Legs can be exercised by running at variable speed, that is, sprinting for a while and jogging for a while, repeating it two or three times alternately, taking a break for a minute or two and repeating it again.
Skipping rope is also available, but there must be a cushion. Jumping rope on the concrete floor will hurt your knees.
You need to stretch your muscles well after each exercise, so that the lines will be tight and beautiful, not bulky.