When I first started training with my mentor Charles Anderson I learned what this old adage meant. Now days it is a lost art because more people are concerned about the superficial aspects of weight training but in the days where huge social media platforms weren't around and the gym wasn't a new workout outfit contest this saying was relevant. No matter your age, your goal, or how long you have been training; you can benefit from this technique.
What is a mind muscle connection? Research shows that when you think about a muscle, greater muscular activity occurs there. For example, one study looked at how much muscles worked in three conditions: (1) thinking exclusively about the muscles that were working, (2) thinking about the weight that was being lifted, and (3) thinking about whatever the participants wanted. Results showed that there was significantly greater muscle activity in the first condition. And more muscle activity during weight training corresponds to the muscles getting stronger.
Let's say you are doing barbell bicep curls. Your brain instinctively wants to concentrate on the weight: "Move this weight up and down." You need to rewire your brain to concentrate on the muscle: "Squeeze and release the biceps." To practice this, imagine flexing in front of a mirror while doing the curls. Using the mind-muscle connection lets you stimulate a muscle effectively with less weight, which spares your joints. It also leads to less cheating - breaking form just to perform an action without engaging your muscles properly. You'll get better results with less risk of injury when you put your mind into it.
Some movements can be completed by more than one muscle, and your body will tend to use the stronger one. For example, maybe you shove your shoulders up toward your ears during a side raise. This means that when you are done with the set your traps and neck are hurting more than the meat of your shoulder (middle deltoid muscle). To target the weaker muscle that is 'supposed' to be the trained muscle, your brain must shut off the dominant muscles and turn on the weaker ones. The mental focus required to do this not only improves your results, but also helps block distractions, relieve stress, and enhance your relationship with exercise.
How do I practice mind muscle connection? I recommend a quick mental systems check for each new strength exercise. Ask yourself: 1) Are the right muscles contracting when I execute the motion? 2) Do I feel mild soreness in the muscles (a sign to take it a bit easier on that area)? 3) Do I feel any pain there (a sign to stop)? 4) Do I feel extraneous contractions anywhere else? 5) Am I completing the full range of motion? By being mindful of everything happening inside your body, you'll get much more from your training than you would by just going through the motions.
To put your mind into your muscle requires organizing your thoughts and concentrating them on the specific task at hand during a workout. Although this sounds like a simple idea, it's not easy to do because there are plenty of distracting thoughts to get in the way. To minimize the distractions, manage your time so that your workout is a priority, which helps your mind be less agitated about other things you think you should be doing. If you start worrying about how you look at the gym or noticing the person next to you, remind yourself that you're there to maintain and improve your health, not to see and be seen by others.