Action Observation Combined With Motor Imagery Training to Improve Motor Function in People With Stroke: Systematic Review and Meta-Analysis

Introduction

Stroke represents a major cause of long-term adult disability worldwide [1]. About 60% of patients with stroke will have different degrees of limb dysfunction [2], which will not only have a significant impact on the quality of life of patients and caregivers but also increase the additional economic burden [3,4].

Action observation (AO) refers to watching human movement either via a prerecorded video or a live demonstration [5]. Motor imagery (MI) is defined as the mental simulation of a given movement that is internally reproduced in the brain without any actual motor output [6]. Both AO and MI can activate the neurons in the motor area [7-9], improve brain structure, and positively affect the motor behavior and performance of the patients [10-12], which are considered effective interventions to promote motor learning and rehabilitation [13,14]. In recent years, systematic reviews have been conducted to analyze the effectiveness of AO or MI on limb function rehabilitation of patients with stroke. Silva et al [6] synthesized data from 6 randomized controlled trials and found that, compared to other therapies, MI is more beneficial for improving poststroke gait (walking speed) at the end of treatment (standardized mean difference [SMD]=0.44). Barclay et al [15] systematic review revealed moderate-quality evidence indicating that MI combined with other treatments improves upper extremity activity (SMD=0.66) and reduces upper extremity impairment (SMD=0.59) in adult survivors of stroke with deficits in upper extremity activity. Borges et al [16] meta-analysis demonstrated that AO improved arm function (SMD=0.39) and enhanced hand function (mean difference=2.76). Peng et al [17] meta-analysis results indicated that, compared to control treatments, AO had a moderate-to-large effect size on walking outcomes (Hedges g=0.779), a large effect size on gait velocity (Hedges g=0.990), and a moderate-to-large effect size on activities of daily function (Hedges g=0.728). When patients with hemiplegia after stroke cannot complete rehabilitation training, AO or MI can replace or supplement traditional rehabilitation training and become a feasible therapy.

The combined intervention of AO and MI (AO+MI) is typically defined as observing an action while simultaneously imagining the feelings associated with performing it [18]. More recently, it has been found that the brain regions involved in MI and AO overlap extensively with each other and with the regions involved in motor execution, so combined use may promote cortical activation in the premotor, rostral parietal, and somatosensory areas [19,20]. A population-independent meta-analysis revealed that AO+MI increased corticospinal excitability compared to AO and control interventions [21]. The training measures of AO+MI have been applied to healthy participants [22], Parkinson disease [23], and limb injuries [24]. A systematic review study on populations with Parkinson disease found that AO+MI can improve individuals’ freezing of gait, speed, physical function, and balance [25]. Some studies [26,27] have applied AO+MI to rehabilitating limb function in patients with stroke. However, most of these studies are small sample trials, and there is heterogeneity among the results of the studies, so the validity is unclear.

The combination of AO and MI has 2 modes: synchronous and asynchronous. In synchronous mode, participants observe human movement, and at the same time, imagine themselves executing either the same or a different action. In asynchronous mode, AO happens at a different time than MI [28]. Some scholars believe synchronous AO+MI has unique advantages [5], but others argue that it is unclear whether synchronous indeed improves performance beyond asynchronous [29-31].

Therefore, our systematic review and meta-analysis aim to explore (1) whether AO+MI has more advantages in limb function rehabilitation of patients with stroke compared with routine rehabilitation, (2) whether AO+MI has an advantage in limb function rehabilitation of patients with stroke compared with their independent use, and (3) whether there are differences in limb function rehabilitation of patients with stroke between synchronous AO+MI and asynchronous AO+MI. Through this review, we discuss the feasibility and effectiveness of applying AO+MI in the rehabilitation of limb function in patients with stroke to provide evidence-based evidence for clinical practice. We hope that this systematic review can provide clinical rehabilitation therapists with some implications for alternative therapy in poststroke limb rehabilitation.

Methods

Overview

The systematic review was registered a priori to PROSPERO (CRD42023488270) and reported following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses; checklist provided in Checklist 1).

