I purchased a spin bike, had tried them and liked them, but I find I am not using it because it hurts my knees and it stresses my neck and shoulders from how I must be positioned on the seat/handle bars. I want to get a machine of some kind……I used to have a treadmill and sold it, but I want something aerobic that will also tone…..do you have any recommendations? I am also looking at the Bowflex Tread Climber…it says it combines, stair, elliptical and treadmill for low impact and I really need low impact. If it hurts me, I won’t do it…..thanks for any light you can shed.