The present disclosure relates to a mechanical extension apparatus for an extendable chair unit and a chair unit including such mechanical extension apparatus. The mechanical extension apparatus includes: a reclining apparatus that include multiple links attached to the seat, the backrest and the footrest of the extendable seat, and such reclining apparatus is configured to convert the extendable seat between a sitting position, a TV position, and a lying position. The mechanical extension apparatus also includes an actuator that is attached to the reclining apparatus, and the actuator is configured to electronically convert the extendable seat between the sitting position and the TV position; and the reclining apparatus is configured to convert the extendable seat between the TV position and the lying position by non-electric actuation.