Physical strength can be gained solely by imagining working out
the verdict
INSUFFICIENT LEANING
refutedsupported
the weight of evidence
2 sources for · 0 against
Peer-reviewed literature indicates that motor imagery training can yield measurable improvements in specific muscle force measures when practiced alone, but evidence supporting absolute or comprehensive physical strength gains solely through imagination remains limited and partial.
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
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.
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, PT), imagining producing these same isometric contractions (motor imaging training group, MIT), or having no training of the muscle at all (no-exercise control group, CTRL).
After the 4-weeks training, the maximal little finger abduction force increased significantly for the MIT group and the PT group (22 and 30%, respectively), but not for the CTRL group (3.7%). Since MI is a process to internally simulate an actual motor action without physically executing it, it is not expected to have any changes in muscle fiber hypertrophy through repetitive rehearsal of MI of the maximum voluntary muscle contraction (MVC) of the muscle. Muscle fiber hypertrophy has been shown to be one of the potential factors accounting for the muscle strength increases after physical resistance training ( Jones et al., 2008 ; Krzysztofik et al., 2019 ).
There are two common types of mental imagery—internal and external imagery. In internal imagery (IMI; also known as kinesthetic or first-person imagery), a person imagines or mentally creates the feeling of performing the exercise from within the body (i.e., from a first-person perspective). For example, mental strength training using internal imagery emphasizes that the subject generates a similar feeling as he/she felt during a physical MVC ( Ranganathan et al., 2004 ; Sidaway and Trzaska, 2005 ; Yao et al., 2013 ).
In addition, the Meta-regression analysis showed that two out of six training volume variables, the number of repetitions per training session ( p = 0.01) and per study ( p = 0.05), predicted the effects of MIT on muscle strength enhancement and additional dose–response analysis further showed that the largest effects were found after the use of the greatest number of repetitions ( Paravlic et al., 2018 ). Due to the limited number of available studies in old adults at the time, age was not included as a moderator variable in their meta-analysis ( Paravlic et al., 2018 ).
FIGURE 6 Effects on maximal muscle strength: Mental imagery training (MIT) vs. physical training (PT). MIT combined with PT (MITPT) vs. PT only Overall, the estimated effect of MITPT in enhancing MVC force was almost same as PT’s estimated effect (ES = 0.04, 95% CI −0.32–0.39) ( Figure 7 ). FIGURE 7 Effects on maximal muscle strength: Mental imagery training combined with physical training (MITPT) vs. physical training (PT). The chi-square test for heterogeneity was significant (Q 5 = 3.48, p = 0.62). The I 2 value was 0%, indicating no heterogeneity ( Higgins et al., 2003 ).
The intervention of the combination of MIT and PT is equivalent to PT alone in enhancing MVC force. The subgroup group analyses further suggest that older adults and small finger muscles may be beneficial more from MIT than young adults and larger muscles. In summary, the current review suggests that MIT is an effective substitute or addition to PT in muscle strength training.
In the present study, we examined the development of mental fatigue during the kinesthetic motor imagery (MI) of isometric force contractions performed with the dominant upper limb. Participants (<i>n</i> = 24) underwent four blocks of 20 MI trials of isometric contractions at 20% of the maximal voluntary contraction threshold (20% MVC<sub>MI</sub>) and 20 MI trials of maximal isometric contractions (100% MVC<sub>MI</sub>). Mental fatigue was assessed after each block using a visual analogue scale (VAS). We assessed maximal isometric force before, during and after MI sessions. We also assessed MI ability from self-report ratings and skin conductance recordings. Results showed a logarithmic pattern of increase in mental fatigue over the course of MI, which was superior during 100% MVC<sub>MI</sub>. Unexpectedly, maximal force improved during 100% MVC<sub>MI</sub> between the 1st and 2nd evaluations but remained unchanged during 20% MVC<sub>MI</sub>. MI ease and vividness improved during 100% MVC<sub>MI</sub>, with a positive association between phasic skin conductance and VAS mental fatigue scores. Conversely, subjective measures revealed decreased MI ability during 20% MVC<sub>MI</sub>. Mental fatigue did not hamper the priming effects of MI on maximal force performance, nor MI's ability for tasks involving high physical demands. By contrast, mental fatigue impaired MI vividness and elicited boredom effects in the case of motor tasks with low physical demands.
