Prefrontal cortex oxygenation during a mentally fatiguing task in normoxia and hypoxia.

Mental fatigue (MF) and hypoxia impair cognitive performance through changes in brain hemodynamics. We want to elucidate the role of prefrontal cortex (PFC)-oxygenation in MF. Twelve participants (22.9 ± 3.5 years) completed four experimental trials, (1) MF in (normobaric) hypoxia (MF_HYP) (3.800 m; 13.5%O2), (2) MF in normoxia (MF_NOR) (98 m; 21.0%O2), (3) Control task in HYP (CON_HYP), (4) Control in NOR (CON_NOR). Participants performed a 2-back task, Digit Symbol Substitution test and Psychomotor Vigilance task before and after a 60-min Stroop task or an emotionally neutral documentary. Brain oxygenation was measured through functional Near Infrared Spectroscopy. Subjective feelings of MF and physiological measures (heart rate, oxygen saturation, blood glucose and hemoglobin) were recorded. The Stroop task resulted in increased subjective feelings of MF compared to watching the documentary. 2-back accuracy was lower post task compared to pre task in MF_NOR and CON_NOR, while no differences were found in the other cognitive tasks. The fraction of inspired oxygen did not impact feelings of MF. Although performing the Stroop resulted in higher subjective feelings of MF, hypoxia had no effect on the severity of self-reported MF. Additionally, this study could not provide evidence for a role of oxygenation of the PFC in the build-up of MF.

The impact of an active and passive industrial back exoskeleton on functional performance.

Due to differences in actuation and design, active and passive industrial back exoskeletons could influence functional performance, i.e., work performance, perceived task difficulty, and discomfort, differently. Therefore, this study investigated and compared the impact of the active CrayX (7 kg) and passive Paexo Back (4.5 kg) on functional performance. Eighteen participants performed twelve work-related tasks with both types of exoskeletons and without (NoExo). The CrayX hindered work performance up to 22% in multiple tasks, compared to the Paexo Back and NoExo, while work performance between NoExo and the Paexo Back condition was more comparable, except for stair climbing (13% hindrance). Perceived task difficulty and discomfort seldomly varied between both exoskeletons. Although the CrayX shows promise to benefit workers, limitations in hindrance and comfort should first be addressed. The Paexo Back has demonstrated an advantage in certain static tasks. However, increasing its potential across a broader range of tasks seems warranted.Practitioner Summary: Differences between industrial back exoskeletons with regard to functional performance, i.e. work performance, discomfort and perceived task difficulty, were investigated by evaluating the active CrayX and passive Paexo Back back exoskeletons. The CrayX significantly hindered functional performance, while the Paexo Back seldomly affected functional performance.Abbreviations: WMSD: Work-related musculoskeletal disorder; NoExo: No Exoskeleton; GD: General discomfort; PTD: Perceived task difficulty; BMI: Body Mass Index.

Continuous relative phases of walking with an articulated passive ankle-foot prosthesis in individuals with a unilateral transfemoral and transtibial amputation: an explorative case-control study.

BACKGROUND: A mechanical ankle-foot prosthesis (Talaris Demonstrator) was developed to improve prosthetic gait in people with a lower-limb amputation. This study aims to evaluate the Talaris Demonstrator (TD) during level walking by mapping coordination patterns based on the sagittal continuous relative phase (CRP). METHODS: Individuals with a unilateral transtibial amputation, transfemoral amputation and able-bodied individuals completed 6 minutes of treadmill walking in consecutive blocks of 2 minutes at self-selected (SS) speed, 75% SS speed and 125% SS speed. Lower extremity kinematics were captured and hip-knee and knee-ankle CRPs were calculated. Statistical non-parametric mapping was applied and statistical significance was set at 0.05. RESULTS: The hip-knee CRP at 75% SS walking speed with the TD was larger in the amputated limb of participants with a transfemoral amputation compared to able-bodied individuals at the beginning and end of the gait cycle (p = 0.009). In people with a transtibial amputation, the knee-ankle CRP at SS and 125% SS walking speeds with the TD were smaller in the amputated limb at the beginning of the gait cycle compared to able-bodied individuals (p = 0.014 and p = 0.014, respectively). Additionally, no significant differences were found between both prostheses. However, visual interpretation indicates a potential advantage of the TD over the individual's current prosthesis. CONCLUSION: This study provides lower-limb coordination patterns in people with a lower-limb amputation and reveals a possible beneficial effect of the TD over the individuals' current prosthesis. Future research should include a well-sampled investigation of the adaptation process combined with the prolonged effects of the TD.

