The capacity of firefighters to consistently mobilize their full physical potential during duty shifts is of paramount importance. One promising approach to achieving this goal involves developing operational protocols that effectively activate the sympathetic nervous system and vagal regulation prior to each professional action. This study investigated the effects of combining mental imagery and conscious breathing exercises with a conventional and standard warm-up on cardiac modulations, muscular strength and endurance performance in 34 firefighters randomly assigned to one of two groups: a control group (n = 17), which performed only the conventional and standard warm-up, and an experimental group (n = 17), which performed the standard warm-up in combination with mental imagery and breathing exercises. The results showed that incorporating such psychophysiological techniques into a conventional warm-up routine during repeated physical efforts optimizes sympathetic spectral power, heart rate responses, and physical performances, including maximal voluntary isometric handgrip contraction, maximum push-ups, and the maximal abdominal plank duration. Altogether, these findings indicate that brief mental imagery and controlled breathing exercises incorporated into standard warm-up routines effectively preserve muscular performance under repeated exertion while enhancing sympathetic activation, offering a practical and immediately applicable strategy to optimize firefighters' operational readiness.

IntroductionProcedural Perceptual-Motor Learning (PPML) enables the acquisition of new motor procedures and is fundamental for a wide range of human behaviors. While traditional research has focused on task-related characteristics, there is growing interest in individual factors to account for inter-individual differences in PPML. This study aims to investigate the roles of two individual factors related to learners’ strategies and mindsets: (a) explicit knowledge of the task’s characteristics and regularities and (b) subjective evaluation of the task and performance. We hypothesized that (a) participants reporting explicit knowledge of the task would exhibit higher PPML scores compared to those who did not, and (b) PPML scores would be related to subjective evaluation.MethodsParticipants were invited to practice two types of PPML tasks: motor sequence learning assessed by a Serial Reaction Time Task (SRTT) (Experiment 1) and visuomotor adaptation assessed by a Target Jumping Task (TJT) (Experiment 2). After each task, they were asked to answer post-learning questions about (a) their explicit knowledge of the task’s rules and (b) their subjective evaluations, including perceived levels of stress, tiredness, motivation, attention, and perceived progress.ResultsThe findings of Experiment 1 revealed that participants reporting explicit knowledge of the SRTT exhibited higher learning scores, which were related to perceived stress and progress. In Experiment 2, participants reporting explicit knowledge of the TJT exhibited lower learning scores, which were related to perceived stress, tiredness, concentration, and progress.DiscussionThis study offers a novel and comprehensive perspective on inter-individual differences in PPML by considering the roles of explicit knowledge and subjective evaluations in two types of PPML tasks. Although further replication and generalization are necessary, the findings provide valuable insights into how learner-task interactions may explain inter-individual differences and highlight the importance of considering participants’ subjective reports research for future studies on PPML.

Procedural Perceptual-Motor Learning (PPML) refers to the process leading to the acquisition of new motor skills through repeated practice. It is crucial to (re-)acquire skills needed in daily life and rehabilitation. It can be divided in two processes: motor sequence learning (SL) and sensorimotor adaptation (SA). SL refers to the acquisition of a sequence of actions that follows a precise order, while SA involves continuously adjusting motor outputs to compensate for environmental or internal disturbances. These two processes are typically measured using different lab-based tasks and are presumed to play a role in ecological/ naturalistic tasks. However, to our knowledge, no study examined the relationship between performance on lab-based tasks and ecological/ naturalistic tasks. To address this gap, we designed two lab-based tasks and six ecological tasks assessing SL and SA in an original research including 42 participants (young adults). After ensuring with non-parametric repeated measures ANOVA that all the tasks presented features of learning (all 15.1 < χ ² < 142; p < 0.5), Spearman’s rank correlation tests were performed between each lab-based task measuring SL and SA and the six ecological tasks. Our findings reveal low to moderate correlations between lab-based and ecological tasks measuring SL and SA (0.265 < rho < 0.395; p < 0.05). This suggests that the lab-based tasks partially reflect PPML as it occurs in everyday life. We believe that the partial ecological validity of these lab-based tasks is essential for their use, especially in the context of clinical evaluation prior to rehabilitation.

