Mesencephalic Locomotor Region and Presynaptic Inhibition during Anticipatory Postural Adjustments in People with Parkinson's Disease.

Individuals with Parkinson's disease (PD) and freezing of gait (FOG) have a loss of presynaptic inhibition (PSI) during anticipatory postural adjustments (APAs) for step initiation. The mesencephalic locomotor region (MLR) has connections to the reticulospinal tract that mediates inhibitory interneurons responsible for modulating PSI and APAs. Here, we hypothesized that MLR activity during step initiation would explain the loss of PSI during APAs for step initiation in FOG (freezers). Freezers (n = 34) were assessed in the ON-medication state. We assessed the beta of blood oxygenation level-dependent signal change of areas known to initiate and pace gait (e.g., MLR) during a functional magnetic resonance imaging protocol of an APA task. In addition, we assessed the PSI of the soleus muscle during APA for step initiation, and clinical (e.g., disease duration) and behavioral (e.g., FOG severity and APA amplitude for step initiation) variables. A linear multiple regression model showed that MLR activity (R2 = 0.32, p = 0.0006) and APA amplitude (R2 = 0.13, p = 0.0097) explained together 45% of the loss of PSI during step initiation in freezers. Decreased MLR activity during a simulated APA task is related to a higher loss of PSI during APA for step initiation. Deficits in central and spinal inhibitions during APA may be related to FOG pathophysiology.

Extroversion-Related Differences in Gaze Behavior during a Computer Task for Assessing Speed-Accuracy Trade-Off: Implications for Sensor-Based Applications.

The principle of Fitts' law explains that the difficulty of movement increases when targets are farther away and narrower in width, particularly when touching two parallel targets as quickly as possible. Understanding the differences in motor and gaze behaviors between extroverts and introverts when performing tasks that require speed and accuracy is crucial for the development of sensor-based interfaces for games and rehabilitation. This study aimed to investigate such differences in a computer task that assesses the speed-accuracy trade-off (Fitts' task). Twenty introverts and seventeen extroverts wore an eye tracker and an accelerometer attached to their hand while performing 12 trials through six levels of difficulty presented on a computer screen. The results showed that introverts had longer visual fixations at the higher difficulty levels and reduced pupil diameter variability when difficulty was intermediate, suggesting that their gaze behavior may be different from that of extroverts. However, no significant differences were found in the speed and accuracy performance or kinematic variables between extroverts and introverts. These findings have important implications for the design of interventions that require both speed and accuracy in movement, such as in the development of virtual reality/games for rehabilitation purposes. It is important to consider individual differences in motor and gaze behaviors, particularly in those who may struggle with longer visual fixations, for the design of sensor-based applications and to promote successful interventions and recovery.

Exacerbating patellofemoral pain alters trunk and lower limb coordination patterns and hip-knee mechanics.

The exacerbation of patellofemoral pain (PFP) may lead to compensatory trunk and lower limb movement patterns in order to minimize patellofemoral joint loading. However, joint kinematics are often analysed in isolation, which limits the understanding of how the underlying segments were coordinated to produce limb postures and distribute load across the limb. In this study we used a dynamical systems approach to investigate how women with PFP coordinate trunk, hip, and knee motion and distribute hip-knee moment demands following symptom exacerbation. Coordination patterns and coordination variability of the trunk, hip, and knee from 61 women with PFP were obtained during stair descent, ascent, and step down tasks, before and after a pain exacerbation protocol. Hip-knee extensor moment impulse ratio was also calculated. Following the exacerbation of PFP, women utilized knee dominant coordination patterns less often (p = 0.039-0.027; d = 0.51-0.53), while coordination patterns with the trunk leaning forward were utilized more during stair negotiation (p = 0.043-<0.001; d = 0.52-0.96). Although no significant differences in hip-knee coordination patterns were found, there was an increase in the hip-knee impulse ratio during stair negotiation (p = 0.014-<0.001; d = 0.27-0.36). These findings seem to display a movement strategy utilized by women with PFP in order to distribute more load to the hip joint and less to the knee joint, possibly in an attempt to avoid/manage pain.

