The effect of motor imagery on ankle function and performance in persons with and without a lateral ankle sprain: a systematic review and meta-analysis

doi:10.21203/rs.3.rs-2079657/v1

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The effect of motor imagery on ankle function and performance in persons with and without a lateral ankle sprain: a systematic review and meta-analysis

https://doi.org/10.21203/rs.3.rs-2079657/v1

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published 04 Oct, 2023

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Background: Lateral ankle sprains are highly prevalent and result in tissue damage, impairments of muscle strength, instability and muscle activation. Up to 74% will experience ongoing symptoms after a lateral ankle sprain. Motor imagery might be supportive in rebuilding motor networks or creating new networks to restore impairments such as muscle activation and movement patterns. This systematic review was undertaken to summarize the current body of evidence.

Methods: A systematic review with meta-analysis of randomized controlled trials was conducted in healthy participants and participants with a lateral ankle sprain. Movement representation techniques (motor imagery or action observation) in isolation, or in combination with usual care were compared to controls. Any relevant variables related to (self-reported) function and performance were included in the analysis.

Results: Nine studies, six examining healthy participants and three examining participants with an acute lateral ankle sprain, were included. All studies were rated with moderate to high risk of bias overall. Quality of the motor imagery interventions differed largely between studies. The results showed a large and significant effect of motor imagery on lower leg strength (SMD 1.47, 95% CI 0.44 to 2.50). Evidence showed a non-significant effect on ankle range of motion (SMD 0.25, 95% CI -0.43 to 0.93), a non-significant on edema (SMD -1.11, 95% CI -1.60 to 3.81), a non-significant effect on the anterior reach direction of the Star Excursion Balance Test (SEBT) (SMD 0.73, 95% CI -0.62 to 2.08), the posterolateral direction (SMD 0.32, 95% CI -0.94 to 1.57), and on the posteromedial direction (SMD 0.52, 95% CI -0.07 to 1.10). The certainty of evidence for the different comparisons was very low.

Conclusions: There is a significant, positive effect for motor imagery to improve lower leg muscle strength. The certainty of evidence was however low. The effect on balance, range of motion and edema was uncertain, non-significant and of very low certainty.

Systematic review registration: PROSPERO CRD42021243258.

Imagery

Psychotherapy

Systematic Review

Lateral Ligament

Ankle

Rehabilitation

Motor imagery

Lateral ankle sprains are highly prevalent in the general population and during sports activities.^1,2 It is estimated that 20–40% of all sports injuries are ankle sprains³ resulting in considerable time loss from sports activities.⁴ On average, 15 to 28 days lost was reported in amateur and professional soccer players.^5,6 Particularly athletes involved in basketball, volleyball and field sports are at increased risk of sustaining an ankle sprain.⁷ Lateral ankle sprains are often classified as a one-time injury, yet evidence suggests that up to 74% of the persons with a lateral ankle sprain will experience persistent symptoms.⁸ There is evidence for a multifactorial contribution of impaired balance, reaction time and strength to the development of ankle instability.⁹ Vice versa, lateral ankle sprains might result in instability and impairments in strength, peroneal muscle activation, proprioception, range of motion, joint laxity and decreased self-reported functioning.^10–12 The initial sprain results in tissue damage, but additionally causes impairments in the sensory-perceptual and motor-behavioural systems.¹² For instance, participants with ankle instability were found to activate the muscles of the hip, knee and ankle later than control participants without ankle instability during a shift from double leg stance to single leg stance.¹³ The impaired movement patterns have been related to changes within the central nervous system¹⁴ due to functional reorganization of the cortex, increasing the contribution of secondary sensorimotor areas.¹⁵ Brain areas responsible for generating movement are activated extensively during the execution of movement, but similarly also during observation and imagination of the same movement.^16–18

Imagination of movement, or motor imagery, is widely used in sport and in a rehabilitation context and is defined as the mental representation of a given motor act or movement, without any overt motor output.¹⁹ Positive effects on motor performance, such as movement speed, accuracy, variability and muscle strength, have been demonstrated in athletes.²⁰ In rehabilitation, motor imagery might be supportive to rebuild motor networks or create new networks to restore impairments such as muscle activation and movement patterns¹⁷ and is of specific interest in a setting where movement is impaired due to pain or injury and could provide a substitute to actual exercise.^21,22 Positive effects on muscle activation, muscle strength and functional outcomes were demonstrated in persons after a total knee arthroplasty²³ and anterior cruciate ligament reconstruction.²⁴

Over the last twenty years, several studies have looked at the effect of motor imagery on ankle function and performance in healthy participants^10,25 and after an ankle injury.^26–28 However, there is a considerable heterogeneity in the methodology and interventions studied, for instance the type and duration of motor imagery. To date, no systematic review has been undertaken into the topic and there is a need for a clear overview of the effect of motor imagery on ankle function and performance. Therefore, the goal of this systematic review was to summarize the current body of evidence. Our research question was:

What is the effect of motor imagery or action observation on ankle function and performance in persons with, and without, a lateral ankle sprain?

