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The prediction of the stability of future steps taken by a biped robot is a very important task, since it allows the robot controller to adopt the necessary measures in order to minimize damages if a fall is predicted. We present a classifier to predict the viability of a given planned step taken by a biped robot, i.e., if it will be stable or unstable. The features of the classifier are extracted from a feature engineering process exploiting the useful information contained in the time series generated in the trajectory planning of the step. In order to state the problem as a supervised classification one, we need the ground truth class for each planned step. This is obtained using the Predicted Step Viability (PSV) criterion. We also present a procedure to obtain a balanced and challenging training/testing dataset of planned steps that contains many steps in the border between stable and non stable regions. Following this trajectory planning strategy for the creation of the dataset we are able to improve the robustness of the classifier. Results show that the classifier is able to obtain a 95% of ROC AUC for this demanding dataset using only four time series among all the signals required by PSV to check viability. This allows to replace the PSV stability criterion, which is safe, robust but impossible to apply in real-time, by a simple, fast and embeddable classifier that can run in real time consuming much less resources than the PSV.

In this paper, we address the challenge of ensuring stability in bipedal walking robots and exoskeletons. We explore the feasibility of real-time implementation for the Predicted Step Viability algorithm (PSV), a complex multi-step optimization criterion for planning future steps in bipedal gait. To overcome the high computational cost of the PSV algorithm, we performed an analysis using 11 classification algorithms and a stacking strategy to predict if a step will be stable or not. We generated three datasets of increasing complexity through PSV simulations to evaluate the classification performance. Among the classifiers, k Nearest Neighbors, Support Vector Machine with Radial Basis Function Kernel, Decision Tree, and Random Forest exhibited superior performance. Multi-Layer Perceptron also consistently performed well, while linear-based algorithms showed lower performance. Importantly, the use of stacking did not significantly improve performance. Our results suggest that the feature vector applied with this approach is applicable across various robotic models and datasets, provided that training data is balanced and sufficient points are used. Notably, by leveraging classifiers, we achieved rapid computation of results in less than 1 ms, with minimal computational cost.

Exploring the fundamental mechanisms of locomotion extends beyond mere simulation and modeling. It necessitates the utilization of physical test benches to validate hypotheses regarding real-world applications of locomotion. This study introduces cost-effective modular robotic platforms designed specifically for investigating the intricacies of locomotion and control strategies. Expanding upon our prior research in electric-pneumatic actuation (EPA), we present the mechanical and electrical designs of the latest developments in the EPA robot series. These include EPA Jumper, a human-sized segmented monoped robot, and its extension EPA Walker, a human-sized bipedal robot. Both replicate the human weight and inertia distributions, featuring co-actuation through electrical motors and pneumatic artificial muscles. These low-cost modular platforms, with considerations for degrees of freedom and redundant actuation, (1) provide opportunities to study different locomotor subfunctions-stance, swing, and balance; (2) help investigate the role of actuation schemes in tasks such as hopping and walking; and (3) allow testing hypotheses regarding biological locomotors in real-world physical test benches.

Robotic devices can be used in upper limb rehabilitation in order to help the total or partial functional recovery. Robots can perform repetitive activities for a long period of time, which may be beneficial for rehabilitation processes. In this context, this study uses a bi-manual robotic device to investigate motor learning and control for the upper limbs among different game guided tasks, and inspect the user's grip force exerted in response to perturbations. The robotic device resembles a bicycle handlebar, instrumented with load cells to measure torques and grip forces. It is equipped with a DC motor to apply external torques to the guiding system. A game was developed containing in-game and physical perturbations to the natural movement of the handlebar. Tests were carried out with 16 healthy subjects that were instructed to move the handlebar guiding a character displayed on the screen with the objective of collecting tokens to get the higher score in the game. During the trials, corresponding data from the game and the load cells were collected and used to infer the learning process, the mean error in the trajectory and the variations in the force applied to the handles of the handlebar. Analyses showed that there was learning in the first repetitions, and the learning was retained further. The higher values of the grip force occurred when there was a physical perturbation to the handlebar's natural movement. The larger errors in the trajectories occurred immediately after the perturbations ended. In conclusion, there was a performance improvement, probably related to learning. The increase of the mean error at the transitions of the perturbations indicates the need for adaptation to the new conditions of the task.

Shoulder-controlled hand neuroprostheses are wearable devices designed to assist hand function in people with cervical spinal cord injury (SCI). They use preserved shoulder movements to control artificial actuators. Due to the concurrent afferent (i.e., shoulder proprioception) and visual (i.e., hand response) feedback, these wearables may affect the user's body somatosensory representation. To investigate this effect, we propose an experimental paradigm that uses immersive virtual reality (VR) environment to emulate the use of a shoulder-controlled hand neuroprostheses and an adapted version of a visual-tactile integration task (i.e., Crossmodal Congruency Task) as an assessment tool. Data from seven non-disabled participants validates the experimental setup, with preliminary statistical analysis revealing no significant difference across the means of VR and visual-tactile integration tasks. The results serve as a proof-of-concept for the proposed paradigm, paving the way for further research with improvements in the experimental design and a larger sample size.

Approximately 80% of patients submitted to radiotherapy develop radiodermatitis. Photobiomodulation based on light-emitted diode (LED) is one of the therapeutic strategies for treating inflammation. This study aimed to investigate the effect of the photobiomodulation with two wavelengths, in an acute radiodermatitis animal model., Methods: Twenty rats were submitted to one radiotherapy session. After 15 days, the rats that developed radiodermatitis were divided into control groups, LED-630 nm, LED-850 nm, and LED-630 + 850 nm. The treatment regimen was one session lasting 10 minutes on alternate days for 21 days. We analyzed macroscopy aspects (RTOG scale), vascular density, dermal appendages, VEGF-a, TNF-alpha, MMP-9, and MMP-9 genic expression level., Results: All LED groups revealed a two-point reduction on the radiodermatitis severity grade compared with the baseline classification. Dermal appendage and vascular analysis showed a higher counting in all LED groups compared to control. This study showed dermal appendages twice in the 630/850 nm group compared with the control group. The 630/850 nm group showed six times more arterioles than the control group. Regarding genic expression, this study showed a 10-fold decrease between LED-630 nm versus LED-630 + 850 nm ( P = 0.02) interleukin-10 expression and a 12-fold decrease between control versus LED-630 nm ( P = 0.006) and LED-850 nm ( P = 0.002) in TNF-alpha., Conclusion: LED (630 nm, 850 nm, and 630 nm + 850 nm) showed benefit in the treatment of radiodermatitis, and the association of the 630 nm + 850 nm and 630 nm parameters demonstrated the best macroscopic and microscopic results., (Copyright © 2023 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The American Society of Plastic Surgeons.)

