Recumbents can be harder on the knees than a diamond frame. The max force you can exert on a regular bike is your body weight. The recumbent bike allows you to push off a back rest. In this you are limited by your leg strength not weight. I have heard that recumbent riders can hAve more knee problems if not careful to spin and gear down for stops. I don't know why they don't put IGHs on recumbents.