A 2017 study by Slimani and colleagues investigated the degree to which mental training could improve strength training results.
Over 12 weeks, two groups of high-level kickboxers completed the same training program, focusing on bench press, half squats, medicine ball throws, and countermovement jumps. One group performed “motivational self-talk” during their rest intervals between sets, while the other did not. After the workout, the mental training group also performed 30 minutes of motor imagery training (participants were instructed to imagine themselves performing each exercise, looking out through their own eyes, and maximally exerting themselves through the exercise), while the other group performed “neural cognitive tasks” (which weren’t adequately explained, unfortunately).
After 12 weeks of training, the mental training group had superior outcomes for every exercise assessed (the differences all associated with medium-to-large effect sizes).
Click to expand any of the corresponding figures for more info.
It’s worth noting that the size of the effects observed in this study were a bit larger than we tend to see in the research, but this is FAR from the first study finding that mental training (specifically active mental imagery training) can positively affect performance. For more on the topic, check out this Stronger By Science article by Luke Mitchell: “Strong Starts in the Mind: The Benefits of Active Imagery for Lifters.” This specific study was also discussed in more depth in Volume 1, Issue 5 of MASS.
The actual Xs and Os of your training program clearly matter, but mental training – especially mental imagery training – can improve your performance in the gym and your training outcomes.