That's a means of protection. When doing actions that may damage the waist, the belt has a certain degree of protection. This is also because the barbell used by bodybuilders is very heavy and more dangerous than the family dumbbells we usually use. On the other hand, it is not necessary to use it for fitness. As long as the actions are correct, there will be no danger. No matter how good the belt is, it can't protect your body better than the correct actions. Strictly follow the correct fitness.