First of all, talk about the role of the belt in the squat movement. It plays the role of maintaining lateral pressure and abdominal pressure to maintain the stability of lumbar spine. Let's see, if there is no belt, which muscle plays this role? First, erector spinae and quadratus lumborum are in the lower back, but not them, they all grow vertically. Then the rectus abdominis in front, too. Only the external oblique and transverse abdominis muscles play the role of lateral stability, so the belt compensates their functions, mainly to compensate the internal absorption of transverse abdominis muscles and the extremely heavy squat. This is the force exerted by the external oblique muscle of abdomen. Without a belt, the relatively weak transverse abdominis muscle will be stretched and the belly will become bigger, so you can see that many strong male and female athletes have thick waistlines and little fat in their bellies.