Search Strategy

We systematically searched publications in the following databases in June 2025: PubMed, Cochrane Library, Web of Science, Embase, Proquest, Physiotherapy Evidence Database, and clinical trial registries: ClinicalTrials.gov and ChiCTR. Two researchers (PS and CN) developed and performed the search strategy together. The following keywords were used for the search: “Stroke,” “Motor Imagery,” “Action Observation,” “MI,” “AO,” etc. The search method uses the combination of Medical Subject Headings (MeSH) and free terms, and the search strategy is shown in Table 1.

Inclusion Criteria and Exclusion Criteria

The studies were selected based on the PICOS verification method (P-participants; I-intervention; C-comparison; O-outcome; and S-study design), as shown in Table 2.

Study Selection and Data Extraction

Two reviewers (XL and XZ) carried out the study selection independently in accordance with the eligibility criteria, and in case of disagreement, a third reviewer (PS) was asked to resolve this. Initially, all potential articles were screened according to the title, abstract, and keywords. Then the full text of all selected articles was checked, and the final selection was made based on the predefined selection criteria.

Three reviewers (PS, XL, and XZ) independently extracted data from the included studies using a predefined form. Data abstraction included study characteristics, participant characteristics, sample size, intervention measures and intervention content, duration of experiments, assessment instrument, and outcomes. Pre-post differences data were extracted directly. For studies that did not report the mean and SD of the pre-post differences, we used the Follmann et al [32] method to convert the means and SDs of the baseline and final values into the mean and SD of the pre-post differences, as described in version 3.0.2 of the Cochrane Collaboration Handbook (page 213). In case of missing or unclear data, we tried to obtain additional information from the study authors.

Risk of Bias and Certainty of the Evidence

Methodological quality assessment will be conducted independently by 2 researchers, following the Cochrane Risk of Bias tool (RoB 2.0; The Cochrane Collaboration) for assessing the risk of bias in randomized trials [33] recommended in the Cochrane Handbook [34]. If 2 reviewers (XL and XZ) cannot determine the evaluation results in the quality evaluation, a third independent reviewer (PS) makes the decision.

Two independent reviewers (XZ and XL) used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to assess the certainty for each meta-analysis outcome. There are 4 classification levels to assess the quality of evidence: high, moderate, low, and very low. We used the GRADEpro GDT (GRADEpro GDT; Evidence Prime, Inc) to create the “Summary of findings” tables.

Data Analysis

Statistical analysis was performed using Review Manager software (RevMan 5.3; The Cochrane Collaboration). Measurement data with the same outcome index unit were calculated using mean difference and 95% CI. SMD and 95% CI were used for different outcome index units. The difference was statistically significant at P<.05. For studies reporting median, we converted these values to mean and SD using the method proposed by Hozo et al [35].

Heterogeneity was tested using the chi-square test and I² statistic [36]. The heterogeneity was considered low when P>.1 and I²<50%, and the fixed-effects model estimated the combined effect size. The heterogeneity was considered significant when P<.1 and I²>50%, and the random effects model was adopted. When it was impossible to combine effect sizes, we performed only a descriptive analysis of the results. Subgroup analyses were conducted to explore potential sources of heterogeneity through subgroup analysis.

For interventions that could not be directly compared, a mesh meta-analysis was performed using Stata 14.1 software (StataCorp LLC). SMD and 95% CI were used to calculate the effect size of this study. The surface under the cumulative ranking curve (SUCRA) was used to predict and rank the efficacy of rehabilitation measures [37]. When there was a closed loop in the network map, the inconsistency model was used for testing. If P>.05, the consistency model was used for analysis. If P≤.05, the source of heterogeneity should be identified and eliminated.

We conducted the sensitivity analysis using the one-by-one elimination method and changing the combined model. If more than 10 studies were included, the funnel plot was used to analyze publication bias.

Results

Study Selection and Characteristics

A total of 7563 results were retrieved from 8 databases, and 5850 results remained after removing duplicates. After the preliminary screening, 219 articles remained. After reading the full text and rescreening, 13 articles [38-50] were finally included, and the flowchart is shown in Figure 1.