This systematic review was performed in accordance with the guideline Preferred Reporting Items for Systematic reviews and Meta-Analysis: The PRISMA statement²⁹ and was prospectively registered (PROSPERO CRD42021243258).

Identification and selection of studies

An electronic search was conducted using the databases MEDLINE, EMBASE, Cinahl, Psychinfo, Sportdiscus, Web of Science, Cochrane and Google Scholar. The search strategy was designed in consultation with two experienced information specialists [TP and DM]. Articles published up to 24-02-2022 were included in the search. The results were uploaded to Rayyan,³⁰ and duplicate results were removed. Additionally, reference lists of original articles were checked manually to identify additional literature.

Boolean operator “AND” was used to combine keywords and “OR” was used to combine the keywords within each group. The following search terms were used and combined to search the databases: motor, mental, movement, mirror, imagery, ankle, injuries. The final searches for all databases can be found in appendix 1. The electronic search was conducted by the information specialist [TP] and two reviewers [LS and MW] screened titles and abstracts for relevancy using the inclusion criteria listed in Box 1.^29,31 If disagreement upon article relevancy existed between the two reviewers, consensus was achieved by discussion. Full texts of eligible articles were retrieved and evaluated individually by the two reviewers. Again, disagreements were resolved using discussion to reach consensus. A third reviewer [HN] was consulted to make the final decision if disagreement remained during the process.

Assessment of characteristics of studies

Study quality

Randomized controlled trials published in peer-reviewed journals were included. Restrictions to language were made, articles were included when written in English, German or Dutch. A risk of bias assessment was conducted blinded and individually by two reviewers [LS and MW]. The Cochrane risk-of-bias tool 2 for randomized trials was used to judge the domains: bias arising from the randomization process; bias due to deviations from intended interventions; bias due to missing outcome data; bias in measurement of the outcome and bias in selection of the reported result.³² Upon disagreement, consensus was reached through discussion. A third reviewer [HN] was available in case of persisting disagreement. The risk of bias judgement was presented in a Table alongside the results of the systematic review.³³

Participants

Trials including both healthy participants and participants with a lateral ankle sprain. No restriction to age were made.

Intervention

Movement representation techniques (motor imagery or action observation) in isolation, or in combination with usual care.

Outcome measures

Articles were included if they reported any relevant variable related to (self-reported) function and performance, such as strength, or range of motion.

Comparison

The control group received usual care, an intervention which differed from the movement representation techniques, a placebo intervention, or did not receive any intervention.

Data analysis

The data collection process was performed using a data extraction form.³⁴ The items were discussed by the reviewer and colleagues [LS, MW, HN, NS, and JBS] in order to develop the form. The extraction form was pilot tested by two reviewers on three randomly articles and the extraction form were revised where needed. The primary reviewer [LS] extracted the information and the second reviewer [MW] checked the extracted results. Disagreement was settled using discussion. If agreement could not be reached, a third reviewer [HN] was consulted to provide the final decision.²⁹ The final version of the data extraction form can be found in appendix 2. The following key information was extracted: author(s), year of publication, origin/country of origin, the aim of the study, inclusion and exclusion criteria, demographic description of the population (gender, age, type of injury, duration of injury) and sample size, the methodology, the intervention (detailed information about the design, the application and theory), duration of the intervention, the comparison group, the outcomes measures (i.e. range of motion, functional tests, PROM’s, validated questionnaires), the measurement instruments and their validity and reliability, the follow-up (and duration), and key findings.

Meta-analysis using a random effect model was performed when two, or more, studies reported the same outcome measures in a comparable study population. Statistical heterogeneity of the intervention effect was assessed using the I² as it is preferred over the Chi-square test and was considered not important if I² was between 0% and 30%; moderate between 30% and 50%, substantial between 50% and 75%, and considerable above 75%.³⁵ Review Manager (4.5)³⁶ and SPSS, version 28, were used to prepare and maintain the systematic review and conduct the meta-analysis. Outcomes on a continuous scale were presented as the weighted average using the mean difference and standard deviation. The standardized mean difference and standard deviations were presented if studies used different instruments to measure the same construct. The MD or SMD were calculated over the change from baseline scores, ³⁷ authors were contacted if the published results were insufficient for the data analysis. The trial registers ClinicalTrials.gov, EU Clinical Trials Register, Netherlands Trial Register, WHO International Clinical Trials Registry Platform (ICTRP) and ISRCTN registry were checked to identify unpublished trials.

