Towards efficient motor imagery interventions after lower-limb amputation.

BACKGROUND: The therapeutic benefits of motor imagery (MI) are now well-established in different populations of persons suffering from central nervous system impairments. However, research on similar efficacy of MI interventions after amputation remains scarce, and experimental studies were primarily designed to explore the effects of MI after upper-limb amputations. OBJECTIVES: The present comparative study therefore aimed to assess the effects of MI on locomotion recovery following unilateral lower-limb amputation. METHODS: Nineteen participants were assigned either to a MI group (n = 9) or a control group (n = 10). In addition to the course of physical therapy, they respectively performed 10 min per day of locomotor MI training or neutral cognitive exercises, five days per week. Participants' locomotion functions were assessed through two functional tasks: 10 m walking and the Timed Up and Go Test. Force of the amputated limb and functional level score reflecting the required assistance for walking were also measured. Evaluations were scheduled at the arrival at the rehabilitation center (right after amputation), after prosthesis fitting (three weeks later), and at the end of the rehabilitation program. A retention test was also programed after 6 weeks. RESULTS: While there was no additional effect of MI on pain management, data revealed an early positive impact of MI for the 10 m walking task during the pre-prosthetic phase, and greater performance during the Timed Up and Go Test during the prosthetic phase. Also, a lower proportion of participants still needed a walking aid after MI training. Finally, the force of the amputated limb was greater at the end of rehabilitation for the MI group. CONCLUSION: Taken together, these data support the integration of MI within the course of physical therapy in persons suffering from lower-limb amputations.

Implicit and explicit motor imagery ability after SCI: Moving the elbow makes the difference.

Cervical spinal cord injury (SCI) causes dramatic sensorimotor deficits that restrict both activity and participation. Restoring activity and participation requires extensive upper limb rehabilitation focusing elbow and wrist movements, which can include motor imagery. Yet, it remains unclear whether MI ability is impaired or spared after SCI. We investigated implicit and explicit MI ability in individuals with C6 or C7 SCI (SCIC6 and SCIC7 groups), as well as in age- and gender-matched controls without SCI. Inspired by previous studies, implicit MI evaluations involved hand laterality judgments, hand orientation judgments (HOJT) and hand-object interaction judgments. Explicit MI evaluations involved mental chronometry assessments of physically possible or impossible movements due to the paralysis of upper limb muscles in both groups of participants with SCI. HOJT was the paradigm in which implicit MI ability profiles differed the most between groups, particularly in the SCIC6 group who had impaired elbow movements in the horizontal plane. MI ability profiles were similar between groups for explicit MI evaluations, but reflected task familiarity with higher durations in the case of unfamiliar movements in controls or attempt to perform movements which were no longer possible in persons with SCI. Present results, obtained from a homogeneous population of individuals with SCI, suggest that people with long-term SCI rely on embodied cognitive motor strategies, similar to controls. Differences found in behavioral response pattern during implicit MI mirrored the actual motor deficit, particularly during tasks that involved internal representations of affected body parts.

Inter-task transfer of force gains is facilitated by motor imagery.

Introduction: There is compelling evidence that motor imagery (MI) contributes to improve muscle strength. While strong effects have been observed for finger muscles, only few experiments with moderate benefits were conducted within applied settings targeting large upper or lower limb muscles. The aim of the present study was therefore to extend the investigation of embedded MI practice designed to improve maximal voluntary strength on a multi-joint dynamic exercise involving the lower limbs. Additionally, we tested whether targeting the content of MI on another movement than that physically performed and involving the same body parts might promote inter-task transfer of strength gains. Methods: A total of 75 participants were randomly assigned into three groups who underwent a physical training on back squat. During inter-trial recovery periods, a first MI group (n = 25) mentally rehearsed the back squat, while a second MI group (n = 25) performed MI of a different movement involving the lower limbs (deadlift). Participants from the control group (n = 25) completed a neutral cognitive task during equivalent time. Strength and power gains were assessed ecologically using a velocity transducer device at 4 different time periods. Results: Data first revealed that participants who engaged in MI of the back squat improved their back squat performance (p < 0.03 and p < 0.01, respectively), more than the control group (p < 0.05), hence supporting the positive effects of MI on strength. Data further supported the inter-task transfer of strength gains when MI targeted a movement that was not physically trained (p = 0.05). Discussion: These findings provide experimental support for the use of MI during physical training sessions to improve and transfer force development.