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The 13 included studies [38-50] involved a total of 399 participants, and most of them were small sample trials. The participants were mainly patients with stroke with upper limb paralysis. A total of 12 studies compared AO+MI with their independent use or conventional rehabilitation [38-49]. In addition, one [50] compared synchronous and asynchronous combination models. Most of these studies had an intervention duration of about 4 weeks. Most of the primary outcome indicators were upper extremity function, while only 2 studies [39,45] assessed the lower extremity function and 1 study [49] assessed the overall motor function. The features of literature inclusion are shown in Table 3. In this table, age and stroke course were expressed as mean (SD) or median (IQR) or median (maximum, minimum).

Risk of Bias and Certainty of the Evidence

The RoB 2.0 tool was used to evaluate literature quality. All 13 randomized controlled studies were included, of which 6 [39-42,46,47] had a low risk of selection bias, 2 [42,46] used assignment concealment, 3 [39,42,43] blinded participants and implementors, 8 [38,39,42-44,46,47,50] blinded outcome evaluators, only one [48] outcome measure was incomplete, all studies reported full results, and 7 [42,43,45-47,49,50] had a low risk of other bias. The final evaluation results are shown in Figure 2.

We assessed the certainty of evidence for the 7 outcomes in the meta-analysis. The overall certainty of evidence was rated as low to very low. The GRADE results are shown in Table 4.

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Outcomes

Comparison of AO+MI and Routine Rehabilitation

A total of 10 studies compared the effects of AO+MI and routine rehabilitation on patients’ motor function [38,39,41,42,44-47,49,50]. One study [49] evaluated the impact of AO+MI on overall motor function, demonstrating that AO+MI enhanced Fugl-Meyer assessment (FMA) scores versus routine rehabilitation (SMD=3.22, 95% CI 1.55‐4.89; P<.001), as shown in Figure 3A.

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A total of 7 studies [38,40,41,46-48,50] assessed the effect of AO+MI on upper extremity motor function and were included in the meta-analysis. Among these 7 studies, 4 studies [38,41,46,47] used Fugl-Meyer assessment of upper extremity (FMA-UE) as the main evaluation index to evaluate the upper extremity motor function of patients, one study [42] used Action Research Arm Test (ARAT), one study [43] used Motor Activity Log (MAL), and one study [44] used the data of 1-minute drinking movements of patients. A random effects model was used as the studies had high heterogeneity (P=.002, I²=71%). The results showed a significant difference between the 2 groups (SMD=1.02, 95% CI 0.28‐1.75; P=.007), as shown in Figure 3B.

A total of 2 studies [39,45] evaluated the effects on lower extremity motor function, with one study [39] using the Fugl-Meyer assessment lower extremity (FMA-LE) as the evaluation index and one study [45] using gait speed. Analysis using a fixed-effects model (P=0.95, I²=0%) and meta-analysis results showed a significant difference between the 2 groups (SMD=6.31, 95% CI 4.75‐7.87; P<.001), as shown in Figure 3C.

A total of 2 studies [42,46] evaluated the effects on activities of daily living (ADL), with one study [42] using the Barthel index as the evaluation index and one study [46] using the Functional Independence Measure (FIM). Analysis using a fixed-effects model (P=0.63, I²=0%) and meta-analysis results showed no statistically significant difference in ADL between the 2 groups (SMD=0.06, 95% Cl −0.35 to 0.47; P=.77), as shown in Figure 3D.

Comparison of AO+MI and Their Independent Use

A total of 3 studies [40,41,48] compared the effects of AO+MI and their independent use on patients’ motor function. One study [40] compared the effects of AO+MI and AO on patients’ upper extremity function. The results demonstrated a statistically significant improvement in FMA-UE scores with AO+MI relative to AO alone (SMD=1.92, 95% CI 0.66‐3.81; P=.003), as shown in Figure 4A. Two studies [41,48] compared the effects of AO+MI and MI independently on patients’ upper extremity function; both used FMA-UE as an evaluation index. A meta-analysis was performed using a fixed-effects model (P=.69, I²=0%), and results showed that AO+MI could promote the recovery of upper extremity function in patients compared with MI independently (SMD=0.97, 95% Cl 0.13‐1.80; P=.02), as shown in Figure 4B.

