Abstract: Mental training, as physical training, enhances muscle strength. Whereas the repetition of maximal voluntary contractions (MVC) induces neuromuscular fatigue, the effect of maximal imagined contractions (MIC) on neuromuscular fatigue remains unknown. Here, we investigated neuromuscular alterations after a mental training session including MIC, a physical training session including MVC, and a combined training session including both MIC and MVC of the elbow flexor muscles.
Methods: Ten participants performed 80 MIC (duty cycle, 5-s MIC and 10-s rest), 80 MVC (identical duty cycle), or 80 MVC and 80 MIC (5-s MVC, 2-s rest, 5-s MIC, and 3-s rest) in three separate sessions. MVC torque was assessed five times over the course of the training and 10 min after the end of the training in the three protocols. Central activation ratio (CARc), reflecting central fatigue, and corticospinal excitability, at rest and during MIC, were estimated using transcranial magnetic stimulation.
Results: Both the physical training and the combined training induced an approximately 40% drop of MVC torque, accompanied with an approximately 10% decrease of CARc without significant difference between the two sessions. On the contrary, the repetition of MIC did not reduce maximal force production capacity and did not alter CARc. Corticospinal excitability was always facilitated during MIC compared with that during rest, ensuring that the participants imagined the desired movement.
Conclusions: These results suggested that one session of mental training alone or combined with physical training do not induce (additional) neuromuscular fatigue despite the repetitive activation of the corticospinal track. Motor imagery may be added to physical practice to increase the total workload without exacerbating neuromuscular fatigue.
Alex’s Notes: Motor imagery (MI) is a mental process during which an individual imagines oneself performing a bodily movement without actually doing the movement. It is an interesting concept that has received a bit of attention lately, as studies have demonstrated that MI may enhance physical performance. But let’s be honest; thinking is hard. Those days where you strain to focus and have a very mentally demanding schedule drain the life-force from the body. So why would imagining to maximally contract a muscle be any different?
“The aim of the present study was to investigate neuromuscular alterations after a mental session with maximal imagined contractions (MIC) (mental training), a physical session with MVC (physical training), and a combined session with maximal imagined and voluntary contractions (combined training).”
Ten healthy active males (28-years old; 22.7 BMI) who had experienced maximal voluntary contractions in the past were recruited to perform isometric elbow flexion via one of the three protocols mentioned above. EMG of the biceps brachii was continuously recorded, as well as motor-evoked potentials (MEP) to determine the neural stimulus reaching the biceps. The subjects underwent four testing sessions separated by at least 48 hours in the following manner: familiarization session, a mental training session with MIC, a physical training session with MVC, and a combined training session with MVC and MIC. The familiarization session had the participants perform the Movement Imagery Questionnaire (MIQ-R) to ensure that they we imagining the proper movements, and also the BRUMS mood test.
“The mental training session consisted in 80 intermittent MIC of the elbow flexors. The specific pattern used was 5 s of MIC and 10 s of rest. During the physical training session, subjects followed the same pattern, with the difference that MIC were replaced by MVC. At the beginning of the mental training protocol and every 20 MIC, subjects performed a 5-s MVC (noted MVC1–5) to detect any physical fatigue. We also added five trials of MVC (MVC1–5) in the 80 MVC of the physical training to have the same number of trials as that during the mental training session (5 MVC + 80 MIC). During the combined training session, subjects followed the same pattern as that during the physical training session, with the difference that a 5-s MIC was performed during the 10-s rest period (80 MVC + 80 MIC).
At the end of the three sessions, participants also performed a last MVC after 10 min of recovery (noted MVCpost10).”
The MEP amplitude during the MIC was greater than when resting throughout the entire training session, which does indeed confirm that the subjects were engaged in MI when they were supposed to be. Additionally, the MEP amplitudes were similar in all three sessions. However, only the physical and combined training had a drop in MVC throughout the sessions, with no difference between the two. Interestingly, however, the BRUMS questionnaire revealed a significant increase in perceived fatigue after all three protocols, while vigor only decreased in the physical and combined training.
In other words, mental training did not further reduce the decreases in maximal voluntary contractions or muscle activation (CARc) that were brought about by physical training, nor did it impair recovery. However, the subjects still reported greater perceived fatigue at the end of the mental training session. This means that performing mental imagery before or during a physical training session could help improve technique and motivation of the athlete without having an effect on performance. Although MI can’t outright replace physical training, it does indeed appear that there may be benefits to replacing a small amount of physical work with MI.
So what would I do with this information? Personally, this just provides more support that there is a benefit to “psyching” up for the gym. I personally will take some of my intra-set rest time to close my eyes and imagine my next set. Other times, usually on the more strenuous lifts, I will visualize myself absolutely destroying the lift and setting new personal records, and I can say that every time I do the muscles that the lift targets always twitch and a cold, invigorating shiver runs down my spine.