Researchers from multiple disciplines have studied the simulation of actions through motor imagery, action observation, or their combination. Procedures used in these studies vary considerably between research groups, and no standardized approach to reporting experimental protocols has been proposed. This has led to under-reporting of critical details, impairing the assessment, replication, synthesis, and potential clinical translation of effects. We provide an overview of issues related to the reporting of information in action simulation studies, and discuss the benefits of standardized reporting. We propose a series of checklists that identify key details of research protocols to include when reporting action simulation studies. Each checklist comprises A) essential methodological details, B) essential details that are relevant to a specific mode of action simulation, and C) further points that may be useful on a case-by-case basis. We anticipate that the use of these guidelines will improve the understanding, reproduction, and synthesis of studies using action simulation, and enhance the translation of research using motor imagery and action observation to applied and clinical settings.

Introduction For people who have had a stroke, recovering upper-limb function is a barrier to independence. When movement is difficult, mental practice can be used to complement physical therapy. In this within-participants study we investigated the effects of combined action observation and motor imagery (AO + MI) therapy on upper-limb recovery in chronic stroke survivors. Methods A Graeco-Latin Square design was used to counterbalance four mental practice conditions (AO + MI, AO, MI, Control) across four cup-stacking tasks of increasing complexity. Once a week, for five consecutive weeks, participants (n = 10) performed 16 mental practice trials under each condition. Each trial displayed a 1st person perspective of a cup-stacking task performed by an experienced model. For AO, participants watched each video and responded to an occasional color cue. For MI, participants imagined the effort and sensation of performing the action; cued by a series of still-images. For combined AO + MI, participants observed a video of the action while they simultaneously imagined performing the same action in real-time. At three time points (baseline; post-test; two-week retention test) participants physically executed the three mentally practiced cup-stacking tasks, plus a fourth unpractised sequence (Control), as quickly and accurately as possible. Results Mean movement execution times were significantly reduced overall in the post-test and the retention test compared to baseline. At retention, movement execution times were significantly shorter for combined AO + MI compared to both MI and the Control. Individual participants reported clinically important changes in quality of life (Stroke Impact Scale) and positive qualitative experiences of AO + MI (social validation). Discussion These results indicate that when physical practice is unsuitable, combined AO + MI therapy could offer an effective adjunct for neurorehabilitation in chronic stroke survivors.

This study analysed the longitudinal relationship between short sprint time and the leapfor-distance test using novel motion tracking in young soccer players.Players (n = 144, age 14.8 ± 1.8 years) from six English Elite Player Performance Plan category three clubs completed two linear sprints (10 m, 20 m) and a leap-for-distance test (cm), on three to seven occasions across three seasons.Within-player (repeated measures) and betweenplayer (mean of the repeated measures) correlation coefficients were calculated and stratified by pre-and post-peak height velocity (PHV).Very large, negative between-player correlations were found for leap-for-distance vs. sprint time (10 m: r = -0.70,95% CI [-0.77, -0.61]; 20 m: r = -0.77,95% CI [-0.83, -0.70]).Correlations were large for pre-PHV (10 m: r = -0.52,95% CI [-0.71, -0.26]; 20 m: r = -0.62,95% CI [-0.78, -0.39]) and moderate-to-large for post-PHV (10 m: r = -0.43,95% CI [-0.60, -0.24]; 20 m: r = -0.54,95% CI [-0.68, -0.36], respectively).Within-player correlations were trivial-to-small for all players (10 m: r = -0.14, 95% CI [-0.24, -0.06]; 20 m: r = -0.24,95% CI [-0.34, -0.16]) and for pre-and post-PHV subgroups (r's < -0.30).Leap-for-distance is a useful discriminator of sprint performance but should not be used for tracking intra-player sprint changes in young soccer players, irrespective of maturation.