This paper investigates how predictions of a convolutional neural network (CNN) suited for myoelectric simultaneous and proportional control (SPC) are affected when training and testing conditions differ. We used a dataset composed of electromyogram (EMG) signals and joint angular accelerations measured from volunteers drawing a star. This task was repeated multiple times using different combinations of motion amplitude and frequency. CNNs were trained with data from a given combination and tested under different combinations. Predictions were compared between situations in which training and testing conditions matched versus when there was a training-testing mismatch. Changes in predictions were assessed through three metrics: normalized root mean squared error (NRMSE), correlation, and slope of the linear regression between targets and predictions. We found that predictive performance declined differently depending on whether the confounding factors (amplitude and frequency) increased or decreased between training and testing. Correlations dropped as the factors decreased, whereas slopes deteriorated when factors increased. NRMSEs worsened when factors increased or decreased, with more accentuated deterioration for increasing factors. We argue that worse correlations could be related to differences in EMG signal-to-ratio (SNR) between training and testing, which affected the noise robustness of the CNNs' learned internal features. Slope deterioration could be a result of the networks' inability to predict accelerations outside the range seen during training. These two mechanisms may also asymmetrically increase NRMSE. Finally, our findings open further possibilities to develop strategies to mitigate the negative impact of confounding factor variability on myoelectric SPC devices.

Postural control relies on three principal sensory systems: vision, vestibular and proprioceptive; that are affected by aging. When performing a cognitive task concomitantly with a motor task, those sensory impairments lead to even greater deleterious effects on balance. We aimed to study the effects of a sensory aid (a light touch) on a dual task paradigm and sought to understand the different responses on balance due to aging. Fifty healthy and highly physical active women were divided in two groups: young (N = 25, 24.2 ± 4.0 years) and older adults (N = 25, 67.3 ± 4.2 years). In a random and balanced order, all participants performed five tasks: Stroop test while seated (Seated); Stroop test while standing quiet (ST); Standing quiet (BL); Standing quiet with a haptic input (LT); and Stroop test with a haptic input while standing quiet (SL). In the Stroop test, older women committed more errors (50 vs 11 errors, p < 0.001) and had higher reaction time (1.001 ± 0.191 vs 0.699 ± 0.081 s, p < 0.001). The haptic input (LT) reduced all body sway parameters, in both groups, regardless the condition. This means that postural control under a dual task paradigm (ST) deleterious effect can be mitigated by a haptic input., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Stroke recovery is a critical public health problem. It involves cognitive and physical impairments leading to physical inactivity. In addition, there are also sleep problems and disruption of the circadian rhythm. In this paper, we analyze the relation between cognitive impairments level, walking performance, sleep and circadian parameters of a group of chronic stroke survivors. Five stroke survivors enrolled in the study. The clinical assessments were: cognitive function (MoCA), the 10 meter-walking test (10MWT), and the 6 minutes walking test (6MWT). The circadian rhythm parameters were obtained for at least one week wearing the actimeters. There was a positive correlation between the duration of the main sleep episode and the MoCA scores. There were significant correlations between the 10MWT and 6MWT and the circadian parameters that were positive for most active period (M10), Interdaily stability (IS), Mesor and Amplitude and negative for intradaily variability (IV). Our results indicate that gait speed and resistance are correlated to circadian rhythm synchronization, lower rhythm variability and more defined activity-rest episodes. This preliminary study underscores the importance of including a continuous measure of sleep and activity cycles in the assessment of stroke survivors.

Background: Recovery of hand function is crucial for the independence of people with spinal cord injury (SCI). Wearable devices based on soft robotics (SR) or functional electrical stimulation (FES) have been employed to assist the recovery of hand function both during activities of daily living (ADLs) and during therapy. However, the implementation of these wearable devices has not been compiled in a review focusing on the functional outcomes they can activate/elicit/stimulate/potentiate. This narrative review aims at providing a guide both for engineers to help in the development of new technologies and for clinicians to serve as clinical guidelines based on the available technology in order to assist and/or recover hand function in people with SCI., Methods: A literature search was performed in Scopus, Pubmed and IEEE Xplore for articles involving SR devices or FES systems designed for hand therapy or assistance, published since 2010. Only studies that reported functional outcomes from individuals with SCI were selected. The final collections of both groups (SR and FES) were analysed based on the technical aspects and reported functional outcomes., Results: A total of 37 out of 1101 articles were selected, 12 regarding SR and 25 involving FES devices. Most studies were limited to research prototypes, designed either for assistance or therapy. From an engineering perspective, technological improvements for home-based use such as portability, donning/doffing and the time spent with calibration were identified. From the clinician point of view, the most suitable technical features (e.g., user intent detection) and assessment tools should be determined according to the particular patient condition. A wide range of functional assessment tests were adopted, moreover, most studies used non-standardized tests., Conclusion: SR and FES wearable devices are promising technologies to support hand function recovery in subjects with SCI. Technical improvements in aspects such as the user intent detection, portability or calibration as well as consistent assessment of functional outcomes were the main identified limitations. These limitations seem to be be preventing the translation into clinical practice of these technological devices created in the laboratory., (© 2022. The Author(s).)

We compared the effects of using a commercial exoskeleton on shoulder muscle activity, task completion time, perceived effort and comfort while performing four tasks in different shoulder positions. Fourteen automotive industry workers performed four simulated tasks with shoulder at A≈0°, B ≈ 45°, C ≈ 90° and D ≈ 115° flexion. The electromyographic activity of the Medial Deltoid (MD) and the Anterior Deltoid (AD) decreased when wearing the exoskeleton. The effect sizes (ES) were, for MD: ES = 0, ES = -0.2, ES = -0.6, ES = -0.3; and for AD: ES = 0.3, ES = -0.6, ES = -0.8, ES = -0.6; for tasks A, B, C and D, respectively. We also found increased Anterior Deltoid/Triceps Brachii co-contraction, a typical joint stabilization mechanism. Wearing the exoskeleton increased the completion time of task B and reduced the perceived effort of tasks A and C, improving overall comfort. These findings are useful to organize the logistics of the workstations that use upper limb exoskeletons to improve the effectiveness of this equipment., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Bioinspiration can be used to improve the efficiency of these assistive biomechatronic devices. In this paper, a cable driven actuator for the human ankle was designed using a bioinspired approach. The torque reduction was achieved by means of force amplifying elements such as cables with pulley, and, to reduce the power requirements for the motor, the actuator mimics a muscle using a clutched parallel elastic element. The simulations to validate the model were performed using real gait data and the results prove the viability of the device to be used in anthropomorphic legs and exoskeletons. Although the losses due to friction were not considered, the simulations showed a reduction of 60% in the force peak and 40% in the power peak.