Therapeutic benefits of lower limb prostheses: a systematic review.

BACKGROUND: Enhancing the quality of life of people with a lower limb amputation is critical in prosthetic development and rehabilitation. Yet, no overview is available concerning the impact of passive, quasi-passive and active ankle-foot prostheses on quality of life. OBJECTIVE: To systematically review the therapeutic benefits of performing daily activities with passive, quasi-passive and active ankle-foot prostheses in people with a lower limb amputation. METHODS: We searched the Pubmed, Web of Science, Scopus and Pedro databases, and backward citations until November 3, 2021. Only English-written randomised controlled trials, cross-sectional, cross-over and cohort studies were included when the population comprised individuals with a unilateral transfemoral or transtibial amputation, wearing passive, quasi-passive or active ankle-foot prostheses. The intervention and outcome measures had to include any aspect of quality of life assessed while performing daily activities. We synthesised the participants' characteristics, type of prosthesis, intervention, outcome and main results, and conducted risk of bias assessment using the Cochrane risk of bias tool. This study is registered on PROSPERO, number CRD42021290189. RESULTS: We identified 4281 records and included 34 studies in total. Results indicate that quasi-passive and active prostheses are favoured over passive prostheses based on biomechanical, physiological, performance and subjective measures in the short-term. All studies had a moderate or high risk of bias. CONCLUSION: Compared to passive ankle-foot prostheses, quasi-passive and active prostheses significantly enhance the quality of life. Future research should investigate the long-term therapeutic benefits of prosthetics devices.

Evaluation of an articulated passive ankle-foot prosthesis.

BACKGROUND: Current ankle prostheses for people with unilateral transtibial amputation (TTA) or transfemoral amputation (TFA) are unable to mimic able-bodied performance during daily activities. A new mechanical ankle-foot prosthesis was developed to further optimise the gait of people with a lower-limb amputation. This study aimed to evaluate the Talaris Demonstrator (TD) during daily activities by means of performance-related, physiological and subjective outcome measures. MATERIALS AND METHODS: Forty-two participants completed a protocol assessing performance and functional mobility with their current prosthesis and the TD. The protocol comprised the L-test, 2 min of stair climbing, 2 min of inclined treadmill walking, 6 min of treadmill walking at 3 different speeds in consecutive blocks of 2 min, and a 3-m Backward Walk test (3mBWT). Heart rate was measured during each task, and oxygen uptake was collected during all tasks except for the L-test and 3mBWT. Time of execution was recorded on the L-test and 3mBWT, and the rate of perceived exertion (score = 6-20), fatigue and comfort (score = 0-100) were assessed after each task. Paired sample t-tests and Wilcoxon Signed-rank tests were performed to compare outcomes between prosthetic devices. Benjamini-Hochberg corrections were applied to control for multiple comparisons with a level of significance set at α = 0.05. RESULTS: Subjects with a TTA (N = 28) were faster with their current prosthesis compared to the TD on the L-test and 3mBWT (p = 0.005). In participants with a TFA (N = 14), we observed a tendency towards a higher heart rate during the L-test and towards increased comfort during inclined walking, with the TD compared to the participants' current prosthetic device (0.05 < p < 0.10). Further, no significant results were observed. CONCLUSION: The Talaris Demonstrator is a novel state-of-the-art passive ankle-foot prosthesis for both people with a TTA and TFA. Subjective measures indicate the added value of this device, while overall task performance and intensity of effort do not differ between the Talaris Demonstrator and the current prosthesis. Further investigations unravelling both acute and more prolonged adaptations will be conducted to evaluate the TD more thoroughly.

