The purpose of the Swim Board:
This makes the board a very popular buoyancy aid for swimmers of all levels. It will help you to keep your balance when doing a series of kicks or undulations with fins. Finally, using a board makes the exercise easier.
How can I improve my leg movement?
For effective kicking, start the movement from the hip, not the knees. The knee will bend slightly and naturally in response to the movement of the hip, so you don't have to strain to bend your knees. This means your legs will stay relatively tense. It's important to note that the upward movement is as important as the downward movement. Focusing on the entire stroke movement optimises your propulsion and works all your muscles.