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% MVCMI) and 20 MI trials of maximal isometric contractions (100% MVCMI). 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% MVCMI. Unexpectedly, maximal force improved during 100% MVCMI between the 1st and 2nd evaluations but remained unchanged during 20% MVCMI. MI ease and vividness improved during 100% MVCMI, with a positive association between phasic skin conductance and VAS mental fatigue scores. Conversely, subjective measures revealed decreased MI ability during 20% MVCMI. 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.

Revisiting Motor Imagery Guidelines in a Tropical Climate: The Time-of-Day Effect.

(1) Background: Motor imagery (MI) is relevantly used to improve motor performance and promote rehabilitation. As MI ability and vividness can be affected by circadian modulation, it has been proposed that MI should ideally be performed between 2 p.m. and 8 p.m. Whether such a recommendation remains effective in a hot and humid environment, such as a tropical climate, remains unknown. (2) Methods: A total of 35 acclimatized participants completed a MI questionnaire and a mental chronometry test at 7 a.m., 11 a.m., 2 p.m., and 6 p.m. Visual (VI) and kinesthetic imagery (KI) abilities, as well as temporal congruence between actual walking and MI, were collected. Ambient temperature, chronotypes, thermal comfort, affect, and fatigue were also measured. (3) Results: VI scores were higher at 6 p.m. than at 7 a.m., 11 a.m., and 2 p.m., and temporal congruence was higher at 6 p.m. than at 7 a.m. Comfort, thermal sensation, and positive affect scores were higher at 7 a.m. and 6 p.m. (4) Conclusion: Data support greater imagery ability and accuracy when participants perceive the environment as more pleasant and comfortable. MI guidelines typically provided in neutral climates should therefore be adapted to tropical climates, with MI training sessions ideally scheduled in the late afternoon.

Timing-specific patterns of cerebral activations during motor imagery: A case study of the expert brain signature.

Brain activations elicited during motor imagery (MI) in experts are typically reduced compared to novices, which is interpreted as a neurophysiological correlate of increased neural efficiency. However, the modulatory effects of MI speed on expertise-related differences in brain activation remains largely unknown. In the present pilot study, we compared the magnetoencephalographic (MEG) correlates of MI in an Olympic medallist and an amateur athlete under conditions of slow, real-time and fast MI. Data revealed event-related changes in the time course of alpha (8-12 Hz) power of MEG oscillations, for all timing conditions. We found that slow MI was associated with a corollary increase in neural synchronization, in both participants. Sensor-level and source-level analyses however disclosed differences between the two expertise levels. The Olympic medallist achieved greater activation of cortical sensorimotor networks than the amateur athlete, particularly during fast MI. Fast MI elicited the strongest event-related desynchronization of alpha oscillations, which was generated from cortical sensorimotor sources in the Olympic medallist, but not in the amateur athlete. Taken together, data suggest that fast MI is a particularly demanding form of motor cognition, putting a specific emphasis on cortical sensorimotor networks to achieve the formation of accurate motor representations under demanding timing constraints.

Corticomotor Plasticity Underlying Priming Effects of Motor Imagery on Force Performance.