Characterizing fall risk factors in Belgian older adults through machine learning: a data-driven approach.

BACKGROUND: Falls are a major problem associated with ageing. Yet, fall-risk classification models identifying older adults at risk are lacking. Current screening tools show limited predictive validity to differentiate between a low- and high-risk of falling. OBJECTIVE: This study aims at identifying risk factors associated with higher risk of falling by means of a quality-of-life questionnaire incorporating biological, behavioural, environmental and socio-economic factors. These insights can aid the development of a fall-risk classification algorithm identifying community-dwelling older adults at risk of falling. METHODS: The questionnaire was developed by the Belgian Ageing Studies research group of the Vrije Universiteit Brussel and administered to 82,580 older adults for a detailed analysis of risk factors linked to the fall incidence data. Based on previously known risk factors, 139 questions were selected from the questionnaire to include in this study. Included questions were encoded, missing values were dropped, and multicollinearity was assessed. A random forest classifier that learns to predict falls was trained to investigate the importance of each individual feature. RESULTS: Twenty-four questions were included in the classification-model. Based on the output of the model all factors were associated with the risk of falling of which two were biological risk factors, eight behavioural, 11 socioeconomic and three environmental risk factors. Each of these variables contributed between 4.5 and 6.5% to explaining the risk of falling. CONCLUSION: The present study identified 24 fall risk factors using machine learning techniques to identify older adults at high risk of falling. Maintaining a mental, physical and socially active lifestyle, reducing vulnerability and feeling satisfied with the living situation contributes to reducing the risk of falling. Further research is warranted to establish an easy-to-use screening tool to be applied in daily practice.

Prevalence and incidence of work-related musculoskeletal disorders in secondary industries of 21st century Europe: a systematic review and meta-analysis.

OBJECTIVE: Over the course of the twenty-first century, work-related musculoskeletal disorders are still persisting among blue collar workers. At present, no epidemiological overview exists. Therefore, a systematic review and meta-analysis was performed on the epidemiology of work-related musculoskeletal disorders (WMSD) within Europe's secondary industries. METHODS: Five databases were screened, yielding 34 studies for the qualitative analysis and 17 for the quantitative analysis. Twelve subgroups of WMSDs were obtained for the meta-analysis by means of predefined inclusion criteria: back (overall), upper back, lower back, neck, shoulder, neck/shoulder, elbow, wrist/hand, leg (overall), hip, knee, and ankle/feet. RESULTS: The most prevalent WMSDs were located at the back (overall), shoulder/neck, neck, shoulder, lower back and wrist WMSDs with mean 12-month prevalence values of 60, 54, 51, 50, 47, and 42%, respectively. The food industry was in the majority of subgroups the most prominent researched sector and was frequently associated with high prevalence values of WMSDs. Incidence ratios of upper limb WMSDs ranged between 0.04 and 0.26. Incidence ratios could not be calculated for other anatomical regions due to the lack of sufficient articles. CONCLUSION: WMSDs are still highly present among blue collar workers. Relatively high prevalence values and low incidence ratios indicate a limited onset of WMSDs with however long-term complaints.

Social Processes: What Determines Industrial Workers' Intention to Use Exoskeletons?