Walking and running, the two most basic and functional gait modes, have been often addressed through EMG, kinematics and biomechanical modelling, however, there is no consensus in the literature on which factors trigger the transition from walking to running. Ankle plantarflexors and dorsiflexor were found to play an important role in gait transition due to higher muscular activation to propel the body forward to run. We tested these muscles activation during walking and running at the same speeds, through a musculoskeletal model derived from subjects' kinematic and kinetic data. Compared to EMG data frequently reported in the literature, the results yielded similar activation patterns for all muscles analyzed. Besides, across speeds, dorsiflexor activation kept increasing in walking, especially after PTS (preferred transition speed), which may indicate its contribution to gait transition, as an effort to bring the foot forward to keep up with the unnatural condition of walking at high speeds.

Different levels of sleep restriction affect human performance in multiple aspects. However, it is unclear how sleep deprivation affects gait control. We applied a paced gait paradigm that included subliminal rhythm changes to analyze the effects of different sleep restriction levels (acute, chronic and control) on performance. Acute sleep deprivation (one night) group exhibited impaired performance in the sensorimotor synchronization gait protocol, such as a decrease in the Period Error between the footfalls and the auditory stimulus as well as missing more frequently the auditory cues. The group with chronic sleep restriction also underperformed when compared to the control group with a tendency to a late footfall with respect to the RAC sound. Our results suggest that partial or total sleep deprivation leads to a decrease in the performance in the sensorimotor control of gait. The superior performance of the chronic sleep group when compared to the acute group suggests that there is a compensatory mechanism that helps to improve motor performance., (© 2021. The Author(s).)

Robotic devices can be used for motor control and learning research. In this work, we present the construction, modeling and experimental validation of a bimanual robotic device. We tested some hypotheses that may help to better understand the motor learning processes involved in the interlimb coordination function. The system emulates a bicycle handlebar with rotational motion, thus requiring bilateral upper limb control and a coordinated sequence of joint sub-movements. The robotic handlebar is compact and portable and can register in a fast rate both position and forces independently from arms, including prehension forces. An impedance control system was implemented in order to promote a safer environment for human interaction and the system is able to generate force fields, suitable for implementing motor learning paradigms. The novelty of the system is the decoupling of prehension and manipulation forces of each hand, thus paving the way for the investigation of hand dominance function in a bimanual task. Experiments were conducted with ten healthy subjects, kinematic and dynamic variables were measured during a rotational set of movements. Statistical analyses showed that movement velocity decreased with practice along with an increase in reaction time. This suggests an increase of the task planning time. Prehension force decreased with practice. However, an unexpected result was that the dominant hand did not lead the bimanual task, but helped to correct the movement, suggesting different roles for each hand during a cooperative bimanual task.

Introduction: Lipedema is a chronic feminine disease that causes abnormal fat deposition in lower limbs and occasionally upper limbs. Easy bruising and pain are common. Lipedema patients suffer from both physical and psychological disability. Despite the relatively high prevalence and the impact on the quality of life, little is known about the disease. Most patients are misdiagnosed as lymphedema or obesity. The aim was to perform a non-systematic review on lipedema literature, related to diagnosis and therapy., Evidence Acquisition: A literature search was performed by three researchers, to retrieve pertinent articles in PubMed Web of Science and ResearchGate from the last 20 years. The documents were selected from systematic reviews, reviews, meta-analyses, consensus documents and guidelines, randomized controlled trials and retrospective, cohort and clinical series., Evidence Synthesis: Regarding pathophysiology, alterations are not exclusively confined to adipose tissue. Lymphatic dysfunction, cardiovascular variations, blood capillary fragility and increased permeability are common. Patients often present with neurological alterations and hormonal malfunction. Elevated cutaneous sodium has been documented. Due to the absence of a defined etiology, evidence-based research is difficult in the management of lipedema., Conclusions: The setting of realistic expectations is important for both patient and medical care provider. The major aims of the management are multimodal for improvements in the quality of life; reduction in heaviness and pain, reshaping the affected limbs, weight control, improvements in mobility. Compression garments, physical therapy, exercise regimens, diet and psychological counseling are necessities. For selected patients, surgical treatment is an added option.

The identification of specific components in EEG signals is often key when designing EEG-based brain-computer interfaces (BCIs), and a good understanding of the factors that elicit such components can be helpful when it comes to precise, energy-efficient and time-accurate actuation of exoskeletons. CNVs (Contingent Negative Variations), ERDs or ERSs (Event-Related Desynchronizations/Synchronizations) as well as ErrPs (Error-Related Potentials) are particularly important components can be identified during motor tasks and related to specific events in a Coincident Timing (CT) task. This work investigates offline EEG signals acquired during an upper limb CT task and analyzes the task protocol with the purpose of correlating the aforementioned EEG features to movement onset. CNVs and ERD/ERS were successfully identified after averaging multiple trials, and it was further concluded that complementary information about muscle activity (via EMG) as well as video tracking of arm movement play a critical role in the synchronization of EEG components with movement onset. The framework for EEG analysis presented in this paper allows for future development of a BCI on top of this CT task capable of assessing motor learning and actuating an exoskeleton to enable faster motor rehabilitation.

The use of the electrical activity from the muscles may provide a natural way to control exoskeletons or other robotic devices seamlessly. The major challenges to achieve this goal are human motor redundancy and surface electromyography (sEMG) variability. The goal of this work is to find a feature extraction and classification procedures to estimate accurately elbow angular trajectory by means of a NARX Neural Network. The processing time-step should be small enough to make it feasible its further use for online control of an exoskeleton. In order to do so we analysed the Biceps and Triceps Brachii data from an elbow flexo-extension Coincident Timing task performed in the horizontal plane. The sEMG data was pre-processed and its energy was divided in five frequency intervals that were fed to a Nonlinear Auto Regressive with Exogenous inputs (NARX) Neural Network. The estimated angular trajectory was compared with the measured one showing a high correlation between them and a RMSE error maximum of 7 degrees. The procedure presented here shows a reasonably good estimation that, after training, allows real-time implementation. In addition, the results are encouraging to include more complex tasks including the shoulder joint.

Work-related musculoskeletal disorders (MSDs) are a major concern in industries and working environments. They cause not only suffering to the employee and decrease in performance, but also high economic losses to the companies and the society. Workers from assembly lines and machine operators are one of the most frequently affected working population. Moreover, one of the main types of MSDs in occupational environments are shoulder injuries. Exoskeletons have been applied and tested in rehabilitation and they are gaining ground in occupational environments as assistive devices to augment human force and minimize loads on muscles and joints. However, more evidence about the effects of several exoskeletons models in assisting different tasks is needed. We measured shoulder muscles activity (AD - anterior deltoid and MD - medial deltoid) of seven automotive workers using the SuitX® upper limb exoskeleton while performing different screwing tasks, at different shoulder levels while handling different tools. We found significant muscle activity reduction for 2 of the 4 proposed tasks, suggesting a task-specificity effectiveness. Therefore, it seems to be a viable option to reduce muscle effort in certain tasks.

