Question about Cycling / Biking for exercsie?

Mr K · Yahoo User

I starting running not too long ago for some much needed exercise. Yet i noticed after a few months my knees started to hurt all the time. So now I'm thinking about getting a bike for exercise. anyone have some insight.first, Will i get as much exercise from cycling as i would form running?also, i have a few bikes in mind, can anyone give me some good advice about which might be best. Looking at a comfort/hybrid bike. like the Trek 7100 / 7200 http://www.trekbikes.com/us/en/bikes/2008/bike_path/or a road bike I'm not really sure which might be best for me. I do get some lower back pain, So i'm leaning a little more toward the hybrid bike ( i don't know how leaning over on a road bike might be for me.)Thanks for any advice.