Some years ago, I had the good fortune to come across a bit of research, from a Swedish University, on Recliner Chairs and back health. The study found that people whom owned recliner chairs have a higher rate of back pain than people who sat on typical chairs, i.e., fixed nonmechanical chairs. The back pain is due to the spinal column natural alignment acting like a stack of coins; the stack sits comfortably and without stress in a vertical column.
However, were you to lay down the stack of coins it will spread out, and each coin will touch the surface it is sitting on and the edge of the next coin. The coin is a metaphor for the vertebrae in your back. The coins and your back have a stress point where there is intense pressure, the points where the coin/vertebrae touch. The sideways stacking causes back pain.
In my experience recliner chairs are often sold for their comfort value. The comfort you feel from sitting in a recliner chair is the psychological comfort similar to the feel of carrying a bag of potatoes on your back and then setting it down after a long distance. You feel light a rested with energy to go another long distance, but it is the removal of the heavyweight that is causing you euphoria, not the absence of pain. The sideways stacking of the vertebrae causes damage to the long-term health of your back.
People with back pain often buy Recliner Chairs and find them very comfortable, but the long-term effect of this sitting position is a worse back that is lethargic from lack of passive exercise. Please consider this when you are out looking for a suitable chair for your Grandfather or Mothers and Fathers comfort needs.