Today I visited the taoist White Cloude Monastery. There I did an exercise for the straight abdominals and the stretching of the backside of the legs.
I layed down on my back and extended the arms backwards. Then I started to roll myself up upwards until I was sitting and bent my torso forward until my fingers touched my toes. Then I slowly went back into the starting position. The back must be straight or slightly rounded during the exercise.