Current musculoskeletal models often oversimplify the neural strategies underlying muscle activation, potentially leading to unsatisfactory estimates of muscle forces. Numerous studies in motor control have established that the central nervous system synchronizes muscle activation by sending a common drive to synergistic muscles, measurable through intermuscular coherence - the frequency correlation between two EMG signals. As interest grows in understanding how muscles synchronize during movement coordination, leveraging intermuscular coherence into musculoskeletal models represents an innovative approach. This could enhance the accuracy of muscle effort estimation and introduce a physiologically meaningful component of motor control. In this study, we introduce a new method that decomposes EMG signals into common and independent components, informed by intermuscular coherence, and integrates them into an EMG-driven model to estimate muscle moments. Using data from twenty-four healthy subjects performing horizontal upper limb extensions, we estimated moments of the four main muscles actuating the elbow and compared these estimations with those from a traditional EMG-driven model informed by full-wave rectified signal envelopes. Our results demonstrate that incorporating intermuscular coherence significantly enhanced kinetic data tracking and improved the robustness of muscle moment estimations against variations in model parameters, addressing a major limitation of traditional EMG-driven models. Furthermore, antagonist muscle moments were more accurately represented, resulting in more realistic co-contraction index values. By integrating neural control strategies via intermuscular coherence into musculoskeletal models, the proposed approach offers a more accurate representation of muscle coordination. We recommend that future neuromusculoskeletal models incorporate intermuscular coherence to improve physiological realism of muscle effort estimations.

Sensorimotor synchronization (SMS) is a natural human behavior associated with the perception of predictable, isochronous and environmental rhythmic stimuli. The main objective of this study is to test the conditions that improve the behavioral stability and accuracy of rhythmic SMS. We tested the interaction between different sensory modalities and tempos on the behavior and cerebral activities related to the production and perception of rhythmic stimuli. To this aim, participants were required to produce a SMS and continuation task (production task) and a perception task with 4 modalities (unimodal auditory stimuli, unimodal visual stimuli, bimodal audio-visual congruent - presented simultaneously - or bimodal audio-visual incongruent - presented non-simultaneously - rhythmic stimuli) and 3 different tempos (500 ms, 700 ms and 900 ms). Firstly, both auditory and congruent audiovisual modalities led to more stable SMS compared to the visual modality. Compared to the SMS with incongruent audiovisual modality, SMS with the congruent audiovisual modality led to higher EEG spectral power in the α frequency band over the superior parietal cortex, suggesting lower involvement of attentional/cognitive processes. Secondly, compared to 500 ms, the 900 ms tempo led to the most stable SMS and higher EEG spectral power relative to sensorimotor and attentional/cognitive processes during both SMS and perception. Thirdly, the SMS was the least stable for the 500 ms tempo and for the visual modality. Our results highlight higher stability of SMS and/or lower involvement of sensorimotor and attentional processes for the slowest required tempo (here, 900 ms) and for congruent audio-visual stimuli, suggesting that these conditions are optimal for rhythmic production. These findings provide new cues to understanding the effects of rhythmic-based interventions, especially in the context of sports training and rehabilitation programs.

BackgroundCharacterization of motor deficits after brain injury is important for rehabilitation personalization. While studies reported abnormalities in the kinematics of paretic and non-paretic elbow extension for patients with brain injuries, kinematic analysis is not sufficient to explore how patients deal with musculoskeletal redundancy and the energetic aspect of movement execution. Conversely, interarticular coordination and movement kinetics can reflect patients' motor strategies. This study investigates motor strategies of paretic and non-paretic upper limb after brain injury to highlight motor deficits or compensation strategies.Methods26 brain-injured hemiplegic patients and 24 healthy controls performed active elbow extensions in the horizontal plane, with both upper limbs for patients and, with the dominant upper limb for controls. Elbow and shoulder kinematics, interarticular coordination, net joint kinetics were quantified.FindingsResults show alterations in kinematics, and a strong correlation between elbow and shoulder angles, as well as time to reach elbow and shoulder peak angular velocity in both upper limbs of patients. Net joint kinetics were lower for paretic limb and highlighted a fragmented motor strategy with increased number of transitions between concentric and eccentric phases.InterpretationIn complement to kinematic results, our kinetic results confirmed patients' difficulties to manage both spatially and temporally the joint degrees of freedom redundancy but revealed a fragmented compensatory motor strategy allowing patients upper limb extension despite quality alteration and decrease in energy efficiency. Motor rehabilitation should improve the management of this fragmentation strategy to improve the performance and the efficiency of active movement after brain injury.

