A mental trick to make your body stronger
If you want to use your mind to make your body stronger, all you have to do is take all of your focus and attention on the exercise that you are doing at the moment.
While this sounds really simple and easy, often times people are not doing this. Their mind is thinking about random things as they are doing their exercise and therefore, they are lacking the ability to access their full energy resulting in a weaker workout.
When you keep your mind focused on the exercise that you are doing at the moment and also focused on the way your body feels , this also puts your mind into a meditative state where all your inner resistance is removed, allowing you to perform at your best. It is also referred to as Flow.