In this study we explored training effects for combined action observation and motor imagery (AO+MI) instructions on a complex cup-stacking task, without physical practice. Using a Graeco-Latin Square design, we randomly assigned twenty-six participants into four groups. This counterbalanced the within-participant factor of practice condition (AO+MI, AO, MI, Control) across four cup-stacking tasks, which varied in their complexity. On each of the three consecutive practice days participants experienced twenty trials under each of the three mental practice conditions. On each trial, a first-person perspective video depicted bilateral cup-stacking performed by an experienced model. During AO, participants passively observed this action, responding only to occasional colour cues. For AO+MI, participants imagined performing the observed action and synchronised their concurrent MI with the display. For MI, a sequence of pictures cued imagery of each stage of the task. Analyses revealed a significant main effect of practice condition both at the ’surprise’ post-test (Day 3) and at the one-week retention test. At both time points movement execution times were significantly shorter for AO+MI compared with AO, MI and the Control. Execution times were also shorter overall at the retention compared with the post-test. These results demonstrate that a complex novel motor task can be acquired without physical training. Practitioners can therefore use AO+MI practice to supplement physical practice and optimise skill learning.

Feedforward modeling, the creation of one's own behaviour that is potentially achievable in the future, can support motor performance and learning. While this has been shown for sequences of motor actions, it remains to be tested whether feedforward modelling is beneficial for single complex motor actions. Using an immersive, state-of-the-art, low-latency Cave Automatic Virtual Environment (CAVE), we compared motor imagery during action observation (AOMI) of oneself performing at one's current skill level against AOMI of oneself performing at an achievable future skill level. We performed 3D scans and created a ready-to-animate virtual human of each participant. During acquisition, participants observed an avatar of themselves performing either one of their own previously executed squats (Me-Novice) or observed an avatar of themselves performing a skilled squat (Me-Skilled), whilst simultaneously imagining the feelings and sensations associated with movement execution. Findings revealed an advantage for the Me-Skilled group as compared to the Me-Novice group in motor performance and cognitive representation structure, while self-efficacy improved in both groups. In comparison to watching and imagining oneself performing at the current novice skill level, watching and imagining oneself performing at a more advanced skill level prevented from making errors in motor performance and led to perceptual-cognitive scaffolding as shown by functional changes in underlying representations. Simultaneous imagery whilst observing future states of action may therefore help to establish cognitive prerequisites that enable better motor performance. To this end, virtual reality is a promising tool to create learning environments that exceed an individual's current performance level.

In this paper, we discuss a variety of ways in which practising motor actions by means of motor imagery (MI) can be enhanced via synchronous action observation (AO), that is, by AO + MI. We review the available research on the (mostly facilitatory) behavioural effects of AO + MI practice in the early stages of skill acquisition, discuss possible theoretical explanations, and consider several issues related to the choice and presentation schedules of suitable models. We then discuss considerations related to AO + MI practice at advanced skill levels, including expertise effects, practical recommendations such as focussing attention on specific aspects of the observed action, using just-ahead models, and possible effects of the perspective in which the observed action is presented. In section "Coordinative AO + MI", we consider scenarios where the observer imagines performing an action that complements or responds to the observed action, as a promising and yet under-researched application of AO + MI training. In section "The dual action simulation hypothesis of AO + MI", we review the neurocognitive hypothesis that AO + MI practice involves two parallel action simulations, and we consider opportunities for future research based on recent neuroimaging work on parallel motor representations. In section "AO + MI training in motor rehabilitation", we review applications of AO, MI, and AO + MI training in the field of neurorehabilitation. Taken together, this evidence-based, exploratory review opens a variety of avenues for future research and applications of AO + MI practice, highlighting several clear advantages over the approaches of purely AO- or MI-based practice.

