If you have ever tried this (and you are not a gymnast) you probably had to work really hard to pull yourself up! Check out the arm muscles on this champion. High level athletes have to do a lot of strength training and really work on their upper body strength. It takes a lot of muscle power to pull yourself up and then keep yourself up and do the various skills.
Male gymnasts get really ripped with all the training they do. They spend a lot of time working to learn the equipment as artistic gymnastics requires men to perform 5 skill sets: vault, rings, pommel horse, parallel bars and floor routines.
They also spend a lot of time doing conditioning and strength training. Stretching is also really important because you want to be sure the muscles are stretched and warmed up before beginning the training. It is also important to stretch at the end of a workout to prevent injuries. Flexible, well-stretched muscles are less prone to injury.
While athletes spend a lot of time working on each apparatus to learn the required skills, they also do a lot of their training on the floor to prevent injury. Athletes are judged based on their difficulty level, their performance, presentation, form, and more.
One of the main components of the routine is the dismount, where the athlete can show some extra skills and flips. The dismount from the rings in this routine is especially cool.