You may sometime have heard the recommendation that one should focus on the muscle, have a “mind-muscle connection”, while lifting in order to achieve optimum results in terms of muscle growth. Now scientific research shows that it's probably right.
An American research group aimed to investigate how an individual's attentional focus affects muscle growth. They conducted a study in which a group of young men trained 3 times per week for 8 weeks, with either an internal or external attentional focus.
The subjects in the internal focus group were told to “squeeze the muscle” on each repetition whereas the subjects in the external focus group were told to “get the weight up!” on each repetition. The results were amazing. The group with an internal focus had a much greater muscle growth in the biceps (12.4%) compared to the group with an external focus (6.9%).
Surprisingly, there was no difference in muscle growth in the leg muscles (Quadriceps). According to the researchers behind the study, this could be because untrained individuals (such as the subjects in the study) find it harder to get a "mind-muscle connection" with the muscles in the lower body. This is probably something that improves with time, the more well-trained you are.
Future studies, involving well-trained individuals, will give us a clearer picture of how muscle growth is affected by our focus of attention. Until then try focusing on the muscles you are training instead of just moving weights and letting your mind wander around. You might be surprised by the results.
Source: Differential effects of attentional focus strategies during long-term resistance training. Schoenfeld, B. J., Vigotsky, A., Contreras, B., Golden, S., Alto, A., Larson, R., Paoli, A. (2018). European Journal of Sport Science, 18(5), 705-712.