OBJECTIVE: The aim of this study is to test the unified theory of acceptance and use of technology (UTAUT) model for explaining the intention to use exoskeletons among industrial workers. BACKGROUND: Exoskeletons could help reduce physical workload and risk for injuries among industrial workers. Therefore, it is crucial to understand which factors play a role in workers' intention to use such exoskeletons. METHOD: Industrial workers (N = 124) completed a survey on their attitudes regarding the use of exoskeletons at their workplace. Using partial least squares (PLS) path modeling, the UTAUT model and a revised version of the UTAUT model were fitted to these data. RESULTS: The adapted UTAUT model of Dwivedi et al. (2017) was able to explain up to 75.6% of the variance in intention to use exoskeletons, suggesting a reasonable model fit. CONCLUSION: The model fit suggests that effort expectancy (how easy it seems to use an exoskeleton) plays an important role in predicting the intention to use exoskeletons. Social influence (whether others think workers should use exoskeletons) and performance expectancy (how useful exoskeletons seem to be for work) play a smaller role in predicting the intention to use. APPLICATIONS: This research informs companies about the optimal implementation of exoskeletons by improving the determinants of acceptance among their workers.

Continuous Knee Cooling Affects Functional Hop Performance - A Randomized Controlled Trial.

Cryotherapy is widely used in sports and rehabilitation to aid recovery and injury management. The purpose was to examine if a low temperature computer controlled continuous knee cooling protocol (10°C) for one hour and a moderate continuous knee cooling protocol (18°C) for one hour affected neuromuscular activity and functional performance tests. We used a randomized controlled study design. Twenty healthy male subjects (age = 24 ± 3 years) were included and randomized into 2 groups (10°C and 18°C). On day one, participants performed a maximal voluntary contraction of the quadriceps (MVC), single leg hop for distance (SLHD), and crossover hop for time (COHT) with both legs before and after cooling of their right leg. At day two, the same tests were performed with both legs before and after cooling of the left leg. Participants exposed to the 10°C-protocol showed a significant decrease in SLHD and COHT performance. For the 18°C-group, no significant changes in SLHD and COHT outcomes were noted. In both groups, EMG frequency during MVC decreased, but no significant increases were found in EMG amplitude. Continuous knee cooling at 18°C for one hour does not affect functional hop performance, though adaptations at the muscle level (EMG frequency decrease) can be observed. Applying a similar cooling protocol with 10°C results in a significant decrease in functional hop performance and EMG frequency. EMG amplitude remained unaffected. This infers that changes at muscle level due to local temperature manipulations may not always be detrimental to functional performance.

The influence of a mild thermal challenge and severe hypoxia on exercise performance and serum BDNF.

AIM: To examine the isolated and combined effects of severe hypoxia and a mild thermal challenge on performance, physiological measures, cognition, and serum brain-derived neurotrophic factor (BDNF). METHODS: Nine trained male athletes (age: 23 ± 3 years; W max: 333 ± 45 W) completed four experimental trials (CON: 15 °C/0 m, ALT: 15 °C/3800 m, TEMP: 25 °C/0 m, ALT + TEMP: 25 °C/3800 m) in a double blind, randomized, cross-over design. Subjects cycled for 30 min in a self-paced test starting at 75% W max, their goal was to 'perform as much work as possible in 30 min.' Power output, heart rate, blood lactate, pulse oximetry, core and skin temperature, thermal sensation, ratings of perceived exertion, reaction time (RT), and BDNF were assessed. RESULTS: The amount of work produced in 30 min was reduced by temperature (F(1,8) = 7.1; p = 0.029; 360 ± 19 kJ in 15 °C; 344 ± 18 kJ in 25 °C) and altitude (F(1,8) = 94.2; p < 0.001; 427 ± 24 kJ at sea level; 277 ± 15 kJ at altitude), yet there was no interaction effect. Altitude increased mean RT (F(1,8) = 8.0; p = 0.022; 281.9 ± 9.4 ms at sea level; 289.3 ± 10.0 ms at altitude) and RT variability (F(1,8) = 8.5; p = 0.020; 44 ± 3 ms at sea level: 50 ± 4 ms at altitude). Exercise increased BDNF (F(1,8) = 15.2; p = 0.005; PRE: 21.8 ± 1.3 ng/mL; POST: 26.5 ± 2.1 ng/mL). CONCLUSION: Exercise capacity was significantly reduced due to an increase in altitude (3800 m; -34.3%) or a 10 °C increase in ambient temperature (-3.2%). The combination of both stressors showed to be additive (-38.0 %). Altitude induced an increase in RT and RT variability presenting a deterioration in cognitive functioning during acute hypoxia. Exercise significantly increased BDNF, but no effect of altitude on the BDNF concentration was observed.