The qualitative analysis of the body of evidence was performed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. The certainty of evidence was classified as high, moderate, low, or very low certainty. Evidence from randomized controlled trials began as high certainty evidence yet were downgraded based on concerns in any of the following five categories: risk of bias, imprecision, inconsistency, indirectness, and publication bias.^38–41

Quality of the motor imagery intervention

The quality of the motor imagery interventions was analysed using fifteen predefined criteria by Schuster et al.⁴² Motor imagery interventions might differ in type, duration, and context. Differences in the administration of the intervention might produce different results, and these differences might be responsible for variation in the estimates of effect between the studies.⁴³

Motor imagery sessions were scored successful when: (1) performed individually; (2) added after physical practice; (3) were supervised; (4) not directed; (5) the location of the motor imagery and (6) position of the participants was task-specific; (7) accompanied by acoustic and (8) detailed MI instructions; (9) performed with the eyes closed; (10) the used perspective during MI was an internal view with (11) kinaesthetic mode and (12) MI interventions included primarily motor-focused activities. (13) The average duration of a study was around 34 days, (14) with a total of 3 MI training sessions per week, and (15) had an average duration of 17 minutes per training session (with a minimum of 178 minutes).⁴²

Flow of studies through the review

The electronic search of the databases identified 685 records (see Fig. 1). After removing duplicates, 438 records were screened for title and abstract. In total, 414 records were excluded based on study design, population, outcome, or intervention. From the 24 included reports, 22 full text articles were retrieved, two reports led to ongoing studies and could therefore not be retrieved. Thirteen papers were excluded based on study design (no control group, n = 3),^10,44,45 outcomes (no outcomes on ankle function or performance, n = 5), ^46–50 language (Korean, n = 2; Arabic, n = 2),^51–54 or publication type (not peer reviewed, n = 1).⁵⁵ In total, nine randomized controlled trials were included.^{25–28,56−60} Reference lists were checked manually for relevant studies, no additional reports were identified.

Characteristics of studies

Risk of bias assessment revealed at least some concerns in six studies ^{25,26,56,57,59,60} and high concerns in three^27,28,58 of the included studies (see Table 1). All studies used a random allocation sequence. Due to the nature of the intervention, in all studies participants and researchers delivering the intervention were probably aware of the assignment during the trial. In two studies a blinded assessor performed the pre-intervention measurements of range of motion, postural control, swelling and functional instability; however, the post-intervention measurements were not conducted by a blinded assessor.^26,59 The other seven studies lacked information about the blinding of the assessor during the measurements.^{25,27,28, 56–58,60} Risk of bias assessments were conducted per outcome measure, as recommended by the Cochrane Handbook for Systematic Reviews.⁶¹ Results of the risk of bias assessments were presented per study when the result for outcomes were equal. For the study of Nagar & Noohu⁵⁶ a small difference in risk of bias between the outcome measures was observed and these results were presented individually (see Table 1).

One trial protocol was identified, no further (published) pre-analysis plans were discovered, increasing risk of bias in the ‘selection of the reported result’ domain.²⁶ Five trial registers were checked to study non-reporting bias and in total, 334 results were located using the search criteria ‘ankle’ and ‘motor imagery’. Two trials in subjects with lateral ankle sprain were identified, one recent trial is in the recruiting phase, and one has been included in the current systematic review. Publication bias was not assessed by testing for funnel plot asymmetry due to insufficient number of studies (n = < 10) included per meta-analysis.⁶²

The characteristics of the nine included studies can be found in Table 2. Three studies^26–28 recruited athletes with an acute ankle sprain and six studies recruited healthy participants.^{25, 56–59,63} Participants in the studies were aged 13 to 15 years⁵⁹, 16 to 18 years⁵⁸, 16 to 20 years²⁶ and 18 to 30 years.^{25,27,28,56,57,60,63} The sample sizes differed between 18^27,57 and 37.⁶⁰ The study of Deghan et al.⁵⁸ recruited 16 football squads (n = 375). Most studies divided participants in an intervention group and a control group, except for two studies,^25,60 one used a three-arm-design²⁵ and one used three intervention groups and one control group.⁶⁰ When assigned to the groups, sample sizes were between 7⁶⁰ and 15⁵⁶ participants.

In the studies using injured athletes, the control groups received normal physiotherapy and the intervention groups received normal physiotherapy and an additional motor imagery intervention. ^26–28 The study with healthy dancers compared a motor imagery intervention with upper body exercises,⁵⁹ and the study with healthy basketball players compared strength training, balance training and motor imagery to a control group receiving strength training and balance training.⁵⁶ In one study motor imagery was compared to a control group which did not perform any exercise⁵⁷ and in the study of Sidaway & Trzaska,²⁵ participants were randomly divided in a motor imagery group, exercise group and a control group. The study using four groups compared differences between a motor imagery group, neuromuscular electrical stimulation group, a group combining motor imagery with neuromuscular electrical stimulation, and a control group.⁶⁰ One study performed “a proprioception training with mental imagery” and compared it to a control group. However, it is unclear what the intervention exactly encompassed and how it was delivered as there is no description provided in the article about the content of the motor imagery intervention, duration, or frequency of the intervention.⁵⁸

An assessment of the quality of the motor imagery intervention based on the criteria of Schuster et al.⁴² can be found in Table 3. Most of the studies directed the motor imagery using a verbally read aloud prespecified protocol,^{25,27,28,56,59} one study combined it with an audio file,⁵⁷ and in one study ankle-foot images were presented on a computer.²⁶ In some studies, the intervention took less than 17 minutes per session⁵⁶ or did not reach a total of 178 minutes during the intervention period⁵⁷ or lacked to satisfy both criteria (volume per session and in total).²⁶ The studies from the Greek research group included 12 motor imagery sessions lasting 45 minutes.^27,28 The study of Nunes et al.²⁶ scored no, no information, or not applicable on 12 out of 15 criteria. This was largely due to the nature of the intervention: participants in the motor imagery intervention were shown 40 left-right images (lateralization) in contrast to the movement-related visualization given in most other studies. For the study of Dehghan et al.,⁵⁸ no information was provided on any of the items in the article.

