Boxers have an order of magnitude differentiation, that is, according to weight, it is basically impossible to be mostly fat, so it is basically muscle weight, because it affects speed. Not everyone is born strong, but more is a uniform figure, so the longer it takes to reach more muscle mass, the longer it will take to really start the competition. Saving experience is a waste of money. If you gain weight gradually, your actual sports performance will also change. Obviously, it is more risky to change your weight and it is easier to lose weight than to keep your weight and keep your original exercise pattern. So most boxers are small-sized, that is, the muscle mass you see is small, but it doesn't mean that they are not heavy. For example, in Tai Sen, boxers are athletes. If the muscle mass is greatly improved, there is no need to play heavyweight, as long as you can win any order of magnitude. Unless you really want to play or the company requires, you don't need to deliberately increase the order of magnitude.
This is the target level, let's talk about the physical level.
Muscles have supporting units and contracting units. Support units refer to organizations that store water and energy. Contraction units are tissues that can contract and provide strength. Both must grow at the same time, but who is more and who is less different. This is determined by training. In bodybuilding training, there are many parts aimed at metabolic stress, that is, energy consumption in muscles is fast and waste discharge is slow. Under this pressure, muscles tend to grow and support. Units have to cope with metabolic pressure, so at this time, the supporting units are much longer and the contraction units are less. Moreover, because the supporting units have more water and larger volume, the muscles will become bigger quickly, but the strength will gradually increase, and the strength training is the opposite. Therefore, you can see that even if the muscles are similar, the strength of bodybuilding will not be better than the strength lifting. This is the adaptation in different directions brought by training.
Boxers don't need much strength, what they need is explosive power, that is, high output and endurance in a short time. To ensure sufficient endurance, it is necessary to ensure sufficient explosive force when the muscle mass and body fat rate are as low as possible, that is, the contraction unit mentioned above rises quickly and the support unit grows slowly.
For these reasons, most boxers don't need to have many muscles.