The vest line is the groove between the abdominal muscle and the external oblique muscle. Against the background of abdominal muscles with a certain thickness and sufficiently developed external oblique muscles, people with a certain body fat will form two symmetrical lines on both sides of the abdomen, which are often called vest lines in fitness circles.

Because of the different physiological structures of men and women, the results of their exercise are also different. Usually, women will expose the vest line after exercise, while men's abdominal muscles tend to become bulky after exercise, but the vest line can also be exposed by reducing the body fat rate.