Mental fatigue induced by prolonged motor imagery increases perception of effort and the activity of motor areas

Neurophysiologically Meaningful Motor Imagery EEG Simulation With Applications to Data Augmentation

Motor imagery-based Brain-Computer Interfaces (MI-BCIs) have gained a lot of attention due to their potential usability in neurorehabilitation and neuroprosthetics. However, the accurate recognition of MI patterns in electroencephalography signals (EEG) is hindered by several data-related limitations, which restrict the practical utilization of these systems. Moreover, leveraging deep learning (DL) models for MI decoding is challenged by the difficulty of accessing user-specific MI-EEG data on large scales. Simulated MI-EEG signals can be useful to address these issues, providing well-defined data for the validation of decoding models and serving as a data augmentation approach to improve the training of DL models. While substantial efforts have been dedicated to implementing effective data augmentation strategies and model-based EEG signal generation, the simulation of neurophysiologically plausible EEG-like signals has not yet been exploited in the context of data augmentation. Furthermore, none of the existing approaches have integrated user-specific neurophysiological information during the data generation process. Here, we present PySimMIBCI, a framework for generating realistic MI-EEG signals by integrating neurophysiologically meaningful activity into biophysical forward models. By means of PySimMIBCI, different user capabilities to control an MI-BCI can be simulated and fatigue effects can be included in the generated EEG. Results show that our simulated data closely resemble real data. Moreover, a proposed data augmentation strategy based on our simulated user-specific data significantly outperforms other state-of-the-art augmentation approaches, enhancing DL models performance by up to 15%.

Relationship between physical fatigue and mental fatigue based on multimodal measurement under different load levels

Based on multimodal measurement methods of NASA task load index (NASA-TLX), task performance, surface electromyography (sEMG), heart rate (HR), and functional near-infrared spectroscopy (fNIRS), this study conducted experimental measurements and analyses under 16 different load levels of physical fatigue and mental fatigue combination conditions. This study observed the interaction between physical fatigue and mental fatigue at different levels, and at the subjective level, the effect of physical fatigue on mental fatigue was greater than that of mental fatigue on physical fatigue. Secondly, the results of fNIRS analysis showed that the premotor cortex is affected by physical fatigue, and the dorsolateral prefrontal cortex is affected by mental fatigue. Finally, this study constructed a fatigue classification model with an accuracy of 95.3%, which takes multimodal physiological data as input and 16 fatigue states as output. The research results will provide a basis for fatigue analysis, evaluation, and improvement in complex working situations.

Enhancing endurance performance with combined imagined and actual physical practice

PURPOSE

The perception of effort exerts influence in determining task failure during endurance performance. Training interventions blending physical and cognitive tasks yielded promising results in enhancing performance. Motor imagery can decrease the perception of effort. Whether combining motor imagery and physical training improves endurance remains to be understood, and this was the aim of this study.

METHODS

Participants (24 ± 3 year) were assigned to a motor imagery (n = 16) or a control (n = 17) group. Both groups engaged in physical exercises targeting the knee extensors (i.e., wall squat, 12 training sessions, 14-days), with participants from the motor imagery group also performing motor imagery. Each participant visited the laboratory Pre and Post-training, during which we assessed endurance performance through a sustained submaximal isometric knee extension contraction until task failure, at either 20% or 40% of the maximal voluntary contraction peak torque. Perceptions of effort and muscle pain were measured during the exercise.

RESULTS

We reported no changes in endurance performance for the control group. Endurance performance in the motor imagery group exhibited significant improvements when the intensity of the sustained isometric exercise closely matched that used in training. These enhancements were less pronounced when considering the higher exercise intensity. No reduction in perception of effort was observed in both groups. There was a noticeable decrease in muscle pain perception within the motor imagery group Post training.

CONCLUSION

Combining motor imagery and physical training may offer a promising avenue for enhancing endurance performance and managing pain in various contexts.

Effect of mental fatigue on hand force production capacities

Mental fatigue is common in society, but its effects on force production capacities remain unclear. This study aimed to investigate the impact of mental fatigue on maximal force production, rate of force development-scaling factor (RFD-SF), and force steadiness during handgrip contractions. Fourteen participants performed two randomized sessions, during which they either carried out a cognitively demanding task (i.e., a visual attention task) or a cognitively nondemanding task (i.e., documentary watching for 62 min). The mental fatigue was evaluated subjectively and objectively (performances and electroencephalography). Maximal voluntary contraction (MVC) force, RFD-SF, and force steadiness (i.e., force coefficient of variation at submaximal intensities; 25, 50, and 75% of MVC) were recorded before and after both tasks. The feeling of mental fatigue was much higher after completing the cognitively demanding task than after documentary watching (p < .001). During the cognitively demanding task, mental fatigue was evidenced by increased errors, missed trials, and decreased N100 amplitude over time. While no effect was reported on force steadiness, both tasks induced a decrease in MVC (p = .040), a force RFD-SF lower slope (p = .011), and a reduction in the coefficient of determination (p = .011). Nevertheless, these effects were not explicitly linked to mental fatigue since they appeared both after the mentally fatiguing task and after watching the documentary. The study highlights the importance of considering cognitive engagement and mental load when optimizing motor performance to mitigate adverse effects and improve force production capacities.