INTRODUCTION:Research indicates that both observed and imagined actions can be represented in the brain as two parallel sensorimotor representations. One proposal is that higher order cognitive processes would align these two hypothetical action simulations.METHODS:We investigated this hypothesis using an automatic imitation paradigm, with functional near-infrared spectroscopy recordings over the prefrontal cortex during different motor simulation states. On each trial, participants (n = 14) observed a picture of a rhythmical action (instructed action) followed by a distractor movie showing the same or different action. Participants then executed the instructed action. Distractor actions were manipulated to be fast or slow, and instructions were manipulated during distractor presentation: action observation (AO), combined action observation and motor imagery (AO+MI) and observe to imitate (intentional imitation). A pure motor imagery (MI) condition was also included.RESULTS:Kinematic analyses showed that although distractor speed effects were significant under all instructions (shorter mean cycle times in execution for fast compared to slow trials), this imitation bias was significantly stronger for combined AO+MI than both AO and MI, and stronger for intentional imitation than the other three automatic imitation conditions. In the left prefrontal cortex, cerebral oxygenation was significantly greater for combined AO+MI than all other instructions. Participants reported that their representation of the self overlapped with the observed model significantly more during AO+MI than AO.CONCLUSION:Left prefrontal activation may therefore be a neural signature of AO+MI, supporting attentional switching between concurrent representations of self (MI, top-down) and other (AO, bottom-up) to increase imitation and perceived closeness.

Following theories of emotional embodiment, the facial feedback hypothesis suggests that individuals' subjective experiences of emotion are influenced by their facial expressions. However, evidence for this hypothesis has been mixed. We thus formed a global adversarial collaboration and carried out a preregistered, multicentre study designed to specify and test the conditions that should most reliably produce facial feedback effects. Data from n = 3,878 participants spanning 19 countries indicated that a facial mimicry and voluntary facial action task could both amplify and initiate feelings of happiness. However, evidence of facial feedback effects was less conclusive when facial feedback was manipulated unobtrusively via a pen-in-mouth task.

A growing body of research has addressed the application of movement-based biofeedback techniques for improving sports performers’ gross motor skills. Unlike in previous research, we aimed in this study to quantify the effects of this “external” biofeedback on selected performance and technique variables for the boxing jab among both novices and experts. The technical setup included two inertial measurement units linked wirelessly to a video game system with audio output. The units were configured to provide auditory external biofeedback, based on the peak acceleration of the bag (i.e., biofeedback with an external attentional focus). Sixteen participants (8 novices and 8 experts) performed boxing jabs against the bag in blocked phases of biofeedback. When compared to baseline, the acute effects of externally focused biofeedback on peak bag acceleration were possibly positive in both retention phases for novices (d = 0.29; d = 0.41) and likely positive for experts (d = 0.41; d = 0.30), respectively. The experts’ performance improvements were accompanied by substantive increases in trunk rotation, though this was not true for the novices. Thus, technique improvements can be promoted indirectly via externally focused biofeedback, but only when these actions are within the performers’ motor repertoire. Overall, biofeedback via inertial sensors appears to be a potent technique for modifying human movement patterns in both experts and novices. This low-cost technology could be used to support training across sports, rehabilitation and human-computer interactions.

We investigated the reliability of fundamental movements in thirteen youth football players (mean age = 16.8 ± 0.6 y).Following a habituation warm-up, players performed three trials of stride-for-distance and bodyweight squats between two weeks.A motion tracking device was used to measure stride distance and squat depth.The weekly mean changes in mean and maximum performance were moderate for the stride (2.8%; 90% confidence interval: 1.1 to 4.5 and 3.6%; 2.1 to 5.2, respectively) and small for the squat (-2.7%; -12.3 to 7.9 and 3.3%; -5.2 to 12.6).ICCs for stride mean and maximum performance were moderate (0.74; 0.43 to 0.90) and high (0.76; 0.46 to 0.90), respectively, and low for the squat (0.22; -0.27 to 0.61 and 0.42; -0.04 to 0.74, respectively).Typical errors for mean and maximum performance were moderate for the stride (2.4%; 1.8 to 3.6 and 2.1%; 1.6 to 3.3, respectively) and large for the squat (15.9%; 11.8 to 25.1 and 13.1%; 9.7 to 20.5, respectively).The motion tracking reliability was encouraging in the stride.This finding warrants further investigation and consideration of the stride test for use in applied practice with a group of youth footballers.

