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

Abstract

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.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. CONSORT flow diagram.

Fig 2. Correlations between the motor imagery ability assessments at baseline.

The heatmap presents Spearman’s Rank correlation coefficients (ranging from-1 to +1) of MI ability measures, where darker blue and red fields signify stronger correlations. (A) All participants. (B) Activating MI group. (C) Relaxing MI group. (D) Control group.

Fig 3. Effects of activating and relaxing motor imagery ability on motor imagery ability.

(A) Visual MI ability. (B) Kinaesthetic MI ability. (A and B) Medians at baseline (pre) and post-intervention (post) are represented by squares and interquartile ranges by error bars. Units of measurement are indicated on the y-axis. Motor Imagery Questionnaire-Revised (MIQ-R) data were analysed using Kruskal-Wallis test, followed by Dunn’s correction for multiple comparisons, with overall p-values and partial eta squared effect sizes shown on top of the figures. (C to H) Means at baseline (pre) and post-intervention (post) are represented by squares and lower and upper 95% confidence intervals by error bars. Units of measurement are indicated on the y-axis. Mental chronometry (MC) and hand laterality judgements (HLJ) were analysed using a two-factor mixed analysis of variance ANOVA, followed by a Bonferroni correction for multiple comparisons, with overall p-values shown on top of the figures. (C) MC between imagined and real walking using a 6-Metre Walk Test, where the dotted line indicates identical durations of real and imagined walking. (D) Mental chronometry using a writing task, where the dotted line indicates identical durations of real and imagined writing. (E to F) HLJ. (E) Right-left discrimination (RLD) time (seconds) for the left hand. (F) RLD time (seconds) for the right hand. (G) RLD accuracy (percentage of correct responses) for the left hand. (H) RLD accuracy (percentage of correct responses) for the right hand.

Fig 4. Effects of activating and relaxing motor imagery ability on metabolic function.

(A to D) Means at baseline (pre) and post-intervention (post) are represented by squares and lower and upper 95% confidence intervals by error bars. Units of measurement are indicated on the y-axis. Data were analysed using a two-factor mixed analysis of variance ANOVA, followed by a Bonferroni correction for multiple comparisons, with overall p-values shown on top of the figures. (A) RMR resting metabolic rate—caloric expenditure (B) BMR basal metabolic rate. (C) Fat metabol fat substrates used for energy metabolism. (D) CHO metabol carbohydrate substrates used for energy metabolism.

Fig 5. Effects of activating and relaxing motor imagery ability on cardiorespiratory function.

(A to G) Means at baseline (pre) and post-intervention (post) are represented by squares and lower and upper 95% confidence intervals by error bars. Units of measurement are indicated on the y-axis. Data were analysed using a two-factor mixed analysis of variance ANOVA, followed by a Bonferroni correction for multiple comparisons, with overall p-values shown on top of the figures. (A) RQ respiratory quotient. (B) VO2 oxygen uptake. (C) VCO2 carbon dioxide production. (D) VE minute ventilation. (E) RF respiratory frequency. (F) FEO2 concentration of oxygen in the exhaled gases. (G) FECO2 concentration of carbon dioxide in the exhaled gases.

Fig 6. Motor imagery recommendations from study participants.

Numbers on the radar graph represent the numbers of participants in the two intervention groups who expressed the respective opinions.