Effect of intervention

Meta-analysis was performed for studies that compared motor imagery to control groups for lower leg strength, ankle range of motion, edema, and balance and was calculated over the changes from baseline. One author was contacted, and further information on the change from baseline scores was provided. Analysis was done using the standardized difference of mean, due to a difference in measurement instruments measuring the same construct (see Figs. 2 to 5). A random effects model was chosen due to the variety in study backgrounds. Results for the assessment of the certainty of the body of evidence are presented in Table 4.

Effect of motor imagery on strength

Meta-analysis of four studies (Fig. 2) with a total of 64 healthy participants showed very low certainty evidence of a large, significant effect of motor imagery on lower leg strength when compared to controls (SMD 1.47, 95% CI: 0.44 to 2.50; I²: 73%; p = 0.005). The evidence was downgraded to very low certainty due to substantial heterogeneity (I² = 73%), limitations in the studies (some concerns in risk of bias in all studies), and imprecision (n = < 300) (Table 4).

Effect of motor imagery on range of motion

Meta-analysis of three studies (Fig. 3) with a total of 60 participants (35 subjects with a lateral ankle sprain, and 25 healthy subjects) demonstrated very low certainty evidence that motor imagery, when compared to control groups, had a small positive effect on ankle range of motion (SMD 0.25, 95% CI: -0.43 to 0.93; I²: 41%; p = 0.47). The evidence was downgraded to very low certainty due to moderate heterogeneity (I² = 42%), limitations in the studies (high risk of bias in one study and some concerns for risk of bias in two studies), indirectness (due to differences in study populations and interventions), and imprecision (n = < 300).

Effect of motor imagery on edema

Meta-analysis of two studies (Fig. 4) with a total of 35 participants with a lateral ankle sprain provided very low certainty evidence of a large, non-significant effect in favour of controls on edema (SMD − 1.11, 95% CI: -3.82 to 1.60; I²: 91%; p = 0.42). The evidence was downgraded to very low certainty due to considerable heterogeneity (I² = 91%), limitations in the two studies (high risk of bias in one study and some concerns for risk of bias in the other study), indirectness (due to differences in the intervention), and imprecision (n = < 300).

Effect of motor imagery on balance

Meta-analysis of two studies (Fig. 5a) with a total of 47 participants (17 subjects with a lateral ankle sprain, and 30 healthy subjects) demonstrated very low certainty evidence of a moderate, non-significant effect of motor imagery when compared to controls on the anterior direction of the modified star balance excursion test (SMD 0.73, 95% CI: -0.62 to 2.08; I²: 79%; p = 0.29), very low certainty evidence of a small, non-significant effect of motor imagery on the posterolateral direction (SMD 0.32, 95% CI: -0.94 to 1.57; I²: 76%; p = 0.62) (Fig. 5b), and low certainty evidence of a moderate, non-significant effect of motor imagery on the posteromedial direction (SMD 0.52, 95% CI: -0.07 to 1.10; I²: 0%; p = 0.08) (Fig. 5c) of the modified Star Balance Excursion Test. The evidence was downgraded to very low certainty due to limitations in the studies (some concerns for risk of bias in both studies), imprecision (n = < 300), indirectness (due to differences in the study population and intervention), and considerable heterogeneity for the anterior and posterolateral direction (I² = 79% and 76%).

This systematic review with meta-analysis provides an overview of the evidence on the effect of motor imagery on ankle function and performance in persons with, and without, a lateral ankle sprain. Significant, positive, but very low-certainty evidence for motor imagery to improve lower leg muscle strength in healthy participants was found. The evidence for balance, ankle range of motion and edema in healthy and injured subjects was uncertain, non-significant and of very low certainty due to risk of bias, heterogeneity and small sample sizes.

Several methodological strengths for this systematic review can be defined: the protocol was designed using the Cochrane Handbook for Systematic Reviews⁶¹ and Preferred Reporting Items for Systematic reviews and Meta-Analysis (The PRISMA statement)²⁹; a focused review question was formulated; a thorough systematic literature search of multiple databases was conducted; only randomized controlled trials were included; the body of evidence was rated using the GRADE criteria; and the motor imagery interventions were rated using the criteria of a successful motor imagery intervention outcome⁴². The assessment of the quality of the motor imagery intervention provides a clear overview of the content and background of the motor imagery intervention (see Table 3). Furthermore, it might give an indication about the chance of finding a positive result.