IntroductionSeveral studies in psychology provided compelling evidence that emotions significantly impact motor control. Yet, these evidences mostly rely on behavioral investigations, whereas the underlying neurophysiological processes remain poorly understood.MethodsUsing a classical paradigm in motor control, we tested the impact of affective pictures associated with positive, negative or neutral valence on the kinematics and patterns of muscle activations of arm pointing movements performed from a standing position. The hand reaction and movement times were measured and electromyography (EMG) was used to measure the activities from 10 arm, leg and trunk muscles that are involved in the postural maintenance and arm displacement in pointing movements. Intermuscular coherence (IMC) between pairs of muscles was computed to measure changes in patterns of muscle activations related to the emotional stimuli.ResultsThe hand movement time increased when an emotional picture perceived as unpleasant was presented as compared to when the emotional picture was perceived as pleasant. When an unpleasant emotional picture was presented, beta (β, 15–35 Hz) and gamma (γ, 35–60 Hz) IMC decreased in the recorded pairs of postural muscles during the initiation of pointing movements. Moreover, a linear relationship between the magnitude of the intermuscular coherence in the pairs of posturo-focal muscles and the hand movement time was found in the unpleasant scenarios.DiscussionThese findings reveal that emotional stimuli can significantly affect the content of the motor command sent by the central nervous system to muscles when performing voluntary goal-directed movements.

AbstractDuring movement, corticomuscular coherence is a measure of central-peripheral communication, while intermuscular coherence is a measure of the amount of common central drive to the muscles. Although these two measures are modified in stroke subjects, no author has explored a correlation between them, neither in stroke subjects nor in healthy subjects. Twenty-four chronic stroke subjects and 22 healthy control subjects were included in this cohort study, and they performed 20 active elbow extension movements. The electroencephalographic and electromyographic activity of the elbow flexors and extensors were recorded. Corticomuscular and intermuscular coherence were calculated in the time–frequency domain for each limb of stroke and control subjects. Partial rank correlations were performed to study the link between these two variables. Our results showed a positive correlation between corticomuscular and intermuscular coherence only for stroke subjects, for their paretic and non-paretic limbs (P < 0.022; Rho > 0.50). These results suggest, beyond the cortical and spinal hypotheses to explain them, that stroke subjects present a form of simplification of motor control. When central-peripheral communication increases, it is less modulated and more common to the muscles involved in the active movement. This motor control simplification suggests a new way of understanding the plasticity of the neuromuscular system after stroke.

Different research fields, such as biomechanics, medical engineering or neurosciences take part in the development of biomechanical models allowing for the estimation of individual muscle forces involved in motor action. The heterogeneity of the terminology used to describe these models according to the research field is a source of confusion and can hamper collaboration between the different fields. This paper proposes a common language based on lexical disambiguation and a synthesis of the terms used in the literature in order to facilitate the understanding of the different elements of biomechanical modeling for force estimation, without questioning the relevance of the terms used in each field or the different model components or their interest. We suggest that the description should start with an indication of whether the muscle force estimation problem is solved following the physiological movement control (from the nervous drive to the muscle force production) or in the opposite direction. Next, the suitability of the model for force production estimation at a given time or for monitoring over time should be specified. Authors should pay particular attention to the method description used to find solutions, specifying whether this is done during or after data collection, with possible method adaptations during processing. Finally, the presence of additional data must be specified by indicating whether they are used to drive, assist, or calibrate the model. Describing and classifying models in this way will facilitate the use and application in all fields where the estimation of muscle forces is of real, direct, and concrete interest.

Facial mimicry is a reaction to facial expressions. It plays a role in social interaction. Indeed, scholars associated facial mimicry with emotional contagion and understanding others' mental states such as intentions. This is the case for facial mimicry toward human facial expressions, but we know that facial expressions are widely depicted in art through face representations (visual creations that depict facial expressions). However, despite face representation involvement in social interactions, facial reactions toward face representations in art are still unknown. The reason could be that interaction with art objects is usually analyzed within anthropology and art theories, such as conveying social agencies (a desire of action, intentions). Here, we show that facial mimicry is also observed toward face representations. This could be a means that might facilitate social interaction including emotions. Using the electromyography technique, we could show that participants mimic involuntarily face representations when these depict mouth expressions. Participant's zygomaticus and depressor were significantly activated when the pictures depict an expression including zygomaticus or depressor representation respectively. This result led us to infer that when it comes to mouth expressions, face representations in art might trigger spontaneously emotional contagion (of the expressed emotion). It might also convey information about the expressed mental states, which might help to indicate social agencies. Mimicry could participate to explain partly the social agencies of art, that might be no more just abstract concepts, but could find a real correlate in cognitive processes.

