Feasibility of motor imagery and effects of activating and relaxing practice on autonomic functions in healthy young adults: A randomised, controlled, assessor-blinded, pilot trial

Introduction Motor imagery (MI) is the mental rehearsal of a motor task. Between real and imagined movements, a functional equivalence has been described regarding timing and brain activation. The primary study aim was to investigate the feasibility of MI training focusing on the autonomic function in healthy young people. Further aims were to evaluate participants’ MI abilities and compare preliminary effects of activating and relaxing MI on autonomic function and against controls. Methods A single-blinded randomised controlled pilot trial was performed. Participants were randomised to the activating MI (1), relaxing MI (2), or control (3) group. Following a MI familiarisation, they practiced home-based kinaesthetic MI for 17 minutes, 5 times/week for 2 weeks. Participants were called once for support. The primary outcome was the feasibility of a full-scale randomised controlled trial using predefined criteria. Secondary outcomes were participants’ MI ability using the Movement Imagery Questionnaire-Revised, mental chronometry tests, hand laterality judgement and semi-structured interviews, autonomic function. Results A total of 35 participants completed the study. The feasibility of a larger study was confirmed, despite 35% attrition related to the COVID-19 pandemic. Excellent MI capabilities were seen in participants, and significant correlations between MI ability measures. Interview results showed that participants accepted or liked both interventions. Seven major themes and insider recommendations for MI interventions emerged. No significant differences and negligible to medium effects were observed in MI ability or autonomic function between baseline and post-intervention measures or between groups. Conclusions Results showed that neither activating nor relaxing MI seems to change autonomic function in healthy individuals. Further adequately powered studies are required to answer open questions remaining from this study. Future studies should investigate effects of different MI types over a longer period, to rule out habituation and assess autonomic function at several time points and simultaneously with MI.

the interviews. Interviewers were identical to the blinded raters and not aware of the participants' group allocations until the start of the interview. Initially, interviewers introduced themselves to the participants. Interviews were taken down simultaneously by one of the interviewers and additional field notes were made by the other one (duration 20-30 minutes). Interview transcripts were returned to the participants for comment and/or correction. In S1 Table 1, the pre-defined questions of the semistructured interview are shown.

Qualitative data analysis
Data were organised based on the research question. Reoccurring ideas, concepts, words and phrases were identified and scrutinised. Based on that, a coding frame was developed to group them into meaningful categories. Requirements for categories and subcategories were their mutual exclusiveness and exhaustiveness, apparent onedimensionality and saturation, where each subcategory is used at least once. Relevant material was selected and text segments structured and generated, marked and defined, subdivided, revised and expanded and central subcategories identified, based on the MI theory (1,2). Categories were defined, named, and characterised and decision rules defined for any cases of overlapping subcategories, to allow for a consistent assignment of data segments. The coding frame was tried out, revised and expanded according to the data as appropriate. The material was progressively summarised, subsumed and contrasted. Categories and subcategories were illustrated using citations. This was followed by creating a data matrix suitable for quantitative data analysis. Descriptive statistics (frequencies) were employed.

Results
Seven major themes emerged from the analysis, which are listed together with relevant categories as follows.  Subjective MI effects: MI practice increases or decreases fatigue; enhances mood; relaxes; is (not) exhausting; feeling of calmness, comfort, and relaxation; feeling disburdened from stressors; being surprised by the newness of the MI experience; wellbeing induced by MI.
Participants expressed their experiences with MI [of planks] and referred to reduced MI ability if they were not able to carry out a particular exercise in real. They also described fatigue as a hindrance to concentration (group 1).

"Some exercises were easy to do. Making one was particularly difficult. Because it was a move I couldn't normally perform, and I always focus on what I can't do. It was easy
to make the starting position, but I had trouble coming back while making the descents of the movement." (ID 40, group 1) "I had some troubles focusing because of tiredness, so it was hard to imagine when I was tired. (ID 15, group 1) Participants in group 2 also raised the matter of familiarity with motion tasks. They also referred to their perception of relaxation that was induced by the MI: All participants mentioned that they would recommend practising MI to somebody else, for several reasons: "I think that being able to imagine increases the ability to feel the movement I make.
Therefore, I recommend it." (ID 15, group 1) "Excessive fatigue may occur while doing the [real activating] exercises. This is not the case during motor imagery so I can recommend it to others. And I would recommend it as it provides calmness and relaxation as you get away from daily thoughts." (ID 30, group 2)