Supplementation Strategies for Strength and Power Athletes: Carbohydrate, Protein, and Amino Acid Ingestion.

It is a common belief amongst strength and power athletes that nutritional supplementation strategies aid recovery by shifting the anabolic/catabolic profile toward anabolism. Factors such as nutrient quantity, nutrient quality, and nutrient timing significantly impact upon the effectiveness of nutritional strategies in optimizing the acute responses to resistance exercise and the adaptive response to resistance training (i.e., muscle growth and strength expression). Specifically, the aim of this review is to address carbohydrates (CHOs), protein (PRO), and/or amino acids (AAs) supplementation strategies, as there is growing evidence suggesting a link between nutrient signaling and the initiation of protein synthesis, muscle glycogen resynthesis, and the attenuation of myofibrillar protein degradation following resistance exercise. Collectively, the current scientific literature indicates that nutritional supplementation strategies utilizing CHO, PRO, and/or AA represents an important approach aimed at enhancing muscular responses for strength and power athletes, primarily increased muscular hypertrophy and enhanced strength expression. There appears to be a critical interaction between resistance exercise and nutrient-cell signaling associated with the principle of nutrient timing (i.e., pre-exercise, during, and post-exercise). Recommendations for nutritional supplementation strategies to promote muscular responses for strength and athletes are provided.

Deficits in neurocognitive performance in patients with chronic ankle instability during a neurocognitive balance task - A retrospective case-control study.

OBJECTIVES: To assess the neurocognitive performance while maintaining balance of patients experiencing CAI compared to healthy controls. In patients with CAI, the affected limb was also compared to the contralateral limb. DESIGN: A retrospective case-control study. SETTING: Laboratory study. PARTICIPANTS: We included 27 patients with CAI and 21 healthy controls. METHODS: The study consisted of two sessions, namely familiarisation and experimentation, which were scheduled with a gap of at least one week between them. During the experimental trial, both groups performed the Y-Balance Test and Reactive Balance Test once on each limb. MAIN OUTCOME MEASURES: The main outcome measures are accuracy and visuomotor response time (VMRT) calculated via video-analysis and with the Fitlight™-hardware and software respectively during the Reactive Balance Test (RBT). RESULTS: No data was excluded from the final analysis. Patients with CAI exhibited significantly lower accuracy than healthy controls, with a mean difference of 8.7% (±3.0)%. There were no differences for VMRT between groups. Additionally, no significant differences were observed between the affected and contralateral limb of the patient group for both accuracy and VMRT. CONCLUSIONS: Patients with CAI showed lower accuracy, but similar VMRT compared to healthy controls during a neurocognitive balance task, indicating impaired neurocognitive function. Patients exhibit comparable speed to healthy individuals when completing neurocognitive balance tasks, yet they display a higher frequency of accuracy errors in accurately perceiving their environment and making decisions under time constraints. Future research should gain more insights in which other cognitive domains are affected in patients with CAI for a better grasp of this condition's underlying mechanism.

Test-retest, intra- and inter-rater reliability of the reactive balance test in patients with chronic ankle instability.