Cerebral palsy (CP) describes a group of disorders of movement, posture and balance caused by a non-progressive brain injury in the immature brain. It is the most prevalent cause of chronic motor disability in childhood, and although two thirds of CP children are able to walk, they show gait limitations. In this context, rehabilitation therapy can improve muscle balance and gait. Previous studies showed the importance of gait analysis as part of multidisciplinary tools for effective rehabilitation treatment. However, the high cost and the infrastructure required for the implementation of commercial gait analysis systems as well as the time-consuming preparation procedures, limit the access to this service. A low cost, non-restrictive, portable and of simple operation and installation system was developed based on Kinect v2 sensor. This study aims to validate it for capturing and analysing gait parameters in children with cerebral palsy. Several gait parameters from eleven CP patients with different levels of disability classified as a function of the Gross Motor Function Classification System (GMFCS) from II to III were recorded while they walked on a flat surface. The Kinect-based gait analysis system was compared with video-recording that yielded the same results. These results show the potential of Kinect to analyse gait in frail patient populations unobtrusively and with very low cost. More importantly, regarding to spatial parameters, the Kinect system was useful even for the worst case of GMFCS III that show a large gait variability with abnormal patterns.

Introduction: The effects of ageing on bone can be mitigated with different types of physical training, such as power training. However, stimuli that combine increasing external and internal loads concomitantly may improve bone quality. The goal of this study was to assess the efficacy of a combined power and plyometric training on lumbar spine and distal tibia microstructure and function. Methods: 38 sedentary elderly women between 60 and 70 years were randomly allocated in experimental (N = 21) and control group (N = 17). The effects of the 20-week protocol on lumbar spine microstructure and tibia microstructure and function were assessed by trabecular bone score (TBS), high resolution peripheral quantitative computed tomography (HR-pQCT) and microfinite element analysis. Results: when compared to the effects found in the control group, the experimental group showed significant improvements in lumbar spine TBS (Hedges' g = 0.77); and in distal tibia trabecular thickness (g = 0.82) and trabecular bone mineral density (g=0.63). Conclusion: our findings underscore the effectiveness of the proposed intervention, suggesting it as a new strategy to slow down and even reverse the structural and functional losses in the skeletal system due to ageing.

Background: Different types of sound cues have been used to adapt the human gait rhythm. We investigated whether young healthy volunteers followed subliminal metronome rhythm changes during gait., Methods: Twenty-two healthy adults walked at constant speed on a treadmill following a metronome sound cue (period 566 msec). The metronome rhythm was then either increased or decreased, without informing the subjects, at 1 msec increments or decrements to reach, respectively, a low (596 msec) or a high frequency (536 msec) plateaus. After 30 steps at one of these isochronous conditions, the rhythm returned to the original period with decrements or increments of 1 msec. Motion data were recorded with an optical measurement system to determine footfall. The relative phase between sound cue (stimulus) and foot contact (response) were compared., Results: Gait was entrained to the rhythmic auditory stimulus and subjects subconsciously adapted the step time and length to maintain treadmill speed, while following the rhythm changes. In most cases there was a lead error: the foot contact occurred before the sound cue. The mean error or the absolute mean relative phase increased during the isochronous high (536 msec) or low frequencies (596 msec)., Conclusion: These results showed that the gait period is strongly "entrained" with the first metronome rhythm while subjects still followed metronome changes with larger error. This suggests two processes: one slow-adapting, supraspinal oscillator with persistence that predicts the foot contact to occur ahead of the stimulus, and a second fast process linked to sensory inputs that adapts to the mismatch between peripheral sensory input (foot contact) and supraspinal sensory input (auditory rhythm).

There are several efforts to use the electrical signals generated by the human muscles to control virtual or even physical devices. It is expected that, the development of this method will provide a natural way to control these devices, requiring little user training, depending on the task complexity. With respect to the control of exoskeletons from the electric signals generated by the muscles, it is desirable that the exoskeleton acts in synergy with the user using surface electromyography (sEMG) signals to detect user intentions. One of the challenges of this approach is the variability of the sEMG signals due to factors such as electrode positioning and conditions of the volunteer at the time of acquisition. In previous work, a procedure based on an Autoregressive with Exogenous Input (ARX) linear model was developed to translate sEMG from biceps, triceps and brachioradialis muscles to elbow joint angle. In this work, we developed a method based on a Genetic Algorithm (GA) to update the ARX model coefficients online to minimize the training periods and we have used the EMG signals to control a one-degree of freedom exoskeleton.vThe GA was able to obtain ARX model coefficients that generate the joint angle reference from the EMG signals. In addition, the joint angle references generated from the offline sEMG from three muscles via an ARX model were used to control a device. At this point we are carrying out tests with the exoskeleton using real-time signals from sEMG.

It is well-known that acute sleep deprivation affects negatively postural control. The analysis of sleep quality during long periods and its impact on motor control and learning performance are crucial aspects of human health. Nevertheless, there is conflicting evidence regarding which postural control variables are more prone to change due to sleep deprivation. Moreover, very few clinicians have at their disposal expensive force plates to measure such variables, so the use of a low-cost portable device could be very interesting. Therefore, we aimed to identify which posture control variables, obtained from a low-cost plate, are more sensitive to sleep deprivation. In order to do so, we have performed a set of experiments with volunteers before and after a night without sleep. Eight participants took part of the study and had their balance measured by a Wii Balance Board before and after one night of sleep deprivation. They were asked to keep a quiet stance on top of the plate with their eyes open and closed, in a balanced design. The main results showed that, regardless the visual information, sleep deprivation has deepest impact on the anterior-posterior center of pressure displacement. Sleep deprivation without visual information had a more pronounced (large effect size) impact on the mean sway in the anterior-posterior direction and its distribution variation. The information that sleep deprivation has a more meaningful impact on anterior-posterior center of pressure excursion may help clinicians and healthcare professionals to better deal with its implications.