A weakness of the current systematic review and meta-analysis is the small number of studies (n = 8) with heterogeneous backgrounds. The small number of studies could have underpowered the results. There was moderate to high risk-of-bias in the included studies, due to problems in the blinding of the assessors performing the pre- and post-measurements which could have led to performance bias. Further, no placebo interventions were given to the control groups. A well-developed placebo is hard to construct in motor imagery study designs, however, several published randomized controlled trials in other areas than the ankle joint have used a placebo intervention.^24,64−66 For instance, a study in persons with an anterior cruciate ligament reconstruction used a neutral task, e.g., mental calculation, or crosswords and showed increased muscle activation of the vastus medialis after five weeks of motor imagery when compared to the mental calculation task in the control group.²⁴ In a study in persons with non-specific chronic neck pain, mixed results for motor imagery on mobility tasks were found between a motor imagery group, an action observation group, and a placebo action observation group. The intervention groups imagined movement (motor imagery group) and watched a video of the same motor task (action observation group), and the placebo control group watched a video that showed nature landscapes, without any human motor actions.⁶⁴

Although caution must be exercised in interpreting the results of the current meta-analysis, the pooled results (n = 81, 4 studies) revealed a large, significant effect for motor imagery to improve lower leg strength (SMD 1.47; 95% CI: 0.44–2.50), i.e., the plantar and dorsal flexor muscles. The quality of the motor imagery intervention according to criteria of Schuster et al.⁴² was rated 10 out of 15 points in two studies,^{57, 60} and 12 out of 15 points in the other two studies.^25,56 To obtain a higher quality rating the studies of Grosprêtre et al., Bouguetoch et al., and Sidaway & Trzaska could have added physical practice sessions to their motor imagery intervention and lengthen the duration of the intervention.^25,57,60 However, it is questionable to assume these modifications would have led to different results as it was previously noted that motor imagery might enhance strength after only a few sessions.⁶⁷ Only a small additional increase in strength is expected from a longer training period. In a 4-week training study in upper extremity strength, the major improvement in strength was observed in the first week after four motor imagery and strength training sessions, yet the increase in strength continued over the 4-week period.⁶⁸

Further, some differences in comparisons across the included studies were noted: one study added motor imagery to a strength training intervention,⁵⁶ while the other three studies used a control group who did not participate in any physical or mental activity.^25,57,63 In addition, the sample of participants (n = 81) included in the meta-analysis for lower leg strength consisted entirely of young (18 to 26 years), healthy participants and generalization towards conditions after an acute injury is not possible.

The positive effect of motor imagery on lower leg strength found in the current systematic review is in line with results from several recent systematic reviews which studied the effect of motor imagery on strength, but in other body regions than the ankle.^69–71 In one of these systematic reviews, a large, positive effect with moderate certainty evidence of motor imagery increasing knee extensor strength was demonstrated in participants following a total knee arthroplasty.⁶⁹

The pooled results (n = 60, 3 studies) of the meta-analysis for ankle range of motion revealed a small (SMD 0.25; 95% CI: -0.43-0.93), positive effect of motor imagery improving range of motion of the ankle compared to a control group. The result was non-significant and of very low certainty. An important difference between the three studies can be found in the content of the motor imagery interventions. Especially the study of Nunes et al.²⁶ differed largely from the other studies: a computer showed 40 left-right images of the ankle, the total duration was approximately 2:40 minutes, the motor imagery was not motor focused, and no detailed and acoustic instruction was given. Therefore only 3 out of 15 criteria for a successful motor imagery intervention were met (see Table 3). The study of Abraham et al.⁷² (10/15 criteria) provided a group intervention, did not combine it with physical practice, participants were free to have their eyes open and was applied twice a week⁷², despite evidence suggesting better effects when the exercise is done individually, combined with physical practice, with participants having their eyes closed in a quiet place and provided three times per week.⁴² Other systematic reviews studying different populations in other regions of the body have found contradictory evidence for motor imagery.^{69–71, 73} For instance, a meta-analysis in persons with various musculoskeletal conditions, such as shoulder, knee, and ankle disorders, found no significant effect in acute musculoskeletal conditions on range of motion.⁷³ Another review stated that the effect of adding motor imagery to standard therapy on active range of motion in patients with a total knee arthroplasty was unclear.⁷¹ Both studies are in line with the results of the current systematic review and do not show a clear effect in acute injuries.^71,73

With respect to balance, the body of evidence (n = 47, 2 studies) showed a non-significant, small to large effect, with only a trend for the posteromedial direction on the Star Balance Excursion Test. When comparing the motor imagery interventions between the two included studies in the meta-analysis for balance, heterogeneity is observed. Nagar & Noohu⁵⁶ scored positive on 12 out of 15 criteria for the quality of the intervention, while Nunes et al.²⁶ scored positive on only 3/15 criteria (see Table 3). This large difference might explain some of the variation between the results of both studies. Other recent systematic reviews, yet directed at different populations, found low certainty, small to moderate effects of action observation and motor imagery on balance.^70,74 However, those reviews did not use the Star Balance Excursion test as a measurement instrument for balance, but used the Tinetti test,⁷⁰ Berg Balance Scale, Functional Reach Test, body sway, or rated balance functionally during an obstacle course.⁷⁴ Direct comparison of the results of the current meta-analysis with those reviews is therefore limited.

