You will find computerized and non-computerized stationary bikes, but those extra features don't necessarily provide a better workout. Computerized models may have a display that shows your cadence or heart rate. Calorie counters on exercise machines are known to be largely inaccurate so they're not necessarily worth using, in my opinion.
Most gyms have both traditional, upright stationary bikes and recumbent (semi-reclined) bikes. Upright bikes are almost identical to regular bikes -- expect for the fact that they're stationary. Recumbent bikes position you differently; you sit in them with the pedals and your feet in front of you, rather than below you. These bikes are ideal for someone who has back problems because they support the lower back while upright bikes do not.
You can set the resistance level on most exercise bikes. It is important that you do not set the resistance too high when you are first starting out. You want to get a good work out, but cycling should not actually hurt, even for a beginner. If you are in continual pain, it is a sign that your resistance is set too high for your fitness level.
Spin classes are a relatively new variation on indoor cycling. Spin classes attempt to replicate more closely the experience of on-road biking. The pedal action and resistance in a spin class will differ from what a beginner would experience with a regular stationary bike.
Spin classes are led by an instructor and include upbeat music. They offer varied levels of intensity and may sometimes include guided imagery, which means the instructor helps you envision different scenarios as you complete the workout. Spin classes are usually quite intense so you may wish to ride a regular stationary bike for some time and work up to joining a spin class.
You can also ride a spin bike on your own without being in a spin class. Spin bikes have a more narrow seat, are more adjustable, and provide a wider range of resistance. You will find that the pedals are smoother to operate on a spin bike than on a regular bike.
Spin bikes do not offer the electronic gizmos that some other bikes do, but most spin bikers I know say it is worth sacrificing the bells and whistles to experience an exercise that is so similar to true outdoor biking in the comfort of their gym.
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