The neurophysiological processes underlying the priming effects of motor imagery (MI) on force performance remain poorly understood. Here, we tested whether the priming effects of embedded MI practice involved short-term changes in corticomotor connectivity. In a within-subjects counterbalanced experimental design, participants (n = 20) underwent a series of experimental sessions consisting of successive maximal isometric contractions of elbow flexor muscles. During inter-trial rest periods, we administered MI, action observation (AO), and a control passive recovery condition. We collected electromyograms (EMG) from both agonists and antagonists of the force task, in addition to electroencephalographic (EEG) brain potentials during force trials. Force output was higher during MI compared to AO and control conditions (both p < 0.01), although fatigability was similar across experimental conditions. We also found a weaker relationship between triceps brachii activation and force output during MI and AO compared to the control condition. Imaginary coherence topographies of alpha (8−12 Hz) oscillations revealed increased connectivity between EEG sensors from central scalp regions and EMG signals from agonists during MI, compared to AO and control. Present results suggest that the priming effects of MI on force performance are mediated by a more efficient cortical drive to motor units yielding reduced agonist/antagonist coactivation.

Effects of relaxing breathing paired with cardiac biofeedback on performance and relaxation during critical simulated situations: a prospective randomized controlled trial.

BACKGROUND: Active participation in high-fidelity simulation remains stressful for residents. Increased stress levels elicited during such simulation impacts performance. We tested whether relaxing breathing, paired or not with cardiac biofeedback, could lead to enhanced performance of residents during simulation. METHODS: This randomized pilot study involved the fifth-year anesthesiology and critical care residents who participated in high-fidelity at Lyon medical simulation center in 2019. Residents were randomized into three parallel interventions: relaxing breathing, relaxing breathing paired with cardiac biofeedback, and control. Each intervention was applied for five minutes immediately after the scenario briefing. The primary endpoint was the overall performance during the simulation rated by two blinded independent investigators. The secondary endpoints included component scores of overall performance and changes in psychological states. RESULTS: Thirty-four residents were included. Compared to the control group, residents in the relaxing breathing (+ 7%, 98.3% CI: 0.3 to 13.7, P = 0.013) and relaxing breathing paired with cardiac biofeedback (+ 8%, 98.3% CI: 0.82 to 14.81, P = 0.009) groups had a higher overall performance score. Following the interventions, compared to the control group, stress level was lower when participants had performed relaxing breathing alone (P = 0.029) or paired with biofeedback (P = 0.035). The internal relaxation level was higher in both the relaxing breathing alone (P = 0.016) and paired with biofeedback groups (P = 0.035). CONCLUSIONS: Performing five minutes of relaxing breathing before the scenario resulted in better overall simulation performance. These preliminary findings suggest that short breathing interventions are effective in improving performance during simulation. TRIAL REGISTRATION: The study protocol was retrospectively registered on clinicaltrials.gov ( NCT04141124 , 28/10/2019).

Evaluating the Effect of the Combat Style Congruency on Performance and Fatigability in Brazilian Jiu-Jitsu: A Pilot Study.

PURPOSE: Brazilian jiu-jitsu is a martial art emphasizing ground combat with multiple ramifications to self-defense and military training. Some Brazilian jiu-jitsu athletes prefer fighting on their back (Guardadors), while others preferentially adopt a standing or kneeling position (Passadors). Whether the combat scenario leading to adopt a preferential or nonpreferential combat style influences the combat outcomes remains unexplored. METHODS: In a counterbalanced design, 13 athletes performed simulated combats from either a congruent or incongruent scenario with regard to their preferred combat style. We collected combat scores from the official ranking system and measured upper- and lower-limb explosive performance before and after the combats, as well as the rating of perceived exertion and blood lactate concentrations to index fatigability. RESULTS: Passadors had greater grip strength than Guardadors (Rp2 = .23, P = .03), whereas Guardadors showed higher lower-limb performance (Rp2 = .16, P = .05). When forced to combat as Passadors, Guardadors exhibited greater grip-strength impairment and a greater increase in perceived exertion (Rp2 = .12, P = .04; Rp2 = .15, P = .05, respectively). They also had higher blood lactate concentrations (Rp2 = .19, P = .02). CONCLUSION: Guardadors exhibited greater fatigability after fighting from an incongruent combat situation compared to Passadors, presumably due to greater difficulties to adjust to the loss of initiative when restricted to a primarily defensive role. Future studies should examine how combat style congruency might affect performance and influence recovery strategies during high-level competitive events.

