Performance During Whole Body Reaching Movements Is Impaired In Hypergravity While Preserved In Microgravity

While recent findings demonstrated the importance of initial state estimates about gravity for optimized motor control, it remains unclear whether novel initial states are rapidly implemented movement planning (and control) in the same way when gravity is removed or increased. Here, we investigated the effect of microgravity and hypergravity exposure on whole-body reaching movements performed by standing subjects during parabolic flights. Reaching movements were analyzed regarding spatial accuracy (finger endpoint deviation), arm kinematics (arm angular displacement), whole-body kinematics (body bending) and EMG activity (muscular activation and synergies) of eight muscles. Results showed that kinematics and muscular activity are adjusted in microgravity allowing accurate whole-body reaching, thus confirming the perfectly scaled sensorimotor reorganization reported in previous recent studies. Contrasting with these observations, participants hardly reached the targets in 1.8g (systematic undershot). Strikingly, whole-body kinematics remained unchanged in hypergravity compared to 1g observations. Finally, while the analysis of synergies highlighted a comparable muscular organization in all gravitational contexts, our main findings revealed local muscular adjustments leading to accurate motor responses in microgravity, but not in hypergravity.

Effect of Visualization on Muscular Activation for Stability in Adolescent Ballet Students

The purpose of this study is to determine whether commonly used visualization techniques, whose results have been solely anecdotal, produce tangible, scientific results in muscular activation and improvement to ballet balances. Ballet training methods include imagery techniques however, much of this practice is solely based on the experience of the instructor and its results are anecdotal so that there are many gaps between research on imagery and dance instruction. Few published studies focus on the effect of the imagery training for dance students on either motor and nonmotor outcomes (Abraham, 2019). A survey will be administered to ballet instructors to determine the most used visualization cues for stability. Three adolescent female ballet students studying under said instructors will be asked to perform three balances. Surface electromyography data will be taken on the gluteus maximus, hip adductors, and abdominal oblique. The length of balance will also be taken. The dancers will then be exposed to a short visualization session or stimulus of anatomical images with arrows showing bodily adjustments and targeted muscles accompanied by verbal cues developed based on the instructor techniques from the survey. The same balances and data will be taken following the session. Results will be compared to the control data taken prior to the session to reveal whether the visualization training had significant results by determining statistically significant changes in balance times and changes in neuron spikes following spike analysis. Dancers will also be asked for qualitative feedback. Subject 2 yielded a significant increase in length of balance in all three types and the most consistent increase in neuron spikes in all of their muscles. This suggests a positive correlation between an increase in the degree of neuron activation or recruitment of those stability muscles and the ability for an individual to balance. This was also supported by increased confidence they felt in their balances after the visualization session. Subject 1 yielded no significant change in balance time before and after the visualization stimulus and the number of neuron spikes decreased after the session. This suggests that decreased activity in the tested muscles for stability resulted in lower balance times. This lack of muscular activation could be attributed to fatigue as reported by the dancer. The rest of the balances yielded significant increases in lengths of balance which were accompanied by increases in neuron spikes in the gluteus maximus and hip adductors for Degage a la Seconde and in the gluteus maximus for Releve en Retire. Subject 3 yielded insignificant changes in balance times for the first two types of balances but produced increases in the number of neuron spikes in most of the tested muscles in all of the balances. Reports from the dancer of being “less wobbly” the unexpected data to be attributed to an allocation to quality of the balance. The results on length of balances, number of neuron spikes, and confidence/reflection feedback obtained by this study supports the scientific validity of commonly-used visualization techniques in ballet by showcasing a higher degree of activation in the targeted stability muscles and longer average balance lengths should ensue following visualization training. Results also suggest that visualization techniques and stimuli for stability are the most effective when applied to learning unfamiliar movements. Further research could apply such visualization techniques to other movements, and even outside of dance.

Neck Active Movements Assessment in Women with Episodic and Chronic Migraine

We aimed to compare movement parameters and muscle activity during active cervical spine movements between women with episodic or chronic migraine and asymptomatic control. We also assessed the correlations between cervical movement measures with neck-related disability and kinesiophobia. Women with episodic (n = 27; EM) or chronic (n = 27; CM) migraine and headache-free controls (n = 27; CG) performed active cervical movements. Cervical range of motion, angular velocity, and percentage of muscular activation were calculated in a blinded fashion. Compared to CG, the EM and CM groups presented a reduced total range of motion (p < 0.05). Reduced mean angular velocity of cervical movement was also observed in both EM and CM compared to CG (p < 0.05). Total cervical range of motion and mean angular velocity showed weak correlations with disability (r = −0.25 and −0.30, respectively; p < 0.05) and weak-to-moderate correlations with kinesiophobia (r = −0.30 and −0.40, respectively; p < 0.05). No significant correlation was observed between headache features and total cervical range of motion or mean angular velocity (p > 0.05). No differences in the percentage of activation of both flexors and extensors cervical muscles during active neck movements were seen (p > 0.05). In conclusion, episodic and chronic migraines were associated with less mobility and less velocity of neck movements, without differences within muscle activity. Neck disability and kinesiophobia are negative and weakly associated with cervical movement.