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Comparison of Synchronous Mode and Asynchronous Mode

Of the studies included in this review, 7 studies [38,41-43,45,47,49] used the asynchronous AO+MI mode, 5 studies [39,40,44,46,48] used synchronous mode, and one study [50] directly compared the therapeutic effects of synchronous and asynchronous combined mode. A total of 10 studies [38,40-44,46-48,50] were included in the network meta-analysis to compare the effects of the 2 combination interventions on upper extremity motor function across 5 rehabilitation measures: routine rehabilitation, AO, MI, synchronous AO+MI and asynchronous AO+MI; the network diagram is shown in Figure 5A. FMA-UE, ARAT, MAL, and 1-minute drinking movements of patients were used as indices to evaluate extremity function rehabilitation.

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The global inconsistency test revealed no inconsistency between the studies (χ²df=1.53, P=.67). The results of the node-splitting analysis demonstrated local inconsistency between synchronous mode and asynchronous mode (P=.02). The forest map results showed no statistically significant difference between synchronous mode and asynchronous mode effects on upper extremity function rehabilitation of patients after stroke (SMD=−1.04, 95% Cl −2.56 to 0.48), as shown in Figure 5B. The results of the SUCRA analysis showed that the interventions most likely to promote the rehabilitation of patients’ upper extremity function were asynchronous (89.3), synchronous (46.4), AO (49.9), MI (38.6), and routine rehabilitation (25.8), as shown in Figure 5C.

Publication Bias

The analysis of the effect index for limb motor function was conducted, generating a funnel plot. The results showed good symmetry, indicating that publication bias was not noticeable. The comparison-correction funnel plot is shown in Figure 5D.

Discussion

Principal Findings

This study review aimed to synthesize the evidence on the effects of AO+MI on limb functional rehabilitation in patients after stroke through a systematic review and meta-analysis. We included 13 trials with 399 participants in this review.

The meta-analysis showed that compared with routine rehabilitation therapy, AO+MI could improve limb motor function in patients with stroke. And compared with their independent use, AO+MI could improve upper extremity motor function in patients with stroke. These findings are consistent with the results of a meta-analysis by Chye et al [21] that included all populations (encompassing patients with Parkinson disease, older individuals, children, and healthy adults et al). Relevant and experience-dependent practice encourages the brain to create and reorganize functionally appropriate neural connections, which is pivotal for neurorehabilitation following stroke [52]. A related functional magnetic resonance imaging study [53] has revealed that when individuals engage in AO+MI, blood oxygen level-dependent (BOLD) signals increase and become more widespread in brain regions involved in motor execution. Electroencephalography investigation demonstrates that during AO+MI, individuals exhibit significantly decreased power spectral densities in the alpha and beta bands, indicating heightened activity in the primary sensorimotor cortices [54]. For patients with stroke who have difficulty performing actual movements, the increased neural activity during AO+MI may support repeated Hebbian modulation of intracortical and subcortical excitatory mechanisms through synaptic plasticity, producing effects similar to those of physical practice [21]. This may be the reason why AO+MI improves motor function in patients with stroke. However, our meta-analysis showed that AO+MI did not improve ADL in patients after stroke compared with routine rehabilitation. A potential explanation is that poststroke ADL improvement requires a longer intervention duration, while the 2 studies [42,46] included in this meta-analysis featured relatively short intervention periods (2‐4 weeks).

Although the only direct evidence suggests that synchronous may enhance motor function in patients with stroke compared to asynchronous [50], the network meta-analysis results in this review indicate no significant difference between synchronous and asynchronous AO+MI in improving upper extremity function in patients with stroke. The potential reason for the inconsistency between direct evidence and meta-analysis results may stem from differences among participants. As Eaves and colleagues point out [5], synchronous AO+MI may impose greater cognitive load compared to asynchronous AO+MI. This could result in the synchronous mode being overly demanding for certain patient populations or rehabilitation stages. In such cases, asynchronous intervention might be more advantageous. Consequently, variations in key characteristics among participants across included studies—such as severity of neurological deficits and baseline cognitive levels—may modulate the boundaries of effectiveness between synchronous and asynchronous intervention modalities. Therefore, future studies with more direct evidence are needed to compare the effects of these 2 modalities on poststroke recovery. In addition, asynchronous AO+MI does not rule out the possibility of participants spontaneously performing MI during the AO component of AO then MI. This may result in some studies using asynchronous mode inadvertently including elements of synchronous mode, which might also explain why no significant difference in effectiveness has been observed between the 2 combined approaches.