Introduction: The Reactive Balance Test (RBT) could be a valuable addition to research on chronic ankle instability (CAI) and clinical practice, but before it can be used in clinical practice it needs to be reliable. It has already been proven reliable in healthy recreational athletes, but not yet in patients with CAI who have shown persistent deficits in dynamic balance. The study aimed to determine the test-retest, intra-, and inter-rater reliability of the RBT in patients with CAI, and the test-retest and inter-rater reliability of the newly developed RBT score sheet. Methods: We used a repeated-measures, single-group design to administer the RBT to CAI patients on three occasions, scored by multiple raters. We included 27 participants with CAI. The study used multiple reliability measures, including Pearson r, intra-class correlations (ICC), standard error of measurement (SEM), standard error of prediction (SEP), minimal detectable change (MDC), and Bland-Altman plots, to evaluate the reliability of the RBT's outcome measures (visuomotor response time and accuracy). It also assessed the test-retest and inter-rater reliability of the RBT score sheet using the same measures. Results: The ICC measures for test-retest reliability were similar for accuracy (0.609) and VMRT (0.594). Intra-rater reliability had high correlations and ICCs for accuracy (r = 0.816, ICC = 0.815) and VMRT (r = 0.802, ICC = 0.800). Inter-rater reliability had a higher ICC for VMRT (0.868) than for accuracy (0.690). Conclusion: Test-retest reliability was moderate, intra-rater reliability was good, and inter-rater reliability showed moderate reliability for accuracy and good reliability for VMRT. Additionally, the RBT shows robust SEM and mean difference measures. The score sheet method also demonstrated moderate test-retest reliability, while inter-rater reliability was good to excellent. This suggests that the RBT can be a valuable tool in assessing and monitoring balance in patients with CAI.

The Impact of Mental Fatigue on a Strength Endurance Task: Is There a Role for the Movement-Related Cortical Potential?

PURPOSE: Several mechanisms have been proposed to explain how mental fatigue degrades sport performance. In terms of endurance performance, a role for an increased perceived exertion has been demonstrated. Using electroencephalography and, more specifically, the movement-related cortical potential (MRCP), the present study explored the neural mechanisms that could underlie the mental fatigue-associated increase in perceived exertion. METHODS: Fourteen participants (age, 23 ± 2 yr; 5 women, 9 men) performed one familiarization and two experimental trials in a randomized, blinded, crossover study design. Participants had to complete a submaximal leg extension task after a mentally fatiguing task (EXP; individualized 60-min Stroop task) or control task (CON; documentary). The leg extension task consisted of performing 100 extensions at 35% of 1 repetition maximum, during which multiple physiological (heart rate, electroencephalography) and subjective measures (self-reported feeling of mental fatigue, cognitive load, behand motivation, ratings of perceived exertion) were assessed. RESULTS: Self-reported feeling of mental fatigue was higher in EXP (72 ± 18) compared with CON (37 ± 17; P < 0.001). A significant decrease in flanker accuracy was detected only in EXP (from 0.96 ± 0.03% to 0.03%; P < 0.05). No significant differences between conditions were found in MRCP characteristics and perceived exertion. Specifically in EXP, alpha wave power increased during the leg extension task ( P < 0.01). CONCLUSIONS: Mental fatigue did not impact the perceived exertion or MRCP characteristics during the leg extension task. This could be related to low perceived exertion and/or the absence of a performance outcome during the leg extension task. The increase in alpha power during the leg extension task in EXP suggests that participants may engage a focused internal attention mechanism to maintain performance and mitigate feelings of fatigue.

Human-Prosthetic Interaction (HumanIT): A study protocol for a clinical trial evaluating brain neuroplasticity and functional performance after lower limb loss.