Study Design: Cross-sectional study., Background: Sleep disturbances are frequently reported by individuals with spinal cord injury (SCI) and are associated both with poor quality of life and reduced ability to participate in rehabilitation and daily life activities., Objectives: This study investigated sleep quality based on self-reports and actigraphy in individuals with SCI as compared to able-bodied. We also explored the relationship between sleep quality, physical activity, and neuropathic pain., Setting: Institute Guttmann, Neurorehabilitation Hospital, Badalona, Barcelona, Spain., Methods: Fourteen SCI patients (12 males, 43.10 ± 10.59 y.o.) and 10 healthy individuals (7 males, mean age 46.21 ± 12.58 y.o.) were enrolled in the study. Participants wore wrist actigraphs for 7 consecutive days to characterize their sleep-wake cycle, rest-activity circadian rhythm and physical activity. Sleep quality, chronotype, daytime sleepiness, neuropathic pain severity and interference were assessed based on questionnaires., Results: SCI individuals reported poorer sleep quality compared to healthy individuals. Actigraphy-based sleep measurements revealed that patients woke up later, spent more time in bed and slept longer compared to the healthy controls but did not differ significantly in the estimated sleep efficacy and number of awakenings from the able-bodied controls. In individuals with SCI greater physical activity predicted higher sleep efficacy and less awakening episodes as well as shorter sleep latency and lower sleep disturbance., Conclusions: The actigraphy-based sleep estimates indicate that patients with SCI spent more time in bed and slept longer but their sleep efficacy was similar to able-bodied controls. Maintaining regular physical activity could improve pain control and sleep quality., Competing Interests: The authors declare that they have no conflict of interest.This study was approved by the Clinical Research Ethics Committee of the Institute Guttmann and has been conducted in accordance with the Declaration of Helsinki for ethical conduct and report of research.

This paper provides an update on the neural control of bipedal walking in relation to bioinspired models and robots. It is argued that most current models or robots are based on the construct of a symmetrical central pattern generator (CPG). However, new evidence suggests that CPG functioning is basically asymmetrical with its flexor half linked more tightly to the rhythm generator. The stability of bipedal gait, which is an important problem for robots and biological systems, is also addressed. While it is not possible to determine how biological biped systems guarantee stability, robot solutions can be useful to propose new hypotheses for biology. In the second part of this review, the focus is on gait perturbations, which is an important topic in robotics in view of the frequent falls of robots when faced with perturbations. From the human physiology it is known that the initial reaction often consists of a brief interruption followed by an adequate response. For instance, the successful recovery from a trip is achieved using some basic reactions (termed elevating and lowering strategies), that depend on the phase of the step cycle of the trip occurrence. Reactions to stepping unexpectedly in a hole depend on comparing expected and real feedback. Implementation of these ideas in models and robotics starts to emerge, with the most advanced robots being able to learn how to fall safely and how to deal with complicated disturbances such as provided by walking on a split-belt.

Sleep disturbances in modern life lead to cognitive and motor performance impairments in everyday tasks such as gait. The most common symptom of these disturbances is daytime sleepiness, which can be assessed by questionnaires such as the Epworth Sleep Scale (ESS). The ESS evaluates sleep health and daytime dysfunction. The goal of this study is to assess the influence of sleepiness on a motorauditory synchrony task, rhythmed gait. High and low sleepiness clusters were formed based on the participants ESS scores. Walking on a treadmill, two different rhythmic auditory stimulus conditions were set with a metronome: isochronous and non-isochronous. Reflective markers on both heels with seven infrared cameras were used to assess the difference between footfall and metronome beep, what is named synchronization error (SE). There was a tendency to anticipate the beep in the HS group when compared to the LS group only in the non-isochronous stimulus condition that was statistically significant. Sleep disturbances that generate daytime sleepiness may bring detrimental effects on brain areas that could be responsible for the real-time adjustment of gait and sustained attention. These impairments may be responsible for the larger synchronization error with larger relative phase of the group with high sleepiness. More studies are necessary involving other parameters of sleep and gait to identify sleep disturbances through gait analysis.

This paper presents a method to estimate the elbow joint angle from surface electromyography (sEMG) measurements of biceps, triceps and brachioradialis. This estimation is of major importance for the design of human robot interfaces based on sEMG. It is also relevant to model the muscular system and to design biomimetic mechanisms. However, the processing and interpretation of electromyographic signals is challenging due to nonlinearities, unmodeled muscle dynamics, noise and interferences. In order to determine an estimation model and a calibration procedure for the model parameters, a set of experiments were carried out with six subjects. The experiments consisted of series of continuous (cyclical) and discrete elbow flexo-extensions with three different loads (i.e. 0 kg, 1.5kg and 3 kg). The sEMG data from the biceps brachii, triceps brachii and brachioradialis and the joint angle were recorded. Four different modeling techniques were evaluated: State Space (SS), Autoregressive with Exogenous Input (ARX), Autoregressive Moving-Average with Exogenous Input (ARMAX), Autoregressive Integrated Moving-Average with Exogenous Input (ARIMAX). After the model was selected, a second experiment was performed in order to validate the estimation procedure. The results show a procedure to estimate the EMG-to-angle relation with high correlation and low meansquare- root errors with respect to the measured angle data.

We assessed the impact of a common sleep disturbance, the social jetlag, on postural control during a period involving workdays and free days. The sleep habits of 30 healthy subjects were registered with a wrist actimeter for nine days (starting on Friday) and they participated in a set of four postural control tests carried out on Friday and on Monday. In addition, the subjects filled questionnaires about their sleep conditions and preferences. Actimetry measurements were used to calculate the Mid Sleep Phase (MSP). The difference between the MSP values on the workdays and free days measures the social jetlag. There were significant differences in sleep variables between workdays and free days. Postural control performance improved on Monday, after free sleep over the weekend, when compared with the tests performed on Friday. It seems that social jetlag affects brain areas involved in the control of posture, such as thalamus and the prefrontal cortex as well as the cerebellum, resulting in a worse performance in postural control. The performance improvement in the posture tests after the free days could be attributed to a lower sleep debt.

Sleep quality analysis is crucial for human health and it is related to duration, rhythm and quality. The goal of this study is to analyze objective assessment of the sleep-wake cycles with actigraphy, subjective questionnaires and their relationship with sleep quality indices. A wearable actigraph registered the sleep habits of 41 healthy subjects for 9 days. Afterwards, the subjects filled two questionnaires about sleep quality (Pittsburgh Sleep Quality Index) and sleepiness (Epworth Sleepiness Scale). The subjects were divided into two groups based on cut-off scores and the actigraphy parameters were compared between groups. Group 1 in ESS and PSQI categorization had less diurnal sleepiness and better sleep quality, respectively, than Group 2. Measurements of regularity (IS), fragmentation (IV), active phase amplitude (M10), rest amplitude (L5), and relative amplitude (RA) were compared between groups. Group 2 had higher L5 values. Parameter L5 (lowest of 5 consecutive hours of activity) was concluded to be relevant to identify the sleep conditions of the subjects.

The present study analyzes the learning in a coincident timing task with force perturbation. We aimed to verify whether a predictable load (constant spring) applied to hand movements could facilitate learning and, thus, performance improvement with respect to movements without any external load and an unpredictable load to perform a coincident timing task with a few number of repetitions (n = 28) under acquisition and transfer phases. The results showed that the group with a predictable load had a significant better performance with lower percentage of errors and smaller time variance in the acquisition and transfer phase. The groups with no load and unpredictable load had a similar performance in the transfer phase. It can be concluded that adding a predictable force to the coincident timing task results in performance improvement. Therefore, learning to reach a target at a correct time could be improved with the application of predictable external loads.

