This basically means mentally focussing on the muscle group that you’re in the process of training, so that your brain and nervous system engages that muscle predominantly, to give it a better workout with good form.
To be able to use it properly, it’s necessary to understand what muscles are being trained with each of your exercises.
The mind-muscle connection should be used for all exercises, but it’s particularly important in compound movements, where you may be targeting one particular muscle, but you’re actually using more than one.
I often see people in the gym for example doing back exercises and they’re clearly not focussing on their back because you can see them pulling strongly with their arms, so they’re engaging their biceps more than they should be.
For example, a lat pull-down isn’t about pulling the bar down emphasising your arms. You should be raising your chest and shoulders up high in the up position, and then focusing on your lats pulling your shoulders down and retracting your shoulder blades as you pull the bar down. This way you’re generating the power in your back, and your arms are left to do whatever they need to do as synergists (helpers).
From now on be sure to concentrate closely on the muscle you’re exercising. Focus on it doing most of the work for the exercise and see it working and growing in your mind as you work out!
— The Little League Gym team