Usually because of the small amount of exercise before, sudden exercise, local skeletal system imbalance, fascia expansion.

There are also special circumstances, and my wrist will ring when I move. That's because the structure is special and the gap between bones is too small, but it doesn't affect my exercise. I've been here for years.

Junior high school started fitness. I could do 20 before and 80 after one year. I don't know what the standard is, because physical education class didn't take this test at school. High school requires 20 points to pass and 30 points to be excellent.