Hi Corky9999,
Biking can help your build up endurance. However, I would not rely on just one area here: cross-train instead by running, swimming, use ellipse machines, play basketball, etc. Everyone's body responds differently to certain things. One good thing about an exercise bike is that you can increase the settings to make it harder on you. I would choose some endurance exercises that allow you to increase the difficulty so that you do not plateau and keep getting gains.
Hope this helps,
Jack Elliott
Baseball Pitching Tips