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.