Regarding edema (n = 35, 2 studies), a large, non-significant effect (SMD 1.11; 95% CI: -1.60 to 3.82) in favour of the control group was found. The results were classified as very low- certainty evidence. Only two studies could be included in the meta-analysis, again the large effect in favour of the control group in the study of Nunes et al.²⁶ had a strong influence on the overall effect. A search for other studies evaluating the effect of motor imagery on edema in the field of musculoskeletal disorders resulted in no hits, therefore, a further exploration of the results was not possible.

Except for edema, all outcomes favoured the motor imagery group. Due to the very low certainty of the evidence, the effect of motor imagery on muscle strength, ankle range of motion, balance, and edema, in persons with and without a lateral ankle sprain is still uncertain. It is recommended to undertake more high-quality studies with larger sample sizes. Studies should use a randomized controlled trial design with blinded assessors during pre- and post-intervention measurements to decrease the changes of performance bias. Placebo motor imagery intervention should be developed to at least blind the participants, and the motor imagery intervention should score positive on as many of the 15 criteria of Schuster et al. as possible.⁴² The criteria from Table 3 provide a framework for the design of a successful motor imagery intervention, and it is likely that a high number of fulfilled criteria results in a higher-quality motor imagery intervention. Researchers, as well as practitioners, are encouraged to use the criteria in developing future motor imagery interventions. Further, pre-specified analysis plans should be published to promote unbiased assessment of the data and studies should aim at recruiting athletes with lateral ankle sprains.

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Table 1. Risk of bias assessment

Study ID	Experimental	Comparator	Outcome	D1	D2	D3	D4	D5	Overall
Abraham et al.⁵⁹	Motor imagery	Upper body exercises	Range of Motion tests	+	+	+	-	!	!
Bouguetoch et al.⁶⁰	Motor imagery	Control group	Maximal voluntary contraction	+	+	+	+	!	!
Christakou et al. ²⁸	Physiotherapy + motor imagery	Physiotherapy	Muscular endurance, functional stability, dynamic balance	+	+	+	-	!	-
Christakou & Zervas²⁷	Physiotherapy + motor imagery	Physiotherapy	Range of Motion, swelling	+	+	+	-	!	-
Dehghan et al. ⁵⁸	Motor imagery + proprioceptive exercise	Control groups	Proprioception	+	-	-	-	!	-
Grosprêtre et al.⁵⁷	Motor imagery	Control group	Muscle torque	+	+	+	!	!	!
Nagar & Noohu⁵⁶	Strength + balance + motor imagery	Strength + balance exercises	1RM ankle plantar flexion strength	+	+	+	+	!	!
Nagar & Noohu⁵⁶	Strength + balance + motor imagery	Strength + balance exercises	Balance (mSEBT)	+	+	+	!	!	!
Nunes et al.²⁶	Physiotherapy + motor imagery	Physiotherapy	Ankle ROM, balance (mSEBT), swelling, functional instability questionnaire	+	+	+	!	!	!
Sidaway & Trzaska²⁵	Motor imagery	Exercise	Maximal dorsal flexion torque	+	+	+	+	!	!

+: low risk; !: some risk; -: high risk; D1: randomization process; D2: deviations from the intended interventions; D3: missing outcome data; D4: measurement of the outcome; D5: selection of the reported result; 1RM: 1 repetition maximum; ROM: range of motion; mSEBT: modified star balance excursion test

Table 2. Characteristics of included studies.