The analysis of sleep quality during long periods and its impact on motor control and learning performance are crucial aspects for human health. The aim of this study is to analyze effects of chronic sleep restriction on motor performance. It is intended to establish motor control indicators in sleep quality analysis. A wearable actigraphy that records accelerometry, ambient light, and body temperature was used to monitor the sleep habits of 12 healthy subjects for two weeks before performing motor control and learning tests. The day of the motor test, the subjects filled two questionnaires about the quality of sleep (Pittsburgh Sleep Quality Index - PSQI) and sleepiness (Epworth Sleepiness Scale - ESS). Afterwards they performed a coincident timing task that consisted of hitting a virtual target falling on the screen with the hand. An elbow flexion in the horizontal plane had to be performed on the correct time to reach the real target on a table at the same time as the virtual target on the screen. The subjects performed three sets of acquisition and transfer blocks of the coincident timing task. The subjects were clustered in two groups based on the PSQI and ESS scores. Actigraphy and motor control parameters (L5, correct responses, time variance) were compared between groups and experimental sets. The group with better sleep parameters did show a constant performance across blocks of task acquisition while the bad sleeper group improved from the first to the second acquisition block. Despite of this improvement, their performance is not better than the one of the good sleepers group. Although the number of subjects is low and it should be increased, these results indicate that the subjects with better sleep converged rapidly to a high level of performance, while the worse sleepers needed more trials to learn the task and their performance was not superior to the other group.

The lack of sleep, both in quality and quantity, is an increasing problem in modern society, often related to workload and stress. A number of studies have addressed the effects of acute (total) sleep deprivation on postural control. However, up to date, the effects of chronic sleep deficits, either in quantity or quality, have not been analyzed. Thirty healthy adults participated in the study that consisted of registering activity with a wrist actigraph for more than a week before performing a series of postural control tests. Sleep and circadian rhythm variables were correlated and the sum of activity of the least active 5-h period, L5, a rhythm variable, obtained the greater coefficient value with sleep quality variables (wake after sleep onset WASO and efficiency sleep). Cluster analysis was performed to classify subjects into two groups based on L5 (low and high). The balance tests scores used to asses postural control were measured using Biodex Balance System and were compared between the two groups with different sleep quality. The postural tests were divided into dynamic (platform tilt with eyes open, closed and cursor) and static (clinical test of sensory integration). The results showed that during the tests with eyes closed, the group with worse sleep quality had also worse postural control performance. Lack of vision impairs postural balance more deeply in subjects with chronic sleep inefficiency. Chronic poor sleep quality impairs postural control similarly to total sleep deprivation., Competing Interests: The authors have declared that no competing interests exist.

Little is known about the ability of blind people to cross obstacles after they have explored haptically their size and position. Long-term absence of vision may affect spatial cognition in the blind while their extensive experience with the use of haptic information for guidance may lead to compensation strategies. Seven blind and 7 sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed an obstacle after a haptic exploration. Blind and blindfolded subjects used different strategies to cross the obstacle. After the first 20 trials the blindfolded subjects reduced the distance between the foot and the obstacle at the toe-off instant, while the blind behaved as the subjects with full vision. Blind and blindfolded participants showed larger foot clearance than participants with vision. At foot landing the hip was more behind the foot in the blindfolded condition, while there were no differences between the blind and the vision conditions. For several parameters of the obstacle crossing task, blind people were more similar to subjects with full vision indicating that the blind subjects were able to compensate for the lack of vision.

There are several control mechanisms that contribute to keep gait stability under the presence of perturbations. For larger perturbations, responses with longer latencies produce adequate reactions to the perturbation. Latencies might be shorter, and the risk for falling might decrease provided that the reaction is adequate. It is possible that training the recovery responses through a sequence of perturbations induce some changes in the reactions. The goal of this paper is to test if the recovery response mechanisms might change during a training session with multiple perturbations. Differences in the recovery reactions executed at the beginning and at the end of a sequence of perturbations were analyzed. The latency of the burst in the Rectus Femoris (RF), measured with surface EMG (sEMG), showed a significant reduction during the course of the experimental session. When trials are repeated, subjects are able to generate a more appropriate response to the perturbations.

Lipedema is a disproportionate, symmetrical fatty swelling characterized by pain and bruising existing almost exclusively among women. We undertook a systematic review of the available literature about lipedema, given the lack of knowledge and little evidence about this disorder especially among obesity experts. Diagnosis of lipedema is usually based on clinical features. Symmetrical edema in the lower limbs with fatty deposits located to hips and thighs usually appears at puberty and often affects several members of the same family. Main disorders considered for differential diagnosis are lymphedema, obesity, lipohypertrophy and phlebedema. Treatment protocols comprise conservative (decongestive lymphatic therapy) and surgical (liposuction) approaches. Early diagnosis and treatment are mandatory for this disorder otherwise gradual enlargement of fatty deposition causes impaired mobility and further comorbidities like arthrosis and lymphatic insufficiency., (© 2012 The Authors. Clinical Obesity © 2012 International Association for the Study of Obesity.)

Background: Central cord syndrome (CCS) is considered the most common incomplete spinal cord injury (SCI). Independent ambulation was achieved in 87-97% in young patients with CCS but no gait analysis studies have been reported before in such pathology. The aim of this study was to analyze the gait characteristics of subjects with CCS and to compare the findings with a healthy age, sex and anthropomorphically matched control group (CG), walking both at a self-selected speed and at the same speed., Methods: Twelve CCS patients and a CG of twenty subjects were analyzed. Kinematic data were obtained using a three-dimensional motion analysis system with two scanner units. The CG were asked to walk at two different speeds, at a self-selected speed and at a slower one, similar to the mean gait speed previously registered in the CCS patient group. Temporal, spatial variables and kinematic variables (maximum and minimum lower limb joint angles throughout the gait cycle in each plane, along with the gait cycle instants of occurrence and the joint range of motion - ROM) were compared between the two groups walking at similar speeds., Results: The kinematic parameters were compared when both groups walked at a similar speed, given that there was a significant difference in the self-selected speeds (p < 0.05). Hip abduction and knee flexion at initial contact, as well as minimal knee flexion at stance, were larger in the CCS group (p < 0.05). However, the range of knee and ankle motion in the sagittal plane was greater in the CG group (p < 0.05). The maximal ankle plantar-flexion values in stance phase and at toe off were larger in the CG (p < 0.05)., Conclusions: The gait pattern of CCS patients showed a decrease of knee and ankle sagittal ROM during level walking and an increase in hip abduction to increase base of support. The findings of this study help to improve the understanding how CCS affects gait changes in the lower limbs.

