A nice one, get a fit ball put it behind you against a wall the centre of your back near the bottom of your back. Put your feet 9ins in front of you with your toes on a bit of 3x2 wood so the heels are lower than the toes by 2ins. Now drop the knees an inch every 10 secs until you reach the sitting position then come up using the same technique 5 times. The 3x2 is important it protects your cruciats its a nice one . Or use a skate board instead of the Ball.