Motor imagery and action observation following immobilization-induced hypoactivity: A narrative review.

BACKGROUND: In sports, the risk of pathology or event that leads to an injury, a cessation of practice or even to an immobilization is high. The subsequent reduction of physical activity, or hypoactivity, induces neural and muscular changes that adversely affect motor skills and functional motor rehabilitation. Because the implementation of physical practice is difficult, if not impossible, during and immediately following injury or immobilization, complementary techniques have been proposed to minimize the deleterious impact of hypoactivity on neuromuscular function. OBJECTIVE: The current narrative review aimed to discuss the contributions of motor imagery and action observation, which enhance motor (re)learning and induce neural adaptations in both healthy individuals and injured athletes. METHODS: Online literature research for studies of the effects of motor imagery, action observation and their combination on hypoactivity, extracting relevant publications within the last decade (2009-2020). RESULTS: From published studies and the authors' knowledge of both motor imagery and action observation, some elements are provided for developing applied protocols during and after the immobilization period. Such interventions consist of associating congruent action observation with kinesthetic motor imagery of different movements, organized in increasing difficulty. The aim is to maintain motor functions and promote motor relearning by activating sensorimotor cortical areas and corticomotor pathways of the injured effector. CONCLUSION: This narrative review supports the implementation of combined motor imagery and action observation protocols in the context of sports rehabilitation.

Translation and validation of the movement imagery questionnaire-3 second French version.

INTRODUCTION: Motor imagery (MI) can be defined as the mental simulation of an action without performing it. Its effectiveness can be substantially influenced by imagery ability, and it is currently accepted that three main modalities are used in MI (kinaesthetic imagery, and internal or external visual imageries). In the context of rehabilitation, MI combined with physical therapy is further known to facilitate functional improvements, and promote cortical reorganization and long-term recovery. This study aimed to test the reproducibility and the validity of constructs (internal consistency and factorial structure) of the Movement Imagery Questionnaire-3 Second French version (MIQ-3Sf). METHOD: The internal consistency as well as the validity of constructs and the test-retest inter-rate reproducibility of the MIQ-3Sf was examined, in 553 participants, for the kinaesthetic and visual items. RESULTS: The composite reliability scores (≥0.92) and the intraclass correlation coefficients (>0.88) for the kinaesthetic, internal visual and external visual imagery subscales revealed satisfactory internal consistency and reproducibility. Moreover, Pearson correlations revealed a strong relationship between the MIQ-3Sf and the MIQ-3f. CONCLUSIONS: /Implications. The MIQ-3Sf can be considered as a valid, reliable and useful questionnaire for examining MI ability in the context of rehabilitation.

Combining proactive transcranial stimulation and cardiac biofeedback to substantially manage harmful stress effects.

