http://www.youtube.com/watch?v=tz2CAHJGZkQ
Lie on your back,knees bent shoulder apart,feet flat on the floor,
straighten you lower back,so that there is no gap between your
lower back and the floor,clasp the back of one thigh,bring to your
chest as far as you can,then lift up the ankle of the same leg and
kick upward a few times,return to the original position and repeat
with the other leg.
This pose relaxes the lower back,by stretching the hamstring.