I ride a Lifecycle every day. The key is your heart-rate. I used to cycle competitively, and ran out of time to train. Running does more for you, but also beats you up. Anyone with knee, hip, or even back problems, will benefit from the bike. You will use different muscles than running (quads can get huge), but your hams will not really benefit, and neither will calves. Cycling can be as tough as you want it to be, just like running, but you will rarely get sore. You will always benefit from a heart rate monitor, no matter the activity.
CHL holder and Conservative...AKA "Domestic Terrorist"