BACKGROUND: Previous studies have identified the dorsolateral prefrontal cortex (dlPFC) as a core region in cognitive emotional regulation. Transcranial direct current stimulations of the dlPFC (tDCS) and heart-rate variability biofeedback (BFB) are known to regulate emotional processes. However, the effect of these interventions applied either alone or concomitantly during an anticipatory stress remains unexplored. OBJECTIVE: The study investigated the effect of anodal tDCS and BFB, alone or combined, on psychophysiological stress responses and cognitive functioning. METHODS: Following a stress anticipation induction, 80 participants were randomized into four groups and subjected to a 15-min intervention: neutral video viewing (ctrl), left dlPFC anodal tDCS (tdcs), heart-rate variability biofeedback (bfb), or a combined treatment (bfb + tdcs). Participants were then immediately confronted with the stressor, which was followed by an assessment of executive functions. Psychophysiological stress responses were assessed throughout the experiment (heart rate, heart-rate variability, salivary cortisol). RESULTS: The tdcs did not modulate stress responses. Compared with both ctrl and tdcs interventions, bfb reduced physiological stress and improved executive functions after the stressor. The main finding revealed that bfb + tdcs was the most effective intervention, yielding greater reduction in psychological and physiological stress responses than bfb. CONCLUSIONS: Combining preventive tDCS with BFB is a relevant interventional approach to reduce psychophysiological stress responses, hence offering a new and non-invasive treatment of stress-related disorders. Biofeedback may be particularly useful for preparing for an important stressful event when performance is decisive.

The effects of body position and actual execution on motor imagery of locomotor tasks in people with a lower-limb amputation.

Motor imagery (MI) is usually facilitated when performed in a congruent body position to the imagined movement, as well as after actual execution (AE). A lower-limb amputation (LLA) results in important structural and functional changes in the sensorimotor system, which can alter MI. In this study, we investigated the effects of body position and AE on the temporal characteristics of MI in people with LLA. Ten participants with LLA (mean age = 59.6 ± 13.9 years, four females) and ten gender- and age-matched healthy control participants (mean age = 60.1 ± 15.4 years, four females) were included. They performed two locomotor-related tasks (a walking task and the Timed Up and Go task) while MI times were measured in different conditions (in congruent/incongruent positions and before/after AE). We showed that MI times were significantly shorter when participants imagined walking in a congruent-standing position compared to an incongruent-sitting position, and when performing MI after actual walking compared to before, in both groups. Shorter MI times in the congruent position and after AE suggest an improvement of MI's temporal accuracy (i.e. the ability to match AE time during MI) in healthy individuals but not in the LLA group.

Revisiting the acute effects of resistance exercise on motor imagery ability.

Motor imagery (MI) shares psychological and physiological similarities with the physical practice of the same action. Yet, it remains unclear whether fatigue elicited by exercise impairs MI ability. Fourteen participants performed MI of a self-paced walking sequence of 22 m before and after a resistance exercise eliciting muscle fatigue from upper and lower limbs, selectively. We indexed MI ability using psychometric and behavioral methods. Electromyography of the quadriceps was also recorded during physical practice trials of the walking sequence. For both experimental conditions, we recorded improved temporal congruence between MI and physical practice of the walking sequence (9.89 %, 95 % CI [7.03, 12.75], p < 0.01). Vividness decreased immediately after the fatiguing exercise (6.35 %, 95 % CI [5.18, 7.51], p < 0.05), before rapidly returning to pre-fatigue values during recovery trials. The results challenge the hypothesis of an effect of acute fatigue elicited by a resistance exercise on MI ability, i.e. restricted to MI tasks focusing fatigued effectors. The beneficial effects of fatigue conditions on the psychometric and behavioral indexes of MI ability are discussed in the broader context of psychobiological fatigue models linking perceived exertion with the reallocation of attentional resources. The general perception of fatigue, rather than local muscle fatigue, appeared linked to the acute effects of resistance exercise on MI ability.

Motor imagery practice benefits during arm immobilization.

Motor imagery (MI) is known to engage motor networks and is increasingly used as a relevant strategy in functional rehabilitation following immobilization, whereas its effects when applied during immobilization remain underexplored. Here, we hypothesized that MI practice during 11 h of arm-immobilization prevents immobilization-related changes at the sensorimotor and cortical representations of hand, as well as on sleep features. Fourteen participants were tested after a normal day (without immobilization), followed by two 11-h periods of immobilization, either with concomitant MI treatment or control tasks, one week apart. At the end of each condition, participants were tested on a hand laterality judgment task, then underwent transcranial magnetic stimulation to measure cortical excitability of the primary motor cortices (M1), followed by a night of sleep during which polysomnography data was recorded. We show that MI treatment applied during arm immobilization had beneficial effects on (1) the sensorimotor representation of hands, (2) the cortical excitability over M1 contralateral to arm-immobilization, and (3) sleep spindles over both M1s during the post-immobilization night. Furthermore, (4) the time spent in REM sleep was significantly longer, following the MI treatment. Altogether, these results support that implementing MI during immobilization may limit deleterious effects of limb disuse, at several levels of sensorimotor functioning.

