Fast grip force adaptation to friction relies on localized fingerpad strains.

During object manipulation, humans adjust the grip force to friction, such that slippery objects are squeezed more firmly than sticky ones. This essential mechanism to keep a stable grasp relies on feedback from tactile afferents innervating the fingertips, that are sensitive to local skin strains. To test if this feedback originates from the skin-object interface, we asked participants to perform a grip-lift task with an instrumented object able to monitor skin strains at the contact through transparent plates of different frictions. We observed that, following an unbeknown change in plate across trials, participants adapted their grip force to friction. After switching from high to low friction, we found a significant increase in strain inside the contact arising ~100 ms before the modulation of grip force, suggesting that differences in strain patterns before lift-off are used by the nervous system to quickly adjust the force to the frictional properties of manipulated objects.

A haptic illusion created by gravity.

Human dexterity requires very fine and efficient control of fingertip forces, which relies on the integration of cutaneous and proprioceptive feedback. Here, we examined the influence of gravity on isometric force control. We trained participants to reproduce isometric vertical forces on a dynamometer held between the thumb and the index finger in normal gravity and tested them during parabolic flight creating phases of microgravity and hypergravity, thereby strongly influencing the motor commands and the proprioceptive feedback. We found that gravity creates the illusion that upward forces are larger than downward forces of the same magnitude. The illusion increased under hypergravity and was abolished under microgravity. Gravity also affected the control of the grip force employed to secure the grasp. These findings suggest that gravity biases the haptic estimation of forces, which has implications for the design of haptic devices to be used during flight or space activities.

Translation and cross-cultural adaptation of the Brazilian version of the PM-Scale: A specific measure of participation after stroke.

BACKGROUND: The PM-Scale was developed specifically to assess participation in individuals after stroke based on the concepts contained in the International Classification of Functioning, Disability and Health. However, this measure is only available in English and French. OBJECTIVE: To translate and cross-culturally adapt the PM-Scale to Brazilian Portuguese, followed by the validation and testing of reliability of the translated version. METHODS: The translation process followed standard guidelines. Preliminary test-retest reliability was determined using the intraclass correlation coefficient (ICC2,1). The Rasch model was employed to analyse the validity, unidimensionality, invariance, and internal consistency of the Brazilian version of the PM-Scale. RESULTS: The final translated version of the PM-Scale presented appropriate semantic, idiomatic, cultural, and conceptual equivalence. The preliminary analysis revealed excellent intra-observer and inter-observer reliability (ICC2,1 = 0.91; 95%CI: 0.83, 0.95 and ICC2,1 = 0.81; 95%CI: 0.64, 0.89, respectively). The analysis of the Rasch model revealed only one erratic item. An excellent overall fit was found for items (mean ± SD = 0.01 ± 1.02) and adequate fit was found for persons (mean ± SD = 1.16 ± 0.88). Internal consistency was considered adequate (person separation index = 1.77, reliability = 0.76). No significant invariance was found with regards to the personal characteristics of the sample (p > 0.05). CONCLUSION: The Brazilian version of the PM-Scale is a valid, unidimensional, linear, reliable scale for measuring participation in stroke survivors and can be administered in less than five minutes.

Effect of mixed and collective physical activity in chronic stroke rehabilitation: A randomized cross-over trial in low-income settings.