Accurate assessment of upper-limb movement alterations is a key component of post-stroke follow-up. Motion capture (MoCap) is the gold standard for assessment even in clinical conditions, but it requires a laboratory setting with a relatively complex implementation. Alternatively, inertial measurement units (IMUs) are the subject of growing interest, but their accuracy remains to be challenged. This study aims to assess the minimal detectable change (MDC) between spatiotemporal and quality variables obtained from these IMUs and MoCap, based on a specific protocol of IMU calibration and measurement and on data processing using the dead reckoning method. We also studied the influence of each data processing step on the level of between-system MDC. Fifteen post-stroke hemiparetic subjects performed reach or grasp tasks. The MDC for the movement time, index of curvature, smoothness (studied through the number of submovements), and trunk contribution was equal to 10.83%, 3.62%, 39.62%, and 25.11%, respectively. All calibration and data processing steps played a significant role in increasing the agreement. The between-system MDC values were found to be lower or comparable to the between-session MDC values obtained with MoCap, meaning that our results provide strong evidence that using IMUs with the proposed calibration and processing steps can successfully and accurately assess upper-limb movement alterations after stroke in clinical routine care conditions.

Mirror contractions refer to unintended contractions of the contralateral homologous muscles during voluntary unilateral contractions or movements. Exaggerated mirror contractions have been found in several neurological diseases and indicate dysfunction or lesion of the cortico-spinal pathway. The present study investigates mirror contractions and the associated interhemispheric and corticomuscular interactions in adults with spinal cord injury (SCI) - who present a lesion of the cortico-spinal tract - compared to able-bodied participants (AB). Eight right-handed adults with chronic cervical SCI and ten age-matched right-handed able-bodied volunteers performed sets of right elbow extensions at 20% of maximal voluntary contraction. Electromyographic activity (EMG) of the right and left elbow extensors, interhemispheric coherence over cerebral sensorimotor regions evaluated by electroencephalography (EEG) and corticomuscular coherence between signals over the cerebral sensorimotor regions and each extensor were quantified. Overall, results revealed that participants with SCI exhibited (1) increased EMG activity of both active and unintended active limbs, suggesting more mirror contractions, (2) reduced corticomuscular coherence between signals over the left sensorimotor region and the right active limb and increased corticomuscular coherence between the right sensorimotor region and the left unintended active limb, (3) decreased interhemispheric coherence between signals over the two sensorimotor regions. The increased corticomuscular communication and decreased interhemispheric communication may reflect a reduced inhibition leading to increased communication with the unintended active limb, possibly resulting to exacerbated mirror contractions in SCI. Finally, mirror contractions could represent changes of neural and neuromuscular communication after SCI.

Objective: Stroke results in limitation of active range of motion involving antagonist co-contraction. The analysis of brain-muscle connectivity can be used to deepen understanding of motor control alterations associated with the loss of motor function after stroke. This preliminary study aims to investigate the combined effects of botulinum toxin and rehabilitation on corticomuscular coherence to better understand the altered functional reorganization of the central-peripheral network. Methods: Kinematic, electromyographic and electroencephalographic data were recorded during twenty active elbow extensions in eleven chronic stroke patients and nine healthy control subjects. Active range of motion, antagonist co-contraction and corticomuscular coherence were calculated. Results: The initial increase in corticomuscular coherence in stroke patients was significantly reduced five weeks after the first botulinum toxin injection and twenty weeks away from the third injection, in both agonist and antagonist muscles, with moderate to large effect sizes, concomitantly with a decrease in antagonist co-contraction and an improvement in the active range of motion. Conclusions: This study highlights for the first time an effect of botulinum toxin injections combined with rehabilitation on corticomuscular coherence in stroke patients. Significance: Notwithstanding the relatively small sample, the results provide original evidence supporting treatment-induced effective functional reorganization of the central-peripheral network. CO 2022 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Background Stroke alters muscle co-activation and notably leads to exaggerated antagonist co-contraction responsible for impaired motor function. However, the mechanisms underlying this exaggerated antagonist co-contraction remain unclear. To fill this gap, the analysis of oscillatory synchronicity in electromyographic signals from synergistic muscles, also called intermuscular coherence, was a relevant tool. Objective This study compares functional intermuscular connectivity between muscle pairs of the paretic and non-paretic upper limbs of stroke subjects and the dominant limb of control subjects, concomitantly between two muscle pairs with a different functional role, through an intermuscular coherence analysis. Methods Twenty-four chronic stroke subjects and twenty-four healthy control subjects were included. Subjects performed twenty elbow extensions while kinematic data and electromyographic activity of both flexor and extensor elbow muscles were recorded. Intermuscular coherence was analyzed in the beta frequency band compared to the assessment of antagonist co-contraction. Results Intermuscular coherence was higher in the stroke subjects’ paretic limbs compared to control subjects. For stroke subjects, the intermuscular coherence of the antagonist-antagonist muscle pair (biceps brachii—brachioradialis) was higher than that of the agonist-antagonist muscle pair (triceps brachii—brachioradialis). For the paretic limb, intermuscular coherence of the antagonist-antagonist muscle pair presented a negative relationship with antagonist co-contraction. Conclusion Differences in intermuscular coherence between the paretic limbs of stroke subjects and control subjects suggest a higher common central drive during movement. Furthermore, results highlight the association between stroke-related alteration of intermuscular functional connectivity and the alteration of motor function.

