SKLZ Shoe Weights Variable Speed Trainers Adjusts to fit women's size 5 to Men's size 15, Heel adjustment strap for a more secure fit Heavy duty rubber strap wraps around the bottom of the shoe, Matches the shape of the shoe 3 single weight stretch pockets per shoe are designed to hold integrated flexible weights Nylon Mesh for high visibility, Soft bound edges for extra comfort and tight pocket design prevents any movement of the weight Oversized arch securing strap, Top strap secures weight for sprinting