Objective The current review was aimed to determine the effectiveness of mental imagery training (MIT) on the enhancement of maximum voluntary muscle contraction (MVC) force for healthy young and old adults. Data sources Six electronic databases were searched from July 2021 to March 2022. Search terms included: “motor imagery training,” “motor imagery practice,” “mental practice,” “mental training,” “movement imagery,” “cognitive training,” “strength,” “force,” “muscle strength,” “performance,” “enhancement,” “improvement,” “development,” and “healthy adults.” Study selection and data extraction Randomized controlled trials of MIT in enhancing muscle strength with healthy adults were selected. The decision on whether a study met the inclusion criteria of the review was made by two reviewers independently. Any disagreements between the two reviewers were first resolved by discussion between the two reviewers. If consensus could not be reached, then it would be arbitrated by a third reviewer. Data synthesis Twenty-five studies including both internal MIT and external MIT were included in meta-analysis for determining the efficacy of MIT on enhancing muscle strength and 22 internal MIT were used for subgroup analysis for examining dose-response relationship of MIT on MVC. Results MIT demonstrated significant benefit on enhancing muscle strength when compared with no exercise, Effect Size (ES), 1.10, 95% confidence interval (CI), 0.89–1.30, favoring MIT, but was inferior to physical training (PT), ES, 0.38, 95% CI, 0.15–0.62, favoring PT. Subgroup analysis demonstrated that MIT was more effective for older adults (ES, 2.17, 95% CI, 1.57–2.76) than young adults (ES, 0.95, 95% CI, 0.74–1.17), p = 0.0002, and for small finger muscles (ES, 1.64, 95% CI, 1.06–2.22) than large upper extremity muscles (ES, 0.86, 95% CI, 0.56–1.16), p = 0.02. No significant difference was found in the comparison of small finger muscles and large lower extremity muscles, p = 0.19 although the ES The combination of MIT and PT is equivalent to PT alone in enhancing muscle strength. The subgroup group analysis further suggests that older adults and small finger muscles may benefit more from MIT than young adults and larger muscles. Keywords: motor imagery practice, mental practice, movement imagery, muscle strength, performance, strength enhancement, aging status released display-pdf yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2022 Sep 24; Accepted 2022 Dec 5; Collection date 2022. The study by Yue and Cole (1992) included three groups (MIT, physical training, and control groups) and examined not only the MIT effect on improving muscle strength but also neuromuscular mechanisms underlying the MIT-induced strength increase. The young-healthy subjects trained their left hypothenar (little finger abductor) muscles for 4 weeks by either producing real maximal isometric contractions of the muscle (physical training group, In external imagery (EMI; also known as third-person visual imagery), the person sees or visualizes performing the task from outside the body—similar to watching oneself in a mirror performing an exercise ( Herbert et al., 1998 ). Performing IMI generates significantly more physiological responses (i.e., heart rate, blood pressure, and respiration rate) compared to doing EMI ( Ranganathan et al., 2004 ) and is superior to EMI for elevating MVC-related cortical potentials on scalp locations over primary motor (M1) and supplementary motor cortices and for enhancing muscle strength ( Yao et al., 2013 ). Overall, accumulating evidence suggests that MIT is effective in enhancing muscle strength. Thus, the main objective of the current study was to undertake a systematic review and a meta-analysis of randomized controlled studies with either PIV or CBV available, published in peer-reviewed journals or unpublished dissertation or thesis, investigating the beneficial and adverse effects of motor imagery training (MIT) on enhancing muscle strength for both healthy young and older adults. It was hypothesized that both young and older adults should benefit from MIT to enhance their muscle strength. The hypothesis was developed based on the facts that imagery abilities are sustained with aging ( Saimpont et al., 2013 ) and sarcopenia, the age-related decrease in lean muscle mass ( Siparsky et al., 2014 ), makes it feasible to augment old adults’ muscle strength by increasing net excitation of the motoneurons, and increasing activation of prime movers and inhibition of antagonists ( Sale, 1987 ) as the results of MIT. TABLE 2 Training volume variables with the effect size (ES): Motor imagery training * vs. no-exercise control. Key words used were: “motor imagery training,” “motor imagery practice,” “mental practice,” “mental training,” “movement imagery,” “strength,” “force,” “muscle strength,” “performance,” “enhancement,” “improvement,” and “healthy adults.” To find additional articles, the authors hand-searched reference lists of obtained articles (reference and author tracking). The search was terminated on March 15, 2022. To insure effective and accurate search, the titles and abstracts were first analyzed by the two reviewers based on the pre-determined inclusion and exclusion criteria. (2013) 6 Male and Female 18–35 MIT = 6 EMIT = 6 CTRL = 6 Elbow flexion; Isometric 6 5 30 900 MIT 10.5% * EMIT 4.8% CTRL NC Yue and Cole (1992) 6 Male and Female 21–29 MIT = 10 PT = 8 CTRL = 9 Abduction of little finger of the hand 4 5 15 300 MIT 22.03% ** PT 29.75% ** CRTL 3.7% BP, bench press; CTRL, control group; Freq/WK, number of MIT sessions per week; LP, leg press exercise; MIT, motor imagery training; MITABD, MIT with little finger abductor muscle; MITELB, MIT with elbow flexor muscles; N/A, not available; NC, no change; PT, physical training; SD, standard deviation; T/S, number of trials per training session; TT/MIT, total trials in whole study period.