Motor imagery ability

Four different MI ability assessments were employed because using at least two different approaches is recommended [35, 36].

Movement Imagery Questionnaire-Revised (MIQ-R). It assesses the visual and kinaesthetic MI ability and comprises 4 visual and 4 kinaesthetic items [37]. Each item involves performing a movement, followed by imaging that same movement using a visual or kinaesthetic mode. Participants are then asked to rate the ease or difficulty of generating that image on a 7-point Likert scale. Higher scores indicate greater visual or kinaesthetic MI ability. A cut-off point of 25 out of the maximum score of 56 has been suggested previously [38] and hence for each of the two subscales, a 12.5 cut-off point was used to signify good or poor MI ability. Acceptable validity and reliability of the Turkish version of the MIQ-R have been demonstrated [39].

Mental chronometry (MC) tests. They assess the temporal equivalence of actual and imagined movements [40]. MC was evaluated employing a walking and writing task [41]. For the walking task, participants imagined and executed walking a 6-metre distance at a comfortable speed. For the writing task, participants imagined and executed writing the following sentence in Turkish: "Türkiye’nin başkenti Ankara" meaning “Ankara is the capital of Turkey.” For time taking, participants kept an electronic stopwatch in their non-dominant hand. MI quality was evaluated using the formula 1-((actual movement duration-MI duration)/actual movement duration) [42], where ideal values would be close to 1.

Hand Laterality Judgement (HLJ). It was measured using the Recognise™ App (Neuro Orthopaedic Institute, NOI, Adelaide) on a tablet. This App has been found to be valid and reliable in healthy individuals, and minimum detectable changes are available [43, 44]. The accuracy and reaction time for the right and left sides were reported. High values in accuracy and low values in reaction time indicate high MI ability [45]. A meta-analysis has shown values of 2.08 (95% confidence interval (CI): 2.02, 2.15) seconds and 91.9% (95%CI: 91.3%, 92.5%) for the HLJ time and accuracy in healthy controls, respectively [46].

Motor imagery experiences and acceptability of the intervention. It was considered important that participants accepted the MI practice as otherwise, one could not expect people to maintain MI training for a prolonged period of time. So, at post-intervention, participants in the intervention groups were invited for semi-structured face-to-face interviews by the study PI. They were asked about their perceptions of the MI interventions, their experiences during the MI and their suggestions for a future MI intervention [47]. Interviews were designed according to recommendations on qualitative interviewing [48] (S2 Checklist) and conducted by two Master’s students in physiotherapy (SCG and TI, female and male). Details are presented in S2 File and S1 Table.