Effects of light finger touch on the regularity of center-of-pressure fluctuations during quiet bipedal and single-leg postural tasks.

BACKGROUND: The use of extra sources of sensory information associated with light fingertip touch to enhance postural steadiness has been associated with increased attentional demands, whereas the regularity of center of pressure (COP) fluctuations has been interpreted as a marker of the amount of attention invested in posture control. RESEARCH QUESTION: This study addressed whether increased attentional demands associated with postural tasks involving light finger touch might be reflected by measures of COP regularity. METHODS: The experiments involved quiet bipedal stance (n = 8 participants) and single-legged stance (n = 14 participants). Each participant was instructed to stand as quietly as possible on a force plate, either touching an external rigid surface (applied force < 1 N, light touch condition), or not (no touch condition). Postural steadiness was assessed by traditional COP measurements (COP Area, RMS, and velocity), whereas the regularity of postural sway was based on estimates of the sample entropy (SaEn) of the COP time series. RESULTS: Traditional parameters of postural sway and COP regularity (inversely related to SaEn COP measurements) were reduced during the touch conditions as compared to the no-touch conditions, for both bipedal quiet stance and single-legged stance. Decreased COP regularity with light touch was mainly reflected in the direction of the largest postural sway (i.e. in the sagittal plane for bipedal stance and in the frontal plane for single-legged stance). SIGNIFICANCE: The present results suggest that actively touching an external surface with the fingertip, besides increasing postural steadiness, generated an externally oriented (presumably cognitive-dependent) focus of attention, so that participants invested less attention on the postural task per se (as suggested by increased SaEn), which might be associated with a more "automatic" control of posture.

Effects of Fatigue on Postural Sway and Electromyography Modulation in Young Expert Acrobatic Gymnasts and Healthy Non-trained Controls During Unipedal Stance.

This study investigated whether expert acrobatic gymnasts respond differentially than their non-trained counterparts during a single-legged stance task performed before and after a protocol designed to induce fatigue in the ankle plantarflexor muscles in terms of (a) postural steadiness and (b) electromyography (EMG) activation. We hypothesized that neuromuscular adaptation due to training would lead to different behavior of center of pressure (COP) and EMG quantifiers after fatigue. Twenty eight female volunteers (aged 11 to 24 years) formed two groups: expert acrobatic gymnastics athletes (GYN, n = 14) and age-matched non-gymnasts [control (CTRL), n = 14]. Fatigue of the ankle plantarflexors (dominant leg) was induced by a sustained posture (standing on the toes) until exhaustion. Traditional COP parameters (area, RMS, mean velocity, and power spectrum at low and high frequency ranges) were obtained with a force plate, and time and frequency-domain EMG parameters were obtained by surface electrodes positioned on the tibialis anterior, soleus, lateral gastrocnemius, medial gastrocnemius, vastus lateralis, biceps femoris, spinal erector and rectus abdominis muscles. The main results showed that fatigue induced a significant increase in postural oscillations in the ML axis (including RMS, velocity and frequency components of the power spectrum), with no significant effects in the AP axis. In terms of postural sway parameters (i.e., COP quantifiers), no superior balance stability was found for the GYN group as compared to CTRL, irrespective of the fatigue condition. On the other hand, the modulation of EMG parameters (in both time and frequency domains) indicated that expert acrobatic gymnastics athletes (as compared to healthy untrained matched controls) used different neuromuscular control strategies to keep their postures on single-legged quiet standing after the fatiguing protocol. The present results improve our knowledge of the mechanisms behind the interplay between fatigue and postural performance associated with the neuromuscular adaptations induced by sport practice. The design of gymnastics training might consider strategies aimed at improving the performance of specific muscles (i.e., tibialis anterior, soleus, biceps femoris, spinal erector) for which particular activation patterns were used by the acrobatic gymnastics to control single-legged quiet standing.

Can Individuals Poststroke Improve Their Performance in Reaction and Movement Times in a Nonimmersive Serious Game with Practice? A Cross-Sectional Study.

