See A-Z of rehabilitation exercises
In case you cannot see the video, here is a still sequence -
The hamstrings curl with a Swiss ball helps to build up both the hamstrings and the lower back muscles.
Lie on your back on a firm surface, with your hands by your side. Position your feet on the Swiss ball.
Straighten your lower back so that your body makes a straight line and your bottom lifts off the surface.
Bending the knees, roll the Swiss ball towards your buttocks.
Keeping the bottom up, roll the ball back to the starting position, and then back to the buttocks and home again. Repeat the exercise 10 times.