Perturbations during human gait such as a trip or a slip can result in a fall, especially among frail populations such as the elderly. In order to recover from a trip or a stumble during gait, humans perform different types of recovery strategies. It is very useful to uncover the mechanisms of the recovery to improve training methods for populations at risk of falling. Moreover, human recovery strategies could be applied to implement controllers for bipedal robot walker, as an application of biomimetic design. A biomechanical model of the response to a trip during gait might uncover the control mechanisms underlying the different recovery strategies and the adaptation of the responses found during the execution of successive perturbation trials. This paper introduces a model of stumble in the multibody system framework. This model is used to assess different feedforward strategies to recover from a trip. First of all, normal gait patterns for the musculoskeletal system model are obtained by solving an optimal control problem. Secondly, the reference gait is perturbed by the application of forces on the swinging foot in different ways: as an instantaneous inelastic collision of the foot with an obstacle, as an impulsive horizontal force or using a force curve measured experimentally during gait perturbation experiments. The influence of the type of perturbation, the timing of the collision with respect to the gait cycle, as well as of the coefficient of restitution was investigated previously. Finally, in order to test the effects of different muscle excitation levels on the initial phases of the recovery response, several muscle excitations were added to selected muscles of the legs, thus providing a simulation of the recovery reactions. These results pave the way for future analysis and modeling of the control mechanisms of gait.

Background: Many studies have reported the benefits of Decongestive treatment in patients with breast-cancer-related lymphedema (BCRL) but few have study what are the predictive factors of response., Methods: We performed a prospective, multicenter controlled cohort study of 171 patients with BCRL to identify independent predictive factors of response to decongestive treatment (CDT). Demographic data and clinical and lymphedema characteristics were collected prospectively. The end point was the "percentage reduction in excess volume (PREV)." Volumes were measured prior and at the end of CDT. Factors associated with response (PREV) were tested in univariate and multivariate analyses using linear regression techniques., Results: Median age was 60.4 years (range 32-84); mean lymphedema chronicity 4 years [95% confidence interval (95% CI): 3.1-5.0]; mean baseline excess volume (EV) was 936 mL (95% CI: 846-1026), and mean percentage EV was 35.3% (95% CI: 32.0-38.7); compliance to bandages was good in 81.3% of patients. PREV was 71.7% (95% CI: 65.2-78.2). After univariate screening, 11 variables were found to be associated with PREV but only 4 variables were independent predictive factors of response to CDT in the multivariate analysis: Venous insufficiency, percentage of EV (the higher the EV, the lower the reduction with CDT); compliance to bandages (a good compliance improved PREV in 25%), and treatment in autumn (better results than during the rest of the year)., Conclusions: This study shows that compliance to bandages during CDT is one of the most important predictors of response. Moreover, data support the idea that more severe lymphedemas have a worse response to treatment, and it should be recommended in early stages. The association between the season of treatment and response was also very strong, so weather conditions are an additional factor that must be taken into account in further studies.

The present study examined the principles underlying inter and intralimb coordination constraints during performance of bimanual elbow-wrist movements at different cycling frequencies (from 0.75 Hz to 2.50 Hz). Participants performed eight coordination tasks that consisted of a combination of in-phase (IN) and/or anti-phase (AN) coordination modes between both elbows and wrists (interlimb), with isodirectional (Iso) or non-isodirectional (NonI) coordination modes within each limb (intralimb). As expected, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the mid-sagittal plane, had a powerful influence on the quality of global coordinative behavior both between and within limbs. When this principle was violated (i.e., when the anti-phase mode was introduced in one or both joint pairs), the non-isodirectional intralimb mode exhibited a (de)stabilizing role in coordination, which became more pronounced at higher cycling frequencies. However, pattern loss with increasing cycling frequency resulted not only in convergence toward the more stable in-phase patterns with the elbows and wrists but also to the anti-phase patterns (which were associated with directional compatibility of within-limb motions). Moreover, participants generally preserved their initial mode of coordination (either in-phase or anti-phase) in the proximal joints (i.e., elbows) while shifting from anti-phase to in-phase (or vice versa) with their distal joint pair (i.e., wrists). Taken together, these findings reflect the impact of two immanent types of symmetry in bimanual coordination: mirror-image and translational symmetry.

The evolution of joint dynamics and muscle patterning in the shoulder and elbow was studied for cyclical line drawing tasks at different frequencies, amplitudes, and orientations in the horizontal plane. Three main modes of control were identified: elbow-centered, shoulder-centered, and elbow-shoulder, each referring to the principal joints or joint combinations that were used to achieve the behavioral goals. The contribution of the shoulder joint was most prominent across the majority of movement orientations and largely paralleled changes in the dynamic (inertial) forces in the end effector (shoulder-centered control). The two joints either exchanged roles during the performance of the right diagonal movement (elbow-centered control) or shifted from a single-joint strategy to a dual-joint strategy during the performance of large amplitudes with low or medium cycling frequencies (shoulder-elbow control). These behavioral results support the existence of a modular control mode that allows the central nervous system to effectively tune motor commands to meet a broad variety of orientations, amplitudes, and frequencies. This refers to the emergence of a context-dependent control mode for the shoulder and elbow that optimizes the implementation of the underlying motor goals under a rich combination of spatial and temporal manipulations.

The present experiment addressed whether increases in corticospinal excitability following sensory stimulation with muscle tendon vibration are accompanied by reorganization of the forearm musculature representation within the primary motor cortex. Using transcranial magnetic stimulation, we mapped the corticomotor projection to the dominant flexor carpi radialis (FCR) and extensor carpi radialis brevis (ECR) muscle before and after interventional sensory stimulation obtained via muscle tendon vibration (80Hz, 60 min) to the dominant distal wrist flexor tendons. Following vibration, MEP amplitude at the optimal stimulation position, motor output area, as well as map volume, increased significantly for the ECR. None of these effects reached significance for the FCR. These results suggest that the antagonistic vibratory response (AVR), which is considered to be of cortical origin, induces a delayed facilitation of musculature that is antagonistic to the site of the directly activated Ia afferent pathways. This example demonstrates that peripheral sensory stimulation can induce lasting increases in corticospinal excitability in the absence of actual movements.

