It's simple. You just have to persevere. How to do it: Do arm and leg lifts on the parallel bars (at a 90-degree angle with the body), gradually increase from less to more, and do it with your endurance. Take a break for about a minute before doing the second group (group: how much at a time), and start with three groups as an exercise. The second is to lie down and start sitting, and lift your legs (that is, the upper body and legs are at the same time until your fingers touch your toes), and you can gradually increase the number of groups according to your own situation. If you persist, you can see the muscles you want to see in three months.