventions to improve postural control is analyzed. A strategy for intervention to improve postural control systems at the impairment and functional activity levels based on a systems theoretical perspective is presented. Suggestions for research to improve evidence for best practice are provided.

Uncontrolled manifold analysis of single trials during multi-finger force production by persons with and without Down syndrome

Recently, the framework of the uncontrolled manifold (UCM) hypothesis has been used to study multi-finger synergies based on analysis of motor variability across large sets of trials. We introduce a similar method of analysis, which can be applied to single trials, and hence may be more relevant to studies of atypical populations. In one experiment, results of across-trials and single-trial UCM analysis were compared for control participants who performed accurate ramp force production trials by pressing with four fingers of the hand. Both types of analysis revealed selective stabilization of total force by co-variations of individual finger forces. The stabilization was more pronounced at higher forces. When the participants purposefully varied the relative involvement of fingers during the ramp, significantly higher UCM effects were observed. However, high-pass filtering of the data at 4 Hz made these results similar to those observed in trials with natural patterns of force production. These observations allow assessment of the contribution of processes at two levels of a hypothetical hierarchical control system to the stabilization of total force. We also applied the single-trial UCM method to re-analyze previously published data from another experiment to study the motor variability in a group of persons with Down syndrome (DS) because these persons have difficulty in motor planning and timing as well as in force stabilization. Results of single-trial UCM analysis demonstrated force stabilization in these persons. The degree of force stabilization improved significantly after three days of practice. The analysis also showed that the total pronation/supination moment generated by the four fingers with respect to the midpoint was stabilized. The degree of moment stabilization did not change with practice. We conclude that the single-trial method of UCM analysis allows the analysis of hypotheses about stabilization of different performance variables by alleged multi-finger synergies in both typical individuals and individuals with DS.

Comparison of different therapy approaches in children with Down syndrome

BACKGROUND

Children with Down syndrome have sensory integrative dysfunction as a result of limited sensory experience from lack of normal motor control. The aim of the present study was to compare the effects of sensory integrative therapy alone, vestibular stimulation in addition to sensory integrative therapy and neurodevelopmental therapy, on children with Down syndrome.

METHODS

The present study was carried out at the Occupational Therapy Unit, School of Physical Therapy and Rehabilitation of Hacettepe University. Forty-five children who were diagnosed as having Down syndrome by the Departments of Paediatric Neurology and Medical Genetics at Hacettepe University were assessed and randomly divided into three groups. Sensory integrative therapy was given to the first group (n=15), vestibular stimulation in addition sensory integrative therapy was given to the second group (n=15) and neurodevelopmental therapy was given to the third group (n=15). All children were evaluated with Ayres Southern California Sensory Integration Test, Pivot Prone Test, Gravitational Insecurity Test and Pegboard Test. The hypotonicity of extensor muscles, joint stability, automatic movement reactions and locomotor skills were tested. Treatment programs were 1.5 h per session, 3 days per week for 3 months.

RESULTS

When these groups were compared, statistically significant differences were found in subjects' performance of balance on right foot-eyes open, pivot prone position-quality score and locomotor skills-front tests (P<0.05). There were no significant differences in the other tests (P>0.05).

CONCLUSIONS

The results of the present study showed that sensory integration, vestibular stimulation and neurodevelopmental therapy were effective in children with Down syndrome. It was concluded that when designing rehabilitation programs for children with Down syndrome, all treatment methods should be applied in combination, and should support each other according to the individual needs of the child.

Prehension in young children with Down syndrome

Prehension was examined in 3-year old children with Down syndrome (DS, n = 3) and in typically-developing children matched in chronological age (3-year olds; n = 3) or mental age and motor experience (2-year olds; n = 3). The task required reaching to grasp dowels. Video-based movement analysis yielded temporal and kinematic measures. Children with DS were hypothesized to have deficits in feedback-dependent components of prehension (anticipatory grip-closure and deceleration of reach), whereas feedforward components (reach's acceleration phase; grasp's preshaping) were assumed to be unimpaired [Latash, 1993, Control of human movement, pp. 283-292; Latash, 1994, What is clumsiness? In: Motor Control and Down Syndrome II Proceedings of the second international conference, pp. 68-71]. The findings supported these hypotheses. In comparison to control groups, children with DS had significantly: (a) less time in deceleration of reaching, (b) fewer anticipatory grip-closures, and (c) longer movement times for dowel-lift. Young children with DS appeared to use dowel-contact to decelerate the limb and initiate grip-closure. In contrast, reach-acceleration time and grasp-preshaping did not differ across groups. These findings suggest that children with DS display qualitative differences in motor capabilities rather than simply a delayed rate of typical developmental progression.