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.

Cortical activation and BCI performance during brief tactile imagery: A comparative study with motor imagery

Brain-computer interfaces (BCIs) rely heavily on motor imagery (MI) for operation, yet tactile imagery (TI) presents a novel approach that may be advantageous in situations where visual feedback is impractical. The current study aimed to compare the cortical activity and digit classification performance induced by TI and MI to assess the viability of TI for use in BCIs. Twelve right-handed participants engaged in trials of TI and MI, focusing on their left and right index digits. Event-related desynchronization (ERD) in the mu and beta bands was analyzed, and classification accuracy was determined through an artificial neural network (ANN). Comparable ERD patterns were observed in both TI and MI, with significant decreases in ERD during imagery tasks. The ANN demonstrated high classification accuracy, with TI achieving a mean±SD of 79.30 ± 3.91 % and MI achieving 81.10 ± 2.96 %, with no significant difference between the two (p = 0.11). The study found that TI induces substantial ERD comparable to MI and maintains high classification accuracy, supporting its potential as an effective mental strategy for BCIs. This suggests that TI could be a valuable alternative in BCI applications, particularly for individuals unable to rely on visual cues.

Sleep-related motor skill consolidation and generalizability after physical practice, motor imagery, and action observation

Sleep benefits the consolidation of motor skills learned by physical practice, mainly through periodic thalamocortical sleep spindle activity. However, motor skills can be learned without overt movement through motor imagery or action observation. Here, we investigated whether sleep spindle activity also supports the consolidation of non-physically learned movements. Forty-five electroencephalographic sleep recordings were collected during a daytime nap after motor sequence learning by physical practice, motor imagery, or action observation. Our findings reveal that a temporal cluster-based organization of sleep spindles underlies motor memory consolidation in all groups, albeit with distinct behavioral outcomes. A daytime nap offers an early sleep window promoting the retention of motor skills learned by physical practice and motor imagery, and its generalizability toward the inter-manual transfer of skill after action observation. Findings may further have practical impacts with the development of non-physical rehabilitation interventions for patients having to remaster skills following peripherical or brain injury.

A Quantitative Investigation of Mental Fatigue Elicited during Motor Imagery Practice: Selective Effects on Maximal Force Performance and Imagery Ability

In the present study, we examined the development of mental fatigue during the kinesthetic motor imagery (MI) of isometric force contractions performed with the dominant upper limb. Participants (n = 24) underwent four blocks of 20 MI trials of isometric contractions at 20% of the maximal voluntary contraction threshold (20% MVC_MI) and 20 MI trials of maximal isometric contractions (100% MVC_MI). Mental fatigue was assessed after each block using a visual analogue scale (VAS). We assessed maximal isometric force before, during and after MI sessions. We also assessed MI ability from self-report ratings and skin conductance recordings. Results showed a logarithmic pattern of increase in mental fatigue over the course of MI, which was superior during 100% MVC_MI. Unexpectedly, maximal force improved during 100% MVC_MI between the 1st and 2nd evaluations but remained unchanged during 20% MVC_MI. MI ease and vividness improved during 100% MVC_MI, with a positive association between phasic skin conductance and VAS mental fatigue scores. Conversely, subjective measures revealed decreased MI ability during 20% MVC_MI. Mental fatigue did not hamper the priming effects of MI on maximal force performance, nor MI's ability for tasks involving high physical demands. By contrast, mental fatigue impaired MI vividness and elicited boredom effects in the case of motor tasks with low physical demands.

Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-analysis

BACKGROUND

The perception of effort provides information on task difficulty and influences physical exercise regulation and human behavior. This perception differs from other-exercise related perceptions such as pain. There is no consensus on the role of group III/IV muscle afferents as a signal processed by the brain to generate the perception of effort.

OBJECTIVE

The aim of this meta-analysis was to investigate the effect of pharmacologically blocking muscle afferents on the perception of effort.

METHODS

Six databases were searched to identify studies measuring the ratings of perceived effort during physical exercise, with and without pharmacological blockade of muscle afferents. Articles were coded based on the operational measurement used to distinguish studies in which perception of effort was assessed specifically (effort dissociated) or as a composite experience including other exercise-related perceptions (effort not dissociated). Articles that did not provide enough information for coding were assigned to the unclear group.