BACKGROUND: Lower limb amputation contributes to structural and functional brain alterations, adversely affecting gait, balance, and overall quality of life. Therefore, selecting an appropriate prosthetic ankle is critical in enhancing the well-being of these individuals. Despite the availability of various prostheses, their impact on brain neuroplasticity remains poorly understood. OBJECTIVES: The primary objective is to examine differences in the degree of brain neuroplasticity using magnetic resonance imaging (MRI) between individuals wearing a new passive ankle prosthesis with an articulated ankle joint and a standard passive prosthesis, and to examine changes in brain neuroplasticity within these two prosthetic groups. The second objective is to investigate the influence of prosthetic type on walking performance and quality of life. The final objective is to determine whether the type of prosthesis induces differences in the walking movement pattern. METHODS: Participants with a unilateral transtibial amputation will follow a 24-week protocol. Prior to rehabilitation, baseline MRI scans will be performed, followed by allocation to the intervention arms and commencement of rehabilitation. After 12 weeks, baseline functional performance tests and a quality of life questionnaire will be administered. At the end of the 24-week period, participants will undergo the same MRI scans, functional performance tests and questionnaire to evaluate any changes. A control group of able-bodied individuals will be included for comparative analysis. CONCLUSION: This study aims to unravel the differences in brain neuroplasticity and prosthesis type in patients with a unilateral transtibial amputation and provide insights into the therapeutic benefits of prosthetic devices. The findings could validate the therapeutic benefits of more advanced lower limb prostheses, potentially leading to a societal impact ultimately improving the quality of life for individuals with lower limb amputation. TRIAL REGISTRATION: NCT05818410 (Clinicaltrials.gov).

Evaluating the real-world usability of BCI control systems with augmented reality: a user study protocol.

Brain-computer interfaces (BCI) enable users to control devices through their brain activity. Motor imagery (MI), the neural activity resulting from an individual imagining performing a movement, is a common control paradigm. This study introduces a user-centric evaluation protocol for assessing the performance and user experience of an MI-based BCI control system utilizing augmented reality. Augmented reality is employed to enhance user interaction by displaying environment-aware actions, and guiding users on the necessary imagined movements for specific device commands. One of the major gaps in existing research is the lack of comprehensive evaluation methodologies, particularly in real-world conditions. To address this gap, our protocol combines quantitative and qualitative assessments across three phases. In the initial phase, the BCI prototype's technical robustness is validated. Subsequently, the second phase involves a performance assessment of the control system. The third phase introduces a comparative analysis between the prototype and an alternative approach, incorporating detailed user experience evaluations through questionnaires and comparisons with non-BCI control methods. Participants engage in various tasks, such as object sorting, picking and placing, and playing a board game using the BCI control system. The evaluation procedure is designed for versatility, intending applicability beyond the specific use case presented. Its adaptability enables easy customization to meet the specific user requirements of the investigated BCI control application. This user-centric evaluation protocol offers a comprehensive framework for iterative improvements to the BCI prototype, ensuring technical validation, performance assessment, and user experience evaluation in a systematic and user-focused manner.

Electrophysiological impact of mental fatigue on brain activity during a bike task: A wavelet analysis approach.

This study explored how mental fatigue affects brain activity during a low-intensity bike task utilising a continuous wavelet transformation in electroencephalography (EEG) analysis. The aim was to examine changes in brain activity potentially linked to central motor commands and to investigate their relationship with ratings of perceived exertion (RPE). In this study, sixteen participants (age: 21 ± 6 y, 7 females, 9 males) underwent one familiarization and two experimental trials in a randomised, blinded, cross-over study design. Participants executed a low-intensity bike task (9 min; 45 rpm; intensity (W): 10 % below aerobic threshold) after performing a mentally fatiguing (individualized 60-min Stroop task) or a control (documentary) task. Physiological (heart rate, EEG) and subjective measures (self-reported feeling of mental fatigue, RPE, cognitive load, motivation) were assessed prior, during and after the bike task. Post-Stroop, self-reported feeling of mental fatigue was higher in the intervention group (EXP) (74 ± 16) than in the control group (CON) (37 ± 17; p < 0.001). No significant differences in RPE during the bike task were observed between conditions. EEG analysis revealed significant differences (p < 0.05) in beta frequency (13-30 Hz) during the bike task, with EXP exhibiting more desynchronization during the pedal push phase and synchronization during the pedal release phase. These results suggest that mental fatigue, confirmed by both subjective and neurophysiological markers, did not significantly impact RPE during the bike task, possibly due to the use of the CR100 scale or absence of a performance outcome. However, EEG data did reveal significant beta band alterations during the task, indicating increased neural effort under mental fatigue. These findings reveal, for the first time, how motor-related brain activity at the motor cortex is impacted during a low-intensity bike task when mentally fatigued.