BACKGROUND: The prevalence of physical inactivity after stroke is high and exercise training improves many outcomes. However, access to community training protocols is limited, especially in low-income settings. OBJECTIVE: To investigate the feasibility and efficacy of a new intervention: Circuit walking, balance, cycling and strength training (CBCS) on activity of daily living (ADL) limitations, motor performance, and social participation restrictions in people after stroke. METHODS: Forty-six community-dwelling individuals with chronic stroke who were no longer in conventional rehabilitation were randomized into an immediate CBCS group (IG; initially received CBCS training for 12 weeks in phase 1), and a delayed CBCS group (DG) that first participated in sociocultural activities for 12 weeks. In phase 2, participants crossed over so that the DG underwent CBCS and the IG performed sociocultural activities. The primary outcome was ADL limitations measured with the ACTIVLIM-Stroke scale. Secondary outcomes included motor performance (balance: Berg Balance Scale [BBS], global impairment: Stroke Impairment Assessment Set [SIAS] and mobility: 6-minute and 10-metre walk tests [6MWT and 10mWT] and psychosocial health [depression and participation]). Additional outcomes included feasibility (retention, adherence) and safety. RESULTS: ADL capacity significantly improved pre to post CBCS training (ACTIVLIM-stroke, +3,4 logits, p < 0.001; effect size [ES] 0.87), balance (BBS, +21 points, p < 0.001; ES 0.9), impairments (SIAS, +11 points, p < 0.001; ES 0.9), and mobility (+145 m for 6MWT and +0.37 m/s for 10mWT; p < 0.001; ES 0.7 and 0.5 respectively). Similar improvements in psychosocial health occurred in both groups. Adherence and retention rates were 95% and 100%, respectively. CONCLUSION: CBCS was feasible, safe and improved functional independence and motor abilities in individuals in the chronic stage of stroke. Participation in CBCS improved depression and social participation similarly to participation in sociocultural activities. The benefits persisted for at least 3 months after intervention completion. PROTOCOL REGISTRATION NUMBER: PACTR202001714888482.

Relationships between walking speed, activities and participation in people with chronic stroke in Burundi.

Background: Reduced walking speed because of a stroke may limit activities of daily living (ADLs) and restrict social participation. Objectives: To describe the level of balance impairment, activity limitations, and participation restrictions and to investigate their relationship with walking speed in Burundians with chronic stroke. Methods: This cross-sectional study involved adult stroke survivors. Walking speed, balance, ADLs and social participation were assessed with the 10-meter walk test (10 mWT), the Berg balance scale (BBS), the activity limitation stroke scale and the participation measurement scale, respectively. In order to determine ambulatory independence status, participants were stratified into three walking speed groups (household ambulation, limited ambulation and full-community ambulation), based on the Perry classification. Results: Fifty-eight adults (mean age 52.1 ± 11.4 years) with chronic stroke were included in our study. Most participants had severe balance impairments (median BBS score, 27). Their mean (± standard deviation [SD]) walking speeds, ADL levels and social participation levels were 0.68 ± 0.34 m/s, 50.8% ± 9.3% and 52.8% ± 8.6%, respectively. Walking speed correlated moderately with balance (rho = 0.5, p < 0.001) and strongly with ADL level (r = 0.7, p < 0.001) but not with participation level (r = 0.2, p = 0.25). Conclusion: Using socio-culturally suitable tools, our study showed that walking speed correlates robustly with balance and ADL ability, but not with social participation, in Burundi, a low-income country. Clinical implications: Exercises targeting walking speed would be very useful for people with chronic stroke living in low-resource countries, in order to promote their functional independence.

Biopsychosocial factors associated with chronic low back pain-related activity limitations in Burundi.

Background: Chronic low back pain (CLBP) is an increasing burden worldwide. The biopsychosocial factors associated with CLBP-related activity limitations have not yet been investigated in Burundi. Objective: The aim of our study was to investigate the biopsychosocial factors that influence the CLBP-related activity limitations in a Burundian sample population. Method: We carried out a cross-sectional study of 58 adults with nonspecific CLBP from Bujumbura city. Univariate and bivariate analyses were used to investigate the association between biopsychosocial factors and CLBP activity limitations. Sequential multiple regression analyses were subsequently used to predict CLBP activity limitations. Results: Fifty-eight individuals with a mean age of 41.3 ± 10.20, 58.6% of female gender, were recruited. The univariate and bivariate analyses demonstrated that educational level, gender, healthcare coverage, profession, height, pain intensity, depression and physical fitness were significantly associated with CLBP-related activity limitations (p range, < 0.001 to < 0.05). The multivariate regression analysis showed that the significant biopsychosocial factors accounted for 49% of the variance in self-reported activity limitations. Predictors of activity limitations were education level (ß = -0.369; p = 0.001), abdominal muscle endurance (ß = -0.339; p = 0.002) and depression (ß = 0.289; p = 0.011). Conclusions: Our study provides evidence of biopsychosocial factor associations with CLBP-related activity limitations in Burundi. Evidence-based management and prevention of CLBP in Burundi should incorporate a biopsychosocial model. Clinical implications: Biopsychosocial factors should be regularly evaluated in people with chronic low back pain and efforts to improve the burden of chronic low back pain in Burundi should take these factors into account.

