Start by sitting on a sturdy chair facing a corner of a wall with an exercise ball in front of you on the floor and against the corner. Lift one leg and place the foot against an exercise ball.
Press your foot against the ball and try to straighten your leg. Feel the muscles of your front thigh working. Then relax.
Note: Place your foot in the middle of the ball so that it stays in place when you press your leg against it.