Conversely, subjective measures revealed decreased MI ability during 20% MVC MI . Mental fatigue did not hamper the priming effects of MI on maximal force performance, nor MI’s ability for tasks involving high physical demands. By contrast, mental fatigue impaired MI vividness and elicited boredom effects in the case of motor tasks with low physical demands. mental practice mental fatigue motor performance recuperation This research received no external funding.
They were off medication and instructed to not consume alcohol or modify their caffeinated beverage habits the days of experimentation. We included participants aged 20–30 years old (body mass index ranging 19–24 kg·m −2 ), with a regular practice of physical or sporting activities (>2 sessions of 1 h/week over the last 6 months). We also screened for low MI ability by including participants with a score > 5 out of 7 on kinesthetic subscale of the French translation of the MIQ-3f questionnaire, which assesses MI ease on a Likert-type scale ranging from 1 = “Very hard to perceive” to 7 = “Very easy to perceive” [ 32 ].
This aimed at getting participants familiar with MI before engaging in the MI practice session. We then collected the perceived workload post-warm up from the NASA-TLX [ 37 ]. The NASA-TLX measures 6 different dimensions (“mental demand”, “physical demand”, “temporal demand”, “performance”, “effort” and “frustration”) on a 21-point Likert-type scale. For the present study, we only analyzed results from the mental demand, physical demand, temporal demand and effort subscales as indicators of the workload of the MI practice session.
The timing of the MI practice session was externally cued by auditory stimuli, using Presentation ® software (Version 23.0, Neurobehavioral Systems, Inc., Berkeley, CA, USA). Participants were instructed to mentally reproduce the sensations associated with physical practice of the force task at different intensities. During the first experimental condition, participants completed the MI practice session using kinesthetic MI of isometric contractions of elbow flexor muscles against the force plate at 20% of their MVC (20% MVC MI condition) sustained for 10 s.
We implemented two practice conditions involving MI of maximal vs. submaximal isometric contractions. We first observed a logarithmic pattern of mental fatigue increase throughout the MI practice session. This was measured from subjective mental fatigue scores on a VAS, which represents a reliable and frequently used measure to study mental fatigue. Specifically, data indicate that most of the mental fatigue developed after 40 MI trials for both MI practice conditions. After 40 trials, mental fatigue plateaued within a range of 6–8 points out of 10.
Past experiments emphasized greater autonomic nervous system arousal, increased corticospinal facilitation and increased residual somatic activity during MI of more demanding motor tasks [ 48 , 49 , 50 ]. An original finding of the present study is that the amount of effort required to complete imagined actions is mirrored by mental fatigue. This confirms the embodied nature of MI and corroborates past observations of comparable mental fatigue profiles after physical practice or MI training [ 15 ].
Under both MI practice conditions, we found no decrement in maximal isometric force at the intermediate or final performance assessments. This was attested by the peak force and the total force
[ 12 ] and supports the independence between mental fatigue and neuromuscular factors underlying maximal isometric force performance. Particularly, mental fatigue did not elicit central fatigue, which refers to supraspinal and spinal mechanisms that contribute to decreased force production. Possibly, physical efforts of short durations and high intensity may be less susceptible to mental fatigue compared to the repetition of submaximal efforts in endurance paradigms [ 14 , 15 ].
For instance, implementing electroencephalography measures of ongoing brain oscillations might contribute to further elucidating the influence of mental fatigue on MI ability and motor performances [ 69 , 70 ]. 5. Conclusions Present findings demonstrated the critical influence of the MI content on the development of mental fatigue and its effects on MI ability and force performance. We found facilitatory effects of MI focusing on intense physical demands compared to low physical demands, in spite of a loglinear emergence of mental fatigue under both conditions.
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