Lever Pulled
The Springs
The springs are attached to the frame and positioned to help the recliner return to its starting position. As the recliner spreads out, the springs are stretched and naturally want to return to their starting states. When you sit up, the chair will begin to close slightly, and when you sit forward and close the chair, the springs coil back up and the frame locks back into the original position.
Variations
Automatic models use an electrical source to power their internal motor. Pressing the button on an electronic recliner causes the the chair to slowly recline with power from the motor. Unlike lever-pulled models, electronic models aren't limited to a basic amount of positions--the reclining motion is fluid but can be paused at any time.
Lever-less Models
Lever-less models allow you to recline without using a lever. Leaning back on the chair pushes the frame back and allows you to recline. When you lean forward, the tension on the springs is relieved and they move back in place. This causes the chair to return to its original position.
Saving Space
Space-saving models allow you to place the reclining sofa flat against a wall. When you recline in a space-saving, or "wall-hugging" recliner, the back moves forward as the chair reclines, saving you valuable space.