Originally Posted by Fenianz
Elliptical trainers are pretty good for people taking it easy and trying to prevent knee and foot injuries from running. Treadmills are actually getting better and better. Some new treadmills have eight-elastomer cushioning system that provides comfort and so much cushioning. The stability of the frame construction deck, elastomers all help the treadmill be as cushioned as possible.
They may be better but still place a heavy load on the knees and thus tearing away at the mensicus which is the bodies version of the shock absorber. He needs to stay clear of treadmills anyway because of his back pain. Elliptical trainer, deep water running and cycling are the best choice for exercises. Rubber tracks also work well to provide better cushioning than the road.