Because fat is not easy to accumulate in other parts, muscles grow out when you exercise. So it will be very thick,

Moreover, a lot of fat is accumulated in the waist, even if it is not fat, it will accumulate a lot of fat, so after fitness, the disappearance of fat will make the waist thinner.

Generally speaking, a narrow waist is good for both men and women. Girls should have a thin waist, and boys should practice muscles in an inverted triangle, that is, shoulders are wide, waist is thin, and lines are obvious.