Assist-As-Needed Exoskeleton for Hand Joint Rehabilitation Based on Muscle Effort Detection

Robotic-assisted systems have gained significant traction in post-stroke therapies to support rehabilitation, since these systems can provide high-intensity and high-frequency treatment while allowing accurate motion-control over the patient’s progress. In this paper, we tackle how to provide active support through a robotic-assisted exoskeleton by developing a novel closed-loop architecture that continually measures electromyographic signals (EMG), in order to adjust the assistance given by the exoskeleton. We used EMG signals acquired from four patients with post-stroke hand impairments for training machine learning models used to characterize muscle effort by classifying three muscular condition levels based on contraction strength, co-activation, and muscular activation measurements. The proposed closed-loop system takes into account the EMG muscle effort to modulate the exoskeleton velocity during the rehabilitation therapy. Experimental results indicate the maximum variation on velocity was 0.7 mm/s, while the proposed control system effectively modulated the movements of the exoskeleton based on the EMG readings, keeping a reference tracking error <5%.

A Human-Robot Cooperative and Personalized Compliant Joint Controller for Upper-Limb Rehabilitation Robots: The Elbow Joint Validation

Background: Appropriate training modalities for post-stroke upper-limb rehabilitation are key features for effective recovery after the acute event. This work presents a novel human-robot cooperative control framework that promotes compliant motion and renders different high-level human-robot interaction rehabilitation modalities under a unified low-level control scheme. Methods: The presented control law is based on a loadcell-based impedance controller provided with positive-feedback compensation terms for disturbances rejection and dynamics compensation. We developed an elbow flexion-extension experimental setup, and we conducted experiments to evaluate the controller performances. Seven high-level modalities, characterized by different levels of (i) impedance-based corrective assistance, (ii) weight counterbalance assistance, and (iii) resistance, have been defined and tested with 14 healthy volunteers.Results: The unified controller demonstrated suitability to promote good transparency and render compliant and high-impedance behavior at the joint. Superficial electromyography results showed different muscular activation patterns according to the rehabilitation modalities. Results suggested to avoid weight counterbalance assistance, since it could induce different motor relearning with respect to purely impedance-based corrective strategies. Conclusion: We proved that the proposed control framework could implement different physical human-robot interaction modalities and promote the assist-as-needed paradigm, helping the user to accomplish the task, while maintaining physiological muscular activation patterns. Future insights involve the extension to multiple degrees of freedom robots and the investigation of an adaptation control law that makes the controller learn and adapt in a therapist-like manner.

Quasi-Passive Resistive Exosuit for Space Activities: Proof of Concept

The limits of space travel are continuously evolving, and this creates increasingly extreme challenges for the crew’s health that must be addressed by the scientific community. Long-term exposure to micro-gravity, during orbital flights, contributes to muscle strength degradation and increases bone density loss. In recent years, several exercise devices have been developed to counteract the negative health effects of zero-gravity on astronauts. However, the relatively large size of these devices, the need for a dedicated space and the exercise time-frame for each astronaut, does not make these devices the best choice for future long range exploration missions. This paper presents a quasi-passive exosuit to provide muscle training using a small, portable, proprioceptive device. The exosuit promotes continuous exercise, by resisting the user’s motion, during routine all-day activity. This study assesses the effectiveness of the resistive exosuit by evaluating its effects on muscular endurance during a terrestrial walking task. The experimental assessment on biceps femoris and vastus lateralis, shows a mean increase in muscular activation of about 97.8% during five repetitions of 3 min walking task at 3 km/h. The power frequency analysis shows an increase in muscular fatigue with a reduction of EMG median frequency of about 15.4% for the studied muscles.

A cross-species neural integration of gravity for motor optimization

Recent kinematic results, combined with model simulations, have provided support for the hypothesis that the human brain shapes motor patterns that use gravity effects to minimize muscle effort. Because many different muscular activation patterns can give rise to the same trajectory, here, we specifically investigate gravity-related movement properties by analyzing muscular activation patterns during single-degree-of-freedom arm movements in various directions. Using a well-known decomposition method of tonic and phasic electromyographic activities, we demonstrate that phasic electromyograms (EMGs) present systematic negative phases. This negativity reveals the optimal motor plan’s neural signature, where the motor system harvests the mechanical effects of gravity to accelerate downward and decelerate upward movements, thereby saving muscle effort. We compare experimental findings in humans to monkeys, generalizing the Effort-optimization strategy across species.

Influence of Visual Information and Sex on Postural Control in Children Aged 6–12 Years Assessed with Accelerometric Technology

The performance of postural control is believed to be linked to how children use available sensory stimuli to produce adequate muscular activation. Therefore, the aim of the present study was to thoroughly explore postural stability under normal conditions and without visual information in postural control in children aged 6–12 years during static single-leg support. A descriptive cross-sectional study was conducted with 316 children (girls = 158). The analyzed variables were the mean and maximum values obtained in each of the three body axes and their root mean square during two static single-leg support tests: one with eyes open and one with eyes closed. Girls showed lower magnitudes in the recorded accelerations at all ages and in all the variables of both tests. Accelerations during the tests showed progressively lower values from 6 to 12 years of age. The sex had a significant influence on the magnitude obtained in the accelerations recorded during the tests. Improvements in balance with increasing age were greater with visual information than without visual information. The tests of single-leg support showed preferential sensorimotor strategies in boys and girls: boys tend to rely more on visual inputs, and girls process somesthetic information in a preferential way.