RESULTS

The effort dissociated group (n = 6) demonstrated a slight increase in ratings of perceived effort with reduced muscle afferent feedback (standard mean change raw, 0.39; 95% confidence interval 0.13-0.64). The group effort not dissociated (n = 2) did not reveal conclusive results (standard mean change raw, - 0.29; 95% confidence interval - 2.39 to 1.8). The group unclear (n = 8) revealed a slight ratings of perceived effort decrease with reduced muscle afferent feedback (standard mean change raw, - 0.27; 95% confidence interval - 0.50 to - 0.04).

CONCLUSIONS

The heterogeneity in results between groups reveals that the inclusion of perceptions other than effort in its rating influences the ratings of perceived effort reported by the participants. The absence of decreased ratings of perceived effort in the effort dissociated group suggests that muscle afferent feedback is not a sensory signal for the perception of effort.

Perception of effort and the allocation of physical resources: A generalization to upper-limb motor tasks

Purpose

The perception of effort (PE) is widely used to prescribe and monitor exercise during locomotor and resistance tasks. The present study examines the validity of PE to prescribe and monitor exercise during upper-limb motor tasks under various loads and speed requirements.

Methods

Forty participants volunteered in two experiments. In experiment 1, we used four PE intensities to prescribe exercise on a modified version of the box and block test (BBT) and a pointing task. We investigated the possibility of monitoring the exercise intensity by tracking changes in PE rating in response to three different tempos or additional weights. Experiment 2 replicated the possibility of prescribing the exercise with the PE intensity during the BBT and explored the impact of additional weights on performance and PE during the standardized version of the BBT. Muscle activation, heart rate, and respiratory frequencies were recorded.

Results

In experiment 1, increasing the PE intensity to prescribe exercise induced an increased performance between each intensity. Increasing task difficulty with faster movement tempo and adding weight on the forearm increased the rating of PE. Experiment 2 replicated the possibility to use PE intensity for exercise prescription during the BBT. When completing the BBT with an additional weight on the forearm, participants maintained performance at the cost of a higher PE. In both experiments, changes in PE were associated with changes in muscle activation.

Conclusion

Our results suggest that PE is a valid tool to prescribe and monitor exercise during upper-limb motor tasks.

Mental fatigue and negative emotion among nurses during the COVID-19 pandemic

COVID-19 is a major public health event affecting the people worldwide. Nurses are still under immense psychological pressure. This study aimed to explore the relationship between mental fatigue and negative emotions among frontline medical staff during the COVID-19 pandemic. The study was conducted in August 2020, which included 419 medical staff between 17 to 28 years. The Fatigue Scale, Multidimensional Mental Flexibility Questionnaire, Cognitive Fusion Scale, and Depression-Anxiety-Stress Brief Version Scale were used. During the data collection period, the pandemic was under control in China and continued worldwide. The results indicated that 27.7% of the medical staff experienced depression, and 32.3% of them feel stressed. Specifically, first, correlation analyses showed significant positive pairwise correlations between mental fatigue, psychological inflexibility, cognitive fusion, and negative emotions among nurses. Second, mediation model tests showed statistically significant mediating effects of psychological inflexibility and cognitive fusion between mental fatigue on nurses' negative emotions, and statistically, significant chain mediating effects of psychological inflexibility and cognitive fusion. Mental fatigue indirectly affects nurses' negative effects through the mediating effects of psychological inflexibility, cognitive fusion, and the chain mediating effects of psychological inflexibility and cognitive fusion, respectively. the negative effects of mental fatigue come from impairment of cognitive functioning, and interventions using acceptance and commitment therapy for mental fatigue and negative emotions are more effective since both psychological inflexibility and cognitive fusion are important components of the therapy.

Exploring Fatigue Effects on Performance Variation of Intensive Brain-Computer Interface Practice