Normal and tangential forces combine to convey contact pressure during dynamic tactile stimulation.

Humans need to accurately process the contact forces that arise as they perform everyday haptic interactions such as sliding the fingers along a surface to feel for bumps, sticky regions, or other irregularities. Several different mechanisms are possible for how the forces on the skin could be represented and integrated in such interactions. In this study, we used a force-controlled robotic platform and simultaneous ultrasonic modulation of the finger-surface friction to independently manipulate the normal and tangential forces during passive haptic stimulation by a flat surface. To assess whether the contact pressure on their finger had briefly increased or decreased during individual trials in this broad stimulus set, participants did not rely solely on either the normal force or the tangential force. Instead, they integrated tactile cues induced by both components. Support-vector-machine analysis classified physical trial data with up to 75% accuracy and suggested a linear perceptual mechanism. In addition, the change in the amplitude of the force vector predicted participants' responses better than the change of the coefficient of dynamic friction, suggesting that intensive tactile cues are meaningful in this task. These results provide novel insights about how normal and tangential forces shape the perception of tactile contact.

Grip Force is Adjusted at a Level That Maintains an Upper Bound on Partial Slip Across Friction Conditions During Object Manipulation.

Dexterous manipulation of objects heavily relies on the feedback provided by the tactile afferents innervating the fingertips. Previous studies have suggested that humans might take advantage of partial slip, localized loss of grip between the skin and the object, to gauge the stability of a contact and react appropriately when it is compromised, that is, when slippage is about to happen. To test this hypothesis, we asked participants to perform point-to-point movements using a manipulandum. Through optical imaging, the device monitored partial slip at the contact interface, and at the same time, the forces exerted by the fingers. The level of friction of the contact material was changed every five trials. We found that the level of grip force was systematically adjusted to the level of friction, and thus partial slip was limited to an amount similar across friction conditions. We suggest that partial slip is a key signal for dexterous manipulation and that the grip force is regulated to continuously maintain an upper bound on partial slip across friction conditions.

Effectiveness of walking training on balance, motor functions, activity, participation and quality of life in people with chronic stroke: a systematic review with meta-analysis and meta-regression of recent randomized controlled trials.

PURPOSE: To review and quantify the effects of walking training for the improvement of various aspects of physical function of people with chronic stroke. METHODS: We conducted a systematic search and meta-analysis of randomized controlled trials (RCTs) of chronic stroke rehabilitation interventions published from 2008 to 2020 in English or French. Of the 6476-screened articles collated from four databases, 15 RCTs were included and analyzed. We performed a meta-regression with the total training time as dependent variable in order to have a better understanding of how did the training dosage affect the effect sizes. RESULTS: Treadmill walking training was more effective on balance and motor functions (standardized mean difference (SMD)=0.70[0.02, 1.37], p = 0.04) and 0.56[0.15, 0.96], p = 0.007 respectively). Overground walking training improved significantly walking endurance (SMD = 0.38[0.16, 0.59], p < 0.001), walking speed (MD = 0.12[0.05, 0.18], p < 0.001), participation (SMD = 0.35[0.02, 0.68], p = 0.04) and quality of life (SMD = 0.46[0.12, 0.80], p = 0.008). Aquatic training improved balance (SMD = 2.41[1.20, 3.62], p < 0.001). The Meta-regression analysis did not show significant effect of total training time on the effect sizes. CONCLUSION: Treadmill and overground walking protocols consisting of ≥30 min sessions conducted at least 3 days per week for about 8 weeks are beneficial for improving motor impairments, activity limitations, participation, and quality of life in people with chronic stroke.Implications for rehabilitationTreadmill walking training is effective for improving balance and motor functions.Overground walking training improved significantly walking endurance, walking speed, participation and quality of life.Treadmill and overground walking protocols consisting of ≥30 min sessions conducted at least 3 days per week for about 8 weeks are beneficial for improving motor impairments, activity limitations, participation, and quality of life in patient with chronic stroke.

