I usually do some stretching in the morning. Last week I was wondering if I could picture myself and draw all the limbs in their proper places for some of the positions. Squats work the leg muscles well, although I had a bit of trouble rendering the hands holding the weight.
This is a great stretch for your back, but my drawings of it are definitely not there yet.
On the other hand, this arm and leg stretch looks pretty accurate with some help from strategically placed shadows.