Alas, simple questions always attract a bunch of soy sauce parties; Roller is mainly used to exercise the lower abdomen. During flexion, extension and retraction, it plays a stretching role on the lower abdomen, and plays a certain auxiliary role in the exercise of the trapezius muscle of the back when it retreats; The focus of this action is the posture and times of kneeling, and each group cannot be less than 20! ! ! !