Linking of concepts measured by SATIS-Stroke and the PM-Scale to the international classification of functioning, disability and health.

BACKGROUND: Rules have been developed to simplify the understanding of researchers/clinicians and standardize the linking process between concepts contained in the items on assessment measures and the International Classification of Functioning, Disability, and Health (ICF). OBJECTIVE: Link the concepts of the SATISPART Stroke (SATIS-Stroke) and Participation Measurement Scale (PM-Scale) to ICF codes. METHODS: Linking was performed by two evaluators with experience in the ICF taxonomy who applied the ten standard linking rules specifically developed and updated for this purpose. The level of agreement between the evaluators was determined using the Kappa coefficient with 95% confidence intervals. RESULTS: The SATIS-Stroke and PM-Scale address the nine domains of the ICF "Activities and Participation" component. Adequate agreement was found between the researchers during the linking process, mainly between the 1º and 3º evaluators. Identified 41 ICF codes were found among the SATIS-Stroke items and 24 ICF codes were found among the items of the PM-Scale. CONCLUSION: SATIS-Stroke addresses more issues regarding the domains of Learning and Applying Knowledge, Mobility, Self-Care, Domestic Life, and Major Life Areas, whereas the PM-Scale addresses more issues regarding the General Tasks and Demands, Communication, and Community, Social and Civic Life. Both instruments equally address issues related to Interpersonal Interactions and Relationships.

Linking of concepts measured by SATIS-Stroke and the PM-Scale to the international classification of functioning, disability and health / Linking of concepts measured by SATIS-Stroke and the PM-Scale to the international classification of functioning, disability and health

Background: Rules have been developed to simplify the understanding of researchers/clinicians and standardize the linking process between concepts contained in the items on assessment measures and the International Classification of Functioning, Disability, and Health (ICF). Objective: Link the concepts of the SATISPART Stroke (SATIS-Stroke) and Participation Measurement Scale (PM-Scale) to ICF codes. Methods: Linking was performed by two evaluators with experience in the ICF taxonomy who applied the ten standard linking rules specifically developed and updated for this purpose. The level of agreement between the evaluators was determined using the Kappa coefficient with 95% confidence intervals. Results: The SATIS-Stroke and PM-Scale address the nine domains of the ICF "Activities and Participation" component. Adequate agreement was found between the researchers during the linking process, mainly between the 1º and 3º evaluators...

Measuring fingerpad deformation during active object manipulation.

During active object manipulation, the finger-object interactions give rise to complex fingertip skin deformations. These deformations are in turn encoded by the local tactile afferents and provide rich and behaviorally relevant information to the central nervous system. Most of the work studying the mechanical response of the finger to dynamic loading has been performed under a passive setup, thereby precisely controlling the kinematics or the dynamics of the loading. However, to identify aspects of the deformations that are relevant to online control during object manipulation, it is desirable to measure the skin response in an active setup. To that end, we developed a device that allows us to monitor finger forces, skin deformations, and kinematics during fine manipulation. We describe the device in detail and test it to precisely describe how the fingertip skin in contact with the object deforms during a simple vertical oscillation task. We show that the level of grip force directly influences the fingerpad skin strains and that the strain rates are substantial during active manipulation (norm up to 100%/s). The developed setup will enable us to causally relate sensory information, i.e. skin deformation, to online control, i.e. grip force adjustment, in future studies.NEW & NOTEWORTHY We present a novel device, a manipulandum, that enables to image the contact between the finger and the contact surface during active manipulation of the device. The device is tested in a simple vertical oscillation task involving 18 participants. We demonstrate that substantial surface skin strains take place at the finger-object interface and argue that those deformations provide essential information for grasp stability during object manipulation.

Recognizing Manual Activities Using Wearable Inertial Measurement Units: Clinical Application for Outcome Measurement.