Effects of self-myofascial release interventions with or without sliding pressures on skin temperature, range of motion and perceived well-being: a randomized control pilot trial.

BACKGROUND: Self-myofascial release is an emerging technique in strength and conditioning. Yet, there is no consensus regarding optimal practice guidelines. Here, we investigated the acute effects of various foam rolling interventions targeting quadriceps muscles, with or without sliding pressures. METHODS: We conducted a blinded randomized control pilot trial in 42 healthy weightlifting athletes over 4 weeks. Participants were randomly allocated to one of the four intervention (120 s massage routine) groups: foam rolling, roller massager, foam rolling with axial sliding pressures, foam rolling with transverse sliding pressures. Knee range of motion, skin temperature and subjective scores of the perceived heat, range of motion, muscle pain and relaxation were the dependent variables. Measurements were carried on before, after and up to 15 min (follow-up) after the massage intervention. RESULTS: The range of motion increased immediately after the various foam rolling interventions (+ 10.72%, 95% CI 9.51 to 11.95, p < 0.001), but progressively returned back to the pre-intervention baseline along within the 15 min post-intervention. Foam rolling was the most effective intervention to increase skin temperature from thermographic measures (+ 14.06%, 95% CI 10.97 to 17.10, p < 0.001), while the increase in perceived heat was comparable in all experimental groups (107%, 95% CI 91.08 to 122.61, p < 0.001). CONCLUSIONS: Subjective indexes of heat, range of motion, muscle pain and relaxation improved immediately after the intervention, but also gradually returned to the pre-intervention baseline. Overall, combining foam rolling with sliding pressures did not yield additional benefits from objective measures.

Implementing biofeedback as a proactive coping strategy: Psychological and physiological effects on anticipatory stress.

Anticipating a stressful situation involves psychophysiological reactions before the occurrence of the overt stress event. The current challenge in the stress domain is to characterize anticipatory stress reactions and how to effectively modulate them. The present study aimed to characterize the anticipation period and evaluate the benefits of a heart-rate variability biofeedback (BFB) intervention designed to manage anticipatory stress. Healthy participants were exposed to an anticipation stress period (15 min) during which they either practised BFB (stress + bfb, n = 15) or watched a neutral video (stress + video, n = 14). Anticipatory stress was effectively induced by the Trier Social Anticipatory Stress (TSAS) protocol, specifically designed for this study. Control participants, without anticipation stress, practised BFB for an equivalent time (ctrl + bfb, n = 15). Subsequently, all participants performed a set of cognitive tasks assessing executive functions. Heart-rate variability (cardiac coherence, standard deviation of the R-R intervals, root mean square of successive difference measure) and the evolution of the perceived psychological state were measured during the anticipation period. Self-reported judgements of how the intervention influenced stress and performance were further assessed. The main result showed that BFB is a relevant proactive stress-coping method. Compared with the stress + video group, participants who practised BFB attained higher cardiac coherence scores. Post-intervention self-reported measures revealed that BFB contributed to reduce psychological stress and increase perceived levels of performance. Together, these findings provide practical guidelines for examining the stress anticipation period by means of the TSAS protocol.

Evaluating the effects of embedded self-massage practice on strength performance: A randomized crossover pilot trial.