Objective: To verify if individuals' poststroke and healthy controls would improve their performance in reaction and movement times practicing a serious game task using the upper limb movements. Materials and Methods: We evaluated 30 individuals poststroke and 30 healthy controls, matched for age and sex. We used the "Association Game for Rehabilitation" (AGaR) where participants played by matching a pair of images whose meanings were similar. Hand movements were captured by a Kinect system and poststroke participants used their nonparetic upper limb. Reaction time and movement times (time to select an image and movement time to the target) were measured. Data were analyzed using multiple analysis of variance. Results: Performance improved for both groups across all variables with better performance in movement times than reaction time only for poststroke individuals. Conclusions: Upper limb movements using nonimmersive serious games enhanced motor performance in reaction and movement times for healthy controls and individuals poststroke. ReBEC Trial Registration: RBR-4m4pk; Registeted on 08/24/2018.

Relationship between vastus medialis Hoffmann reflex excitability and knee extension biomechanics during different tasks in women with patellofemoral pain.

BACKGROUND: Impaired knee extension biomechanics and spinal excitability have been reported in women with patellofemoral pain, but their relationship has not been explored. A significant relationship between them could indicate the need for investigating the potential benefits of disinhibitory interventions for women with patellofemoral pain. Thus, this study aimed to investigate the relationship between vastus medialis Hoffmann reflex and (1) maximal isometric, concentric and eccentric knee extensor strength and rate of torque development; (2) knee extensor torque steadiness; and (3) knee extensor moment during functional tasks; in women with patellofemoral pain. METHODS: Spinal excitability of twenty-four participants was assessed by the amplitude of maximal vastus medialis Hoffmann reflex. Knee extensor strength, rate of torque development and torque steadiness were assessed using an isokinetic dynamometer. Knee extensor moment during step-down and stair descent tasks were obtained using a three-dimensional motion analysis system. FINDINGS: A moderate negative relationship was found between vastus medialis Hoffmann reflex and knee extensor torque steadiness (r = -0.35; p = 0.05); whereas a moderate positive relationship was found with maximal isometric knee extensor strength (r = 0.37; p = 0.044). No significant relationships were found between vastus medialis Hoffmann reflex and the other variables. INTERPRETATION: Our findings provide insight on the relationship between spinal excitability and neuromuscular control of maximal and submaximal isometric torque production in women with patellofemoral pain. Conversely, spinal excitability does not seem to be related with dynamic torques and moments of the knee extensors in women with patellofemoral pain.

Age-Related Changes in Presynaptic Inhibition During Gait Initiation.

Age-related changes in presynaptic inhibition (PSI) have not been observed during gait initiation, which requires anticipatory postural adjustment (APA). As APA is centrally modulated and is impaired in older compared to young adults, here we aimed to study the presynaptic control and co-contraction levels in the ankle muscles during gait initiation in older compared to young adults. Fifteen older (age range 65-80 years) and 15 young adults (age range 19-30 years) performed a gait initiation task on a force platform under 3 conditions: (i) without electrical stimulation; (ii) test Hoffman reflex (H-reflex); and (iii) conditioned H-reflex. H-reflexes were evoked on the soleus muscle when the APA amplitude exceeded 10%-20% of the average baseline mediolateral force. Participants also performed quiet stance as a control task. Results showed that both age groups presented similar PSI levels during quiet stance (p = .941), while in the gait initiation older adults presented higher PSI levels, longer duration, and lower amplitude of APA than young adults (p < .05). Older adults presented higher co-contraction ratio in both tasks than young adults (p < .05). Correlations between the PSI levels and the APA amplitude (r = -0.61, p = .008), and between the PSI levels and the co-contraction ratio during gait initiation (r = -0.64, p = .005) were found for older adults only. APA amplitude explained 49% of the variance of the PSI levels (p = .003). Our findings suggest that older compared to young adults have increased presynaptic control to compensate for the decreased supraspinal modulation on impaired APAs during gait initiation.

Influence of the exacerbation of patellofemoral pain on trunk kinematics and lower limb mechanics during stair negotiation.

