I can give you a general answer to this question.
The first is the issue of race. European and American people are born stronger than yellow people.
Secondly, it is because of diet. Europeans and Americans love to eat high-protein foods such as beef, and muscle synthesis just needs high protein.
Finally, the problem of fitness. Europeans and Americans love fitness, which is relative. Some people don't. Compared with people in our country, it is common for several people to play ball after work or go to the gym to exercise their muscles. It's as simple as three people playing mahjong, but when they are exercising, we are playing mahjong.