Trial	Participants (age and complaints)	Motor imagery intervention description; setting	Control	Outcome measures	Follow-up	Results
Abraham et al. (2017)⁵⁹	Sample of 25 active female dance students with a minimum of three years dance experience. Intervention group (n=13) aged 13.51±0.49 and control group (n=12) aged 13.63±0.52.	Two elevé tasks, a repeat (10 repetitions of 3 seconds) and static (hold 10 seconds at maximum height) task were imagined for 20 to 25 minutes per session. 2 sessions per week for 6 weeks delivered as a group session in the dance studio.	Upper body exercises (postural awareness, mobility, and strength) while seated, 2 times per week for 6 weeks.	1) Maximal ankle plantarflexion angle 2) plantarflexion ROM 3) symmetry index	Post-intervention	No significant differences between groups during pre-measurements. MI improved repeat task in maximal plantarflexion angle (p=.04) and ROM (p=.02) for the intervention group during post-measurements. No statistically significant results on ankle plantarflexion maximal angle or ROM were noted in the static task.
Bouguetoch et al. (2021)⁶⁰	Sample of 37 (aged 24±5.8 years) healthy participants, 12 females, were recruited. Motor imagery group (n=10, 4 females), control group (n=7, 2 females), NMES +MI group (n=10, 3 females), and NMES group (n=10, 3 females).	10 MI training sessions (5 per week) under supervision in the laboratory. 40 maximal isometric plantar flexion movements of the right leg were imagined over 6s, with 6s rest. Participants were seated on the isokinetic ergometer during the training sessions.	The control group did not perform any exercise. Additional intervention groups: The NMES group underwent 40 evoked contractions of the triceps surae muscles and the NMES + MI group underwent 20 imagined and 20 evoked contractions.	1) isometric torque 2) EMG activity 3) Muscle architecture	Post-intervention	A significant improvement was demonstrated for the NMES and MI group, as compared to the control group (p<0.001 and p=0.0023) and NMES+MI group (p=0.004 and p=0.002). There was no significant difference between the NMES and MI group (p=0.934).
Christakou et al. (2007)²⁸	20 participants with a grade II ankle sprain in sports (±5.0±2.4 days after trauma) aged 25.4±4.76 years (range 18-30)	Participants first underwent 60 minutes of normal physiotherapy and continued with visualization of ankle dorsal- and plantarflexion ROM, strengthening exercises, proprioceptive training, stationary cycling, forward lunges, step-ups and -downs, diagonal hops and stretching exercises for 45 minutes. In total 12 sessions, 3 times per week. Motor imagery was done while seated in a quiet place.	12 sessions of 60 minutes physiotherapy with hydromassage, laser and exercises: ankle dorsal- and plantarflexion ROM, strengthening exercises, proprioceptive training, stationary cycling, forward lunges, step-ups and -downs, diagonal hops and stretching exercises. 3 times per week	1) muscular endurance 2) functional stability 3) dynamic balance	Post-intervention	The MI group showed significantly greater muscular endurance (p=.017) compared to the control group. No other significant differences between the experimental and control group were observed using Bonferroni corrections.
Christakou & Zervas (2007)²⁷	18 athletes with grade II sprain (5±2.49 days after trauma) aged 26±4.47 years (range 18 to 30 years) and at least 2 years of athletic experience.	Participants underwent relaxation and imagery for 45 minutes in addition to 60 minutes physiotherapy. A relaxation technique was used before MI, participants sat on a quiet place and imagined the exercises as conducted during the physiotherapy session as instructed by the investigator.	12 sessions of 60 minutes physiotherapy including hydro-massage, ultrasound, laser, and exercises: ankle ROM, strengthening, proprioceptive, stationary cycling, step-ups and down, diagonal hops and stretching.	1) VAS 2) swelling 3) ROM	Post-intervention	The results did not show a significant difference between the experimental and control group and between the measurements and the intervention group versus control group on pain (p=.74), edema (p=.78) and ROM (p=.78).
Dehghan et al. (2013)⁵⁸	16 sports teams with 25 healthy football players per squad (n=375) aged 16 to 18 years were recruited.	Mental and proprioceptive exercise for 6 months	No mental and proprioceptive exercises	1) proprioception 2) Number of ankle inversion traumas	Post-intervention	Proprioceptive and MI exercises improved proprioception (p=.000) and reduced the number of injuries (p=.027) compared to the control group.
Grosprêtre et al. (2017)⁵⁷	18 healthy young adults not involved in intense sport activities were recruited. Participants in the intervention group (n=9) were aged 22.2±2.6 years and in the control group (n=9) 23.2±2.8 years.	4 series of 25 imagined maximal isometric contractions of the plantar flexors of the right leg were carried out seated and strapped on an isokinetic dynamometer, daily during seven days for 20 minutes per session.	No exercise during the study (one week)	1) isometric torque 2) rate of torque development	Post-intervention	A significant interaction effect between time and group was found on MVC torques (p=.024). Only the MI group significantly improved MVC torque. A significant interaction was found between time and group for EMG activity in the M. soleus (p=.039) and M. gastrocnemius caput medialis (p=.024).
Nagar & Noohu (2014)⁵⁶	30 healthy, male, collegiate basketball players were recruited. The intervention group (n=25) was aged 20.53±2.2 years and participants in the control group (n=15) were aged 20.80±2.4 years.	Mental imagery followed directly after the strength and balance training and took 10 minutes. Participant sat in a quiet place and performed breathing exercises for 2 minutes, followed by 3 sets of imagination of the previous performed strength and balance exercises with a 1-minute rest. The intervention was carried out 3 times per week for 6 weeks.	30 minutes of balance board exercises: double-leg stance, side to side balance with eyes open and closed and functional sports activities on 1 leg. Strength training with leg press, 4 sets building up to 6RM. 3 times per week for 6 weeks.	1) balance 2) strength ankle flexors	Post-intervention	There was no significant effect of the intervention as compared to the control group for the m-SEBT in the anterior direction (p=.118), posteromedial direction (p=.169), the posterolateral direction (p=.303), and for the composite score (p=.22). There was a significant effect for knee extensor strength (p=.023) in favour of the intervention group and no significant effect for ankle plantar flexor strength (p=.052).
Nunes et al. (2015)²⁶	18 male, field soccer players, with a recent ankle sprain (<72 hours). The intervention group was aged 17.2±1.6 years and the control group was aged 17.4±1.8 years (range: 16 - 20 years).	Motor imagery after physical therapy treatment. In a quiet room participants sat in front of a computer. 40 different images of ankle-foot were projected on screen, patient had to identify a left or right ankle using the left-right arrows of the keyboard within 4 seconds. Time and number of right guesses was calculated at the end of the session. Intervention took place5 times per week, 2 hours per session (physical therapy) plus motor imagery (<2:40 min.).	Physical therapy treatment: cryotherapy (20 minutes) in first 2 sessions, electrotherapy (TENS, ultrasound, or laser) in first sessions, kinesiotherapy consisting of stretching, joint mobilization (passive and active), sensorimotor training, strengthening exercises, and return to sport exercises in the final phase. Sessions were 5 times per week and took 2 hours.	1) ROM 2) Postural control 3) Swelling 4) Functional instability	Post-intervention	No significant between-group differences were demonstrated for ankle dorsal flexion ROM (p=.23), plantar flexion ROM (p=.50), the m-SEBT anterior direction (p=.70), the posterolateral direction (p=.29), the posteromedial direction (p=.79), edema (p=.50), and the CAIT (p=.70).
Sidaway & Trzaska (2005)²⁵	24 healthy participants were recruited and allocated to 3 groups of 8 participants: MI, EG and CG. The mean age was 22.7 years (range 19 to 26 years).	Participants in the mental and physical practice group performed 3 sets of 10 repetitions of maximal dorsiflexion contraction while seated on Biodex for 3 times per week, 4 weeks, 15 minutes per session.	Participants did not participate in any form of practice during the 4 weeks of the experiment.	1) maximal dorsiflexion torque	Post-intervention	ANOVA revealed a significant main effect for group (p=<.01). Post-test performance on dorsiflexion peak torque was significantly higher in mental and physical practice group, not in control group (p=<.05). There was no significant difference between the improvement for the mental practice and the physical practice group.

