If you incorporate an exercise bike into your workout routine, you will give your legs, heart and lungs an awesome workout while having much less impact than walking, jogging or running will have.
Every gym worth their salt has an area dedicated to the exercise bike; in fact many have more than one model for you to get your cardio in.
There are many advantages to having an exercise bike for cardio instead of a treadmill, Stairmaster or similar machines. The aforementioned low impact is a big reason- the less stress you put on things like your joints, knees, ankles and hips, the better.
Cardio tends to put a lot of stress on these parts of the body and can sometimes lead to injury if overdone. But an exercise bike gives them all a great workout while going easy on these all-important areas.
There are three types that you may want to have a look at: upright, recumbent and dual action. An upright is the traditional machine that you are used to seeing and is actually much less expensive than you might think it is. These also fit well into small areas.
A recumbent machine has chair-like seats that are high and support the back for optimum workout. They provide better blood flow and prevent you from standing while pedaling that can cause injury or lessen your results.
Dual action machines give both your upper and lower body a workout with the use of moveable handlebars.
You still get the cardio workout by pedaling but get some toning done to your arms, chest and back as well. These do take some getting used to, with the motion being very different from the other machines but they are great for combining two workouts into one.