Motor imagery (MI) is an endogenous mental process and is commonly used as an electroencephalogram (EEG)-based brain-computer interface (BCI) strategy. Previous studies of P300 and MI-based (without online feedback) BCI have shown that mental states like fatigue can negatively affect participants' EEG signatures. However, exogenous stimuli cause visual fatigue, which might have a different mechanism than endogenous tasks do. Furthermore, subjects could adjust themselves if online feedback is provided. In this sense, it is still unclear how fatigue affects online MI-based BCI performance. With this question, 12 healthy subjects are recruited to investigate this issue, and an MI-based online BCI experiment is performed for four sessions on different days. The first session is for training, and the other three sessions differ in rest condition and duration-no rest, 16-min eyes-open rest, and 16-min eyes-closed rest-arranged in a pseudo-random order. Multidimensional fatigue inventory (MFI) and short stress state questionnaire (SSSQ) reveal that general fatigue, mental fatigue, and distress have increased, while engagement has decreased significantly within certain sessions. However, the BCI performances, including percent valid correct (PVC) and information transfer rate (ITR), show no significant change across 400 trials. The results suggest that although the repetitive MI task has affected subjects' mental states, their BCI performances and feature separability within a session are not affected by the task significantly. Further electrophysiological analysis reveals that the alpha-band power in the sensorimotor area has an increasing tendency, while event-related desynchronization (ERD) modulation level has a decreasing trend. During the rest time, no physiological difference has been found in the eyes-open rest condition; on the contrary, the alpha-band power increase and subsequent decrease appear in the eyes-closed rest condition. In summary, this experiment shows evidence that mental states can change dramatically in the intensive MI-BCI practice, but BCI performances could be maintained.

Physical Activity and Music to Counteract Mental Fatigue

Mental fatigue impairs both cognitive and physical performance. Bioactive substances (e.g., caffeine) have been used to counteract mental fatigue but could have side effects. The present study aimed to test two non-bioactive strategies to counteract mental fatigue: physical activity and listening to music. The participants first performed an arm-pointing task, then carried out a 32-min cognitively demanding task to induce mental fatigue (TLDB task), followed by another arm-pointing task at the end of the experiment. Between the end of the cognitively demanding task and the last arm-pointing task, 20 min went during which participants performed either 15 min of physical activity, of listening to music or of discussion (control). The subjective feeling of mental fatigue was assessed before each arm-pointing task and after the cognitively demanding task. For "physical activity" and "listening to music" groups, EEG was recorded at rest after each evaluation of subjective feeling of mental fatigue and during the cognitively demanding task. An increase in alpha power during the cognitively demanding task evidenced the presence of mental fatigue, without recovery during the following 20-min period. In the control condition, the arm-pointing task performance was deteriorated 20-min after the cognitively demanding task, while it remained stable after both physical activity and listening to music. Furthermore, recovery on the subjective feeling of mental fatigue was similar for both groups. The present results suggested that practicing physical activity and listening to music could be efficient strategies to counteract the negative effects of mental fatigue on motor performances.

Work Fatigue in a Hospital Setting: The Experience at Cheng Hsin General Hospital

We aimed to investigate fatigue and its related factors in a medical professional population aged ≥30 years, as appraised by the implementation of an employee health screening program at Cheng Hsin General Hospital in Taipei, Taiwan. The study participants included a total of 2132 (400 males and 1732 females) healthy medical professionals enrolled in a teaching hospital who underwent physical verification in 2019. Demographic characteristics and fatigue information were collected. The overall prevalence of personal- and work-related fatigue in this study population was 41.4% and 39.1%, respectively. The prevalence of a high risk of work- or personal-related fatigue proved to be substantially greater (p-value for chi-square test <0.0001) than it was for a low or moderate risk of personal-related fatigue. Using multinominal logistic regression analysis, seniority and position were statistically significant in relation to a high risk of personal- and work-related fatigue. Personal- and work-related fatigue were found to be prevalent in physicians and nurses. Lower seniority was also related to severe personal- or work-related fatigue. Providing this population with controlled working environments and health improvements is important.

Perception of effort during an isometric contraction is influenced by prior muscle lengthening or shortening

PURPOSE

Following a shortening or lengthening muscle contraction, torque produced in the isometric steady state is lower (residual torque depression; rTD) or higher (residual torque enhancement; rTE), respectively, compared to a purely isometric contraction at the same final muscle length and level of activation. This is referred to as the history dependence of force. When matching a given torque level, there is greater muscle activation (electromyography; EMG) following shortening and less activation following lengthening. Owing to these differences in neuromuscular activation, it is unclear whether perception of effort is altered by the history dependence of force during plantar-flexion.

METHODS

Experiment 1 tested whether perception of effort differed between the rTD and rTE state when torque was matched. Experiment 2 tested whether perception of effort differed between the rTD and rTE state when EMG was matched. Finally, experiment 3 tested whether EMG differed between the rTD and rTE state when perception of effort was matched.

RESULTS

When torque was matched, both EMG and perception of effort were higher in the rTD compared to rTE state. When EMG was matched, torque was lower in the rTD compared to rTE state while perception of effort did not differ between the two states. When perception of effort was matched, torque was lower in the rTD compared to rTE state and EMG did not differ between the two states.

CONCLUSION

The combined results from these experiments indicate that the history dependence of force alters one's perception of effort, dependent on the level of motor command.