Point your spine when leaning back in a chair.
Collapsing in a chair may seem comfortable, but it restricts breathing and causes stiffness. Proper sitting, even reclining as shown, is a lively activity that is part of the continuum of how we move and do things. More liveliness means less stiffness. There is a video of this tip here.
More on sitting in a chair:
Bending Forward Is the Same