Purpose We assessed the reliability of fundamental movement skills in young male footballers within one session. Methods: 197 players from 5 English category 3 football academies across U9 - U18 age groups volunteered (mean: age = 12.6 +/- 2.8 years; stature = 156 +/- 17 cm; weight = 47 +/- 15 kg; years from peak height velocity (PHV) = - 1.1 +/- 2.3). Motion tracking of squat depth and anterior Y-balance test maximum reach was recorded. Reliability was assessed (trial 1 vs. 2; trial 2 vs. 3) via mean change, intraclass correlation coefficient (ICC), and typical error. Results: The overall mean change was trivial (-1.8-2.9%), while Y-balance left showed a small negative change (trial 2 vs. 3; -3.2%). All ICCs across the tests ranged from moderate to high (0.71-0.79). Typical errors for Y-balance tests ranged from 8.3-10.8% and squats from 19.3-21.8%. Pre-PHV vs. post-PHV players had similar typical errors for Y-balance left and right (9.0 vs. 11.5%; 9.0 vs. 7.1%, respectively), and the squat (21.1 vs. 20%). Conclusions: The high within-player typical error scores obtained over three trials suggest that, contrary to some movement screening guidelines, prior habituation is needed to increase both the stability and reliability of these tests.

The dual-action simulation hypothesis proposes that both an observed and an imagined action can be represented simultaneously in the observer's brain. These two sensorimotor streams would either merge or compete depending on their relative suitability for action planning. To test this hypothesis, three forms of combined action observation and motor imagery (AO + MI) instructions were used in this repeated-measures experiment. Participants observed index finger abduction-adduction movements while imagining the same action (congruent AO + MI), little finger abduction-adduction (coordinative AO + MI), or a static hand (conflicting AO + MI). Single-pulse transcranial magnetic stimulation was applied to the left primary motor cortex. The amplitude of motor evoked potential re- sponses were recorded from both the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the right-hand while eye movements were tracked. When con- trolling for the influence of relevant eye movements, corticospinal excitability was facilitated relative to control conditions in the concurrently observed and imagined muscles for both congruent and coordinative AO + MI conditions. Eye-movement metrics and social validation data from post-experiment interviews provided insight into the attentional and cognitive mechanisms underlying these effects. The findings provide empirical support for the dual-action simulation hypothesis, indicating for the first time that it is possible to corepresent observed and imagined actions simultaneously. (C) 2019 The Authors. Published by Elsevier Ltd.

Abstract Wearing textured insoles (TIs) can reduce static postural sway, but the neurophysiological mechanisms by which these changes occur are not well understood. To address this issue, cortical activity was investigated in this study using electroencephalography (EEG) recordings from 19 scalp locations, in 15 healthy young adults (5 females; mean age = 27 ± 4.09 years) during quiet bipedal standing, under different insole conditions (textured versus smooth), with and without vision. Compared to smooth insoles (SIs), TIs significantly reduced postural sway in two measures; anterior–posterior range and standard deviation. In the EEG data, whole-head analyses showed cortical activity in the upper alpha power band was significantly reduced for textured compared to SIs. Exploratory analyses revealed this effect was significant both with and without vision, and was more pronounced over the parietal, compared to central regions, and over central compared to frontal regions. This trend was observed in low alpha and theta bands, but the effect of insole type was not significant. Textured insoles thus appear to affect not only balance outcomes but also cortical activity. The cortical activity adaptation may represent greater information becoming readily available at the cortical level, enhancing the representation of the body in space.