BACKGROUND: Self-administered massage interventions with a roller massager are commonly used as part of warm-ups and post-workout recovery routines. There is yet no clear consensus regarding the practical guidelines for efficient embedded interventions. OBJECTIVES: The present randomized crossover pilot trial aimed at examining the effects of a rolling intervention with a roller massager embedded within the rests periods of a resistance training protocol. The rolling intervention targeted quadriceps muscles. SETTING: Participants (n = 14) performed two resistance training protocols expected to elicit momentary muscle failure. The protocol consisted in 10 sets of 10 rest-pause repetitions of back squats, with a poundage set up at 50% of the maximal one-repetition. Two min were allocated to recovery between sets. During the recovery periods, participants completed a rolling routine with a roller massager for 60 s (Roller-massager), or underwent passive recovery (Control). The total workload, concentric power, thigh circumference rate of perceived exertion (RPE) and delayed onset of muscle soreness (DOMS) from 24 h to 120 h after completion of the protocol were the dependent variables. RESULTS: Roller-massager was associated with a reduction in total workload (-11.6%), concentric power (-5.1%) and an increase in perceived exertion compared to Control (p < 0.05). Roller-massager was also associated with reduced thigh circumference after the resistance training protocol, indicating reduced muscle swelling, and reduced DOMS 24 h to 120 h post-workout (p < 0.001). CONCLUSION: These findings support that embedded rolling with a roller massager hinders performance and increases effort perception. Embedded interventions may not be suitable during conditioning periods designed to maximize training intensity.

Stabilometric Correlates of Motor and Motor Imagery Expertise.

Motor Imagery (MI) reproduces cognitive operations associated with the actual motor preparation and execution. Postural recordings during MI reflect somatic motor commands targeting peripheral effectors involved in balance control. However, how these relate to the actual motor expertise and may vary along with the MI modality remains debated. In the present experiment, two groups of expert and non-expert gymnasts underwent stabilometric assessments while performing physically and mentally a balance skill. We implemented psychometric measures of MI ability, while stabilometric variables were calculated from the center of pressure (COP) oscillations. Psychometric evaluations revealed greater MI ability in experts, specifically for the visual modality. Experts exhibited reduced surface COP oscillations in the antero-posterior axis compared to non-experts during the balance skill (14.90%, 95% CI 34.48-4.68, p < 0.05). Experts further exhibited reduced length of COP displacement in the antero-posterior axis and as a function of the displacement area during visual and kinesthetic MI compared to the control condition (20.51%, 95% CI 0.99-40.03 and 21.85%, 95% CI 2.33-41.37, respectively, both p < 0.05). Predictive relationships were found between the stabilometric correlates of visual MI and physical practice of the balance skill, as well as between the stabilometric correlates of kinesthetic MI and the training experience in experts. Present results provide original stabilometric insights into the relationships between MI and expertise level. While data support the incomplete inhibition of postural commands during MI, whether postural responses during MI of various modalities mirror the level of motor expertise remains unclear.

Acute stress affects implicit but not explicit motor imagery: A pilot study.

Motor imagery (MI) is the capacity to mentally perform one or a set of movements without concomitant overt action. MI training has been show to enhance the subsequent motor performance. While the benefits of MI to manage stress have been extensively documented, the reverse impact of stress on MI received far less attention. The present study thus aimed to evaluate whether acute stress might influence MI abilities. Thirty participants were assigned either to a stress or a control group. The Socially Evaluated Cold Pressor Test (SECPT) was used to induce stress, with heart rate, electrodermal activity, salivary cortisol, and self-report perceived levels of stress being monitored during the experiment. Stress induction was followed by both implicit (laterality judgment) and explicit (sequential pointing) MI tasks. Main results showed a deleterious impact of stress on implicit MI, while explicit MI was not altered. These exploratory findings provide a deeper understanding of stress effects on cognition, and practically support that under stressful conditions, as during a sport competition or rehabilitation contexts, explicit MI should be prioritized.