During isometric contractions, corticomuscular coherence (CMC) may be modulated along with the contraction intensity. Furthermore, CMC may also vary between contraction types due to the contribution of spinal inhibitory mechanisms. However, the interaction between the effect of the contraction intensity and of the contraction type on CMC remains hitherto unknown. Therefore, CMC and spinal excitability modulations were compared during submaximal isometric, shortening and lengthening contractions of plantar flexor muscles at 25, 50, and 70% of the maximal soleus (SOL) EMG activity. CMC was computed in the time-frequency domain between the Cz EEG electrode signal and the SOL or medial gastrocnemius (MG) EMG signals. The results indicated that beta-band CMC was decreased in the SOL only between 25 and 50-70% contractions for both isometric and anisometric contractions, but remained similar for all contraction intensities in the MG. Spinal excitability was similar for all contraction intensities in both muscles. Meanwhile a divergence of the EEG and the EMG signals mean frequency was observed only in the SOL and only between 25 and 50-70% contractions, independently from the contraction type. Collectively, these findings confirm an effect of the contraction intensity on beta-band CMC, although it was only measured in the SOL, between low-level and high-level contraction intensities. Furthermore, the current findings provide new evidence that the observed modulations of beta-band CMC with the contraction intensity does not depend on the contraction type or on spinal excitability variations.

This study compares two methods to quantify the amplitude and frequency of head movements in patients with head tremor: one based on video-based motion analysis, and the other using a miniature wireless inertial magnetic motion unit (IMMU). Concomitant with the clinical assessment of head tremor severity, head linear displacements in the frontal plane and head angular displacements in three dimensions were obtained simultaneously in forty-nine patients using one video camera and an IMMU in three experimental conditions while sitting (at rest, counting backward, and with arms extended). Head tremor amplitude was quantified along/around each axis, and head tremor frequency was analyzed in the frequency and time-frequency domains. Correlation analysis investigated the association between the clinical severity of head tremor and head linear and angular displacements. Our results showed better sensitivity of the IMMU compared to a 2D video camera to detect changes of tremor amplitude according to examination conditions, and better agreement with clinical measures. The frequency of head tremor calculated from video data in the frequency domain was higher than that obtained using time-frequency analysis and those calculated from the IMMU data. This study provides strong experimental evidence in favor of using an IMMU to quantify the amplitude and time-frequency oscillatory features of head tremor, especially in medical conditions.

During voluntary contractions, corticomuscular coherence (CMC) is thought to reflect a mutual interaction between cortical and muscle oscillatory activities, respectively measured by electroencephalography (EEG) and electromyography (EMG). However, it remains unclear whether CMC modulation would depend on the contribution of neural mechanisms acting at the spinal level. To this purpose, modulations of CMC were compared during submaximal isometric, shortening and lengthening contractions of the soleus (SOL) and the medial gastrocnemius (MG) with a concurrent analysis of changes in spinal excitability that may be reduced during lengthening contractions. Submaximal contractions intensity was set at 50% of the maximal SOL EMG activity. CMC was computed in the time-frequency domain between the Cz EEG electrode signal and the unrectified SOL or MG EMG signal. Spinal excitability was quantified through normalized Hoffmann (H) reflex amplitude. The results indicate that beta-band CMC and normalized H-reflex were significantly lower in SOL during lengthening compared with isometric contractions, but were similar in MG for all three muscle contraction types. Collectively, these results highlight an effect of contraction type on beta-band CMC, although it may differ between agonist synergist muscles. These novel findings also provide new evidence that beta-band CMC modulation may involve spinal regulatory mechanisms.