The original low-impact exercise. While a learned activity, biking is something that we've been doing since childhood giving a low perceived exertion to cardiovascular benefit.
Recumbent, or semi-recumbent, bikes are ideal for those needing back support or unaccustomed to outdoor cycling. Recumbent bikes allow you to focus just on the cycling action without worrying about ideal cycling technique.
Mesh back seats are cooler and often more comfortable. Upholstered seat backs typically provide better lumbar support.