In a broad sense, bodybuilding is about training muscles in certain parts of the body according to your own needs ~ As you said, people like Bruce Lee are engaged in martial arts ~ The power of boxing is what they need most ~ And the power of boxing is mainly provided by legs, back and forearms. So Li attaches great importance to squats and pull-ups (there are more than 50 pull-ups with one arm in Bruce Lee), especially forearms (Bruce Lee specially invented a forearm training device). Not just Bruce Lee ~ all of them. Because what they need is muscle ability, not appearance! (that is, the physical training you asked)
In a narrow sense, bodybuilding is the pursuit of muscle shape, from the circumference (commonly known as "block") and separation (commonly known as "painting") to improve their bodybuilding figure, but most people hate this kind of muscle, especially women, and feel sick! Only some men and people who really know bodybuilding will appreciate it! It is also an alternative beauty! (fitness)
Did you also ask about bodybuilding and practicality? I can tell you responsibly that it is absolutely not practical! Because the purpose of fitness is not to hit people, but to show off your figure! It's the appearance of muscles! Just like there are two kinds of human muscle fibers, A and B. A provides strength but the muscle fiber is small, and B is a big fiber with small strength but long weeks. Bodybuilders will never spend too much time paying attention to a fiber, because they are still thin after practicing more! So practicing B fiber will work harder! Therefore, bodybuilders with the same weight must be much worse than weightlifters! And the two types of athletes with equal strength are sure that bodybuilders have more muscles and are more scary, hehe! In addition, human strength is also reflected in the number of transverse bridges on muscle fibers. The greater the number, the greater the strength! Because the transverse bridge is a fiber that provides ATP to the body, and ATP is a substance that provides energy for a short time, just like the fuel tank of a car! And grade a fiber (providing strength) is like an engine! You said that no matter how good the engine is, it can't be without oil ~ haha ~ digression! Back to bodybuilders, I can tell you a little secret! Bodybuilders are very weak when they compete, because they have to lose a lot of fat before the game! Most people will cramp because of excessive dehydration and desalination, so lying down in the end is also a common disease for bodybuilders! So even the old lady can push the strong man down! Ha ha! In fact, we should look at the problem from a learnable perspective! (Practical and impractical answer)
If you really care about the practical questions you ask, you can read more: you can also contact me, because I am a graduate student majoring in biomechanics.