The effectiveness of mental imagery for improving strength in an asymptomatic population

Background: Strength training is one focus for physiotherapy management to help restore function. However, conventional strength training requiring an active muscular contraction is not always possible. Mental imagery (MI) has been proposed as a viable alternative to strength training without the need for actual movement.
Objective: To investigate whether MI is effective in achieving strength gains in an asymptomatic
population.
Methods: A systematic review of key databases was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and risk of bias assessed using Grading of recommendations Assessment, Development and Education (GRADE). Studies were included if they were a randomised control trial (RCT), clinical control trial (CCT) or pre-post study investigating the effect of an MI protocol for improving strength in asymptomatic adult populations.
Results: From 639 articles, 28 full texts were assessed and six were included for review. These studied effect of MI on strength improvements for 5th finger abductors (n553), quadriceps (n551), elbow flexors (n551), ankle dorsiflexors (n551) and plantarflexors (n551). Strength gains were reported in all muscle groups with the exception of elbow flexors. MI may be more effective for muscle groups with larger motor cortex representation, especially 5th finger abductors.
Conclusion: The findings suggest that a course of MI can increase strength greater than a control group but less than a physical practice (PP) group within this population. The findings of this study provide promising
clinical implications for use of MI for improvements or maintenance of strength within a patient group unable to actively strengthen due to pain or immobilisation.