An EMG-Based Objective Function for Human-in-the-Loop Optimization.

Advancements in wearable robots aim to improve the users' motion, performance, and comfort by optimizing, mainly, energetic cost (EC). However, EC is a noisy measurement with a physiological delayed response that requires long evaluation periods and wearing an uncomfortable mask. This study aims to estimate and minimize an EMG-based objective function that describes the natural energetic expenditure of individuals walking. This objective is assessed by combining multiple electromyography (EMG) variables from the EMG intensity and muscle synergies. To evaluate this objective function simply and repeatedly, we prescribed step frequency (SF) via a metronome and optimized this frequency to minimize muscle activity demands. Further, a linear mixed-effects model was fitted for EC, with the EMG variables as fixed-effects and a random intercept that varies by participant. After the model was fitted to the data, a cubic polynomial was used to identify the optimal SF that reduces the overall EMG-based objective function. Our analysis outlines that the proposed objective function is comparable to the EC during walking, the primary objective function used in human-in-the-loop optimization. Thus, this EMG-based objective function could be potentially used to optimize wearable robots and improve human-robot interaction.

The Dynamic Adoption Journey: A Typology for Users and Non-Users of Occupational Exoskeletons.

Various barriers prevent the adoption of occupational exoskeletons. It is therefore important to understand why some people are willing to use occupational exoskeletons, while others are not. To identify why people use or do not use exoskeletons, we created a typology describing different types of users and non-users. These types were created based on existing literature on internet adoption and social robots. Next, literature and empirical data were used to identify reasons why some people use exoskeletons and others do not use them (yet). The typology includes users with pain and users without work-related musculoskeletal disorders, but also non-users: resisters, rejecters, discontinuers, excluded or expelled non-users. It can be used by companies interested in implementing exoskeletons to identify possible early adopters. For exoskeleton designers, it can be used as a tool to identify non-users and focus on design strategies to enable non-users to become users (such as making exoskeletons that would fit people with a wide range of body shapes). Future research can use these types to identify users and non-users in field trials or pilot projects.

Evaluating cognitive and physical work performance: A comparative study of an active and passive industrial back-support exoskeleton.

Occupational back-support exoskeletons, categorized as active or passive, hold promise for mitigating work-related musculoskeletal disorders. However, their impact on combined physical and cognitive aspects of industrial work performance remains inadequately understood, especially regarding potential differences between exoskeleton categories. A randomized, counterbalanced cross-over study was conducted, comparing the active CrayX, passive Paexo Back, and a no exoskeleton condition. A 15-min dual task was used to simulate both cognitive and physical aspects of industrial work performance. Cognitive workload parameters included reaction time, accuracy, and subjective measures. Physical workload included movement duration, segmented in three phases: (1) walking to and grabbing the box, (2) picking up, carrying, and putting down the box, and (3) returning to the starting point. Comfort of both devices was also surveyed. The Paexo significantly increased movement duration in the first segment compared to NoExo (Paexo = 1.55 ± 0.19 s; NoExo = 1.32 ± 0.17 s; p < .01). Moreover, both the Paexo and CrayX increased movement duration for the third segment compared to NoExo (CrayX = 1.70 ± 0.27 s; Paexo = 1.74 ± 0.27 s, NoExo = 1.54 ± 0.23 s; p < .01). No significant impact on cognitive outcomes was observed. Movement Time 2 was not significantly affected by both exoskeletons. Results of the first movement segment suggest the Paexo may hinder trunk bending, favoring the active device for dynamic movements. Both devices may have contributed to a higher workload as the movement duration in the third segment increased compared to NoExo.