Sit with hands behind back. Then slump forward at the thoracic and lumbar spine whilst flexing the neck by placing the chin on the chest.
Extend one knee until you feel a gently pull in the back of the legs.
Release. Then repeat.
Only take the leg until the stretch starts (or the leg begins to shake). There is no need to force the move or hold. We are simply looking at nudging the range.
To increase the mobilisation pull the toes towards you as you raise the leg up.
Repeat 10 times on both sides.