STARTING POSITION:
Lie on a fitball. Make sure you rest your upper back and your head on the fitball. Place your hands on either side of your hips. Place the entire soles of your feet on the floor and your knees around 90º. Contract your pelvic floor and core.
MOVEMENT:
Maintaining the balance, fully extend your right knee. Hold the position during the required time and then do the exercise with the other leg.
TIPS: While your are doing the exercise, move only the knee joint, make sure you don't move any other part of your body.