I have a deep understanding of this problem. Personally, I feel that the first thing is to do some push-ups, so I must stick to it. In addition, running is also very important. Fighting is not strength, but endurance. Sit-ups are ok, depending on your persistence. If you like other sports, follow them. For example, basketball and football can exercise your whole body. Basketball is very helpful for your abdominal muscles. That's all I've experienced.