Sit on the ground or a yoga mat and stretch your legs straight out in front of you. Stretch your arms above your head and breathe in. Lengthen your spine and as you breathe out, stretch forward from the hips. Keep the back and legs as straight as you can.
This stretch will active the Kidney and Bladder channel. The Bladder meridian runs down either side of your spine and follows the length of the back of your leg all the way into the foot. This is an excellent stretch to really feel the channel.