The ability to monitor activities of daily living in the natural environments of patients could become a valuable tool for various clinical applications. In this paper, we show that a simple algorithm is capable of classifying manual activities of daily living (ADL) into categories using data from wrist- and finger-worn sensors. Six participants without pathology of the upper limb performed 14 ADL. Gyroscope signals were used to analyze the angular velocity pattern for each activity. The elaboration of the algorithm was based on the examination of the activity at the different levels (hand, fingers and wrist) and the relationship between them for the duration of the activity. A leave-one-out cross-validation was used to validate our algorithm. The algorithm allowed the classification of manual activities into five different categories through three consecutive steps, based on hands ratio (i.e., activity of one or both hands) and fingers-to-wrist ratio (i.e., finger movement independently of the wrist). On average, the algorithm made the correct classification in 87.4% of cases. The proposed algorithm has a high overall accuracy, yet its computational complexity is very low as it involves only averages and ratios.

Clinimetric properties of the SATIS-Stroke questionnaire in the Brazilian population: A satisfaction assessment measure addressing activities and participation after a stroke.

BACKGROUND: SATIS-Stroke questionnaire has been translated and adapted for use in the Brazilian population, however, it is necessary to test the measurement properties in Brazilian population. OBJECTIVE: To test the reliability, agreement, concurrent validity, and diagnostic accuracy of the SATIS-Stroke. METHODS: Chronic stroke survivors were included. The calculations were made using scores in logits (Rasch Model). Reliability was tested using the intraclass correlation coefficient (ICC2,1), standard error of measurement (SEM), minimal detectable change (MDC), and Bland-Altman plots. Concurrent validity was analyzed using Spearman's correlation coefficient. For such, the correlation between SATIS-Stroke and Stroke Specific Quality of Life (SS-QOL) questionnaires was determined. Diagnostic accuracy was estimated based on the area under the receiver operating characteristic (ROC) curve with a 95% confidence interval and considering the sensitivity and specificity of SATIS-Stroke in differentiating different types of activity and participation. RESULTS: Eighty stroke survivors were analyzed. Mean age was 57.98±13.85 years and 45.2% had severe impairment. Excellent reliability was found (intra-observer ICC2,1 = 0.90; 95% CI: 0.84, 0.93; inter-observer ICC2,1 = 0.89; 95% CI: 0.83, 0.93). The Bland-Altman plot demonstrated satisfactory agreement. In the analysis of concurrent validity, a strong, positive, significant correlation was found between SATIS-Stroke and SS-QOL (rs = 0.74; p <0.001 with an r2=0.44; p=0.001). Diagnostic accuracy was satisfactory, with 80.8% sensitivity and 85.2% specificity. CONCLUSION: The Brazilian version of the SATIS-Stroke questionnaire exhibited adequate reliability, concurrent validity, and diagnostic accuracy. Therefore, this is a valid, reproducible measure for the assessment of satisfaction with regard to activities and participation following a stroke.

High-resolution imaging of skin deformation shows that afferents from human fingertips signal slip onset.

Human tactile afferents provide essential feedback for grasp stability during dexterous object manipulation. Interacting forces between an object and the fingers induce slip events that are thought to provide information about grasp stability. To gain insight into this phenomenon, we made a transparent surface slip against a fixed fingerpad while monitoring skin deformation at the contact. Using microneurography, we simultaneously recorded the activity of single tactile afferents innervating the fingertips. This unique combination allowed us to describe how afferents respond to slip events and to relate their responses to surface deformations taking place inside their receptive fields. We found that all afferents were sensitive to slip events, but fast-adapting type I (FA-I) afferents in particular faithfully encoded compressive strain rates resulting from those slips. Given the high density of FA-I afferents in fingerpads, they are well suited to detect incipient slips and to provide essential information for the control of grip force during manipulation.