This review evaluated the included studies strictly according to the relevant measures in the Cochrane 5.1.0 manual for randomized controlled trial quality assessment. Among the 13 studies [38-50] included, only one study [42] had a low risk of bias in all 7 aspects of bias analysis, while the risk of bias in the other studies mainly focused on selection bias and implementation bias. Although most studies claim randomization, only half clearly state the correct way to generate random sequences. In addition, most studies did not report how the randomization scheme was assigned to hide, which led to high-risk outcomes in both evaluations. Most of the studies included in this review were not blinded, which may be due to the changes in rehabilitation measures and the limitations of human resources, material resources, and venues, making it challenging to perform double blindness. The overall quality of the evidence presented in this review, as assessed by the GRADE approach, was low or very low for all comparisons. The main limitations were imprecision due to very small sample sizes, risk of bias, and inconsistency.

In addition to the low quality of the included articles, this review has several limitations. First, the studies we included may exhibit a certain degree of heterogeneity in terms of interventions. In some studies, the effects of AO +MI might be influenced by other concurrent therapeutic approaches, such as mirror therapy or graded motor imagery. For instance, in the study by Ietswaart et al [42], in addition to the 30-minute AO+MI intervention, each session also included an additional 10 minutes of active motor imagery and 5 minutes of a certain implicit form of motor imagery activity. This multicomponent intervention approach may mean that the observed therapeutic effects cannot be entirely attributed to pure AO+MI, potentially affecting the results of this study in the overall analysis. Second, there are a few included articles, and most are small sample studies, thus limiting the reliability of the research conclusions. Third, we only searched and reviewed articles in English; publications in other languages may have been missed. Fourth, the absence of standardized intervention protocols and variation in outcome assessment tools across the included studies complicates direct comparisons and meaningful synthesis of the findings. In addition, significant heterogeneity was observed in the meta-analysis results. Consequently, the results should be interpreted cautiously.

Dorsch et al 2024 [55] meta-analysis explored the effect of adding nonstimulation-based priming prior to task-specific practice on activity and motor impairment outcomes compared with task-specific practice alone in stroke rehabilitation, searching for manuscripts up to March 2019. This review included 2 trials investigating the impact of AO+MI on activity outcomes in patients after stroke, and the results did not show a significant improvement effect of AO+MI. The reason for the inconsistency with our findings might be that Dorsch et al [55] compared the postintervention scores between the conventional group and the AO+MI group, whereas our study compared the pre-post differences of the 2 groups.

Lin et al [56] systematic review included 9 studies investigating the effects of AO+MI on upper limb function in patients with stroke, and the results demonstrated that AO+MI significantly improves upper limb function in participants. Our study differs from Lin et al [56] review in several key aspects. First, our study adopted broader inclusion criteria, examining not only upper extremity function but also lower extremity function, overall motor function, and activities of daily living, thereby addressing a wider range of clinical outcomes. As a result, the set of included studies differs somewhat from that in Lin et al [56] review. Second, this study conducted separate meta-analyses according to the type of control group (conventional intervention, MI alone, or AO alone), thereby minimizing heterogeneity introduced by differences in control conditions, enhancing the precision of the findings, and offering more specific guidance for clinical practice. In addition, this study incorporated a network meta-analysis to compare the effectiveness of 2 AO+MI integration modes—synchronous versus asynchronous—on upper extremity function after stroke. Therefore, although there are overlapping findings, this study and Lin et al [56] review can complement each other and reinforce key conclusions, serving the valuable purpose of replication and strengthening the evidence base.

Conclusions

This systematic review and meta-analysis examined the effects of AO+MI on motor function in patients with stroke. Our results found that AO+MI can improve the motor function compared to routine rehabilitation, AO, or MI. Furthermore, no conclusive evidence supports AO+MI’s efficacy for improving ADL, nor demonstrates differential effects between synchronous and asynchronous application modes on poststroke limb function. The quality of GRADE‐based evidence in this review varied from low to very low, due to the high risk of bias and small sample sizes. Consequently, large-scale randomized controlled trials with rigorous methodology are imperative to establish definitive clinical recommendations.