CAIT: Cumberland Ankle Instability Tool; CG: control group; EG: exercise group; IG: intervention group; MI: motor imagery; m-SEBT: modified Star Excursion Balance Test; MVC: maximal voluntary contraction; NMES: neuromuscular electrical stimulation; RCT: randomized controlled trial; ROM: range of motion; VAS: visual analogue scal

Table 3. Characteristics and analysis of the quality of the motor imagery interventions.

	Criteria of successful motor imagery interventions	Abraham et al. (2017)	Bouguetoch et al. (2021)	Christakou et al. (2007)	Christakou & Zervas (2007)	Deghan et al. (2013)	Grospretre et al. (2017)	Nagar & Noohu (2014)	Nunes et al. (2015)	Sidaway & Trzaska (2005)
1	Were performed individual;	N	Y	Y	Y	NI	Y	Y	Y	Y
2	Were added after physical practice;	N	N	Y	Y	NI	N	Y	Y	N
3	Were supervised;	Y	Y	NI	Y	NI	Y	Y	NI	Y
4	Were not directed;	N	N	N	N	NI	N	N	N	N
5 & 6	The location of the MITS and position of the participants were task-specific;	Y	Y	Y	Y	NI	Y	Y	N	Y
7 & 8	The participants received acoustic and detailed MI instructions;	Y	Y	NI	Y	NI	Y	Y	N	Y
9	During MI the eyes were closed;	Y	NI	NI	NI	NI	NI	NI	N	Y
10 - 12	The used perspective during MI was an internal view with kinaesthetic mode and MI interventions included primarily motor-focused activities;	Y	Y	Y	Y	NI	Y	Y	N	Y
13	The average duration was 34 days;	Y	N	Y	Y	NI	N	Y	NI	N
14	With a total of 3 MI training sessions per week;	N	Y	Y	Y	NI	Y	Y	Y	Y
15	And had an average duration of 17 minutes per training session (total minimum 178 minutes).	NI	N	Y	Y	NI	N	N	N	Y
	Total score (items rated ‘Yes’)	10	10	10	13	0	10	12	3	12

N= no, Y= yes, NI= no information, N/A= not applicable; criteria based on Schuster et al.⁴²

Table 4. Grades of Recommendation, Assessment, Development and Evaluation (GRADE) of the certainty of the body of evidence.

Outcome	Trials (n)	Participants	SMD (95% CI), I²	Certainty of evidence (GRADE)
Lower leg strength	4	81	1.47 (0.44, 2.50), 73%	Very low certainty^a
Ankle range of motion	3	60	0.25 (-0.43, 0.93), 41%	Very low certainty^b
Edema	2	35	1.11 (-1.60, 3.81), 91%	Very low certainty^a
Balance (SEBT-ant)	2	47	0.73 (-0.62, 2.08), 79%	Very low certainty^a
Balance (SEBT-PL)	2	47	0.32 (-0.94, 1.57), 76%	Very low certainty^a
Balance (SEBT-PM)	2	47	0.52 (-0.07, 1.10), 0%	Low certainty^c

SMD: standardized mean difference, a: downgraded due to study limitations, imprecision, and substantial heterogeneity, b: downgraded due to study limitations, imprecision, and moderate heterogeneity, c: downgraded due to study limitations, and imprecision.

Competing interests: none declared

Source(s) of support: No financial grant was received for the current study.

Acknowledgements: We thank Daan Marcellis for his assistance in designing the search strategy. We also thank Dr. Sidney Grosprêtre for providing additional information.

Correspondence: Luuk Siemes, HAN University of Applied Sciences, [email protected]

Provenance: Nijmegen, The Netherlands

No competing interests reported.

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The effect of motor imagery on ankle function and performance in persons with and without a lateral ankle sprain: a systematic review and meta-analysis

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