Each fingertip hosts thousands of nerve fibers that allow us to handle objects with great dexterity. These fibers relay the amount of friction between the skin and the item, and the brain uses this sensory feedback to adjust the grip as necessary. Yet, exactly how tactile nerve fibers encode information about friction remains largely unknown. Previous research has suggested that friction might not be recorded per se in nerve signals to the brain. Instead, fibers in the finger pad might be responding to localized 'partial slips' that indicate an impending loss of grip. Indeed, when lifting an object, fingertips are loaded with a tangential force that puts strain on the skin, resulting in subtle local deformations. Nerve fibers might be able to detect these skin changes, prompting the brain to adjust an insecure grip before entirely losing grasp of an object. However, technical challenges have made studying the way tactile nerve fibers respond to slippage and skin strain difficult. For the first time, Delhaye et al. have now investigated how these fibers respond to and encode information about the strain placed on fingertips as they are loaded tangentially. A custom-made imaging apparatus was paired with standard electrodes to record the activity of four different kinds of tactile nerve fibers in participants who had a fingertip placed against a plate of glass. The imaging focused on revealing changes in skin surface as tangential force was applied; the electrodes measured impulses from individual nerve fibers from the fingertip. While all the fibers responded during partial slips, fast-adapting type 1 nerves generated strong responses that signal a local loss of grip. Recordings showed that these fibers consistently encoded changes in the skin strain patterns, and were more sensitive to skin compressions related to slippage than to stretch. These results show how tactile nerve fibers encode the subtle skin compressions created when fingers handle objects. The methods developed by Delhaye et al. could further be used to explore the response properties of tactile nerve fibers, sensory feedback and grip.

Manual ability in hand surgery patients: Validation of the ABILHAND scale in four diagnostic groups.

BACKGROUND: Patients treated in hand surgery (HS) belong to different demographic groups and have varying impairments related to different pathologies. HS outcomes are measured to assess treatment results, complication risks and intervention reliability. A one-dimensional and linear measure would allow for unbiased comparisons of manual ability between patients and different treatment effects. OBJECTIVE: To adapt the ABILHAND questionnaire through Rasch analysis for specific use in HS patients and to examine its validity. METHODS: A preliminary 90-item questionnaire was presented to 216 patients representing the diagnoses most frequently encountered in HS, including distal radius fracture (n = 74), basal thumb arthritis (n = 66), carpal tunnel syndrome (n = 53), and heavy wrist surgery (n = 23). Patients were assessed during the early recovery and in the late follow-up period (0-3 months, 3-6 months and >6 months), leading to a total of 305 assessments. They rated their perceived difficulty with queried activities as impossible, difficult, or easy. Responses were analyzed using the RUMM2030 software. Items were refined based on item-patient targeting, fit statistics, differential item functioning, local independence and item redundancy. Patients also completed the QuickDASH, 12-item Short Form Survey (SF-12) and a numerical pain scale. RESULTS: The rating scale Rasch model was used to select 23 mostly bimanual items on a 3-level scale, which constitute a unidimensional, linear measure of manual ability with good reliability across all included diagnostic groups (Person-Separation Index = 0.90). The resulting scale was found to be invariant across demographic and clinical subgroups and over time. ABILHAND-HS patient measures correlated significantly (p<0.001) with the QuickDASH (r = -0.77), SF-12 Physical Component Summary (r = 0.56), SF-12 Mental Component Summary (r = 0.31), and pain scale (r = -0.49). CONCLUSION: ABILHAND-HS is a robust person-centered measure of manual ability in HS patients.

Effectiveness of walking versus mind-body therapies in chronic low back pain: A systematic review and meta-analysis of recent randomized controlled trials.

