A very important thing with cycling is to make sure that your knee is extended the proper amount at the bottom of the stroke:
http://bikedynamics.co.uk/guidelines.htmYou will need to adjust the seat height on the bike. A slight bend is what you should strive for. The site is for road cycles, but the knee extension can be applied to X bikes as well.
This site is pretty explanatory as well:
http://www.bikeradar.com/us/gear/article/how-to-ge...It is a good low impact way to burn calories. I did not start out an an hour, trust me. :-)