A common problem shared by accelerometers, inertial sensors and any motion measurement method based on skin-mounted sensors is the movement of the soft tissues covering the bones. The aim of this work is to propose a method for the validation of the attachment of skin-mounted sensors. A second-order (mass-spring-damper) model was proposed to characterize the behaviour of the soft tissue between the bone and the sensor. Three sets of experiments were performed. In the first one, different procedures to excite the system were evaluated to select an adequate excitation stimulus. In the second one, the selected stimulus was applied under varying attachment conditions while the third experiment was used to test the model. The heel drop was chosen as the excitation method because it showed lower variability and could discriminate between different attachment conditions. There was, in agreement with the model, a trend to increase the natural frequency of the system with decreasing accelerometer mass. An important result is the development of a standard procedure to test the bandwidth of skin-mounted inertial sensors, such as accelerometers mounted on the skin or markers heavier than a few grams.

The authors addressed the interactions between control of bimanual multijoint coordination tasks and posture. Participants (N = 6) performed 8 coordination patterns that differed in degree of complexity by using their bilateral elbows and wrists under 3 scaled motion speeds while standing on 2 force plates. Results indicated that producing complex bimanual multijoint coordinative tasks affected postural sway, thus resulting in an increase of sway activity. Behavioral as well as mechanical factors accounted for the increased disturbance in postural sway. Those findings suggest that performing complex coordination tasks disrupts postural control in normal young adults.

The number of consecutive strides that can be recorded in measurements of gait have been limited due to the number of force plates and dimensions of the measurement field. In addition, the feet are constrained to land on the force plates. A method to calculate the inverse dynamics from the motion and incomplete information from the ground reaction forces (GRF), vertical component and its application point, is presented and compared to the calculations based on force plate measurements. This method is based on the estimation of the three-dimensional GRF during walking with pressure insoles. RMS errors were lower than 20 W for knee joint power compared to those derived from force plate measurements. The errors were larger during double stance phase due to errors in the application point measured with the insoles. This method, with some technical improvement, could be implemented in new gait analysis protocols measuring several consecutive steps either on a treadmill or over ground, depending on the motion-measurement system, without constraining foot placement.

Traditionally, gait analysis has been based on normalizing the stride time to a percentage and then averaging several strides measured under the same conditions. This procedure relies on the questionable assumptions that gait is a cyclic movement with superimposed noise and that there is no variability in the timing of activation or in the angles within the stride so no rescaling occurs during the percentage conversion. However, there is a fluctuation in the timings at which the peak values occur. A typical hallmark of this time-rescaling is the increase of the joint angle standard deviation when the angular velocity increases. The goal of this paper is to present a description of gait to avoid averaging without distorting the original curves. In addition, it allows the analysis of the fluctuation between consecutive strides. In this method, it is assumed that gait is quasi-periodic. The key point is the representation of gait by a state vector that evolves in time. This state vector can be used to calculate the instantaneous period and provides a measure of the time fluctuations between strides. The sequence of states method describes a quasi-periodic movement like gait with a continuous estimate of cycle time and provides measure of the deviations between cycles.

The present study addressed the interactions between interlimb and intralimb constraints during the control of bimanual multi-joint movements. Participants performed eight coordination tasks involving bilateral shoulder-elbow (expt I) and shoulder-wrist (expt II) movements. Three principal findings were obtained. First, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the midsagittal plane, had a powerful influence on the quality of interlimb coordination. In both experiments, the accuracy and stability of inter- and/or intralimb coordination deteriorated as soon as the antiphase mode was introduced in one or both joint pairs. However, the mutual influences between bilateral distal and proximal joint pairs varied across coordination tasks and effectors. Second, the impact of intralimb coordination modes on the quality of intralimb coordination was inconsistent between adjacent (expt I) and non-adjacent joint (expt II) combinations. Third, the mode of interlimb coordination affected the quality of intralimb coordination, whereas strong support for the converse effect was not obtained. Taken together, these observations point to a hierarchical control structure whereby interlimb coordination constraints have a stronger impact on the global coordination of the system than intralimb constraints, whose impact is substantially dependent on effector and task. The finding that intralimb coordination is subordinate to interlimb coordination during the production of bimanual multi-joint coordination patterns indicates that symmetry is a major organizational principle in the neural control of complex movement.

Principal components analysis (PCA) has not been very much in vogue within the field of movement coordination even though it is useful to reduce data dimensionality and to reveal underlying data structures. Traditionally, studies of coordination between two joints have predominantly made use of relative phase analyses. This has resulted in the identification of principal constraints that govern the Central Nervous System's organization and the control of coordination patterns. However, relative phase analyses on pairwise joints have some drawbacks because they are not optimal for revealing convergent patterns among multijoint coordination modes and for unraveling generic control strategies. In this paper, we present a method to analyze multijoint coordination based on the properties of PC, more specifically the eigenvalues and eigenvectors of the covariance matrix. The comparison between relative phase analysis and PCA shows that both provide similar and consistent results, underscoring the latter technique's sensitivity to the study of coordination performance. In addition, it provides a method for automatic pattern detection as well as an index of performance for each joint within the context of the global coordination pattern. Finally, the merit of the PCA technique within the context of central pattern generators (CPG) will be discussed.

The simultaneous performance of movements involving different effectors gives rise to neural and biomechanical interactions between and within limbs. The present study addressed the role of interlimb and intralimb constraints during the control of bimanual multijoint movements. Thirteen participants performed eight tasks involving the bilateral elbows and wrists under different coordination conditions. With respect to interlimb coordination, coordination patterns referred to the in-phase and anti-phase coordination modes, involving the simultaneous timing of homologous versus non-homologous muscles, respectively. With respect to inter-segmental (intralimb) coordination, the isodirectional mode referred to simultaneous flexions and extensions in the ipsilateral wrist and elbow joints, whereas the non-isodirectional mode involved simultaneous flexion in one joint together with extension in the other joint, or vice versa. The analysis of the data focused upon measures of relative phasing between proximal and distal joints within a limb as well as between the homologous joints of both limbs. With respect to interlimb coordination, findings revealed that adoption of the in-phase mode resulted in a higher quality of interlimb coordination than the anti-phase mode. However, the mode adopted in the distal joints had a larger impact on the quality of interlimb coordination than the mode adopted in the proximal joints. More specifically, in-phase coordination of the distal joints had a positive, and anti-phase coordination a negative, influence on the global coordinative behavior of the system. Minor effects of intralimb coordination modes on interlimb coordination were observed. With respect to intralimb coordination between the ipsilateral elbow and wrist, the isodirectional mode was performed with higher stability than the non-isodirectional mode. The mode of interlimb coordination also affected the quality of intralimb coordination, such that generating anti-phase coordination patterns in the distal joints had a negative influence on the accuracy and stability of intralimb coordination. Taken together, the present findings suggest a hierarchical structure whereby interlimb coordination constraints have a stronger impact on the global coordinative behavior of the system than intralimb coordination constraints. Moreover, the global coordinative state of the system is more affected by the coordination between the distal than between the proximal joints. Overall, the findings suggest that the mirror-image symmetry constraint has a powerful influence on bimanual multijoint coordination.