BACKGROUND: Although it is assumed that the presence of patellofemoral pain (PFP) may result in compensatory behaviors that can alter trunk kinematics and lower limb mechanics, the influence of the exacerbation of patellofemoral pain on trunk kinematics and lower limb mechanics during stair negotiation has not been established. RESEARCH QUESTION: Does the exacerbation of PFP symptoms lead to altered trunk kinematics and lower limb mechanics during stair negotiation? METHODS: Three-dimensional kinematics and kinetics were obtained from 45 women with PFP during stair descent and ascent. Data were obtained before and after a pain exacerbation protocol. The variables of interest were peak trunk, hip, and knee flexion, and ankle dorsiflexion; peak hip, and knee extensor, and ankle plantarflexor moments. Paired t-tests were used to compare the variables of interest before and after pain exacerbation. RESULTS: Following pain exacerbation, there was a decrease in peak knee extensor moment during stair descent (Effect size = -0.68; p = 0.01) and stair ascent (Effect size = -0.56; p = 0.02); as well as in peak ankle dorsiflexion during stair descent (Effect size = -0.33; p = 0.01) and stair ascent (Effect size = -0.30; p = 0.01). An increase in ankle plantarflexor moment during stair descent (Effect size = 0.79; p < 0.01) and stair ascent (Effect size = 0.89; p < 0.01) was also observed. No significant differences were observed for peak trunk, hip, and knee flexion or hip extensor moment (p > 0.05). SIGNIFICANCE: Our findings show compensatory strategies used by people with PFP in response to symptoms exacerbation that may have a negative impact on knee and ankle mechanics. Our findings also suggest that people with PFP do not seem to change their trunk, hip, and knee flexion or hip extensor moment during stair negotiation in response to symptom exacerbation.

Effect of Contextual Interference in the Practicing of a Computer Task in Individuals Poststroke.

OBJECTIVES: Sensory and motor alterations resulting from stroke often impair the performance and learning of motor skills. The present study is aimed at investigating whether and how poststroke individuals and age- and sex-matched healthy controls benefit from a contextual interference effect on the practice of a maze task (i.e., constant vs. random practice) performed on the computer. METHODS: Participants included 21 poststroke individuals and 21 healthy controls, matched by sex and age (30 to 80 years). Both groups were divided according to the type of the practice (constant or random) presented in the acquisition phase of the learning protocol. For comparison between the groups, types of practice, and blocks of attempts, the analysis of variance with Tukey's post hoc test (p < 0.05) was used. RESULTS: Poststroke individuals presented longer movement times as compared with the control group. In addition, only poststroke individuals who performed the task with random practice showed improved performance at the transfer phase. Moreover, randomized practice enabled poststroke individuals to perform the transfer task similarly to individuals without any neurological impairment. CONCLUSION: The present findings indicated a significant effect of contextual interference of practice in poststroke individuals, suggesting that applying randomized training must be considered when designing rehabilitation protocols for this population.

Effectiveness of anodal transcranial direct current stimulation to improve muscle strength and motor functionality after incomplete spinal cord injury: a systematic review and meta-analysis.

STUDY DESIGN: Systematic review and meta-analysis. OBJECTIVES: We aimed to investigate the effects of anodal transcranial direct current stimulation (tDCS) against sham on muscle strength and motor functionality after incomplete spinal cord injury (iSCI). SETTING: University of São Paulo, Brazil. METHODS: A preplanned protocol was registered (PROSPERO, CRD42016050444). Pubmed, Embase, Web of Science, Cochrane Central Library and BVS databases were searched independently by two authors up to March 2018. Cochrane Collaboration's Tool was used for the risk of bias assessments. Generic inverse variance and random-effects model were used to calculate pooled effect sizes (ES), 95% confidence intervals (CIs) and p-values in meta-analyses. RESULTS: Six randomized clinical trials met inclusion criteria (n = 78 iSCI individuals) and were included in the meta-analysis. Results showed a marginal significant pooled effect of active tDCS in improving motor functionality with a small ES (SMD = 0.26, 95% CI = -0.00 to 0.53, p = 0.05, I2 = 0%). On the other hand, the pooled effect of active tDCS on muscle strength did not reach statistical significance, in parallel with a small ES (SMD = 0.35, 95% CI = -0.21 to 0.92, p = 0.22, I2 = 0%) when compared with sham tDCS. No significant adverse events were reported. CONCLUSIONS: Overall, there was a significant effect of tDCS in improving motor functionality following iSCI. However, a small ES and the marginal p-value suggest that these results should be interpreted with caution. Further high-quality clinical trials are needed to support or refute the use of tDCS in daily clinical practice.

