Any advice would help worried about baby girl ?

My 4 month old has been doing this thing in her sleep since birth but it gotten alittle worse . At first I thought it was nothing but it hasn’t stop. So when she sleeping she would like pick up both of her legs and slam them down in a repetitive movement for about a min or two . She won’t wake up when this happening and after min she stop . I have a video but don’t know how to post it here . Only give me an image option . Has any other mother experienced this . Should I be concern or is this a normal thing for infant to do in their sleep . Please any advice would really help.