I've had 4 back surgeries, so I didn't want a bike that would put me to upright but also didn't want the way-forward lean of a road bike so I test rode quite a few different style bikes and found that the bikes that felt the best on my back were the Hybrids/fit type framed bikes, most manufactures have them. On the more up right so called comfort bikes it seemed like they would tend to transfer the jars strait up into my lower back and after a short ride my back would be sore and my legs would have a tingle to them. It seemed like the hybrids tended to give enough forward lean to place some of my body wieght on the front wheel so when I hit a bump or hole with the back wheel it would tend to rock my body foward as well as push my butt upward.