Loss of presynaptic inhibition for step initiation in parkinsonian individuals with freezing of gait.

KEY POINTS: Individuals with freezing of gait (FoG) due to Parkinson's disease (PD) have small and long anticipatory postural adjustments (APAs) associated with delayed step initiation. Individuals with FoG ('freezers') may require functional reorganization of spinal mechanisms to perform APAs due to supraspinal dysfunction. As presynaptic inhibition (PSI) is centrally modulated to allow execution of supraspinal motor commands, it may be deficient in freezers during APAs. We show that freezers presented PSI in quiet stance (control task), but they presented loss of PSI (i.e. higher ratio of the conditioned H-reflex relative to the test H-reflex) during APAs before step initiation (functional task), whereas non-freezers and healthy control individuals presented PSI in both the tasks. The loss of PSI in freezers was associated with both small APA amplitudes and FoG severity. We hypothesize that loss of PSI during APAs for step initiation in freezers may be due to FoG. ABSTRACT: Freezing of gait (FoG) in Parkinson's disease involves deficient anticipatory postural adjustments (APAs), resulting in a cessation of step initiation due to supraspinal dysfunction. Individuals with FoG ('freezers') may require functional reorganization of spinal mechanisms to perform APAs. As presynaptic inhibition (PSI) is centrally modulated to allow execution of supraspinal motor commands, here we hypothesized a loss of PSI in freezers during APA for step initiation, which would be associated with FoG severity. Seventy individuals [27 freezers, 22 non-freezers, and 21 age-matched healthy controls (HC)] performed a 'GO'-commanded step initiation task on a force platform under three conditions: (1) without electrical stimulation, (2) test Hoffman reflex (H-reflex) and (3) conditioned H-reflex. They also performed a control task (quiet stance). In the step initiation task, the H-reflexes were evoked on the soleus muscle when the amplitude of the APA exceeded 10-20% of the mean baseline mediolateral force. PSI was quantified by the ratio of the conditioned H-reflex relative to the test H-reflex in both the tasks. Objective assessment of FoG severity (FoG-ratio) was performed. Freezers presented lower PSI levels during quiet stance than non-freezers and HC (P < 0.05). During step initiation, freezers presented loss of PSI and lower APA amplitudes than non-freezers and HC (P < 0.05). Significant correlations were only found for freezers between loss of PSI and FoG-ratio (r = 0.59, P = 0.0005) and loss of PSI and APA amplitude (r = -0.35, P < 0.036). Our findings suggest that loss of PSI for step initiation in freezers may be due to FoG.

Motor learning and transfer between real and virtual environments in young people with autism spectrum disorder: A prospective randomized cross over controlled trial.

Autism spectrum disorder (ASD) is associated with persistent deficits in social communication and social interaction, including impaired multisensory integration, which might negatively impact cognitive and motor skill performance, and hence negatively affect learning of tasks. Considering that tasks in virtual environment may provide an engaging tool as adjuncts to conventional therapies, we set out to compare motor performance between young people with ASD and a typically developing (TD) control group that underwent coincident timing tasks based on Kinect (no physical contact) and on Keyboard (with physical contact) environments. Using a randomized repeated cross-over controlled trial design, 50 young people with ASD and 50 with TD, matched by age and sex were divided into subgroups of 25 people that performed the two first phases of the study (acquisition and retention) on the same device-real or virtual-and then switched to the other device to repeat acquisition and retention phases and finally switched on to a touch screen (transfer phase). Results showed that practice in the virtual task was more difficult (producing more errors), but led to a better performance in the subsequent practice in the real task, with more pronounced improvement in the ASD as compared to the TD group. It can be concluded that the ASD group managed to transfer the practice from a virtual to a real environment, indicating that virtual methods may enhance learning of motor and cognitive skills. A need for further exploration of its effect across a number of tasks and activities is warranted. Autism Res 2020, 13: 307-319. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Individuals with autism spectrum disorder are known to have difficulties with learning motor tasks. Considering that performing motor tasks in virtual environment may be an engaging tool as adjuncts to conventional therapies, we aimed to estimate performance in tasks regardless of physical touch. Results showed that participants had more difficulty using the non-touch task; however, virtual training improved performance on the physical (real) task. This result indicates that virtual methods could be a promising therapeutic approach for the ASD population.

