Recliner chairs can help with back pain for the simple reason that you take the weight off of your back and re balance it. By reclining or laying down, you rest your spine and it gives it time to relax and take pressure off. A reclined position is much better than sitting up straight, because when you are sitting up straight you are still contracting your muscles to remain sturdy.
Lifting your legs and laying and supporting your back helps. This can help in many other medical conditions, for instance, varicose veins and clotting issues also. The blood flow goes back to your heart and that is also good for inflammation and pain in all areas.
How a massage chair can also assist.
Massage chairs can help, but it would also depend on the nature of your pain. Massage chairs that also recline, can help with muscle tightness or spasms. Particularly, heat can help although, if you have back injuries then you are better off using a simple reclining position that supports your back. It is always best to check with your doctor in the first instance.
A semi-reclined position can also help with medical conditions where a person experiences difficulty taking in air or breathing. For instance, a semi-reclined position decreases severity of sleep apnea. It also helps with snoring