Muscle growth, nothing more than two points, one is exercise, and the other is diet. If a person does not exercise, the probability that she/he has strong muscles is 0%, unless he/she uses steroids, testosterone and other hormones. And a person who only exercises and doesn't supplement enough protein is unlikely to have many muscles.

Second, the vast majority of teenagers in China lack exercise or protein intake.

Thin people in our country are generally just thin and have no muscles. Even people who exercise regularly feel that they don't pay attention to the maintenance of muscles and the intake of protein, so muscles are easily lost. Most people have no idea about protein and carbohydrates in their diet. It is precisely because there is no protein's concept that those muscles can only be considered normal, and people who eat enough protein are often people with excessive body fat content. Therefore, most people in our country are in a state of lack of protein. Even with enough exercise, it is difficult to get enough muscles.

Third, Americans do better than China in the above two points.

Americans started systematic fitness very early. For Americans, most people start to contact the gym very early-this is due to social and cultural factors. Don't say a few years. In fact, as long as you systematically practice in the gym for one year, it's completely different from what you haven't practiced. As long as a person starts to exercise at the age of 17, by the time he is 20, he will be very, very strong, although his body is not tough. Americans 15, it is actually very common to start physical exercise at the age of 6.