Bimanual coordination dynamics in adults with Down syndrome

Previous experiments involving discrete unimanual tasks have shown that individuals with Down syndrome (DS) have auditory/verbal-motor deficits. The present study investigated unimanual and bimanual continuous perceptual-motor actions in adults with DS. Ten adults with DS, 10 typical adults, and 10 children drew continuous circles at increasing periods bimanually and unimanually with each hand. Movement was paced by either a visual or an auditory metronome. The results revealed that for circle shape and coordination measures, children and adults were more accurate with the visual metronome, whereas adults with DS were more accurate with the auditory metronome. In the unimanual tasks, adults with DS displayed hand asymmetries on spatial measures. In the bimanual task, however, adults with DS adopted an in-phase coordination pattern and stability more similar to adults than children. These results suggest that bimanual coordination in adults with DS is functioning effectively despite hand asymmetries evident in unimanual performance.

The preparation of reach to grasp movements in adults with Down syndrome

The aim of this study was to determine the extent to which adults with Down syndrome (DS) are able to utilise advance information to prepare reach to grasp movements. The study comprised ten adults with DS; ten children matched to an individual in the group with DS on the basis of their intellectual ability, and twelve adult controls. The participants used their right hand to reach out and grasp illuminated perspex blocks. Four target blocks were positioned on a table surface, two to each side of the midsagittal plane. In the complete precue condition, participants were provided with information specifying the location of the target. In the partial precue condition, participants were given advance information indicating the location of the object relative to the midsagittal plane (left or right). In the null condition, advance information concerning the position of the target object was entirely ambiguous. It was found that both reaction times and movement times were greater for the participants with DS than for the adults without DS. The reaction times exhibited by individuals with DS in the complete precue condition were lower than those observed in the null condition, indicating that they had utilised advance information to prepare their movements. In the group with DS, when advance information specified only the location of the target object relative to the midline, reaction times were equivalent to those obtained when ambiguous information was given. In contrast, the adults without DS exhibited reaction times that were lower in both the complete and partial precue conditions when compared to the null condition. The pattern of results exhibited by the children was similar to that of the adults without DS. The movement times exhibited by all groups were not influenced by the precue condition. In summary, our findings indicate that individuals with DS are able to use advance information if it specifies precisely the location of the target object in order to prepare a reach to grasp movement. The group with DS were unable, however, to obtain the normal advantage of advance information specifying only one dimension of the movement goal (i.e., the position of an object relative to the body midline).

Horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with down syndrome

We examined the systematic variation in shoulder and elbow torque, as well as movement kinematics, for horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with Down syndrome. Eight neurologically normal individuals and eight individuals with Down syndrome performed horizontal, planar reversal movements to four different target locations. The four locations of the targets were chosen such that there is a systematic increase in elbow interaction torque for each of the four different target locations. This systematic increase in interaction torque has previously been shown to lead to progressively larger movement reversal errors, and trajectories that do not show a sharp reversal of direction, for movements to and from the target in patients who have proprioceptive abnormalities. We computed joint torques at the elbow and shoulder and found a high correlation between elbow and shoulder torque for the neurologically normal subjects. The ratio of joint torques varied systematically with target location. These findings extend previously reported findings of a linear synergy between shoulder and elbow joints for a variety of point-to-point movements. There was also a correlation between elbow and shoulder torque in individuals with Down syndrome, but the magnitude of the correlation was less. The ratio of joint torques changed systematically with target direction in individuals with Down syndrome but was slightly different from the ratio observed for neurologically normal individuals. The difference in the ratio was caused by the generation of proportionately more elbow torque than shoulder torque. The fingertip path of individuals with Down syndrome showed a sharp reversal in moving toward and then away from the target. In this respect, they were similar to neurologically normal individuals but dissimilar to individuals with proprioceptive deficits. Finally, we observed that individuals with Down syndrome spend proportionately more time in the vicinity of the target than normal individuals. Collectively these results show that there is a systematic relationship between joint torques at the elbow and shoulder. This relationship is present for reversal movements and is also present in individuals with Down syndrome.

Motor control research in rehabilitation medicine

Progress in rehabilitation medicine requires an understanding of the basic rules of motor coordination, as well as of the contribution of adaptive processes within the central nervous system to the patterns of impaired movements. We assume that patterns of voluntary movements reflect rules of coordination that are used by the intact central nervous system of healthy persons. In pathological conditions that may include cognitive, central neurological, and peripheral disorders, the central nervous system may reconsider these rules leading to different peripheral patterns of voluntary movements. In such conditions, changed motor patterns may be considered adaptive to a primary disorder. They may even be viewed as optimal for a given state of the system of movement production. We suggest that the emphasis of therapeutic approaches must be placed not on restoring the motor patterns to 'as close to normal as possible', but on assisting the central nervous system to develop optimal adaptive reactions to the original underlying problem.

Thought is action

It is difficult to chart “normal movements” in atypical populations, such as those with Parkinson's disease, because there is great variability in the pattern of motor changes, both within and between patients. However, the potential clinical implications of Latash & Anson's theme are positive and powerful.

When are adaptive motor patterns nonadaptive?

The assumption that adaptive changes in motor patterns are optimal is questioned. Instances are cited where alteration of the adaptive motor patterns may be warranted. Other issues discussed are: (1) the relationship between central nervous system (CNS) priorities and the individual's priorities, (2) the use of cognitive bypass strategies by impaired individuals, and (3) conceiving CNS priorities as coordinative rules.