Physiological demands of archery: effect of experience level / Demandas fisiológicas do tiro com arco: efeito do nível de experiência

Abstract The understanding of fatigue development during Archery competition would guide sports scientists, coaches and athletes on how to optimize the training routines of athletes from different competitive levels. This study investigated the effect of expertise level on physiological responses, during simulated archery competition (double-round 70m, 12 series, 6 arrows for an elite Brazilian Archer (EA) and a Novice Archer (NA). Ratings of perceived exertion, blood lactate and glucose, handgrip strength and electromyography were registered at the beginning, after each set from the 2nd to the 12tharrow and, 30-min after the competition simulation. The EA showed a greater handgrip strength for both arms, a constant lower mean RMS value (Baseline 0.279V and 12th set 0.221V, -20.7%), and a stable MF value throughout the competition (Baseline 146Hz to 12th set 140Hz). The NA showed a smaller handgrip strength, an increase in RMS after the 6th set towards the end of the competition (Baseline 0.387V, 6th 0.576V, and 12th set 0.720V, +46.2%) and a minor decrease in MF from the 6th to the end of 12th set (2nd set 122Hz, 4th set 127Hz, 6th set 112Hz and 12th set 117Hz, - 4.1%). In summary, all the fatigue-related markers showed a mild response to the Archery competition simulation, although a greater magnitude was observed in the NA, compared to the EA. This study reported the physiologic demands of an Archery simulated competition, in an official format, allowing coaches and sport scientists to draw more confident decisions on competition strategy and training design.

Resumo O entendimento da fadiga durante a competição de Tiro com Arco pode auxiliar na otimização da rotina de treinamento de atletas em diferentes níveis competitivos. Este estudo investigou o efeito do nível de experiência do atleta sobre as respostas fisiológicas, durante competição simulada de Tiro com Arco para um atleta de elite (EA) e um arqueiro iniciante (NA). Esforço percebido, concentração de lactato e glicose sanguínea, força de preensão manual e eletromiografia foram registrados no início, após cada série e, 30-min após a simulação. O EA apresentou maior força de preensão manual para ambos braços, valor de média RMS constantemente mais baixo (Baseline 0,279V e 12ª série 0,221V, -20,7%), e valor de MF estável no decorrer da competição (Baseline 146Hz a 12a série 140Hz). O NA demonstrou menor força de preensão manual, aumento na RMS após a 6a série até o final da competição (Baseline 0,387V, 6a 0,576V, and 12a série 0,720V, +46,2%) e pequena diminuição na MF da 6ª até o final da 12ª série (2a série 122Hz, 4a série 127Hz, 6a série 112Hz e 12a série 117Hz, - 4,1%). Assim, todos os marcadores relacionados a fadiga apresentaram resposta discreta na simulação de competição de Tiro com Arco, com maior magnitude no NA, em comparação com EA. Este estudo apresentou as demandas fisiológicas da competição simulada de Tiro com Arco, no formato oficial, permitindo que treinadores e cientistas do esporte possam tomar decisões com maior confiança sobre estratégias de competição e treinamento.

Efficacy of Virtual Reality Rehabilitation after Spinal Cord Injury: A Systematic Review.