PURPOSE: Walking and mind-body therapies (MBTs) are commonly recommended to relieve pain and improve function in patients with chronic low back pain (CLBP). The purpose of this study was to compare the effectiveness of walking and MBTs in CLBP. METHODS: We included randomized controlled trials (RCTs) comparing walking or MBTs to any other intervention or control in adults with CLBP. Studies were identified through PubMed, Cochrane Library, PsycINFO, Scopus, and ScienceDirect databases. The research was limited to studies published in English and French between January 2008 and December 2018. Two reviewers independently selected the studies, extracted data, and assessed studies quality using the Physiotherapy Evidence Database (PEDro) scale. Statistical analyses were performed under a random-effects model. We analyzed pain and activity limitation, with the calculation of standardized mean differences and 95% confidence intervals for the different treatment effects. RESULTS: Thirty one randomized controlled trials involving 3193 participants were analyzed. Walking was as effective as control interventions in the short-term and slightly superior in the intermediate term with respect to pain (Standardized mean differences (SMD)  = -0.34; 95% CI, -0.65 to -0.03; P = .03) and activity limitation (SMD = -0.30; 95% CI, -0.50 to -0.10; P = .003). In contrast, yoga was more effective than control interventions in the short term in terms of pain (SMD = -1.47; 95% CI, -2.26 to -0.68; P = .0003) and activity limitation (SMD = -1.17; 95% CI, -1.80 to -0.55; P = .0002). Yoga was no longer superior to the control interventions for pain at the 6-month follow-up. CONCLUSION: MBTs, especially yoga, seem to be more effective in the short term, and walking seems to be more effective in the intermediate term, for the relief of pain and activity limitation in patients with CLBP. A combination of walking and MBTs fits the biopsychosocial model and might be valuable therapy for CLBP throughout follow-up due to combined effects.

A Very Fast Time Scale of Human Motor Adaptation: Within Movement Adjustments of Internal Representations during Reaching.

Humans and other animals adapt motor commands to predictable disturbances within tens of trials in laboratory conditions. A central question is how does the nervous system adapt to disturbances in natural conditions when exactly the same movements cannot be practiced several times. Because motor commands and sensory feedback together carry continuous information about limb dynamics, we hypothesized that the nervous system could adapt to unexpected disturbances online. We tested this hypothesis in two reaching experiments during which velocity-dependent force fields (FFs) were randomly applied. We found that within-movement feedback corrections gradually improved, despite the fact that the perturbations were unexpected. Moreover, when participants were instructed to stop at a via-point, the application of a FF prior to the via-point induced mirror-image after-effects after the via-point, consistent with within-trial adaptation to the unexpected dynamics. These findings suggest a fast time-scale of motor learning, which complements feedback control and supports adaptation of an ongoing movement.

Applicability of International Classification of Functioning, Disability and Health-based participation measures in stroke survivors in Africa: a systematic review.

To appraise available International Classification of Functioning, Disability and Health (ICF)-based tools for the measurement of participation after stroke and to examine their applicability in the African sociocultural context. Pubmed/Medline, Science Direct, Cochrane Library, and Hinari databases were systematically searched. The literature search was limited to studies published in the English or French language from January 2001 up to May 2019. Two reviewers independently screened all identified studies and selected eligible articles. Disagreements about inclusion or exclusion of studies were resolved by consensus. Two reviewers independently extracted the psychometric properties of each instrument using the Consensus-based Standard for the Selection of Health Measurement Instruments checklist and examined the methodological quality of each selected study using the MacDermid checklist. A total of 1030 articles were systematically reviewed for relevance, yielding 22 studies that met inclusion criteria. These studies were related to nine participation tools. The MacDermid scores ranged from 13 to 21 out of 24. The number of investigated psychometric properties and the number of ICF participation domains covered by each tool varied among studies. This systematic review revealed nine ICF-based tools for the measurement of participation after stroke. We examined the content of these tools and provided valuable information that can be used to guide researchers in Africa in their selection of the most appropriate tool for the measurement of participation after stroke.

Fingerpad contact evolution under electrovibration.

Displaying tactile feedback through a touchscreen via electrovibration has many potential applications in mobile devices, consumer electronics, home appliances and automotive industry though our knowledge and understanding of the underlying contact mechanics are very limited. An experimental study was conducted to investigate the contact evolution between the human finger and a touch screen under electrovibration using a robotic set-up and an imaging system. The results show that the effect of electrovibration is only present during full slip but not before slip. Hence, the coefficient of friction increases under electrovibration as expected during full slip, but the apparent contact area is significantly smaller during full slip when compared to that of no electrovibration condition. It is suggested that the main cause of the increase in friction during full slip is due to an increase in the real contact area and the reduction in apparent area is due to stiffening of the finger skin in the tangential direction.