Spontaneous rhythmical movements, like foot-tapping and head-bobbing, often emerge when people listen to music, promoting the enjoyable sensation of 'being in the groove'. Here we report the first experiment to investigate if seeing the music maker modulates this experience. Across trials we manipulated groove level in the audio beats (high vs low), and manipulated the match between the audio beats and a concurrently observed point-light display (PLD) of the drummer. The visual display was either fully corresponding with the audio beats, or incompatible across three conditions: a static PLD, a corresponding but asynchronous PLD (0.5s time shifted); or a non-corresponding PLD (e.g. high groove audio paired with low groove PLD). Participants (n = 36) rated: (a) their desire to move; and (b) their perceived groove, purely in response to the audio beats, using 8-point Likert scales. The main effects of groove level and visual display were significant in both measurements. Ratings increased for high compared to low groove audio overall, and for the fully corresponding condition compared to the other visual conditions. Ratings of the desire to move also increased in the static compared to the non-corresponding condition, and the two-way interaction was significant. Desire to move significantly increased for high compared to low groove audio in the fully corresponding, static and asynchronous conditions, while this effect was absent in the non-corresponding condition. These findings identify the importance of seeing as well as hearing the musician for an enhanced experience of groove, which necessitates a multimodal account of music perception.

Children with developmental coordination disorder (DCD) exhibit deficits both in imitation and motor imagery (MI) compared to typically developing children. Combined action observation and motor imagery (AO + MI) instructions can however enhance automatic imitation in both groups. In the present study we investigated the effects of AO + MI instructions on intentional imitation in children both with (n = 13) and without DCD (n = 12). On each trial participants observed and/or imagined before executing a familiar rhythmical pantomime action. These target actions were either habitually fast (tooth brushing or window wiping) or habitually slow (paint brushing or face washing), in the vertical or horizontal plane. Within each habitual speed, the target action speed was subtly manipulated across trials (fast vs. slow). Instruction condition was manipulated across three blocks of 16 trials: (1) observe before imitating the target action; (2) observe then imagine the action before imitating; (3) observe while imagining the same action before imitating (AO + MI). Kinematic analyses revealed typically developing children imitated the observed cycle times significantly better than children with DCD. A main effect of instruction showed imitation improved for AO + MI compared to the other two instructions. Within-group analyses found a significant advantage in DCD for AO + MI compared to observe then imagine. In typically developing children, imitation was significantly enhanced for AO+ MI compared to observe then imitate. Combined AO + MI instructions therefore represent a promising new approach to refining performance of everyday rhythmical actions in children both with and without DCD, with implications for movement therapy and sports training.

Wearing a textured shoe insole can decrease postural sway during static balance. Previous studies assessed bipedal and/or unipedal standing. In contrast, we aimed to investigate if textured insoles modulated postural sway during four stance types (bipedal, standard Romberg, tandem Romberg, and unipedal), with and without vision. The repeated measures design involved 28 healthy young adults (13 females; mean age = 26.86 ± 6.6 yrs) performing quiet standing in the four stance types on a force platform, under two different insole conditions (textured insole; TI vs. smooth insole; SI), with eyes open and eyes closed. Postural sway was assessed via the range and standard deviation of the COP excursions in the anterior-posterior and medial-lateral sway, and overall mean velocity. The main effect of insole type was statistically significant at the alpha p = 0.05 level (p = 0.045). Compared to smooth insoles, textured insoles reduced the standard deviation of anterior-posterior excursions (APSD). While simple main effect analyses revealed this was most pronounced during eyes closed bipedal standing, insole type did not provide a statistically significant interaction with either stance or vision in this measure, or any other. Postural sway showed statistically significant increases across both stance type (bipedal < standard Romberg < tandem Romberg < unipedal), and vision (eyes closed < eyes open), in almost all measures. Stance and vision did have a statistically significant interaction in each measure, reflecting greater postural disturbances with eyes closed when stance stability decreased. Overall, these results support textured insole use in healthy young adults to reduce postural sway measures. This is because APSD is an index of spatial variability, where a decrease is associated with improved balance and possibly translates to reduced falls risk. Placing a novel texture in the shoe presumably modulated somatosensory inputs. It is important to understand the underlying mechanisms by which textured insoles influence postural sway. As such, utilising a healthy adult group allows us to investigate possible mechanisms of textured insoles. Future research could investigate the potential underlying mechanisms of textured insole effects at a neuromuscular and cortical level, in healthy young adults.