BACKGROUND: Spinal cord injury (SCI) is often associated with long-term impairments related to functional limitations in the sensorimotor system. The use of virtual reality (VR) technology may lead to increased motivation and engagement, besides allowing a wide range of possible tasks/exercises to be implemented in rehabilitation programs. The present review aims to investigate the possible benefits and efficacy of VR-based rehabilitation in individuals with SCI. METHODS: An electronically systematic search was performed in multiple databases (PubMed, BVS, Web of Science, Cochrane Central, and Scielo) up to May 2019. MESH terms and keywords were combined in a search strategy. Two reviewers independently selected the studies in accordance with eligibility criteria. The PEDro scale was used to score the methodological quality and risk of bias of the selected studies. RESULTS: Twenty-five studies (including 482 participants, 47.6 ± 9.5 years, 73% male) were selected and discussed. Overall, the studies used VR devices in different rehabilitation protocols to improve motor function, driving skills, balance, aerobic function, and pain level, as well as psychological and motivational aspects. A large amount of heterogeneity was observed as to the study design, VR protocols, and outcome measures used. Only seven studies (28%) had an excellent/good quality of evidence. However, substantial evidence for significant positive effects associated with VR therapy was found in most of the studies (88%), with no adverse events (88%) being reported. CONCLUSION: Although the current evidence is limited, the findings suggest that VR-based rehabilitation in subjects with SCI may lead to positive effects on aerobic function, balance, pain level, and motor function recovery besides improving psychological/motivational aspects. Further high-quality studies are needed to provide a guideline to clinical practice and to draw robust conclusions about the potential benefits of VR therapy for SCI patients. Protocol details are registered on PROSPERO (registration number: CRD42016052629).

Association Between Plantarflexion Torque Variability In Quiet Stance And During Force And Position Tasks.

This study examined the association between plantarflexion torque variability during quiet bipedal standing (QS) and during plantarflexion force- and position-matching tasks (FT and PT, respectively). In QS, participants stood still over a force plate, and the mean plantarflexion torque level exerted by each subject in QS (divided by 2 to give the torque due to a single leg) served as the target torque level for right leg FT and PT (performed with the participants seated with their right knee fully extended). During FT participants controlled the force level exerted by the foot against a rigid restraint, while during PT they controlled the angular position of the ankle when sustaining equivalent inertial loads. Standard deviation (SD) of plantarflexion torque was computed from torque signals acquired during periods with and without visual feedback. Significant correlations were found between plantarflexion torque variability in QS and FT (r = 0.8615, p < 0.0001 and r = 0.8838, p = 0.0003 for visual and no visual conditions, respectively) as well as between QS and PT (r = 0.8046, p = 0.003 and r = 0.7332, p = 0.0103 for visual and no visual conditions, respectively), regardless of vision availability. No significant differences were found between the correlations for Qs vs FT and QS vs PT (t(8) = 0.4778, p = 0.6455 and t(8) = 1.6819, p = 0.1310 for visual and no visual conditions, respectively), as assessed by "Hotelling-Williams" tests for equality among dependent correlations. The results indicate that simple measurements of plantarflexion torque fluctuations during FT and PT may be used to estimate balance ability. From a practical standpoint, it is suggested that rehabilitation protocols designed to regain/improve balance function may be based on the performance of FTs or PTs executed in a seated position.

Fingertip-Coupled Spindle Signaling Does Not Contribute to Reduce Postural Sway Under Light Touch.

The details of how light touch (LT) of a stable surface reduces postural sway are still not well known. We hypothesized that removal of feedback provided by muscle afferents of the touching fingertip would increase postural sway in standing subjects. Eleven participants stood upright on a force plate with eyes closed and on an unstable surface. The experimental conditions involved two different finger positions: with partial muscle afferents (PMA), which includes sensory information from the fingertip flexor muscles, and no muscle afferents (NMA), without information from either fingertip flexor or extensor muscles. In the control condition, the participants kept the same posture, but with no finger touch (NT). Postural sway in both anteroposterior (AP) and mediolateral (ML) axes were recorded. Results showed that LT decreased all sway quantifiers as compared with the NT condition. The withdrawal of information from the touch finger muscle afferents (NMA condition) did not increase postural sway. Actually, there was a small, albeit statistically significant, decrease in the variability of center of pressure displacement in the AP direction. These results indicate that in some cases, muscle afferent input may either not contribute or even worsen the overall quality of sensory feedback from a given body segment, leading to no improvement or even a slightly decreased performance of the motor control system (evaluated by means of levels of postural sway in the present investigation). The results suggest that non-spindle fingertip afferents provide the bulk of the sensory feedback associated with the fingertip that is touching a ground-referenced object during quiet standing under LT.